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  • Articles  (209)
  • Blackwell Publishing Ltd  (209)
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  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (209)
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  • Articles  (209)
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  • 1995-1999  (180)
  • 1980-1984  (29)
  • 1925-1929
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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: X-ray diffraction (XRD) patterns from nominally β-SiC specimens often differ from those expected for the cubic crystal structure. These differences include the presence of additional peaks, enhanced background intensities, peak broadening, changes in relative peak heights, and shifts in peak positions. It has long been recognized that they are due to the presence of stacking faults, and models relating the experimental observations to stacking fault population have continued to evolve. The presence and relative magnitude of these features vary among different β-SiC specimens. In this work, computer simulations were used to show that the variations are closely related to differences in the type and spatial distribution of stacking faults in each specimen. In these simulations, stacking sequences were generated using a selectively activated 1-D Ising model with a Boltzmann-type probability function for specifying errors, which allows a wide variety of fault configurations to be generated. Direct correlations between different features in the XRD data to the underlying fault population are demonstrated, which are discussed in this paper. It is also shown that this computer model is general, in the sense that many of the models presented in prior work can be interpreted as limiting cases of it.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— This paper examines the application of the Jk, L and M integrals, in complex-variable form, to the Boussinesq wedge. The wedge is symmetrical and subjected to a point couple and point forces at the apex of the wedge. In the case of a point couple acting at the wedge apex the Jy, L and M integrals are found to vanish for all wedge angles whereas Jx displays a 1/r3 path-dependence; where r is a radial dimension measured from the wedge apex. When the wedge is subjected to point forces at the wedge apex then Jx and Jy are 1/r path-dependent whereas L and M are path-independent.The property that the L and M integrals are path-independent for the Boussinesq wedge is applied to the problem of determining the modes I and II stress intensity factors for a corner-loaded edge crack in a half-plane subjected to both normal and parallel point forces to the free surface of the half-plane.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Fatigue tests were performed on thin-walled tubular specimens of S45C steel under tension-compression, pure torsion, in-phase and out-of-phase axial-torsional loadings. The relationship between cracking behaviour and stress components on the crack plane was investigated. Measurement of microcrack density showed that microcracking was governed predominantly by the shear stress amplitude acting on the crack plane for all loading conditions. The failure crack was formed by coalescence of many cracks initiated near the maximum shear planes. The cracks grew turning their orientation to the direction perpendicular to the maximum normal stress. The transition of crack orientation occurred at relatively longer crack lengths at a higher stress ratio. The crack growth behaviour for all loading modes can be correlated using an equivalent strain intensity parameter based on shear and normal strains on the crack plane.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A ductile medium strength steel has been modelled by means of the Gurson model, and been used to investigate the effect of crack tip constraint in several fracture mechanics specimens. Both numerical and experimental results have been obtained, in the course of the crack extension process, for single edge notch bending specimens with different crack length-to-width ratios. The geometries with the shorter cracks always exhibited higher J values at initiation and steeper J crack growth resistance curves, and these results have been explained in terms of the stress and strain fields and damage development in the region ahead of the crack tip.
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— It is shown that autofrettage at low temperatures is superior to autofrettage at room temperature in enhancing the fatigue resistance of thick-walled tubes against pulsating internal pressure. The physical reason is based on the well-known temperature dependence of the mechanical behaviour of metals and alloys which generally exhibit an enhancement of both the yield stress and strain hardening behaviour at lower temperatures. As a consequence, significantly larger compressive residual hoop stresses can be introduced during pressurization at low temperatures than at room temperature. Experimental data obtained on thick-walled tubes of the metastable austenitic stainless steel AISI 304 L which were subjected to pulsating internal pressure at room temperature after autofrettage at temperatures between-110°C and room temperature are presented. These data demonstrate convincingly the advantages offered by low-temperature autofrettage in enhancing both the fatigue life in the finite-life region and the fatigue endurance limit in comparison with autofrettage at room temperature. In conclusion, some specific materials requirements for optimum low-temperature autofrettage performance are discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A new single-specimen testing method, the normalization method with the so-called LMN calibration function, based on the load separation principle and function calibrations from an individual test record, was used to construct J-R curves directly from load versus load-line displacement records without any additional on-line crack-length monitoring equipment. The research was done on CT-specimens of a glassy polymer PVC at different crosshead speeds ranging from 0.01 to 50 mm/min. The J-R curves evaluated from the normalization method are in good agreement with those from the conventional multiple-specimen testing method in the whole range of the tested crosshead speeds. The results demonstrated the applicability of the normalization method for developing J-R curves at different crosshead speeds in PVC. The crack initiation J-integral values, J0.2, showed a two-regime dependence on the crosshead speeds in the tested crosshead speed range.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Biaxial fatigue tests were conducted on a high strength spring steel using hour-glass shaped smooth specimens. Four types of loading system were employed, i.e. (a) fully reversed cyclic torsion, (b) uniaxial push—pull, (c) fully reversed torsion with a superimposed axial static tension or compression stress, and (d) uniaxial push—pull with a superimposed static torque, to evaluate the effects of mean stress on the cyclic stress—strain response and short fatigue crack growth behaviour. Experimental results indicate that a biaxial mean stress has no apparent influence on the stress—strain response in torsion, however a superimposed tensile mean stress was detrimental to torsional fatigue strength. Similarly a superimposed static shear stress reduced the push—pull fatigue lifetime. A compressive mean stress was seen to be beneficial to torsion fatigue life. The role of mean stress on fatigue lifetime, under mixed mode loading, was investigated through experimental observations and theoretical analyses of short crack initiation and propagation. Using a plastic replication technique the effects of biaxial mean stress on both Stage I (mode II) and Stage II (mode I) short cracks were evaluated and analysed in detail. A two stage biaxial short fatigue crack growth model incorporating the influence of mean stress was subsequently developed and applied to correlate data of crack growth rate and fatigue life.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The development of fatigue damage in Co45Ni specimens during push—pull and reversed torsion tests, performed inside a scanning electron microscope, was observed and the different stress states compared. It appeared that transgranular crack initiation and development is delayed and intergranular crack initiation promoted under torsional loading. This was explained in terms of reduced surface distortion at the emergence of persistent slip bands (PSBs) and smaller compatibility stresses at the PSB-matrix interfaces. The influence of the mechanical strength of grain boundaries on the difference between tensile and torsional fatigue lives is discussed.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤a/c≤ 1 and relative depth in the range of 0 ≤a/t≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A conventional finite element method may show a weakness when determining the hot spot stress distributions in the brace/chord intersection region of offshore tubular joints. This is because the chosen element displacement functions do not implicitly satisfy the conditions which prevail on the free surfaces. A procedure has been proposed to modify the conventional finite element method so as to allow the hot spot stresses, which occur at the free boundary of the weld toe of tubular joints, to be determined with improved accuracy. The results obtained by this modified method are compared with both an experimental and a traditional finite element solution. The comparison shows that the modified solution is in better agreement with the experimental data as compared with the traditional solution.
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  • 11
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 12
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Simple extensions to the standard deep notch bend test procedure are suggested to allow the collection of data relevant to the energy dissipation rate, D, crack opening angle, COA, and J, all for arbitrarily large amounts of growth in extensive plasticity. The methods of analysis are detailed for real elastic-plastic behaviour of a high strength low-hardening type metal with a view to encouraging use on a wider range of materials. A proposal is made, and equations given, that the particular version of J used for an R-curve derived from the area under the loading diagram, should correspond to the value of the far-field integral, Jff.The relationship between the global measure of COA that emerges from D and the local crack tip opening angle, CTOA, as used in computational studies, is established. Transferability of CTOA data is examined in the light of effects of size and configuration. An explicit rule of the form CTOA √G =f (material and configuration) is proposed for the modelling of ductile growth in finite element studies. It is applied to a set of data in the literature, for the variation of CTOA with size in the deep notch bend test and for the configurations, bending, double edge and centre cracked tension.
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  • 13
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— In this investigation the Electron Channelling Contrast (ECC) technique in scanning electron microscopy (SEM) was applied to reveal the dislocation structures in the vicinity of surface fatigue cracks in comparison to those of cyclically-deformed recrystallized polycrystalline copper. The plastic zone around a fatigue crack was found to consist of an innermost region containing cells, followed by a region containing dense veins and PSBs, surrounded by a structure of loose veins, bundles and loop patches typical of the cyclically deformed matrix. A relation between plastic strain amplitude values deduced from cyclic stress-strain investigations and the dislocation structures near fatigue cracks are given. Typical regions of damage accumulation were identified and plastic strain contours for surface fatigue cracks established. The essentially non-destructive ECC technique is particularly suited to identify the changes in mesoscopic dislocation structures from surface layers to the interior of specimens over large specimen areas.
