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  • Articles  (1,015)
  • Engineering  (936)
  • NDE  (79)
  • Atomic, Molecular and Optical Physics
  • Life and Medical Sciences
  • Organic Chemistry
  • 1980-1984  (1,015)
  • Mathematics  (1,015)
  • 1
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    Springer
    Journal of nondestructive evaluation 1 (1980), S. 277-286 
    ISSN: 1573-4862
    Keywords: Ultrasonics ; through-transmission ; composite materials ; attenuation ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The steady-state amplitude of the output of an ultrasonic through-transmission measurement is analyzed and the result is given in closed form. Provided that the product of the input and output transduction ratios, the specimen-transducer reflection coefficient, the specimen-transducer phase-shift parameter, and the material phase velocity are known, this analysis gives a means for determining the through-thickness attenuation of an individual thin sample. Multiple stress-wave reflections are taken into account, and so signal echoes do not represent a difficulty. An example is presented for a graphite fiber epoxy composite (Hercules AS/3501-6). Thus, the technique provides a direct method for continuous or intermittent monitoring of through-thickness attenuation of plate structures which may be subject to service structural degradation.
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  • 2
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    Journal of nondestructive evaluation 2 (1981), S. 57-63 
    ISSN: 1573-4862
    Keywords: ultrasonics ; correlation ; pseudorandom codes ; random signals ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A new portable digital random signal flaw detection system is described which uses a digital delay line to replace the acoustic delay line of the original random signal system. Using this new system, a comparison was made between the two types of transmit signals which have been used in previous systems—m-sequences and random signals. This comparison has not been possible with these previous correlation flaw detection systems. Results indicated that for high-speed short code operation, the m-sequences produced slightly lower range sidelobes than typical samples of a clipped random signal. For normal long code operation, results indicated that system performance is essentially equivalent in resolution and signal-to-noise ratio using either m-sequences or clipped and sampled random signals. Further results also showed that for normal long code operation, the system produces outputs equivalent in resolution to pulse-echo systems, but with the added benefit of signal-to-noise ratio enhancement.
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  • 3
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    Journal of nondestructive evaluation 2 (1981), S. 85-111 
    ISSN: 1573-4862
    Keywords: Holographic reconstruction ; ultrasound ; NDE ; Rayleigh-Sommerfeld formula
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract For the purpose of ultrasonic nondestructive testing of materials, holography in connection with digital reconstruction algorithms has been proposed as a modern tool to extract crack sizes from ultrasonic scattering data. Defining the typical holographic reconstruction algorithm as the application of the scalar Kirchhoff diffraction theory to backward wave propagation, we demonstrate its general incapability of reconstructing equivalent sources, and hence, geometries of scattering bodies. Only the special case of a planar measurement recording surface, that is to say, a hologram plane, and a planar crack with perfectly rigid boundary conditions parallel to the hologram plane and perpendicular to the incident field yields a nearly perfect correlation between crack size and reconstructed image; the reconstruction algorithm is then referred to as the Rayleigh-Sommerfeld formula; it therefore represents the optimal case matched to that special geometrical situation and, hence, may be interpreted as a quasi-matched spatial filter. Using integral equation theory and physical optics, we compute synthetic holographic data for a linear cracklike scatterer for both plane and spherical wave incidence, the latter case simulating a synthetic aperture impulse echo situation, thus illustrating how the Rayleigh-Sommerfeld algorithm or its Fresnel approximation increasingly fail for cracks inclined to the hologram plane and excited nonperpendicularly. Furthermore, we point out how the physical data recording process may additionally influence the reconstruction accuracy, and, finally, guidelines for a careful and serious application of these holographic reconstruction algorithms are given. The theoretical results are supported by measurements.
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  • 4
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    Journal of nondestructive evaluation 2 (1981), S. 203-207 
    ISSN: 1573-4862
    Keywords: ultrasonics ; synthetic aperture ; spatial frequency ; interior imaging ; acoustic microscopy ; defect detection ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A new acoustic synthetic aperture geometry is demonstrated in which the image field is sampled in the spatial frequency domain. This means the sampled field is recorded in a particularly convenient form for presentation to the back propagation algorithms used to reconstruct the field at the object plane. The method has applications in interior visualization. It is difficult to image the interior of solid objects using lens based imaging systems because a different lens geometry must be used for each distinct object material. The system presented here overcomes such problems since both the angular variation of the transmission coefficient at the object-water interface and the aberrations introduced by the velocity mismatch at the object surface may be readily compensated for in the back propagation routine. Experimental results are presented illustrating the detection of four half wavelength diameter defects, spaced by three wavelengths, at a depth of eight wavelengths below the surface of an aluminum block.
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  • 5
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    Journal of nondestructive evaluation 2 (1981), S. 241-247 
    ISSN: 1573-4862
    Keywords: ultrasonic field ; numerical methods ; transducer design ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A simple, flexible, accurate, and comprehensive numerical method is presented for theoretically analyzing the diffraction field of a continuous wave transducer of arbitrary size, shape, and frequency. Using the extensively studied circular transducer for comparison, numerical results are shown for an unfocused transducer with uniform velocity excitation as well as for a focused transducer with Gaussian velocity excitation. Data concerning the execution time, program size, and convergence of the method are also presented for its implementation as a design tool on a minicomputer system.
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  • 6
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    Journal of nondestructive evaluation 3 (1982), S. 55-63 
    ISSN: 1573-4862
    Keywords: ultrasonics ; Rayleigh waves ; subsurface defects ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract An ultrasonic inspection method is used to obtain the circumference of a subsurface hole and the depth of the hole below the surface. A pitch-catch Rayleigh wave transducer set-up was used to launch a Rayleigh surface wave at the flaw and to capture and record the scattered waves. The frequency spectrum of the scattered waves can be used to obtain the depth of the hole. The ligament of material between the hole and the surface is sent into resonance, and this feature can be extracted from the scattered waves' frequency spectrum. The frequency is a function of the ligament length; thus the hole depth can be obtained. The circumference of the hole is found from a time of flight measurement. A Rayleigh wave is formed that travels around the hole's surface. The length of time required for the wave to travel around the hole is a measure of the circumference.
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  • 7
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    Journal of nondestructive evaluation 3 (1982), S. 65-76 
    ISSN: 1573-4862
    Keywords: crack measurement ; ac field technique ; arbitrary skin depth ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A general solution is given to describe the ac field around surface-breaking cracks for arbitrary values of the ratio of skin depth δ to crack depthd. This solution allows accurate interpretation of crack depth from voltage readings taken by a Crack Microgauge instrument in cases where δ andd are comparable. It is shown to agree with asymptotic formulae obtained for the cases where δ/d is very small and very large. Provided that the probe length Δ is large compared with δ, the calculations show that a very good approximation to the crack depth may be obtained, irrespective of the ratio δ/d, by using the thin-skin asymptotic formula $$d = \frac{1}{2}\Delta (V_2 - V_1 )/V_1 $$ whereV 1 andV 2 are probe voltages registered at positions just off and across the crack, respectively. The problem is solved for a crack of infinite aspect ratio which has no opening, but it can be applied with confidence at the centerline of cracks of fairly large aspect ratio.
