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  • 1
    Electronic Resource
    Electronic Resource
    Self-similar crack patterns induced by spatial stress fluctuations (2002)
    Oxford, UK : Blackwell Science, Ltd
    Fatigue & fracture of engineering materials & structures 25 (2002), S. 0 
    Details
    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 mechanism of the formation of multiscale self-similar crack structures in brittle materials is proposed based on the action of spatial random stress fluctuations (random stress fields) with vanishing mathematical expectation. The presence of self-equilibrating stress fluctuations is, in many cases, characteristic of heterogeneous brittle materials even in the absence of external loading. Some examples are given by residual stresses—stresses caused by phase transformations or internal microscopic heat sources. If the stress fluctuations are strong enough to cause cracking, the cracks will be originated in regions with and perpendicular to the highest local tension. As a legacy of this special location, additional local tractions opening the crack in its centre are developed even in self-equilibrating stress fields. This mechanism is modelled by disklike cracks opened by a pair of concentrated forces applied at the centre. Two cases are considered: (i) the crack growth in the moving equilibrium conditions caused by the self-equilibrating stress fluctuations of increasing amplitude; and (ii) the subcritical crack growth under the stress fluctuations of either sustained (creep) or oscillating (fatigue) amplitudes. As the cracks grow, the interaction between them leads to a separation of crack sizes. The effects of the interaction are modelled by the differential self-consistent method that is shown to become asymptotically accurate as the ratio between the sizes of the interacting cracks increases. The interaction results in the crack distribution tending to a self-similar one with the distribution function proportional to the inverse fourth power of the crack radius.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.8756-758x.2002.00487.x
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanisms of brittle fracture of rock with pre-existing cracks in compression (1994)
    Springer
    Pure and applied geophysics 143 (1994), S. 117-149 
    Details
    ISSN: 1420-9136
    Keywords: Rock fracture in compression ; 3-D cracks ; laser technique of crack initiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Fracture of rocks containing a multitude of pre-existing cracks is considered from both theoretical and experimental points of view, paying attention mainly to the underlying mechanisms. The competition between a number of mechanisms in producing tear or shear type fractures is discussed in relation to the properties of the rock and the system of pre-existing cracks on the one hand and the type of loading on the other hand. First, 2-D theoretical models and experimental results aimed at the explanation and description of brittle fracture under compression are considered. Their insufficiency and the necessity to address the 3-D peculiarities of crack growth in rock are shown on the basis of new experimental results on 3-D crack propagation in transparent rock-like brittle materials under uniaxial compression. The results show that in contrast to the 2-D case, a single 3-D crack cannot propagate any appreciable distance and the loading results in dynamic, burst-like failure of the sample. Possible mechanisms of the routinely observed extensive fracture propagation in rock samples (splitting), as well as the possibility of shear (oblique) fracture in uniaxial compression, are discussed in connection with these experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00874326
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  • 3
    Electronic Resource
    Electronic Resource
    Virial expansions in problems of effective characteristics. 1. General concepts (1994)
    Springer
    Mechanics of composite materials 30 (1994), S. 157-167 
    Details
    ISSN: 1573-8922
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Conclusion The (virial) power series of the concentration of inhomogeneities (particles) obtained in principle solve the problem of calculating the effective characteristics. The proposed form of the virial expansions does not contain integrals requiring regularization. This was attained by considering virial expansions in finite bodies, where it can be shown that the principal parts of the integrals which give convergence in passing to an infinite body are equal to zero due to the equilibrium equations in summation of the effect of all surrounding particles on the isolated particle. From a practical point of view, calculation of then-th term of the expansion requires solving the problem ofn inhomogeneities, which restricts the applicability of the method. However, the virial series are convenient for analysis of simpler approximate methods such as self-consistent methods, for example. The next communication will treat such an analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00635848
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  • 4
    Electronic Resource
    Electronic Resource
    A study of the mechanism of flexural toppling failure of rock slopes (1997)
    Springer
    Rock mechanics and rock engineering 30 (1997), S. 75-93 
    Details
    ISSN: 1434-453X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Summary The mechanism of flexural toppling failure of jointed rock slopes has been investigated through a series of centrifuge experiments conducted on models manufactured from two types of materials (brittle: a sand-gypsum mixture; and ductile: fibre-cement sheeting). The basal failure plane observed in the centrifuge models, has been found to emanate from the toe of the slope, and orient at an angle of 12 to 20° upward from the normal to the discontinuities. A theoretical model based on a limiting equilibrium approach (Aydan and Kawamoto, 1992) has been adopted to analyse the centrifuge test data. After calibration, the model was found to accurately predict the failure load for all the tests reported in this study. Using this model, a set of charts has been prepared to assist with the analysis of slopes susceptible to flexural toppling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01020126