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  • 14
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    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 15
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The propagation behaviour of fatigue cracks emanating from pre-cracks was numerically simulated to evaluate the development of crack closure with crack growth. The crack opening stress intensity factor at the threshold was approximated as a function of the applied stress and the amount of crack extension. Pre-cracked specimens of a medium-carbon steel with a small surface crack and a single-edge crack were fatigued to investigate experimentally the initiation and propagation of cracks from pre-cracks. Crack closure was dynamically measured by using an interferometric strain/displacement gauge. The threshold condition of crack initiation from pre-cracks was given by a constant value of the effective stress intensity range which was equal to the threshold value for long cracks. The cyclic R-curve was constructed in terms of the threshold value of the maximum stress intensity factor as a function of crack extension approximated on the basis of the experimental and numerical results. The cyclic R-curve method was used to predict the fatigue thresholds of pre-cracked specimens. The predicted values of the fatigue limits for crack initiation and fracture, and the length of non-propagating cracks agreed very well with the experimental results.
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  • 16
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A basic study was performed on the evolution of three-dimensional shapes of small surface fatigue cracks during fatigue, and the effect of this evolution on small-crack growth behavior of a titanium-base alloy. Specifically, the nature and the magnitude of variations in crack aspect ratio, a/c (a is the crack depth and c is the half-surface crack length), during cyclic crack growth and its impact on growth rates have been studied. Experiments were performed on naturally initiated micro-cracks in a microstructure consisting of equiaxed primary-α2 phase in a Widmanstätten (transformed β) matrix. Several cracks under stress ratio (R) levels of 0.1 and −1, were studied. A specialized experimental system, consisting of a laser interferometer (to measure precisely the small-crack surface displacements), and a photo microscope (to automatically and continuously photograph the fatigue micro-cracks) was employed in the study. Apparent aspect ratios of surface cracks were calculated from the compliance response and the surface crack length data as a function of fatigue cycles. These data enabled accurate calculations of growth rates at the surface crack tip as well as the tip at depth in the bulk over the entire crack growth period, thus giving an insight into the crack growth process. Measurements of closure levels of small cracks were also performed and were used to partly account for the differences in growth rates. In the comparisons of small-crack growth data with the large-crack data, surface growth rates correlated relatively well with the large-crack data. Growth rates at depth exhibited large variations due to the irregularity of crack fronts at this location, and these rates deviated significantly from the large-crack behavior. Additionally, these growth rates varied between different cracks. An attempt was made to rationalize these observations in terms of the effects of inhomogeneities present in the microstructure.
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  • 17
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    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A new technique, known as crack modelling, is used here to predict fatigue failure in a crankshaft component. The technique uses a linear elastic finite element (FE) analysis to derive a stress intensity factor (K) for the component under load. The novel feature of the technique is that K is calculated without introducing a crack into a component; the stress field around the maximum stress point is examined and compared to that for a standard centre-cracked plate. The fatigue limit for a crankshaft was successfully predicted, when compared to experimental data. The only material parameter required for this prediction was the threshold stress intensity range, ΔKth.
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  • 18
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    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The effects of bluing, associated with drawing strain, on the fatigue strength of eutectoid steel wires have been investigated. The fatigue limit increases by bluing and the increase is more significant with higher drawing strain. The peak in the fatigue limit with regard to the drawing strain in the wires, at a strain of 2.5, disappears after bluing. On the other hand, in the ferritic steel wires investigated for comparison, the fatigue limit gradually increases with the drawing strain up to 7.7. Furthermore, no appreciable change in the fatigue limit due to bluing is found. Based on the results of hardness tests on fatigue specimens with- and without-bluing, it is deduced that the decrease of the fatigue limit beyond the peak drawing strain in the eutectoid steel wire can partly be attributed to insufficient locking of the high-density dislocations by solute atoms. The effect of relaxation of residual stress during bluing is also briefly discussed.
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  • 19
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    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— It is well known that for very short cracks the stress intensity factor K is not a suitable parameter to estimate the stress level over the small but finite Stage II process zone activation region of size rs near the crack tip, within which crack growth events take place. A critical appreciation of the reasons for the limitations on the applicability of ΔK as a fatigue crack propagation (FCP) parameter, when the crack length a is of the same order of magnitude or smaller than the size of the ‘fatigue-fracture activation region’, rs is presented. As an alternative to ΔK the range Δσs of the cyclic normal stress at a point situated at the fixed distance s=rs/2, ahead of the crack tip, inside the fatigue-fracture activation region, is proposed. It is observed that the limitation on the use of ΔK when the crack is short, is mathematical (and not physical) but this inconvenience is easily circumvented if the stress Δσs at the prescribed distance is used instead of ΔK since nowadays Δσs can be obtained numerically by using finite element methods (FEM). It follows that the parameter Δσs is not restricted by the mathematical limitations on ΔK and so it would seem that there is, a priori, no reason why the validity of the parameter Δσs cannot be extended to short cracks. It is shown that if the Paris law is expressed in terms of Δσs (πrrs)½ instead of ΔK the validity of the modified Paris law can be extended to short cracks.A coherent estimate of the value of the fatigue-fracture activation region rs is derived in terms of the fatigue limit ΔσFL obtained from S-N tests and of the threshold value ΔKth obtained from tests on long cracks where both relate to Stage II crack growth that ends in failure, namely, rs= (ΔKth/ΔσFL)2/π. An overall, threshold diagram is presented based on the simple criterion that, for sustained Stage II FCP, Δσs must be greater than ΔσFL. The study is based on a simple continuum mechanics approach and its purpose is the investigation of the suitability of both ΔK and Δσs to characterise the crack driving force that activates complex fracture processes at the microstructure's scale. The investigation pertains to conditions that lead to the ultimate failure of the component at values of Δσs 〉 ΔσFL.
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  • 20
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    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The boundary value problem for an arbitrarily shaped plane crack embedded in a 3D linear elastic solid can be reduced to a governing hyper-singular integral equation. A discretizing procedure based on a triangulation of the crack area has been offered in Part I of this work. The main goal of Part I is to introduce the analytical results for the 18 resulting finite-part integrals defined over a triangular mesh area. The finite-part integrals occur in those triangles where the source point coincides with one of the element nodes. Mostly the source point lies outside of the considered triangle. In these cases the occurring area integrals are regular.The aim of Part II is, therefore, the derivation of the closed form expressions for the relevant 18 regular area integrals. The resulting relations are of algebraic form which can easily be coded in compact form. Their numerical proof by two different methods shows the highest accuracy and, therefore, the correctness of the final solutions. The relevant numerical results are offered in Appendix I.With the formulae provided in Part I and Part II of the paper the determination of the coefficient matrix, necessary for the calculation of COD values from a linear equation system, is precise and needs only minimum computer time.
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  • 21
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    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Circumferentially notched cylindrical specimens are tested in torsion to obtain critical J values from crack resistance curves. The specimens are explosion cladded, half ferrite, half austenite, with the interface perpendicular to the cylinder axis and the circumferential notch at, or parallel to, the interface. Critical J values for crack extension in mode III were found to be a factor 1.1 to 2.1 higher than under comparable mode I loading.
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  • 22
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    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Strength measurements are becoming increasingly important for electroceramics. Bending of specimens small enough to be cut out of small electroceramic components may be one possibility. Therefore the miniaturisation of the 4-point bend-test for ceramic specimens is now being attempted. In this paper the errors in determining the flexural strength arising from the test principle itself, plus the geometry and measuring inaccuracies are calculated and expressed as a function of the outer span length. Contact pressure and a tolerable total measuring inaccuracy determines the dimensions of miniature specimens and fixtures. The possibilities of appropriate specimen preparation are also investigated.Ceramic materials show a volume (i.e. a specimen size) dependence of strength which is described by Weibull's statistical theory. The applicability of the miniature bend-fixtures is demonstrated by measuring this volume effect.