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  • 8
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    Journal of nondestructive evaluation 3 (1982), S. 99-109 
    ISSN: 1573-4862
    Keywords: thermography ; infrared scanning ; calibration ; inverse problems ; cavity detection ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract An approach for treating nondestructive testing as the solution of inverse problems in mathematical physics has been used for the detection of cavities. The approach is developed based on the use of an additional boundary condition of scanned temperature on the surface to solve for the cavity geometry. For the present study, the condition at the cavity side is taken to be that of a specified temperature, and the experiment is carried out to meet this condition. Two specimens are tested in this paper, a plane slab and a rectangular prism. In both bodies the cavity is rectangular in shape. For the testing of the plane slab, the method is able to detect the cavity wall with high accuracy, whereas the cavity depth error is larger (6%). The detection of the cavity position in the rectangular prism has an error ranging from −9.7 to 7.7%. Errors in the experiment are attributed to the uncertainties in the measurements of temperature and the Biot number. The former is read off from the analog data output of the infrared scanner. The latter is not measured separately, but is computed from the scanned data and thus becomes a portion of the total nondestructive testing output. A final note is also made in this paper to relate how the presented method can be used in actual practice.
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  • 9
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    Journal of nondestructive evaluation 3 (1982), S. 175-182 
    ISSN: 1573-4862
    Keywords: ultrasonic wave scattering ; inclusions ; reciprocity ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper, as part of a series on elastic wave scattering, presents results of measurements and calculations on scattering of ultrasonic waves by a solid spherical inclusion (tungsten carbide) embedded in titanium alloy by the diffusion bonding process. Both direct scattering and mode-converted scattering angular distributions are reported for shear and compressional incident waves. The consequences upon the signals when transmitter and receiver were interchanged are explored in a reciprocity rule.
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  • 10
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    Journal of nondestructive evaluation 2 (1981), S. 23-33 
    ISSN: 1573-4862
    Keywords: austenitic stainless steel ; austenitic stainless steel welds ; eddy current inspection ; eddy current testing ; electromagnetic testing ; ferromagnetic steel inspection ; flaw characterization ; flaw detection ; NDE ; multifrequency eddy current inspection ; weld inspection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper describes the initial phase of a project to develop eddy-current methods to inspect welds joining sections of austenitic stainless steel pipe having walls up to 13 mm (0.5 in.) thick. The objective of this phase was to demonstrate the feasibility of detecting and characterizing flaws in austenitic stainless steel base metals. These materials and welds present challenging eddy-current problems because of their relatively large thickness and ferromagnetism. Multiparameter analysis shows that a reflection coil probe operated with three discrete driver frequencies and phase detection can locate and size a cracklike defect in a single conductor in the presence of variations in conductor resistivity, permeability, and thickness and in the probe-conductor spacing (liftoff). Experiments were performed with a modular three-frequency instrument. Flat-plate specimens of types 304L and 347 stainless steel machined to 12.7 to 15.9 mm thickness simulated pipe walls; saw-cut slots 10 to 30% of nominal specimen thickness simulated cracklike defects. The same slots were used in duplicate experiments as near-side (directly under the test probe) or far-side (in the face opposite the probe) defects. Flaw detection and characterization capability was demonstrated by a series of experimental measurements fitted to specimen properties by least squares techniques. The quality of the fit determined the expected accuracy of measurement. Comparison of accuracy estimates determined the best choice of operating frequencies. From the 1,2,5 sequence of frequencies between 0.5 and 20 kHz, the optimum set of operating frequencies was selected to be 0.5, 2, and 10 kHz. Estimates of measurement accuracy for combined near- and far-side defect cases were: plate thickness, 0.74 mm; probe liftoff, 0.03 mm; defect location (depth of material above defect), 3.48 mm; and defect size (vertical slot depth), 1.09 mm. A few property values were back-calculated from instrument readings; the errors in these values were somewhat larger than the measurement accuracy estimates because of instrument drift and the absence of calibration circuits.
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  • 11
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    Journal of nondestructive evaluation 4 (1984), S. 89-106 
    ISSN: 1573-4862
    Keywords: scattering ; elastic waves ; Lamb waves ; shear waves ; finite difference methods ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper describes the application of finite difference methods to the calculation of the scattering of elastic waves. The emphasis is on cracklike defects in plates, and it is shown that a common numerical technique can span a range of wavelengths from Lamb waves to ultrasonic waves with many reflections from the surfaces of the plate. Quantitative results are given for the scattering of Lamb waves and ultrasonic shear waves from surface-breaking cracks.
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  • 12
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    Journal of nondestructive evaluation 1 (1980), S. 263-276 
    ISSN: 1573-4862
    Keywords: Ultrasonics ; scattering ; diffraction ; defect characterization ; cracks ; voids ; pattern recognition ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Shape and size are the most important defect characteristics that need to be determined for the reliable prediction of the remaining service lifetime of a defective structure or part. The analytical and supporting experimental results presented in this paper concern a general, pattern recognition-based, ultrasonic defect identification and sizing method. The satellite-pulse technique (SPT) is based on the interpretation, in terms of defect types (shapes) and dimensions, of the separation in time of arrival between the readily detected specularly reflected pulse and its generally ignored tip-diffracted or tangentially scattered “satellite” contained in the received waveform. Calibration procedures were also developed that enable the ultrasonic examiner to read the time scale of the oscilloscope for equivalent crack depth or void diameter as appropriate.
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  • 13
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    Journal of nondestructive evaluation 2 (1981), S. 35-41 
    ISSN: 1573-4862
    Keywords: acoustic emission ; crack growth ; 7075 aluminum ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract For slow crack growth (da/dn ≈0.1 µm per load cycle) in 7075-T6 aluminum, quantitative agreement was found between the amplitude distribution of burst acoustic emissions and the area size distribution of intermetallic inclusions ≈10 (µm)2 in area as measured on thepolished fracture face. This observation permits the prediction of the amplitude distribution of acoustic emissions due to crack growth in a particular sample of 7075-T6 aluminum directly from a simple, standard metallographic observation performed on the material in question. It was also found that a reduction of the yield stress from that of 7075-T6 aluminum (503 MPa) to that of 7075-0 aluminum (103 MPa) completely eliminated burst acoustic emission activity due to crack advance in the amplitude range studied.
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  • 14
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    Journal of nondestructive evaluation 4 (1984), S. 39-42 
    ISSN: 1573-4862
    Keywords: Eddy current ; computer analysis ; numerical methods ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Theoretical calculations of eddy-current phenomena often involve the numerical evaluation of various integral expressions. A discussion of some of the possible evaluation methods and of the factors to be considered in choosing a method is presented.
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  • 15
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    Journal of nondestructive evaluation 4 (1984), S. 3-12 
    ISSN: 1573-4862
    Keywords: Ultrasonic ; stress measurements ; interfacial stress ; NiTi ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In seeking to develop an NDE technique for verifying the serviceability of NiTi couplers for plumbing unions, it was found that the reflection coefficient for a normally incident ultrasonic wave correlated with the stress level at the NiTi-tubing interface. Current theory pertaining to interface reflection is not complete but, even at present status, there is semiquantitative accord between theoretical predictions and normalized data for reflection coefficient versus stress level. These results are at fixed frequency and with comparable surface roughness. Variation of either frequency or surface roughness further affects the reflection coefficient. Current studies are being pursued to define this effect.
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  • 16
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    Journal of nondestructive evaluation 4 (1984), S. 75-88 
    ISSN: 1573-4862
    Keywords: object scattering ; edge scattering ; knife edge ; neutron radiography ; buildup factor ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Previously described scattering based edge distortions in optical density scans obtained from a neutron radiographic knife-edge image have been here confirmed using analog Monte Carlo simulation. In an attempt to estimate the effects of additional object scatter on such artifacts, the effect on the edge response of diffusely incident neutrons has been determined both empirically and by Monte Carlo simulation. The diffuse neutron incidence has been found to diminish the relative magnitude of the distortion, offering explanation for the infrequent observation of the corresponding edge scattering halo artifacts. The potential of this edge distortion as a diagnostic indicator of the buildup factor in radiography is suggested and examined.