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  • 5
    Electronic Resource
    Electronic Resource
    Virial expansions in problems of effective characteristics. 2. Antiplanar deformation of a fiber composite. analysis of self-consistent methods (1994)
    Springer
    Mechanics of composite materials 30 (1994), S. 234-243 
    Details
    ISSN: 1573-8922
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Conclusion The virial expansion for the effective shear modulus (condition of antiplanar deformation) was constructed for an isotropic material with parallel cylindrical inclusions and the terms which are quadratic with respect to the concentration of inclusions were precisely calculated. A comparison of the results obtained with the results found with self-consistent methods showed that the differential (step) method gives a precise solution in the case of inclusions which strongly differ in size and a relatively small error (under 25% in the quadratic term) in the case of identical inclusions. The algebraic method and Lorentz method give more significant errors (up to 100 and 50%) in the quadratic term, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616208
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  • 6
    Electronic Resource
    Electronic Resource
    Crack growth criteria incorporating non-singular stresses: Size effect in apparent fracture toughness (1997)
    Springer
    International journal of fracture 83 (1997), S. 191-206 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Simple criteria accounting for the non-singular stresses at the crack tip are considered. They are based on the comparison of the local stress concentration with the material microstrength. The local stress concentration is estimated either as the magnitude of the conventional elastic stress ahead of the process zone, or by its averaging over the process zone length. When a criterion of this type is used to find the critical load and then the conventional fracture toughness, the latter will be dependent of the crack length. This size effect in fracture toughness manifests itself as an increase (if the non-singular part of the near-tip stress field is positive) or decrease (if the non-singular part is negative) in the apparent fracture toughness as the crack length increases. The obtained dependence is compared with available experimental data. It is also shown that when the load can be resolved into a superposition of elementary loads, the size effect can asymptotically (for long cracks) be presented as a weighted sum of the elementary size effects (i.e. the size effects associated with the elementary loads) with the weights equal to the relative contributions of the elementary loads into the total stress intensity factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007304015524
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  • 7
    Electronic Resource
    Electronic Resource
    On modelling of defect interaction (1995)
    Springer
    International journal of fracture 71 (1995), S. R79 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00037823
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  • 8
    Electronic Resource
    Electronic Resource
    Experiments on 3-D crack growth in uniaxial compression (1994)
    Springer
    International journal of fracture 65 (1994), S. R77 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00012382
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  • 9
    Electronic Resource
    Electronic Resource
    On the possibility of bifurcation in linear periodic arrays of 2-D cracks (1994)
    Springer
    International journal of fracture 67 (1994), S. R31 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00019606
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  • 10
    Electronic Resource
    Electronic Resource
    A continuum model of layered rock masses with non-associative joint plasticity (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 245-261 
    Details
    ISSN: 0363-9061
    Keywords: Cosserat continuum model ; equivalent continuum medium ; layered rock mass ; finite element method ; non-associative plasticity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Layered rock masses can be modelled either as standard, orthotropic continua if the layer bending can be neglected or as Cosserat continua if the influence of layer bending is essential. This paper presents a finite element smeared joint model based on the Cosserat theory. The layers are assumed to be elastic with equal thickness and equal mechanical properties. All the cosserat parameters are expressed through the elastic properties of layers, layer thickness and joint stiffness. Plastic-slip as well as tensile-opening of layer interface (joint) are accounted for in a manner similar to the conventional non-associative plasticity theory.As an application, the behaviour of an excavation in a layered rock mass is examined. The displacement and stress fields given by smeared joint models based on the Cosserat continuum and the conventional anisotropic continuum approaches are compared with those obtained from the discrete joint model. The conventional anisotropic continuum model is found to break-down completely when the effective shear modulus in the direction parallel to layering is low in comparison to the shear modulus of the intact layer, whereas the Cosserat model is found to be capable of accurately reproducing complex load-deflection patterns irrespective of the differences in shear moduli. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
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