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  • 23
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    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— This paper describes a versatile technique for simulating the fatigue growth of a wide range of planar cracks of practical significance. Crack growth is predicted on a step-by-step basis from the Paris law using stress intensity factors calculated by the finite element method. The crack front is defined by a cubic spline curve from a set of nodes. Both the 1/4-node crack opening displacement and the three-dimensional J-integral (energy release rate) methods are used to calculate the stress intensity factors. Automatic remeshing of the finite element model to a new position which defines the new crack front enables the crack propagation to be followed. The accuracy and capability of this finite element simulation technique are demonstrated in this paper by the investigation of various problems of both theoretical and practical interest. These include the shape growth trend of an embedded initially penny-shaped defect and an embedded initially elliptical defect in an infinite body, the growth of a semi-elliptical surface crack in a finite thickness plate under tension and bending, the propagation of an internal crack in a round bar and the shape change of an external surface crack in a pressure vessel.
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  • 24
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    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Cold-expansion of fastener holes is now commonly used within the aerospace industry to increase the fatigue endurance of airframes. Although a number of methods of cold expansion are possible, the split-sleeve cold-expansion process is the most widely accepted and is frequently used in the repair and manufacture stages of both military and civil aircraft. In the present work, the redistribution of residual hoop stresses due to the application of constant amplitude fatigue loading at 4% cold-expanded holes has been studied. A modified Sachs method was adopted to evaluate the residual stress profiles and a replication technique was used to quantify crack growth. It was found that the decay of the residual hoop stress profile near the bore of the hole was due to the initiation and growth of small fatigue cracks. Cracks were found to initiate both near and below the fatigue limit, but subsequently arrested so stabilising the overall residual stress profile.
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  • 25
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The factors affecting the fatigue strength of nitrided titanium were clarified. The fatigue strength depended strongly on the fracture strength of the compound layer formed on the surface by nitriding. We found a Hall-Petch relationship between the fatigue strength of nitrided titanium and the grain size. The findings indicated that the reduction in the fatigue strength by nitriding results from both the formation of the compound layer possessing low fracture strength and grain growth occurring from ordinary nitriding. Furthermore, low-temperature nitriding (620°C, 24 h) was proposed to suppress grain growth. This treatment method improved not only the wear resistance and the corrosion resistance but also the fatigue strength of titanium.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Sphere-reinforced metal-matrix composites are modelled as a three dimensional array of hexagonal cylinders, each one with a broken or intact spherical reinforcement at its centre. Using this model, the stress-strain response of the composite in uniaxial tension was obtained. A parametrical analysis of the influence of matrix and reinforcement properties as well as volume fraction on the ductility of these composites was performed. It was found that the decrease in ductility with respect to the unreinforced matrix depended mainly on the reinforcement/matrix strength ratio and on the defect distribution in the particulates.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Since the degradation effect due to environment on the cracking of materials depends on time, the loading rate has an important influence on the parameters that characterise its behaviour. This work analyses the effect of loading rate on the resistance to hydrogen induced cracking (HIC) of two microailoyed steels, E690 and E500. Monotonic loading tests were performed on precracked CT samples using a slow strain rate machine. Tests were done under constant displacement rate varying from 4.1 × 10–7 m/s to 8.2 × 10–10m/s on the two steels that were cathodically charged with hydrogen at different current densities (1, 5 and 10 mA/cm2) to obtain different hydrogen concentration levels inside the material.Based on an analytical study, the initiation conditions for cracking as well as the crack propagation rates were determined in each case, and analysed as a function of K1. An extensive fractographic SEM study has been performed to help in the analysis of the different zones of behaviour obtained as an effect of loading rate, for each material and environmental condition used.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A reaction sintering route is developed to produce, “in situ”, composites of alumina-aluminium titanate using alumina and titania as starting powders. Aluminium titanate, can be formed by a solid state reaction between Al2O3 and TiO2 at temperatures above the eutectoid temperature of 1280°C. These composites have different grain sizes of alumina matrix and a different quantity and distribution of aluminium titanate according to the heating cycle used.In the present work direct push-pull tests under cyclic loads have been carried out with both monolithic alumina and alumina-aluminium titanate composites. It has been found that all the samples show a decrease in tensile strength with the number of applied cycles of loading when plotted in graphical form but the slopes of these graphs for both Al2O3-Al2TiO5 composites are lower than for the alumina specimens. The role of aluminium titanate and the alumina matrix grain size in fatigue crack growth resistance has been studied during push-pull tests, where failure occurs by catastrophic propagation of small surface cracks after a very short regime of subcritical crack growth. These results have been compared with measurements of slow stable fatigue crack growth rates in Al2O3-Al2TiO5 composites carried out elsewhere with pre-notched specimens of the compact tension type. These latter tests provide information about the behaviour of significantly long cracks, i.e. cracks that are several millimetres long.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The Technical Committee “Ceramics” (TC 6) of the European Structural Integrity Society (ESIS) organized a round robin relating to the fracture toughness of ceramic materials at room temperature. Five materials were tested with five testing methods by eighteen laboratories. The five testing methods were: chevron notched beam in four point bending, direct measurement of the cracks emanating from a Vickers indentation, indentation strength by four-point bending, single edge precracked beam in four-point bending, and single edge notched beam in four-point bending. The results of the round robin performed in the period 1993 to 1994 are presented and discussed.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— This paper reviews the stress intensity factor, limit load, compliance and J-integral functions for a centre cracked tensile (CCT) specimen available in the literature. Compliance and J-integral functions are derived from the optimum stress intensity factor and limit load solutions. The functions are compared with the results obtained from two-dimensional finite element analyses of the specimen.The finite element results have confirmed the accuracy of the compliance and limit load functions available in the literature and suggest that the unloading compliance technique, based on crack mouth opening displacement, could be developed for a CCT specimen. Non-linear finite element analyses have shown that J can be estimated from the measured load versus load-point displacement behaviour providing a/W≥ 0.5
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The behaviour of fatigue cracks in an Al-alloy under cyclic compression, either with or without overloads, was studied. For constant-amplitude compressive cycling, a non-catastrophic (saturation) character of the fatigue crack behaviour was confirmed, with the final depth of a crack depending on the applied load level. Single (tensile or compressive) intermittent overloads were shown to re-activate a previously arrested crack while reversed (tensile—compressive or compressive—tensile) ones were also shown to maintain continual fatigue crack extension under otherwise fully compressive cycling.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A new method for accelerating the collection of near-threshold corrosion fatigue crack propagation data, using local hydrogen embrittlement in the crack tip region, has been investigated for ASTM A710 HSLA steel. Fatigue tests were conducted at 10 and 0.2 Hz (stress ratio, R= 0.1) on “constant K” contoured double cantilever beam (CDCB) specimens, to establish near-threshold crack growth rates in a locally hydrogen charged region at the crack tip. Hydrogen charging was then discontinued and crack growth rates were monitored in the uncharged material. Near-threshold fatigue crack growth rates were found to be 100 times faster in the locally hydrogen charged specimens than in the uncharged material. Fatigue thresholds, ΔKth, were defined in less than one fifth the time required for load shedding tests in air at 0.2 Hz. Although demonstrated for HSLA steels, the technique is applicable to any material which can be embrittled by hydrogen.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The objective of this work is to study the delamination growth behaviour of hybrid composite-aluminium bonded laminates. A modified Double Crack Lap Shear (DCLS) specimen was chosen for this study. An expression relating the delamination size and the compliance of a DCLS specimen was derived, and a test method for the delamination growth rate in DCLS specimens developed. The delamination sizes and the delamination growth rates of DCLS specimens were determined by monitoring the compliances of specimens during fatigue. Delamination growth rates at different stress ratios (R= 0.1, 0.3,0.5) were measured. A Walker-type equation for the delamination growth rate was obtained by a multiple linear regression analysis.It was shown that the compliance method for determining the delamination growth rate of DCLS specimens is not only convenient and practical, but also accurate. The delamination size in DCLS specimens increases linearly with cycles during fatigue, i.e. delamination growth rate is constant, independent of delamination size. The energy release rate was adopted to characterize delamination growth behaviour. Good agreement between the Walker equation and test results of the delamination growth rate was found.