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  • 17
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    Journal of nondestructive evaluation 2 (1981), S. 119-124 
    ISSN: 1573-4862
    Keywords: Stress intensity factor ; annular crack ; finite element methods ; fatigue ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Results of finite element static stress intensity factor calculations for an annular crack around a spherical inclusion (void) are presented and compared with those from approximate analytical methods.
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  • 18
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    Journal of nondestructive evaluation 2 (1981), S. 147-149 
    ISSN: 1573-4862
    Keywords: Ultrasonic tomography ; residual stress ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Ultrasonic tomography is being explored as a potential tool to map residual stresses in solids. The angular scanning required in tomography imposed limitations on the stress configuration adaptable to such a treatment. These are discussed in the following note.
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  • 19
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    Journal of nondestructive evaluation 2 (1981), S. 161-172 
    ISSN: 1573-4862
    Keywords: elastodynamic inverse scattering ; ultrasonics ; data reduction ; ill-posed problems ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The practical significance of ill-posedness in a data reduction problem is reviewed. Inverse elastodynamic scattering is shown to be ill-posed in general, although suitably restricted problems may be well-posed. These results underscore the need to analyze carefully the errors of data reduction problems in NDE, and to focus attention on final results of an NDE exercise, rather than on intermediate steps.
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  • 20
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    Journal of nondestructive evaluation 2 (1981), S. 153-159 
    ISSN: 1573-4862
    Keywords: ultrasonics ; scattering ; cracks ; periodic surface perturbation ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The scattering of a plane longitudinal wave from a two-dimensional crack, with a sinusoidal surface perturbation whose amplitude and wavelength are much smaller than the length of the crack, is investigated. The amplitude of the cylindrical body waves in the far field are calculated from a Kirchhoff approximation that utilizes the solution to the reflection from the sinusoidal surface profile of a semiinfinite solid. The results are compared to those for a flat crack, and conditions for significant differences of the amplitude as a function of the angle of observation are discussed. Characteristic changes in the scattered field produced by profiles with different amplitudes and periods are explained.
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  • 21
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    Journal of nondestructive evaluation 2 (1981), S. 195-202 
    ISSN: 1573-4862
    Keywords: ac potential difference ; fatigue crack measurement ; slots ; artificial flaws ; parasitic voltages ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The development of a successful and accurate instrument for measuring surface-breaking cracks in metals using the ac field technique has raised several interesting theoretical problems. Measurements with the instrument, known as the Crack Microgauge, do not rely on any prior calibration against an artificial flaw such as a saw-cut in a test block, but some users accustomed to such a calibration from other devices have nevertheless wished to use the instrument in that fashion and have in some instances reported erroneous results. In this paper, we develop a simple theory to explain and quantify this phenomenon. We calculate the parasitic voltages induced in the instrument probe due to the finite opening possessed by an artificial flaw, and we use these results to reinterpret the instrument readings. Controlled experimental measurements on artificial flaws of rectangular cross-section made in aluminum and in steel are found to be in good agreement with the theory. It is shown, however, that application of the theory requires additional information about the internal phase shift associated with the instrument. To enhance the accuracy of the theory, the effect of the corners of the artificial flaws was also considered, although it was not very influential in this work.
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  • 22
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    Journal of nondestructive evaluation 3 (1982), S. 19-24 
    ISSN: 1573-4862
    Keywords: ac potential difference ; eddy current ; fatigue crack measurement ; skin effect equation ; large skin depth ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper considers the solution of the skin-effect or Helmholtz equation, ∇2ψ=k 2ψ, for the two-dimensional flow of a uniform alternating current perturbed by a plane crack of uniform depth. Herek is the ratio of crack depthd to skin depth δ. When the skin depth is large compared with the crack depth andk f 0, the quasi-static approach to this problem ignores the terms on the right-hand side and constructs solutions from Laplace's equation which are essentially dc solutions and are correct to orderk. In this paper we consider behavior near the limit when the skin depth is large and give solutions which are correct to orderk 2. In an example we relate the results to the interpretation of readings from an ac potential difference instrument applied to the measurement of surface-breaking cracks.
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  • 23
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    Journal of nondestructive evaluation 3 (1982), S. 93-98 
    ISSN: 1573-4862
    Keywords: bounded ultrasonic beam reflectivity ; Rayleigh angle ; beam profile ; surface defects ; nonspecular reflection ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The relationships between characteristics of elastic defects and nonspecular features of bounded ultrasonic beams reflected at the Rayleigh angle from a liquid-solid interface are investigated. The results can serve as a theoretical basis for interpretation of Rayleigh angle nonspecularly reflected beam profiles as characterization of localized surface elastic defects.
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  • 24
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    Journal of nondestructive evaluation 3 (1982), S. 125-136 
    ISSN: 1573-4862
    Keywords: magnetic particle inspection ; magnetic leakage fields ; finite difference method ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Experimental measurements of leakage fields from cylindrical defects were obtained in a geometry which permitted simultaneous measurement of the magnetic induction of the material. The results obtained are compared with calculations using a nonlinear finite difference method. Both the experiments and the calculations indicate that the magnitude of the leakage field continues to grow nearly in proportion with the applied field well into the saturation region of the magnetic material. The implications for magnetic particle inspection are discussed.
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  • 25
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    Journal of nondestructive evaluation 3 (1982), S. 45-53 
    ISSN: 1573-4862
    Keywords: Born approximation ; ultrasonic scattering ; NDE ; time domain
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The time domain Born approximation for ultrasonic scattering from volume flaws in an elastic medium is described. Results are given both for the direct and the inverse problem. The time domain picture leads to simple intuitive formulas, which we illustrate by means of several simple examples. Particular emphasis is given to the front surface echo and its use in reconstructing the properties of the flaw.
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  • 26
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    Journal of nondestructive evaluation 1 (1980), S. 3-9 
    ISSN: 1573-4862
    Keywords: harmonic generation ; fatigue ; microcracks ; aluminum ; surface acoustic waves ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Harmonic generation of surface acoustic waves (SAW) is shown to be a useful tool for the detection of the initiation of surface cracks during fatigue of high strength aluminum alloys. A model that relates the length and density of microcracks to the amplitude of a SAW harmonic signal is described, and an associated coefficient of generation efficiency for the second harmonic amplitude is derived. A correlation between experimentally measured harmonic amplitude and remaining fatigue life is then demonstrated, which allows the mean remaining fatigue lifetime to be estimated to within 5% over the last 50% of the fatigue life for an Al 7075 alloy if the cyclic stress amplitude, but not the duration of fatigue, is known.
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  • 27
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    Journal of nondestructive evaluation 1 (1980), S. 11-19 
    ISSN: 1573-4862
    Keywords: ultrasonic diffraction ; fatigue cracks ; crack closure ; crack surfaces ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper describes an ultrasonic diffraction technique for characterizing fatigue cracks. The angular field of energy scattered from a crack tip was computed. Using the theoretically predicted and experimentally verified optimum range of angles, we measured the crack profiles by the ultrasonic diffraction technique. Ultrasonic measurements agreed very well with direct destructive measurements. In addition, fatigue crack closure was detected and information on crack surfaces was obtained.