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The aim of the paper is to compute the local crack face displacements of a linear elastic body containing an arbitrarily shaped plane crack. From the crack face displacements the local stress intensity factors can be derived.The boundary value problem for a plane crack of arbitrary shape, embedded in a linear elastic medium, has been treated by several authors by the singular integral equation (SIE) approach. Their computations lead to a set of hyper-singular integral equations for the Cartesian components of the unknown crack face displacements. To solve these equations the authors present a discretization procedure based on six-node triangular finite elements. A total set of 24 finite-part integrals defined over a triangular area can be developed. These 2D-finite-part integrals can be split into both a 1D-regular and a 1D-finite-part-integral by means of the polar coordinates so that they can be solved in closed form. Finally, the investigation of the SIEs is reduced to a discrete set of linear algebraic equations for the unknown nodal point values. The necessary steps will be demonstrated in detail. The derived closed-form solutions will be offered in the text and in the appendices.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A new tool is presented to investigate cleavage fracture surfaces. It is based on the combined techniques of crystal orientation measurements using the Electron Back-Scatter Diffraction (EBSD)-technique and 3-dimensional surfaces reconstruction by an Automatic Surface Reconstruction System (ASRS).With this tool we can perform crystallographic fractometry of cleavage fracture facets of polycrystals within the limits of the resolution of a Scanning Electron Microscope (SEM), e.g. we can determine the crystallographic indices of cleavage planes and of directions on such planes.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Ordinary ceramic refractories are used as lining material for industrial pyro-processes. A high resistance to mechanical failure from an imposed strain or thermal shock is usually termed “flexibility”. A scientific approach to enhance this property is hindered by the fact that there is a lack of understanding, definition and measurement of this parameter in relation to its physical basis.Wedge splitting tests were performed on a variety of typically shaped refractories together with standard procedures. This type of test enables stable crack propagation even for relatively large specimen dimensions that are necessary due to the size effect. High “flexibility” proved to be achievable in low brittleness materials and can be characterised by a brittleness number, the characteristic length or the thermal shock fracture resistance parameter according to Hasselman. A sufficient decrease of brittleness can be successfully achieved by the formation of precracks during the burning process which enhance the development of a fracture process zone. For a magnesia refractory (with additions of magnesia-alumina spinel) a friction bridging mechanism plays an important role in reducing brittleness.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— This paper describes the microstructure of Type 304 stainless steel after cyclic loading at room temperature under tension-torsion non-proportional strain paths. The degree of cyclic non-proportional hardening is correlated with changes in the dislocation substructure. Dislocation cells, dislocation bundles, twins and stacking faults are all observed. The type of microstructure formed and resultant stress response is dependent on the degree of non-proportional loading and strain range. Cyclic stress range was uniquely correlated with mean cell size.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Multiple underloads and overloads with constant ΔK were carried out on centre-cracked tension specimens. It was found that when shear lips develop, underloads or overloads affect the crack growth rate da/dN and the subsequent retardation. The appearance of the shear lip fracture surfaces depends on the frequency. At higher frequencies a greater number of rough shear lip fracture surfaces will develop, while at lower frequencies there is a tendency towards smooth shear lips. The amount of crack closure differs in each case. It was found that the type of shear lip, rough or smooth, can be related to the effect on da/dN during and after underloads. The effect of rough and smooth shear lip growth was investigated in constant ΔK tests, performing these tests with and without crack closure.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— In this paper, a stress and modal analysis of an ultrasonic vibration system consisting of a notched specimen and one or two amplifying horns have been performed by using 3D finite element calculations. The stress intensity factors in ultrasonic fatigue crack propagation are evaluated by means of displacement and energy approaches. The particular advantages as well as limitations of the two approaches are briefly discussed. Two types of ultrasonic fatigue loading, with a different stress ratio, are exerted on the specimen. From a comparison of the results a conclusion is formed that the energy approach is more accurate; it also has a wide range of practicality in engineering industries.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— In this study, the relation between fracture toughness and mechanical properties, grain structure, temperature and strain rate is analysed on the basis of a thermo-activation analysis of the plastic deformation of metals.As a result of the study, the relationships obtained are of sufficient accuracy in relation to standard cracked samples of many steels.These relations can be used as a tool when designing new alloys which have a strong resistance to crack growth.This study is limited to temperatures in the range 0 ≤ T ≤ 0.2Tm and BCC metals.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A numerical model for determining the pitting resistance of gear teeth flanks is presented in this paper. The model considers the material fatigue process leading to pitting, i.e. the conditions required for crack initiation and then simulation of fatigue crack propagation. The theory of dislocation motion on persistent slip bands is used to describe the process of crack initiation, where the microstructure of a material plays a crucial role. The simulation of crack growth takes into account both short crack growth, where the modified Bilby, Cottrell and Swinden model is used for simulation of dislocation motion, and long crack growth, where the theory of linear elastic fracture mechanics is applied. The stress field in the contact area of meshing spur gear teeth and the functional relationship between the stress intensity factor and crack length are determined by the finite element method. For numerical simulations of crack initiation and crack propagation in the contact area of spur gear teeth, an equivalent model of two cylinders is used. On the basis of numerical results, and with consideration of some particular material parameters, the service life of gear teeth flanks is estimated. The developed model is applied to a real spur gear pair, which is also experimentally tested. The comparison of numerical and experimental results shows good agreement and it can be concluded that the developed model is appropriate for determining the pitting resistance of gear teeth flanks.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Stress intensity factors for quarter-elliptical corner cracks emanating from a circular hole are determined using a 3-D weight function method combined with a 3-D finite element method. The 3-D finite element method is used to analyze uncracked configurations and provide stress distributions in the region where a crack is likely to occur. Using this stress distribution as input, the 3-D weight function method is used to determine stress intensity factors. Three different loading conditions, i.e. remote tension, remote bending and wedge loading, are considered for a wide range of geometrical parameters. The significance of using 3-D uncracked stress distributions is studied. Comparisons are made with solutions available in the literature.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— This paper presents the results of an experimental testing programme to examine the uniaxial creep, low cycle fatigue and creep/fatigue interaction behaviour of a Ni-base superalloy at 700°C. The material is used in the manufacture of aeroengine turbine discs. A creep continuum damage mechanics model is shown to be capable of accurately predicting the creep and creep rupture behaviour of the material. A healing term has been incorporated into the damage mechanics model to allow the behaviour under creep/fatigue conditions to be described.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The effect of short periods of mixed-mode overloading on the environmental hydrogen induced fracture life of 0.42%C, 0.87%Cr, 0.21%Mo steel has been studied. Tests were performed in 0.5 mol/L H2SO4 solution under continuous hydrogen charging conditions using a weight loading system. Experimental results show that the application of mixed-mode overloads can cause more severe crack growth retardation than those of mode I. Possible mechanisms responsible for the retardation of subsequent crack growth, such as crack deflection, plasticity-induced residual compression stresses, dislocation shielding and overload damage, are examined.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The whole damage process in a finite sized specimen with interacting microcracks is simulated by a method combining the closed form crack solutions with boundary elements. Interactions among microcracks and boundary elements are taken into account with an explicit interaction matrix. A coalescence criterion is assumed to rule the intersection behaviour and propagation arrest. The fatal coalescence cluster resulting in the failure of the specimen, out of many intersections of propagating microcracks, is identified with a particular coalescence matrix. The numerical model proposed in this paper can be used to simulate the damage process in a brittle specimen of any shape, under arbitrary plane stress conditions.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Creep Crack Growth (CCG) tests were performed at 405°C on specimens cut out of the cold bent extrados of five tubes of a C-Mn-Mo steel. Intergranular fracture and grain boundary cavitation was less in the C-Mn-Mo than in the C-Mn steels, in accordance with better CCG resistance of the former material. The dimensions and hardness variation across the crack tip process zone were measured by microhardness profiles performed on metallographic sections of the broken samples. TEM analysis of the dislocation patterns close to the fracture surface confirmed the presence of temperature- and stress-induced plasticity phenomena. A significant enrichment of N at grain boundaries (GB) inside the process zone was detected by Auger spectroscopy; N not only inhibits dislocation motion and stress field relaxation at the crack tip but also causes a decrease in GB cohesion ahead of the crack tip. These results help in understanding the micromechanisms which reduce the creep ductility of C-Mn-Mo and C-Mn cold bent tubes and the role of chemical composition in improving CCG resistance.
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    Notes: Abstract— The effect of specimen size on fracture toughness of a pipe-grade high density polyethylene has been examined using the J integral approach. It was found that the size requirements set up by common standards appear inadequate for this material. Measurements at low temperatures, at which a plane strain fracture toughness value could be obtained, turned out to be very effective in establishing a more appropriate size requirement for this material.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Fractographic peculiarities of fatigue crack development are studied in cruciform specimens of D16T aluminium alloy under out-of-phase biaxial tension and tension-compression. In the range of the biaxial load ratios λ from −0.5 to +0.5 and an R-ratio of 0.3, fatigue striation formation took place beyond a crack growth rate near to 4 × 10−8 m/cycle. The striation spacing and the crack growth rate increase as the φ-angle of the out-of-phase biaxial loads increases in the range of φ-angles from 0° to 180°. The ratio between the increment of crack growth, da/dN, and the striation spacing, δ, is approximately 1 to 1 when da/dN is greater than 4 × 10−8 m/cycle. The relationship between the number of cycles from the beginning of a test up to the growth rate of 10−6 m/cycle (Nd), and the crack growth period, NP, from when the crack initiates up to the instant when that growth rate is reached, was determined for different λ ratios and φ angles. The value of Nd decreases as the φ angle is increased in the range from 0° to 1807deg;.Cycle loading parameters must be taken into account in order to describe the crack growth period when using a unified method that involves an equivalent stress intensity factor Ke=KIF1(λ, R)F2(φ). The values of F2(φ) were determined.The calculated fatigue crack growth period, Nc, applicable up to and including the stage of fatigue striation formation (predicted by using both of the F1(λ, R) and F2(φ) functions) is correlated with the experimental data and the error is of the order of 15%.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The occurrence of brittle stable crack growth before unstable fracture was demonstrated with the aid of heat-tinting, for a ferritic matrix super duplex stainless steel which had been age-hardened at 475°C. The critical crack tip opening displacement for stable crack growth, i.e. the crack initiation toughness, was measured using the direct-current-potential drop crack monitoring technique. A quantitative model for the effect of temperature and age-hardening on the brittle crack initiation toughness is described.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Fatigue crack propagation characteristics are measured by continuously determining the resonant frequency in vibrating systems, which is stabilized through a feedback control loop. The precisely controlled resonant frequency is related to the crack length by a nonlinear model based on fracture mechanics, hence crack growth can be monitored with respect to time with very high accuracy. The nonlinearity due to the opening and closing of the crack needs to be taken into account. In contrast to conventional fatigue tests, which require a long duration of time due to the high numbers of load cycles at low frequencies, the proposed technique operates at much higher frequencies, i.e. in the range of 100 Hz to 100 kHz. Thus the required time for measurements in the high cycle fatigue range is considerably reduced. The experimental setup is simple and inexpensive and does not require high energy inputs.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Microstructure and mechanical properties of HP (Hot Pressed), HP/GP (Gas Pressed), and HP/HIP (Hot Isostatic Pressed)—Si3N4 are studied using scanning electron microscopy, bending tests and the indentation fracture method. The grain diameter distribution is analyzed to clarify the relationship between microstructure and mechanical properties; and also the bending strength and fracture toughness. It is shown that bending strength increases with decreasing grain diameter. The results also show that a Hall—Petch type of relationship is obtained between grain diameter and fracture strength. The fracture toughness shows a linear relationship with 〈inlineGraphic alt="inline image" href="urn:x-wiley:8756758X:FFE829:FFE_829_fu1" location="image_n/FFE_829_fu1.gif" extraInfo="missing"/〉, where σF= bending strength, β= a proportionality factor and da= average grain diameter, and is closely related to the aspect ratio of Si3N4 grains. It is concluded, from the morphological analysis, that a microstructure composed of Si3N4 grains, with both a small grain diameter and a large aspect ratio, is effective in improving both the fracture strength and fracture toughness.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The random temperature fluctuation produced by the incomplete mixing of hot and cold fluid streams passing over the surface of a component or structure is known as thermal striping. This phenomenon may cause thermal fatigue to occur. It is of particular concern in various types of nuclear reactors, for rapid shut-downs of hot plant and in thermal stratification. A computer code, “TBL”, is a design tool which has been developed to assess thermal striping damage in plates. This model is further developed in this paper to assess such damage in cylindrical components. A recent, universal weight function method is examined and incorporated into TBL. Good comparisons are found between TBL and finite element results for a sinusoidally varying temperature-time-striping history. Potential thermal striping damage is assessed for a cylindrical component of material typically found in the above-core region of a fast reactor under a random temperature-time-striping history.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The mechanical behaviour of AISI 329 steel has been investigated for ageing times up to 20,000 h at temperatures of 475, 425, 375, 325 and 275°C. The study has concentrated on the changes in the response to cyclic strains, in the low-and the high-cycle fatigue regimes, and in the resistance to fatigue crack propagation as a function of temperature and time of ageing.It is shown that ageing increases the fatigue resistance in the high-cycle fatigue regime, but the opposite occurs in the low-cycle fatigue regime. Ageing increases the LEFM threshold stress intensity factor range for fatigue crack propagation which reaches high values in these alloys, and is influenced by the fatigue load ratio. Crack closure contributes to the LEFM threshold stress intensity factor range for crack propagation only in the annealed condition of the AISI 329 steel.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Low cycle fatigue tests under axial, torsional and combined axial-torsional loading were conducted using thin-wall tubular specimens of Ti-6A1–4V titanium alloys. Two kinds of alloys with different microstructures, the (α+β) and β alloys, were investigated in fatigue tests at room temperature. When the failure life was correlated with the equivalent plastic strain, the life in axial loading shifted toward the lower life region compared with those in other loading modes in both alloys. Dominant surface cracks propagated in mode I under axial and combined loading in the two alloys. Although growth by the mode II type was predominant under torsional loading, the growth direction of the main crack coincided with the specimen axis in the (α+β) alloy, but the circumferential direction in the β alloy. The cracking morphology depended on the microstructure, especially under the torsional mode of loading, and was simulated successfully by using the proposed model for crack initiation.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Fracture behaviour of injection-moulded polypropylene filled with silane-treated talc was studied as a function of filler volume fraction (0–20%) and compared to that of polypropylene filled with untreated talc. High-rate tests (0.57 m/s) on SENB specimens were carried out using an instrumented Charpy impact pendulum, and linear elastic fracture mechanics (LEFM) was applied to calculate the fracture parameters, KC and GC. It was found that moderate fractions of talc which were added to the polypropylene matrix increased the fracture toughness of the composite independent of the talc surface treatment. This general improvement seems to be due to the peculiar orientation of the talc platelets in the injection-moulded specimens. The fracture behaviour of the composites was also studied at low strain rate (1 mm/min) by tests on J-integral type specimens with the same SENB geometry. In this case, the composites with silane-treated talc presented poor J-integral values compared to those of the samples with untreated talc. This was attributed to a reduction of the plastic zone at the crack tip, since the improved coupling between the talc platelets and matrix increased the yield strength of the composite. All the results are explained on a basis of morphological and microstructural details.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Using experimentally determined data on fibre radius distributions, yarn geometry, matrix and fibre elastic moduli and frictional shear stress at the matrix/fibre interface (obtained by nano-indentation experiments), the failure probability of the composite fibre yarns (after matrix cracking) is estimated. Each fibre is divided into a fixed number of segments above and below the matrix crack. The failure probability on every segment of each fibre is computed using Weibull fibre strength statistics. A fibre is assumed to be broken when the cumulative failure probability for the complete yarn reaches a value of 0.5. The segment and fibre are then selected at “random”, according to their individual failure probabilities. After fibre failure, the broken fibre can only carry the frictional load and the load drop is transferred to its neighbours according to their distances to the broken fibre. The remote stress is then modified to match again the cumulative failure probability of 0.5 and a new fibre is broken. This procedure is repeated until all the fibres are broken. In this way, it is possible to obtain the “characteristic” load carried by the yarn and its corresponding elongation. Fibre extraction and pull-out behaviour are also considered. The roles of different load-transfer laws (from global to highly localised) are examined. The model is applied to simulate the fracture tensile behaviour of individual yarns of SiC/SiC ceramic-matrix composites. The results are compared with those obtained from tensile experiments on SiC/SiC individual yarns. The computed fracture morphology, in terms of individual pull-out lengths, is also compared to the actual SEM fractography of a woven SiC/SiC composite.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The subject of hypersingular boundary integral equations is a rapidly developing topic due to the advantages which this kind of formulation offers compared to the standard boundary integral method. The hypersingular formulation is particularly well suited for fracture mechanics problems, where there are important gradients of the stress field and singularities. This formulation for time domain antiplane problems has been recently addressed by the authors and in the present paper, the formulation for time domain plane problems is presented and applied for the first time. A mixed Boundary Element approach based on the standard integral equation and the hypersingular integral equation is developed. The mixed formulation allows for a very simple discretization of the problem, where no subregion is needed. Conforming quadratic elements are used for the crack and the external boundaries. The hypersingular integral equation is used for collocation points within the crack elements, while the standard integral representation is used for the external boundaries. Several examples with different crack geometries are studied to illustrate the possibilities of the method. The Stress Intensity Factor (S.I.F.) is very accurately computed from the crack tip opening displacements along the crack tip element. The results show that the proposed approach for S.I.F. evaluation is simple and produces accurate solutions.