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  • 28
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    Journal of nondestructive evaluation 1 (1980), S. 21-36 
    ISSN: 1573-4862
    Keywords: ultrasonics ; surface defects ; defect depth ; deconvolution ; correlation ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In previous work by the authors,(1,6) it was demonstrated that the presence of near-surface defects could be detected reliably, even though the defect echo was contained within the near-surface echo. The algorithm consists of examining the variation in the composite (near-surface plus defect) response after it has been deconvolved from a near-surface response known to be defect-free. This paper presents two algorithms that have been developed subsequent to the work presented in ref. (6) for estimating thedepth of a near-surface defect, given that its presence has already been detected. One algorithm uses complex frequency domain techniques, and the other uses time domain analysis. Both procedures operate on the surface-plus-defect signal, using reference signals containing surface-only and defect-only responses. The defect signal is extracted from the composite signal. Defect depth is then computed from the time difference between the centers of the front-surface and extracted defect responses. A mean absolute depth error of 0.015 in. was obtained by applying the algorithms to experimental data containing depths from 0.020 to 0.130 in. below the near-surface.
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    Journal of nondestructive evaluation 1 (1980), S. 37-52 
    ISSN: 1573-4862
    Keywords: failure prediction ; accept/reject decisions ; ceramic materials ; ultrasonics ; fracture ; probabilistic model ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A general probabilistic method for reaching accept/reject decisions and failure prediction based on nondestructive evaluation procedures is described. The method is illustrated for ceramic materials that fail by the activation of microcracks located at void surfaces. The inspection procedure used for the analysis is the long wavelength ultrasonic method. The analysis indicates influences on the decision level and on the false-reject probability of variations in the signal-to-noise ratio and in the preexistent void population. The ultrasonic inspection is shown to exert a relatively minor influence on the false-reject probability, even for low signal-to-noise ratios, low stresses, and a widely dispersed void population, because of the intrinsic variability of the selected failure process. More encouraging results concerning the utility of NDE are anticipated to apply to other failure mechanisms in ceramics.
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    Journal of nondestructive evaluation 1 (1980), S. 53-66 
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    Keywords: ultrasonic transducers ; phased array ; ultrasonic imaging ; impulse response ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The present contribution provides a method for the derivation of analytical near- and far-field expressions for the pressure step-function response of nonuniformly excited ultrasonic transducers modeled as pistons of arbitrary shape in an infinite rigid baffle. Explicit inversion of the Laplace transformed ultrasonic field using Cagniard's idea results in elementary functions or definite integrals of elementary functions, depending on the assumed nonuniform aperture distribution. The basic signal distortion is illustrated in terms of three-dimensional space-time plots of the pressure unit step-function response of a rectangular uniform aperture. The corresponding results for a phased-array transducer are also given. In addition, we investigate the pressure profile on the axis perpendicular to a uniform rectangular piston and its horizontal radiation pattern for different bandwidths of the exciting impulse.
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  • 31
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    Keywords: stress fields ; microstructure ; J integral ; stress intensity factor ; harness acoustic velocity ; acoustic elasticity ; NDE
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    Notes: Abstract A very precise system for measuring two-dimensional velocity fields in solid samples has been used for nondestructive measurements of both externally applied and residual inhomogeneous stresses in solids,J integrals, stress intensity factors of cracks, and hardness of quenched steel. The longitudinal velocity measurement is based on precise determination of the propagation transit time through the stressed solid specimen using a small diameter, water-coupled acoutic transducer, which is scanned mechanically over the sample. Changes in velocity are then related to changes of stress in the sample by the theory of acoustoelasticity. Similar measurements show a high degree of correlation between longitudinal velocity changes and changes in microstructure in steel samples. Applications to problems of solid mechanics and material science illustrate the utility of this nondestructive measuring technique.
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  • 32
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    Journal of nondestructive evaluation 1 (1980), S. 79-85 
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    Keywords: ultrasonic waves ; EMAT ; surface stress ; NDE ; Green's function
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract An analysis of the radiation from a body force shows that it is equivalent to the radiation from a series of surface stresses defined by the moments of the body force taken with respect to the depth coordinate. As the body force becomes localized near the surface, the zeroth moment of the force dominates the radiation and is often thought of as an equivalent surface stress. However, under certain conditions, this can vanish, and the other moments must be considered. It is found that, as the order of the moment of a particular force component increases, the resulting radiation patterns alternate between those characteristic of a compressive surface stress and those characteristic of a shear surface stress, which have considerably different angular variations. Results of experiments in the development of EMAT transducers for nondestructive testing that support these results are cited, and important consequences in the design of inspection systems are indicated.
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    Journal of nondestructive evaluation 1 (1980), S. 225-233 
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    Keywords: Acoustic emission ; energy analysis ; composite materials ; strength ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A new technique which uses the output of a true RMS voltmeter to measure the acoustic emission energy output of a transducer is presented. To demonstrate its use in a typical case, this procedure is used to measure acoustic emission energy during tensile tests on [0°/±30°/90°]s glass-epoxy laminate uniaxial and 10° off-axis tensile coupons. The test results were compared with numerical predictions of laminate response and acoustic emission energy. The experiments indicate that acoustic emission energy can be used to indicate the onset of ply and interlaminar failure.
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  • 34
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    Journal of nondestructive evaluation 1 (1980), S. 235-247 
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    Keywords: Ultrasonics ; acoustic waves ; scattering ; diffraction ; defect characterization ; silicon nitride ; NDE
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    Notes: Abstract The scattering of acoustic waves by different types of spherical defects in a silicon nitride matrix is calculated by using Ying and Truell's scattering theory. The theoretical scattering results are interpreted using a ray tracing approach. Experiments were carried out at a high frequency (150–450 MHz) to characterize defects in silicon nitride. Time and space averaging, Wiener filtering, diffraction, and propagation loss corrections were used to remove the effect of the transducer response and propagation loss in the material from the scattered signal. Our experimental results indicate the presence of a new type of defect in silicon nitride. They give the type and size of voids, cracks, and Si inclusions in good agreement with measurements obtained after sectioning.
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    Journal of nondestructive evaluation 3 (1982), S. 183-188 
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    Keywords: Ultrasonics ; Born inversion ; NDE
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    Notes: Abstract Quantitative reconstruction of volumetric flaws near a surface of an elastic solid has been carried out experimentally by analyzing the scattered ultrasonic waves. The inverse Born approximation (developed for flaws in bulk materials) was tested for the first time in the determination of the size, shape, and orientation of near-surface flaws. We have studied spherical solid inclusions at various depths below the surface. In addition we examined an approximately 2:1 prolate spheroidal inclusion which was located one major axis below the surface. The determination of the flaw's size, shape, and orientation in terms of an equivalent ellipsoid is realized by performing nonlinear least-squares iteration of the one-dimensional Born inversion results obtained at various scattering directions within a finite aperture. The reconstruction is in good agreement with the actual parameters of the flaw.
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  • 36
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    Keywords: Residual Stress ; ultrasonics ; metals ; EMATs ; NDE
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    Notes: Abstract An approach is proposed for obtaining separate measures of stress anisotropy and texture in metal sheet or plate. The approach is based on the propagation characteristics ofSH n modes of ultrasonic waves. Experimental work has established that differences betweenSH 0 modes with orthogonal directions of propagation provide a measure of stress anisotropy that is insensitive to texture, with the restriction that the pseudosymmetry of the polycrystalline matrix of the sheet or plate is orthorhombic or higher. In the present work, it is argued that the differences between elastic constants associated with orthogonal directions of propagation of higher order modes should provide a meaningful measure of texture. The only requirement is that the texture be sufficiently well developed so that the following inequality is obeyed: ∣C′44−C′55∣〉0.002 $$\bar C$$ with $$\bar C$$ =1/2 (C′44+C′55). HereC′44 andC′55 are the effective shear moduli for planes normal to the sheet or plate surface and at right angles to each other. They are measurable by observing the differences between the phase velocities of theSH 0 and theSH n〉0 modes in the principal directions. By using Electromagnetic Acoustic Transducers (EMATs), the phase velocities can be deduced from the frequencies at which an SH mode of fixed wavelength is optimally excited. This approach has the advantage of being independent of specimen geometry and dimensions other than thickness.