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A two-dimensional elastic-plastic finite element analysis is performed for plane stress conditions with 4-node isoparametric elements to examine closure behaviour of fatigue cracks, giving special attention to the determination of the most appropriate mesh sizes. It is found that a smaller mesh size does not always give more accurate simulation results in the fatigue crack closure analysis, unlike a conventional structural analysis. A unique, most-appropriate mesh size exists for a given loading condition that will provide numerical results which agree well with experimental data. The most appropriate mesh size can be determined approximately in terms of the theoretical reversed plastic zone size. In particular, the ratio of the most appropriate mesh size to the theoretical reversed plastic zone size is nearly constant for a given stress ratio in the so-called crack-length-fixed method proposed in this study. By using the concept of the most appropriate mesh size, the finite element analysis can predict fatigue crack closure behaviour very well.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— High strain-rate tensile tests have been carried out on pre-notched specimens of OFHC copper and Remko iron at both elevated and cryogenic temperatures. When properly expressed as a function of stress triaxiality at the centre of the notch (as predicted by numerical simulations of the experiment), the ductility of copper was found to be independent of temperature over a range from —190°C to 300°C. The specially-processed Remko iron was found to undergo a ductile-to-brittle transition at a temperature dependent on the stress triaxiality and the particular batch of the material. Otherwise the fully ductile strains-to-failure (when expressed as a function of stress triaxiality) for iron were found to decrease with increasing temperature up to 400°C; this being the maximum temperature tested.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Fatigue crack growth experiments were carried out on cruciform specimens of D16T Al-alloy, loaded under uniaxial and biaxial loads, including a sequence of various overloads. It is shown that, for biaxial cyclic loads at stress ratios λ and various R-ratios, fracture surface development during overloads and the crack length dependences on the cyclic loads following overloads are similar to those for uniaxial loading.The aim of this investigation was to study interaction effects by analyzing the crack retardation length and associated parameters together with their relationships. These parameters’depend on the biaxial ratio (λ) and the stress ratio (R) and their uses in crack growth modelling are briefly considered.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The fracture behaviour of cast duplex stainless steels, heat treated to different ferrite contents and hardness was investigated using tensile and notched bend tests. The purpose was to identify the microstructural features which controlled the ductile-to-brittle fracture transition of 475°C embrittled duplex stainless steel. The results indicate that twin nucleated cleavage has a tensile stress fracture criteria and the brittle-to-ductile transition temperature depends on ferrite microhardness, ferrite grain size and constraint.
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    Notes: Abstract— A number of fretting fatigue tests were carried out on CMV steel and INCO 718 alloys under closely controlled experimental conditions. A fracture mechanics-based lifing model was developed and the Paris Law employed to predict fatigue lives under a range of experimental conditions. An effective initial flaw size was used to describe initiation and early propagation of cracks. This approach was found to give good predictions of fatigue life of specimens for different values of bulk stress under the same fretting load.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— This paper develops some useful formulae relating the estimated and the actual values of the parameters of the Weibull and of the Exponential Probability Distribution functions. These formulae simplify the calculations for Monte Carlo simulations executed for the estimation of some reference statistics, for instance, the reliability function. The reduction of the calculation is possible because of the reduction of the possible values that the parameters of the random numbers generating function should assume. In some cases of the reliability function, only one Monte Carlo simulation is necessary for a given data sample amplitude. An explanation is made of the use of these formulae when estimating the reliability function.
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    Notes: Abstract— Measurements of CTODi on Charpy-V-specitnens of mild steel St 37 and pressure-vessel steel 22NiMoCr37 have been carried out. Slotted and precracked specimens have been used besides the original V-notched ones. A definition of CTOD = 2(R – Ro) has been proposed which corresponds to δ45, defining the CTOD of fatigue cracks. The symbols Ro and R represent the original and the actual crack tip radii respectively. Additionally, this definition presents the opportunity to measure CTOD and CTODi by a direct metallographic method. It is demonstrated that COD testing, based on the hinge model, can also be applied to slotted bars, delivering CTOD and CTODi values which are equal to those evaluated by direct metallographic measurements.The results obtained on four different tip radii, Ro, show a linear increase of CTODi as a function of Ro, which is steeper for the softer material St 37. The extrapolation to the tip radius Ro=0 gives a CTODi, which is equal to those determined from precracked specimens.
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Stress intensity factors are determined for internally and externally cracked, pressurized thick cylinders with partial autofrettage (less than 100% overstrain). The solutions are based on a superposition of existing solutions which does not involve any loss of accuracy. Implications of the stress intensity factor results for the safe-life design of pressure vessels subjected to fatigue are discussed.
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
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    Notes: Fatigue crack propagation tests were conducted under conditions of equibiaxial, uniaxial and shear loading by using a cruciform specimen in a servo hydraulic testing machine. The effect of non-singular stress cycling on the fatigue crack propagation rate was examined based on the observation of crack opening behavior. The crack propagation rate was significantly influenced by the non-singular stress parallel to the crack when it was correlated to the stress intensity range. The crack closure behavior was greatly affected by the non-singular stress. The crack propagation rate was uniquely correlated to the effective range of the stress intensity factor except for the case of completely reversed shear loading where significant plasticity was detected. The crack opening displacement range was concluded to be a parameter controlling the crack propagation rate for all the stress conditions examined in the present experiments. Some discussion is made on the effect of material anisotropy on fatigue crack propagation in a biaxial stress field.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The paper presents a comprehensive review, supplemented by original data, of the engineering fatigue behaviour of copper. Variations in manufacturing route and softening treatments are shown to have little effect on the fatigue of annealed copper but the high cycle fatigue strength is increased by cold work. The high strain fatigue behaviour is defined in terms of the plastic strain range and the cyclic stress-strain characteristics are documented. Fatigue behaviour in bending and torsion is defined by data and related to that in tension by simple design rules.Notches are found to reduce the laboratory measured fatigue strength of copper by ∼ 30% and the effect of surface finish, surface distortion and surface residual stress is defined in the literature. Fatigue crack growth is defined in terms of stress intensity factor range ΔK by an upperbound law and, together with the conditions for non-growth (ΔK0), shown to relate to the equivalent conditions for steels via the ratio of the respective elastic moduli.The effect of environment on the fatigue of copper has received scant attention in the literature, such results as exist suggesting little if any reduction in strength to be brought about by gaseous or aqueous environments. The most dramatic change is the improvement of about an order of magnitude which results when tests in vacuum are compared with equivalent tests in air. Results of fatigue tests on copper in ammoniacal environments are conspicuously absent from the literature.As the test temperature is reduced below room temperature there is a predictable increase in high cycle fatigue strength, a reduction in fatigue strength occurring above room temperature. High strain fatigue test results presented in terms of plastic strain range appear insensitive to temperature although at very low strain rates and high temperatures a reduction in fatigue strength occurs. A linear life fraction cumulative damage creep-fatigue law appears sometimes to be non-conservative but much more testing is needed to evaluate fatigue damage summation laws generally for copper.Numerical data are given in support of all the aspects of the engineering fatigue behaviour reviewed in the paper.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The birth and growth of short cracks is analysed from an elastic-plastic fracture mechanics viewpoint. Low to high cumulative damage tests from the low stress to high strain regime indicate that there is no crack initiation period in the metallurgical sense and that cracks grow from the first cycle, but at a slow rate. The initiation phase terminates when one crack starts to dominate and accelerates to failure, its initial size being given by 〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:8756758X:FFE263:FFE_263_mu1"/〉 for the medium carbon steel tested here, of grain size 56 μm.
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    Notes: Fractographic analyses have been used to explain the cyclic crack growth behaviour of A533-B, Ducol W30, a C-Mn steel and type 304 stainless steel in simulated light water reactor environments at ambient temperature. Fractographic observations have offered an explanation for anomalous crack growth behaviour and have also indicated where micro structural or environmental variables dominate in producing certain fracture modes and crack growth rates. An understanding of the operative corrosion fatigue mechanisms has been formulated through these fractographic analyses. Environmental crack growth in the ferritic steels has been described by a model involving both anodic dissolution and hydrogen embrittlement. Conditions where only one of these mechanisms would dominate have been identified and limits to their effect postulated. A crystallographic mode of failure observed in the austenitic type 304 stainless steel has also been explained by a selective dissolution process.
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract —Low-cycle fatigue properties were investigated on four carbon steels and five low alloy steels specified in JIS (Japanese Industrial Standard) for machine structural use, which are the most commonly used in Japan. Several different heats from each of several representative manufacturers were sampled so as to represent the average fatigue characteristics of current materials. The cyclic deformation behaviour of material was denned by comparing the monotonie yield stress on the extrapolated tensile work hardening curve with the cyclic yield stress in the cyclic stress-strain curve determined by incremental step test. The normalized ferrite-pearlitic steels cyclically hardened, while the quench-tempered martensitic were cyclically stable or softened. The S–N relations derived from the strain-controlled low-cycle tests were compared with the results obtained by load-controlled high-cycle tests. The extrapolated S–N curves based on the cyclic stress-strain curve predicted the fatigue strength in the high-cycle range to be stronger for cyclic-hardening steels, but weaker for cyclic-softening steels. The predicted S–N curves for stable steels coincided with the high cycle test data. The fatigue limit had a proportional relationship with cyclic yield stress, slightly depending on the cyclic deformation behaviour. On the other hand, the cyclic yield stress was found to exhibit a very good linear correlation with the monotonie tensile strength, independent of cyclic deformation behaviour. This explains the empirical law that the fatigue limit is approximately proportional to the tensile strength.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The magnetic emission (ME) technique is used to determine the onset of crack propagation in brittle and ductile steels under dynamic loading. Brittle fracture is directly indicated by the ME signal; however the onset of stable crack propagation can usually not be seen in this signal. A new result is that the integrated ME signal, which is proportional to the magnetic field at the site where the probe is located, is capable of detecting this event. Critical values of the J-integral derived with this method, in different test series, are compared with conventional R-curve and stretch zone methods. The ME-derived critical dynamic J-integral data fit very well to the stretch zone results which describe physical crack initiation. It is therefore concluded that the easy-to-apply and low-cost ME technique is capable of indicating material failure even with stable crack propagation and can therefore provide critical material parameters.
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    Notes: Abstract— An alternative methodology is presented for determining stress intensity factors for cracks subject to mixed-mode displacements. The methodology involves thermoelastic data generated from a SPATE (Stress Pattern Analysis by Thermal Emission) system and has been adapted from one used successfully in photoelasticity. The thermoelastic data is collected throughout the elastic stress field dominated by the crack tip singularity. The stress field is described using a Fourier series within Muskhelishvili's approach. This method allows different applied stress fields to be described which may include transient or non-uniform stress fields. The results obtained using the new methodology are at least as good as those obtained previously for pure mode I cases, and generally better for mixed mode displacement conditions.
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    Notes: Abstract— The solute-rich beta titanium alloy Ti-3Al-8V-6Cr-4Mo-4Zr was subjected to 1500 bar nitrogen pressure at elevated temperatures (500–920°C), leading to a diffusion layer with a high surface hardness. Microstructural, crystallographic and compositional analyses indicate that TiN (δ) and Ti2N (ε) are formed at temperatures exceeding 815°C. The increased concentration of nitrogen, which is a potent α-stabilizer in titanium, also causes α-Ti to form near the surface. The nitriding treatment does not significantly alter the tensile properties or fatigue limit in solution heat treated material. A subsequent ageing treatment of 72 h at 440°C and 16 h at 500°C reduces toughness significantly, allowing cracks induced by nitriding to propagate more easily into the bulk. Tensile ductility and fatigue performance of aged nitrided Ti-3Al-8V-6Cr—4Mo-4Zr are thus significantly lower than in the untreated reference condition.
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— Fatigue crack growth after a biaxial overload has been investigated. The crack retardation parameters, ND, and, aD, do not have monotonous dependencies on the biaxial stress ratio, λ, because the shear stress, τIII, acting in the perpendicular direction of the specimen face, influenced the values of these parameters.It has been found that the plastic zone size parameters, rab, and Δ, do not increase monotonously with increasing λ ratio. The plastic zone size in the crack growth direction, rho=aD13, was calculated on the basis of newly proposed relations.Crack growth after an overload was simulated on the basis of the equivalent mode I stress intensity factor, ICC, invoking a unified kinetic diagram and calculated crack increments, aD13 and aD=Δc, where Δc is the maximum value of the calculated size of plastic zone. The experimental data for crack growth after an overload had good agreement with the calculated data.
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  • 79
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 80
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— A three dimensional, elastic-plastic, finite element analysis of fatigue crack growth and plasticity-induced crack closure has been performed for a range of small, semi-circular cracks. Predicted crack opening displacements have been compared with data obtained from in-situ SEM measurements for a coarse-grained aluminium alloy 2024-T351. The magnitude of fatigue crack closure measured from in-situ SEM measurements was consistently higher than that predicted from the finite element analysis. It is deduced that the higher closure stresses obtained from in-situ SEM measurements are due to the contact of asperities on the fatigue crack surfaces. A simple mathematical model is suggested to describe the fatigue crack closure stress caused by the combination of both a plastic wake and asperities on the fatigue crack surfaces. The predicted fatigue crack closure stresses and their dependence on crack size are consistent with experimental measurement.
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  • 81
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The precision with which the stress intensity factor (SIF) can be calculated from a finite element solution depends essentially on the extraction method and on the discretization error. In this paper, the influence of the discretization error in the SIF calculation was studied and a method for estimating the resulting error was developed. The SIF calculation method used is based on a shape design sensitivity analysis; this assures that the resulting error in the extracted SIF depends solely on the global discretization error present in the finite element solution. Moreover, this method allows us to extend the Zienkiewicz-Zhu discretization error estimator to the SIF calculation. The reliability of the proposed method was analysed solving a two-dimensional problem using an h-adaptive process. Also the convergence of the error with the h-adaptive refinement was studied.
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  • 82
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Recently a controversy has developed over whether crystallographic crack growth near threshold in Ni-base superalloys occurs along {111} slip planes or {100} planes at room temperature. In this work on Nimonic API crack propagation is shown to occur on both {100} and {111} planes. The most common facet plane is {111} and this is the only orientation observed at the lowest stress intensities, but at higher stress intensities occasional {100} facets are also produced. This behaviour is compared with similar results in aluminium alloys.
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  • 83
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A crack nucleation model is constructed based on the random slip of the dislocations within the fatal persistent slip band (PSB). From such a model, we derive the notch-peak probability function. The crack is considered to nucleate when a critical notch depth is attained. This depth is constant for applied strains corresponding to the plateau of the cyclic stress- strain curve because the stress is constant. The PSBs behave in such a way that the more concentrated their localized slip the fewer the cycles required to attain the critical notch depth. Using the experimental relation between the applied strain and the magnitude of the slip offsets (reported in Part I) in conjunction with observations of the notch distributions along the gage surface, we have obtained the relation between the applied strain and the cycles for crack nucleation. A log-log plot of this relation shows a slightly different slope from that of the Coffin-Manson life data, previously reported. However, by allowing for cycles spent in Stage II propagation, good agreement is obtained.
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  • 84
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The statistical nature of fatigue crack growth rate has been examined for G41400 steel exposed to different heat treatments and for different loading and environmental conditions. Techniques for determining the intrinsic value of the crack propagation rate are discussed. The intrinsic scatter due to the material has been evaluated and considered in terms of its effect on fatigue life prediction, both normal and log normal distributions of fatigue crack growth data being considered. It appears that the intrinsic material scatter in crack propagation rate is closely related to the scatter in total life.
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  • 85
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A d.c. potential drop formula has been established for monitoring crack growth in circular notched members subjected to torsion. Changes in crack depth of 20 μm can be detected in cracks growing up to 2 mm in depth.
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  • 86
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Tensile specimens of Ti-6A1-4V with four levels of interstitial oxygen content and a Ti-8Al-1Mo-1V alloy with different heat treatments to alter grain size and/or microstructural character are subjected to slow strain-controlled cyclic deformation leading to rupture in the 5-500 cycle range. Indication of crack initiation as well as rupture life are compared, relative to the plastic excursion strain. On this basis, the effects of grain size and oxygen content are not clearly discriminated. Yet, some of the materials exhibit markedly superior performance. This improvement seems to be related to a characteristic evolution in the shape of the cyclic stress-strain curve. Here, relative to a full convex hysteresis loop of early cycles, the later cycles exhibit a reduced stress level, or cyclic softening, in the first half of the excursion, followed by a resurgence of strength to initial stress levels in the latter portion. The enhanced strain hardening rate enabling this terminal strength restoration is thought to stabilize the deformation, reducing the amount of stress-relaxation-induced tensile strain. Taking such strain as an increment of damage in a cumulative cyclic creep strain criterion provides a correlation between the evolving shape of the cyclic stress-strain curve and the low cycle fatigue endurance. Results indicate the absolute increase in the terminal plastic strain hardening rate to be a constant of a material, independent of the cyclic strain excursion.