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    Journal of nondestructive evaluation 4 (1984), S. 51-58 
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    Keywords: eddy current testing ; magnetic particle testing ; magnetic sensor ; ferromagnetic resonance ; microwave frequency ; surface flaws ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This article presents some results obtained in the characterization of surface flaws by means of probes using ferromagnetic resonance of yttrium iron garnets (FMR probes). These experiments on artificial flaws show that FMR probes operate like eddy current probes for nonmagnetic materials and like magnetic field sensors for magnetic ones. Consequently, the working distance is larger for magnetic materials (1000–1500 µm) than for nonmagnetic ones (100–300 µm). FMR probes have good sensitivity to narrow flaws, good spatial discrimination, and are sensitive to flaw width and depth. Vector analysis allows the separation of distance and flaw effect by phase analysis on nonmagnetic materials. On magnetic materials this phase separation does not exist and another procedure is suggested. These results, and in particular those obtained on ferromagnetic materials, point to the possibility of replacing some eddy current or magnetic particle inspections by tests with ferromagnetic resonance probes.
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    Journal of nondestructive evaluation 4 (1984), S. 127-131 
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    Keywords: Concrete NDT ; NL-ADC ; crack depth measurement ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper introduces the design and construction of an electronic hybrid signal processing meter that develops an output voltage proportional to the depth of a concrete crack. The circuit employs multiplication, squaring, and square-rooting functions by means of a special nonlinear ADC and counting scheme.
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    Journal of nondestructive evaluation 4 (1984), S. 149-155 
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    Keywords: NDE ; thermal waves ; anisotropy ; composites
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    Notes: Abstract A general formulation for solving the three-dimensional thermal diffusion equation in anisotropic media is presented. The method is based on two-dimensional Fourier transform techniques and can provide a physical insight into the problem. The analysis can easily be adapted to take into account arbitrary spatial variations of the excitation beam (i.e., a laser or an electron beam). Results obtained from propagation of thermal waves in composites are presented and followed by simulations for cases where the source function is defined. Propagation through an anisotropic slab is formulated and applied to specific cases.
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    Journal of nondestructive evaluation 4 (1984), S. 197-202 
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    Keywords: Eddy current ; impedance ; flaw ; Green's function ; Born's limit ; NDE
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    Notes: Abstract Green's function is used in order to derive the analytical solution for the change in impedance due to a presence of the flaws in a conductor. This solution is applied to a cylindrical flaw and a spherical flaw whose radii are much smaller than the radius of the test coil. For both cases, the change in impedance is obtained within Born's limit.
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    Journal of nondestructive evaluation 4 (1984), S. 203-212 
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    Keywords: Acoustic diffraction ; acoustic transmission ; asperity contact ; crack closure ; fatigue cracks ; mode conversion ; NDE ; stress intensity factor
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    Notes: Abstract The partial contact of two rough fatigue crack surfaces leads to transmission, reflection, diffraction, and mode conversion of an acoustic signal at those contacts. This paper reviews recent experimental and theoretical efforts to understand and quantify such contact on actual fatigue cracks in greater detail. It is shown that the size and density of individual contacts, or asperities, can be estimated from acoustic measurements. Furthermore, it is shown that this information is useful to provide the static stress across a partially closed crack as well as the “effective” stress intensity range which activates fatigue crack propagation.
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  • 42
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    Journal of nondestructive evaluation 2 (1981), S. 43-49 
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    Keywords: Rayleigh wave dispersion ; higher mode generation ; cold-working ; rail ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The propagation of the Rayleigh surface wave is experimentally studied along the top surface of used railroad rail under conditions where ultrasonic pulses have carrier frequencies ranging from 0.4 to 3.0 MHz and approximately 10 µs duration. The generation of the first higher (M 21 or Sezawa) mode as well as the fundamental (M 11) mode and their dispersion properties are observed. These phenomena are attributable to the presence of the cold-worked surface layer caused by the wheel passage. It is shown that a theoretical model of a single layer overlying a half space, whose elastic constants are determined by a destructive method, yields results which agree with the dispersion curves obtained experimentally. On the basis of this one-layered model, an inversion method to estimate the layer thickness and its elastic constants is discussed.
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    Journal of nondestructive evaluation 2 (1981), S. 65-74 
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    Keywords: NDE ; cast iron ; vibration analysis ; modulus ; strength
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    Notes: Abstract An outline is given of the existing nondestructive vibration tests for cast irons and their drawbacks in terms of the dimensional accuracy of the components. A proposal is made for a new test based on the change of resonant frequency with vibration amplitude exhibited by cast irons. This proposal is evaluated using material data obtained from dynamic tests of a wide range of cast iron specimens. A test rig is described suitable for testing cylindrical cast bars, and typical results are presented in relation to material strength. There is also a brief description of preliminary testing on cast products.
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    Journal of nondestructive evaluation 2 (1981), S. 113-118 
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    Keywords: Capacitance ; dielectric constant ; voids ; cellular glasses ; NDE
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    Notes: Abstract Cellular (foamed) glasses are a prime candidate for certain structural applications, such as support of the silvered glass concentrator mirrors in solar thermal energy systems. An economical nondestructive measurement of strength-limiting defects in these materials would permit development of designs in which the material is subjected to a higher working stress level and maintains the same probability of failure. This would result in weight and cost savings for any application. A method of measuring the capacitance of well-defined regions of a specimen was investigated. Large voids were found to produce significant localized changes in the capacitance of the specimen. The feasibility of locating the large, strength limiting defects in this porous material has been demonstrated for one type of cellular glass. Means of producing an image from this type of data and an implementation scheme for on-line production measurements are discussed.
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  • 45
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    Journal of nondestructive evaluation 2 (1981), S. 139-146 
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    Keywords: Material defects ; 14 MeV neutrons ; pulse-shape analyzer system ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A 14 MeV neutron generator and fast neutron spectrometer consisting of an organic scintillation detector and a pulse-shape analyzer are used for the nondestructive testing of materials. The 14.6 MeV peak (in the 12.7–15.7 MeV region) is observed to change as a function of both the kind of testing material and the defect condition inside the material. The number of neutron counts under the 14.6 MeV peak for lighter testing materials (e.g., plastic, brass, and aluminum) with a defect will increase, as compared to the number of neutron counts under the same peak region of an identical testing material but with no defect. For heavier testing materials (e.g., steel and lead), the inverse is observed. The method is feasible even with defects of size 0.25 cm3 (i.e., a cylindrical cavity 0.4 cm in diameter and 2.0 cm in length), although quantitative evaluation of the size of the defect as a function of the change of the number of neutron counts under the 14.6 MeV peak region is difficult due to instability of the 14 MeV neutron output.
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    Journal of nondestructive evaluation 2 (1981), S. 219-229 
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    Keywords: acoustics ; surface acoustic waves ; Rayleigh waves ; ceramics ; surface cracks ; residual stresses ; crack extension ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract An investigation of scattering from surface cracks has been conducted. In particular, the change in the reflection coefficient of a Rayleigh wave incident on a surface indentation crack has been measured as the sample is stressed to fracture. The acoustic measurements have been correlated with the stable crack extension that precedes final failure. The crack extension behavior of as-indented specimens was found to differ appreciably from that of annealed specimens. Cracks in the annealed samples exhibited partial crack tip closure, but little stable extension, whereas cracks in the as-indented samples displayed both crack closure and irreversible crack growth. This behavior has been rationalized by invoking concepts based upon the residual stresses created by indentation.
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    Journal of nondestructive evaluation 3 (1982), S. 9-17 
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    Keywords: ac potential difference ; probe characterization ; induction effect ; slots ; fatigue crack ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In the ac field method of crack depth measurement by the Crack Microgauge, the area of the loop formed in the probe gives rise to an induced voltage, which can introduce errors into the depth measurement. In this paper, a method for measuring the probe area is given, and the quality of the probe is thereby characterized. The underlying theory was given previously, and it is applied here to the probe characterization problem. The probe area is determined by two voltage measurements taken on an artificial rectangular flaw machined in an arbitrary metal. By measurements on several such specimens with the same probe, it is confirmed that the area so obtained is a characteristic of the probe and is independent of the specimen material. Thereafter, measurements on various rectangular flaws with probes of different characteristic area were taken, and very good agreement between predicted and real depths was achieved. Both theory and experiments show that probe characterization is of particular importance when this method is used to measure surface crack depths in metals of low permeability such as aluminum.
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    Journal of nondestructive evaluation 3 (1982), S. 37-43 
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    Keywords: eddy current ; impedance ; lift-off ; flaw ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The problem of detection and characterization of a flaw in a conducting half-space using an eddy-current coil oriented parallel to the interface is examined. An expression is derived for a first order approximation for the change in complex impedance due to a flaw located within the conducting medium. The overall impedance is a function of the radius and lift-off distance of the test coil and the conductivity of the material. An analytical expression is derived for the change in impedance as a function of the electric fields at the position of the flaw. It is found to be an integral over the volume of the flaw of the electric fields found with and without the flaw being present. The limiting case of a degenerate point flaw may be examined in greater detail by allowing the field in the presence of the flaw to be approximated by the unperturbed field. For flaws small enough that the field does not vary much over its volume, the field may be even further approximated by using just the value of the field at the position of the centroid of the flaw. Plots are shown to illustrate the behavior of the change in impedance as a function of the radial range of the flaw and the depth of the flaw centroid, using previously derived expressions for the fields for the unflawed case.
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    Journal of nondestructive evaluation 3 (1982), S. 85-91 
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    Keywords: displacement-field ; acoustic radiation ; wave propagation ; absolute velocity ; EMAT ; mode selective ; nonresonant frequency response ; NDE
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    Notes: Abstract A new electromagnetic acoustic transducer (EMAT) is developed that measures velocities and absolute surface displacements in-plane and plane-normal to the direction of wave propagation. This transducer is flexible in shape and design to conform with irregular surfaces and has unique characteristics of nonresonant frequency response. Tests show that the sensitivity of this EMAT can be increased by increasing the applied magnetic field. Because this transducer is mode selective and nonresonent, its response can be related uniquely to the wave motion. This property is highly desirable for research purposes, though generally not wanted in field monitoring situations.
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    Journal of nondestructive evaluation 3 (1982), S. 221-227 
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    Keywords: Radiography ; point-spread function ; corner location ; edge location ; unsharpness ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Two-dimensional imaging properties of locally isotropic and isoplanatic point spread functions are described in a general radiographic context. In particular, the radiographic response to a two-dimensional wedge-shaped object is shown to possess several properties which enable the identification of the wedge corner on the image, thereby alleviating the need for image enhancement techniques. Extensions to the location of flat-edged boundaries are also discussed. The potential dimensioning application of this analysis lies in the precise and objective location of points of interest on radiographs of more complex two-dimensional objects.
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    Journal of nondestructive evaluation 4 (1984), S. 23-27 
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    Keywords: Optical fiber sensor ; distributed strain ; sensor array techniques ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Single mode optical fiber waveguide has been used to determine the two-dimensional strain distribution on a simply supported rectangular plate. Each of the fifty individual fibers in the rectangular grid array attached to one surface of the plate yields a measurement of the strain integrated along the length of that fiber on the specimen. By using similar sensor information from all of the fibers, both the functional form and the amplitude of the distribution may be determined. Limits on the dynamic range and spatial resolution are indicated. Applications in the measurement of internal strain and the monitoring of physically small critical-structural components are suggested.
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    Journal of nondestructive evaluation 4 (1984), S. 133-140 
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    Keywords: Thermography ; infrared scanning ; calibration ; inverse problem ; cavity detection ; NDE
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    Notes: Abstract An inverse problem technique has been developed for detecting irregular cavities in circular cylinders. In this method, the cavity is considered a part of the unknown geometry of the investigated system, and the evaluated temperature is used to locate this geometry. An auxiliary problem is introduced in the solution of this problem; and in the solution, the cavity wall is located by forcing the temperature to satisfy the condition imposed at the cavity. The new methodology is validated by an experiment presented in this paper, and the test results indicate that this method is highly successful in locating cavities. The accuracy of the method is closely related to the accuracy of the temperature that can be measured at the surface. A small error in the surface temperature results in a slight cavity error for deep cavities, while a shallow cavity is not severely affected by a surface temperature error. This method is particularly attractive in detecting shallow cavities in nondestructive evaluation.
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    Journal of nondestructive evaluation 4 (1984), S. 165-175 
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    Keywords: Eddy current ; instrumentation ; probe design ; crack detection ; ferritic steel ; offshore ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The detection and sizing of fatigue cracks in ferritic materials, especially in offshore structures, is of major importance. This paper describes an eddy current system to detect such cracks, operating in an offshore environment with a search probe to electronic instrument separation of up to 600 m. An analysis of the various factors influencing the search coil behavior is given in terms of a mutually coupled primary and secondary electrical circuit; the component values of which are influenced by the coil design, induced electrical currents in the material, and any defects it contains. It is further shown that, with proper coil parameters, the phase variation in the phase angle of the coil complex impedance can be kept almost constant compared with the rapid variation occurring during lift-off. This behavior can be exploited in the instrumentation to give a clear vector display indication of the crack presence on less than ideal surfaces.
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    Journal of nondestructive evaluation 3 (1982), S. 229-239 
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    Keywords: Crack-opening displacement ; crack closure ; ultrasonics ; Kirchoff approximation ; NDE
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    Notes: Abstract The interaction between rough crack faces is modeled by nonlinear relations between the crack-face tractions and the crack-opening displacements. These relations account for crack closure and for the related resistance to crack-face sliding. The relations are used to investigate reflection and transmission of an incident pulse by an infinite flaw plane. The problem statement is reduced to a set of inhomogeneous nonlinear ordinary differential equations for the displacement discontinuities, [u] and [v], across the flaw plane. These equations have been solved numerically. The reflection and transmission of an incident pulse by a crack with interacting crack faces. Both incident longitudinal and transverse waves have been considered. The loss of specular reflection as compared to a perfect (traction-free) crack is exhibited by specific examples.
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    Journal of nondestructive evaluation 4 (1984), S. 43-50 
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    Keywords: Acousto-optic ; light diffraction ; ultrasonics ; phase measurements ; NDE
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    Notes: Abstract An alternative method for nondestructive testing based on light diffraction by ultrasonic waves is presented. It enables us to make more accurate measurements of intensity and phase of reflected waves, and therefore detailed information about the reflecting system can be obtained. Applications are numerous but special attention is payed to examination of the quality of coupling systems.