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  • 87
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
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    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Substantial effects of hydrogen are found on the DBTT and cleavage fracture stress in both cathodically and gas phase charged samples of a BCC Ti alloy. Fatigue thresholds when plotted as a function of temperature exhibit a peak and this peak shifts towards higher temperatures when the hydrogen level is increased. An elastic calculation of static threshold stress intensities using experimentally observed fracture stress parameters show a similar trend to fatigue threshold stress intensities.
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  • 88
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 89
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract —An experimental method was developed to quantify the formation and subcritical propagation of small cracks emanating from artificial surface defects. Continuous crack depth information was obtained from dc electrical potential measurements employing an analytical model. Fatigue experiments were conducted to evaluate the crack monitoring procedures for conditions relevant to the elevated temperature defect tolerance of superalloys. Cracking progressed uniformly and predictably from small surface defects (0.1 mm deep and 1.4 mm long) in A286, 304 and 10Ni steels and in René 95 and MP–159 superalloys. Crack depths, computed based on analytical calibration of measured electrical potentials, agreed to within ±18% of corresponding values measured optically. Similar results were obtained for a penny-shaped defect, 75 μm deep. Applications of the technique were investigated, including characterizations of fatigue crack formation and growth in René 95.
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  • 90
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract —Fatigue tests under four-point bending were carried out on low alloy steel welded I-beams under constant and variable amplitude loading. Four different types of stiffeners welded to flanges and webs were analysed. Particular attention was paid to the effect of configuration at the stiffener-ends. It was shown that the stiffener-ends were the most critical points. Fatigue cracks initiated and propagated in both tension and compression flanges. The fatigue life to crack initiation was calculated on the basis of the local stress-strain analysis. Both theoretically and experimentally estimated stress concentration factors were used for calculation. The predicted fatigue lives were compared with the respective values obtained in experiments.
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  • 91
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Several crack tip stress intensity factor solutions have been published for semi-elliptic, surface breaking cracks in plates subjected to tension or bending forces. These solutions do not agree with each other particularly well and the basis for choosing which one is the best has not been established. In this paper, the development of fatigue crack shape is used as a diagnostic tool to test the accuracy of these theoretical stress intensity solutions in predictive fatigue crack growth calculations. Those solutions giving the best engineering estimate of crack tip stress intensity factors are identified. Single equations are also given for each loading case at the deepest point or surface intersection point of semi-elliptic cracks in order to facilitate calculations on programmable calculators. A rational basis for calculating the progress of a crack which snaps through the thickness and continues to propagate in a stable way by fatigue is suggested.
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  • 92
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In low strain fatigue, cracks often form in persistent slip bands (PSB) in a wide variety of materials. Observations of crack nucleation involving PSB have been made in copper single crystals by careful interferometric studies. The width, length, step height and thus strain localization in the PSBs remain very stable during saturation, even up to three-quarters of the life. For a given applied strain amplitude, the specimen will form PSBs having a certain distribution of slip offsets. The fatal crack is found to nucleate in the group of micro-PSBs having the largest offsets, and the largest strain localization. The PSB volume fraction for a given strain amplitude depends only very slightly on crystal orientation, and the slip offsets not at all. Thus the kinetics of crack nucleation are not affected by orientation. The mechanism of nucleation is concluded to be one of random walk in the slip offsets of PSBs.
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  • 93
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The cyclic strain hardening occurring during fatigue testing at 550°C was studied in terms of the dislocation structures developed. The dislocations are collected in dense tangles which form the boundaries of a cell structure. The stress required to push through, or eject, a dislocation from the cell boundary predicts the flow stress. These values showed good correlation with the cyclic shear stresses obtained by applying the Tresca criterion, which underlies its usefulness in design under cyclic loads. Carbide particles are shown to precipitate on grain and cell boundaries.
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  • 94
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The results of high temperature low cycle fatigue (HTLCF) on IN 738, obtained from two different sources, were used to study the applicability of strain-range partitioning (SRP) to this alloy. In spite of the difficulty in separating the plastic-plastic strain component from the different strain-life relations, an attempt was made to determine the coefficients and exponents for each of these relations from both sets of data. The observation that compressive creep, balanced by tensile plastic deformation, was more damaging than the reverse, could be related to the behaviour of the material. The evidence of the effect of temperature on the plastic-plastic strain-life relation, reported by some researches, was shown to be not decisive in the reported temperature range. The reasonable agreement and the similarity in the material's behaviour, obtained from the analysis of the high temperature low cycle fatigue of the two sets of data, substantiates the applicability of the strain-range partitioning method to IN 738 alloy.
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  • 95
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A literature search has revealed that the most extensive study of impact fatigue reported is still that of Stanton and Bairstow (1908) who were the first to work on this topic. Their results, which were on pearlitic plain carbon steels, have been reanalyzed in an attempt to deduce from them the effects of chemical composition on impact fatigue in this class of materials.The results show that when the number of impacts to failure, Nf, is greater than about 103, Nf and the energy absorbed per impact, Ei, are related by the equation: Ei, =Eo+EkNf−p, where Eo appears to be the impact endurance limit. It is suggested that Ek and p be named respectively the “impact fatigue parameter” and “impact fatigue exponent”. Ek is independent of composition except that it is lower by a factor of about four for two materials which probably failed by an intercrystalline rather than transcrystalline fracture; p has a value of 0.6; and Eo increases monotonically with silicon content but does not vary systematically with the carbon, manganese, sulphur or phorphorus contents. The significance of these results is discussed.
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  • 96
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: –The article describes a method developed at ONERA for predicting the lifetime of gas turbine blades. This method makes use of non-linear viscoplastic constitutive laws, the problem being solved from a plane cross section assumption and through a time-step linearization. The initiation of the first macroscopic crack is calculated from a stabilized cycle condition. A blade test rig has been developed for checking the method under load and temperature conditions that are as close as possible to operational ones. The results of two series of tests on convection cooled IN100 blades prove the method to be acceptable to design engineers.
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  • 97
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract —This report presents the results of a round robin study on the fatigue crack arrest threshold (δKth) of 2618 aluminium alloy and AISI 316 steel.The main purpose of this work was to develop a method for the determination of δKth, and to examine the influence of various test parameters on this threshold.Among the parameters considered, only the load ratio (R) and the environment (vacuum) appear to have a significant influence on very slow fatigue crack growth rates (FCGR). Moreover, while the results obtained with the 316 steel show great scatter, the importance of the adopted procedure is pointed out.
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  • 98
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract —Mixed mode fatigue crack growth is analysed using Sih's strain energy density approach. A centre crack panel geometry loaded under uniaxial cyclic tension is considered. The crack angle is varied from 30° to 90°. A procedure for the determination of crack propagation life is outlined. The crack trajectory due to cyclic loading is predicted. The crack growth rate, the cyclic life and the cyclic life ratio are discussed, for an aluminium alloy and a steel, as a function of initial crack angle, crack length, stress amplitude, and the strain energy density factor.
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  • 99
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    Fatigue & fracture of engineering materials & structures 4 (1981), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract —In recent years the low fatigue growth rate regime has been the subject of extensive study revealing its complex and often seemingly inconsistent nature. The value of alternating stress intensity at threshold ΔKTh) is sensitive to a range of variables which include mean stress, stress history, monotonie and cyclic yield strength, grain size and environment. A degree of coherency may be achieved by interpreting the data in terms of a crack closure mechanism which is a function of surface roughness. Experiments, in which the surface roughness (φ) has been altered by the introduction of non-metallic inclusions, give insight into the significance of crack closure in this regime.
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    Fatigue & fracture of engineering materials & structures 20 (1997), S. 0 
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— The effect of void shape on the mechanical behaviour of an elastic-plastic solid containing an isotropic array of aligned axisymmetric voids is examined. The mechanical response of such a material is studied by means of finite element (FE) analyses of an elementary unit cell containing an isolated void. The void shape is found to have a strong influence on both void growth rate and coalescence strain. This effect is strongest for low stress triaxialities. The numerical results are compared with analytical models of void growth, but none of the examined models give any good predictions of the results obtained numerically. A simple modification of the classical Gurson model is suggested so as to give reasonable correspondence with numerical results. Finally, some practical considerations of void shape effects are given.
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