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    Journal of nondestructive evaluation 4 (1984), S. 59-63 
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    Keywords: eddy current ; theoretical models ; computer analysis ; NDE
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    Notes: Abstract Available theoretical models for predicting defect responses in eddy-current NDE apply only to defects of spheroidal shape. In this paper, the boundary-element integral-equation approach is extended to allow for defects of more irregular shape. Sample results for cylindrical and conical voids are presented and discussed.
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    Journal of nondestructive evaluation 4 (1984), S. 65-73 
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    Keywords: ultrasonic scattering ; photoelastic visualization ; cylindrical cavities ; creeping wave ; cracks ; NDE
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    Notes: Abstract Our efforts in the past few years to visualize the scattering of ultrasound in solids by the photoelastic technique are briefly reviewed. Photoelastic photographs are presented showing the dynamic processes of scattering in glass of plane longitudinal or transverse waves by a cylindrical cavity or cavities as well as by two-dimensional surface-breaking or internal cracks. Phenomena like creeping and multiple scattering are clearly seen, in addition to some details which are not predicted by known theories.
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    Journal of nondestructive evaluation 4 (1984), S. 107-123 
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    Keywords: ultrasonics ; transducers ; focusing ; refractior ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A scalar theory of the propagation of Gaussian ultrasonic beams through lenses and interfaces is presented. For radiation into a fluid, the Fresnel approximation is employed to derive the laws of propagation of Guassian beams (previously employed in the analysis of coherent optical systems). These are then generalized to situations commonly found in nondestructive evaluation by treating the effects of propagation through lenses and through curved interfaces at oblique incidence. A numerical example illustrates the ease with which insight into diffraction phenomena for complex geometries can be gained by this approach. The limitations imposed on the theory by aberrations and the scalar assumption are discussed, and the relationship of the Gaussian theory to the radiation of piston transducers is explored.
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    Journal of nondestructive evaluation 4 (1984), S. 141-148 
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    Keywords: Ultrasonic echography ; signal processing ; flaw detection ; nondestructive control ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The detection of flaws by ultrasonic echography becomes difficult when the flaw is at a shallow depth. The time delay between the interface and flaw echos is less than the width of the impulse-response time of the transducer, and the flaw echo generally has an amplitude much smaller than the dominating interface echo. When the surface is not too rough, the interface echo can be assumed to be known, and its comparison with the signal interface and flaw echo permits the detection of the flaw. In this article it is shown that signal processing techniques allow small flaws to be detected very close to the surface (∼0.5 mm). Two methods are proposed, the first one is based on the minimization of the mean-square error, and the second on the spectral substraction of the two echos.
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    Journal of nondestructive evaluation 2 (1981), S. 51-55 
    ISSN: 1573-4862
    Keywords: Love wave dispersion ; surface layer ; work hardening ; rail ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this paper, experiments show Love wave generation along the top surface of used railroad rail, where the shear wave velocity has been slightly reduced by the cold-working of wheel passage for years. The rf pulses used in the experiments have about 10 µs duration and a relatively narrow frequency spectrum. The group velocity of the Love wave is found to have a strong dependence on the carrier frequency over the tested range of 0.45–3.1 MHz. Application of the seismological one-layered model to the experimental measurements yields an NDE technique for the elastic properties and the thickness of the cold-worked surface layer. The results are interpreted on the basis of a destructive observation by micro-Vickers hardness testing.
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    Journal of nondestructive evaluation 2 (1981), S. 75-84 
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    Keywords: digital signal processing ; microprocessor based system ; binary display ; ordered dither ; ultrasonic C-scan ; image magnification ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The use of a digital microprocessor based system for the acquisition of ultrasonic C-scan information is investigated. The C-scan information is displayed on a binary display device using electronic ordered dither techniques to represent gray levels. The digital system with a binary display increases system flexibility and yields better reproducibility and constant image quality independent of the display medium. Images may be stored on magnetic tape or disk for later retrieval and image processing. The techniques which are described allow for image magnification and a reduction in scan time by replacing the mechanical linkage between the scanner and the display with digital signals. A detailed comparison is made between two dither signals, and the advantages of each are discussed. The combination of digital signal processing and imaging techniques produces results which utilize the capabilities of ultrasonic inspection to the point where the transducer becomes the limiting factor.
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  • 62
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    Journal of nondestructive evaluation 2 (1981), S. 133-138 
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    Keywords: X-rays ; diffraction ; grain size determination ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract It is shown that the grain size of commercial materials can be estimated by x-rays with little or no sample preparation. The method is readily automated and can be employed on-line, for example, in a rolling mill.
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  • 63
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    Journal of nondestructive evaluation 2 (1981), S. 173-188 
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    Keywords: ultrasonics ; acoustic imaging ; computer image analysis ; failure prediction ; inhomogeneous materials ; accept/reject criteria ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A computerized technique is presented which has been developed for analyzing acoustic images of an inhomogeneous material. The acoustic imaging system is briefly described with emphasis on its adaptation to billets of graphite for atmospheric reentry body use. Ultrasonic images of such inhomogeneous material contain a nonuniform distribution of anomalies and few, if any, geometrically regular features which can be assessed to establish material integrity. Results obtained with our new algorithms show, for certain discriminants, a high degree of correlation between the numerical accept/reject values obtained from acoustic image processing and the time-to-failure of the graphitic material in simulated atmospheric reentry tests.
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  • 64
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    Journal of nondestructive evaluation 2 (1981), S. 209-217 
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    Keywords: honeycomb panels ; acoustic inspection ; leaky waves ; SH and Lamb waves ; line scan ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper considers the properties of elastic waves guided by an aluminum plate bonded to a honeycomb core for application to rapid inspection of honeycomb panels. Current acoustic inspection techniques involve the transmission of a signal between a pair of small transducers located on opposite sides of the panel. Scanning the transducers in raster fashion results in a high resolution inspection of the panel, but is very time consuming. An alternative technique would simultaneously inspect all points along a line between two widely spaced transducers located on the same side of the panel. Scanning the pair once over the panel permits rapid inspection, although with decreased resolution. Studies presented here indicate that such a method of inspection is feasible and that the flexural mode is probably the most useful.
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    Journal of nondestructive evaluation 3 (1982), S. 1-8 
    ISSN: 1573-4862
    Keywords: acoustoelasticity ; transverse isotropy ; polycrystalline aggregate ; cubic crystal ; third-order elastic constants ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Acoustoelasticity is an ultrasonic technique which has been used for the determination of active and residual stresses in common structural materials. This paper examines the effect of texture on the acoustoelastic response in polycrystalline bodies. In particular materials which are transversely isotropic aggregates of cubic crystals are studied. The second- and third-order elastic constants of the polycrystal are derived from the elastic properties of the constituent crystals, and the crystalline orientation relative to the body's symmetry axis. The acoustoelastic relations between velocity and deformation are then presented for the aggregate. Finally, evaluation of the acoustoelastic response for several ideal textures using data for aluminum single crystals shows that the response is highly dependent on the texture.
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    Journal of nondestructive evaluation 3 (1982), S. 111-113 
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    Keywords: photoacoustic microscopy ; delamination ; layered structure ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract An adhesive layer, by which a piezoceramic foil is attached to an aluminum membrane for telephone application, is examined in a nondestructive way by thermal waves. The basic principles of the method are outlined, and its detecting power is demonstrated by evaluation of a well-defined delamination.
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    Journal of nondestructive evaluation 3 (1982), S. 147-154 
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    Keywords: finite element modeling ; eddy current ; absolute probe ; steam generator tubing ; NDE
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    Notes: Abstract Finite element analysis techniques are applied to the problem of predicting signals from an absolute eddy current probe in the tube sheet region of a PWR steam generator for the purpose of optimizing the probe coil geometry and determining the feasibility of using such a probe to characterize the condition of the tube and tube sheet crevice.
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  • 68
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    Keywords: Acoustic harmonic generation ; critical angle acoustics ; fatigue crack detection ; alloy microstructure ; load amplitude ; NDE
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    Notes: Abstract Alloy grain size is known to influence both the propagation path and the closure stress of surface fatigue cracks in many alloys. The general trend is for the path to be more tortuous and the closure stress to be larger, the larger the grain size. By use of Ti Al-4V and Al 7075-T6, the effects of grain size on the nondestructive detection of surface cracks which might arise from closure stress and path irregularity variables were evaluated. Titanium specimens were inspected using an acoustic harmonic generation technique, and it was discovered that the major source of harmonic signals was grain sized crystallographic cracks. Harmonic signals were larger during fatigue in an 8-µm compared to a 4-µm grain sized alloy, as there were more grain sized cracks in the large grain material. Crack closure was found to be extremely important in determining the reflected acoustic amplitude obtained in inspecting small (100–1000 µm) cracks in Al 7075-T6 using a critical angle technique. Average received amplitudes were an order of magnitude smaller for cracks at zero load than for those opened by a tensile stress. The scatter in the reflected amplitude was also large, apparently as the result of variations in the degree of the closure from crack to crack. For the 7075 material, the important effect of larger grain size was to increase the irregularity of the crack path, making the small cracks more visible acoustically at azimuthal angles not normal to the crack plane.
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    Journal of nondestructive evaluation 3 (1982), S. 137-145 
    ISSN: 1573-4862
    Keywords: jadeite authentication ; 14 MeV neutrons ; jades ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Fourteen MeV neutron activation of jades was used to test the authenticity of jades: to ascertain whether they are genuine jadeite and whether their greenish colour is genuine, both of which are important criteria for the high market value of jadeite. For given activation and measurement conditions of the jades, the gamma-ray spectrum was observed to change as a function of the type of the jades; the counting ratio of the photopeaks from the two most prominent constituent elements varies greatly as a function of the type of the jades. The ratio of counts for the Compton edges of the 1.779 MeV gamma-ray of28Al, from28Si(n,p)28Al reaction, and the 1.434 MeV gamma-ray of52V, from52Cr(n,p)52V reaction, varied as a function of the type of the jades and also as a function of the color. These results can be applied for a fast and nondestructive evaluation of jades.
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    Journal of nondestructive evaluation 4 (1984), S. 29-38 
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    Keywords: NDE ; eddy currents ; surface layers ; stratification
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Nondestructive inspection of flat and long cylindrical metallic-surface layers is conveniently dealt with using the results of wave propagations in a one-dimensionally stratified medium. Analytical solutions for some special profiles are obtained, and perturbation technique is used to obtain results for more frequently encountered profiles.
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    Journal of nondestructive evaluation 1 (1980), S. 101-109 
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    Keywords: ultrasonic transducers ; NDE ; deconvolution ; signal processing
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A major objective of quantitative nondestructive evaluation is to formulate defect detection, classification, and sizing algorithms that are insensitive to variations in transducer characteristics, material type, and defect depth. With the data used in this research, ultrasonic signals were found to vary significantly with changes in the transducer and only secondarily with changes in material and depth. It is shown that the method for minimizing signal variations due to transducer and material changes is to deconvolve the test signal with respect to the transducer response from a reference defect in a block of the same material. Since depth variation primarily affects signal amplitude and has minor impact on shape, detection, classification, and sizing, insensitivity to depth is achieved by avoiding the use of amplitude-dependent parameters. The notion of a “standard transducer” is introduced. Its mathematical properties and methods of realization are given. It is shown how the effects of variability from different test transducers can be removed by signal processing. When these procedures are applied to the test transducer, the effect is to cause it to resemble the standard transducer and, thereby, to place all ultrasonic waveforms on a common basis.
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    Journal of nondestructive evaluation 1 (1980), S. 137-148 
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    Keywords: composite material ; ultrasonic velocity ; ultrasonic attenuation ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The ultrasonic group velocity and attenuation were measured as a function of frequency for longitudinal and shear waves in the Hercules epoxy matrix (3501-6) and in the principal directions of the unidirectional Hercules graphite fiber epoxy composite (AS/3501-6). Tests were conducted in the frequency ranges 0.25–14 MHz and 0.5–3 MHz for longitudinal and shear wave modes, respectively. While the attenuation increased with frequency for all wave modes, the group velocity was independent of frequency for all wave modes. In studying the effects of transducer-specimen interface couplant and pressure, it was found that for each transducer, there exists a frequency-dependent “saturation pressure” corresponding to the maximum output amplitude of the signal.
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    Journal of nondestructive evaluation 1 (1980), S. 149-155 
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    Keywords: acoustic emission ; fracture ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The far-field characteristics of the emission from a theoretical model for the fracture of brittle inclusions are presented in detail. The model is a circular crack growing at constant speed from zero size until it attains a prescribed size. The far-field radiation pattern is the same as that of a simple combination of force doublets, and some qualitative similarities between force doublets and acoustic dipoles are noted. The initial shape of the far-field pulses due to the growing stage and the stopping is determined, but difficulties arise in accounting for the diffraction of a surface wave on the crack faces generated by the stopping of the crack.
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    Journal of nondestructive evaluation 1 (1980), S. 215-224 
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    Keywords: Acoustic emission ; slip ; microcracking ; deformations ; displacement field ; elastic waves ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The theory of elastic wave emission (i.e., acoustic emission; AE) from damage processes such as slip and microcracking is discussed. Analogous developments in the literature on earth-quake seismology and dynamic dislocation theory are noted and utilized. A general representation of the displacement field of an AE event is given in terms of the double-couple response to a distribution of “moment density tensor” in the source region. Results are specialized to a point source model and to a general far-field analysis of outgoing elastic waves, and conditions for validity of such representations and their low-frequency specializations are noted. Emitted wave fields are compared for tensile opening and slip events, and procedures which might enable the approximate determination of the size or area increase of tensile microcracks are discussed.
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    Journal of nondestructive evaluation 1 (1980), S. 157-181 
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    Keywords: EMAT ; radiation pattern ; transducer ; shear waves ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A Green's function calculation of the far-field radiation patterns of EMATs is presented. The approach is based on (a) closed form expressions for the eddy current and static magnetic field distributions, established by the EMATs, which react to produce the driving Lorentz forces, and (b) a Green's function derived from the steepest descent approximation to the far-field response of an arbitrary surface point force on a half space. Numerical results are presented, illustrating the radiation patterns of the three common EMAT designs. Included are vertically polarized shear waves as radiated by both meander coil and periodic magnet EMATs and horizontally polarized shear waves as radiated by the latter.
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    Journal of nondestructive evaluation 1 (1980), S. 123-136 
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    Keywords: fatigue life ; acoustic surface waves ; NDE ; ultrasonics ; cracks
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The present studies concentrated on predicting the remaining fatigue life for single fatigue cracks in the Paris regime of macrocrack propagation. Acoustic surface waves were used to interrogate the crack during cyclic fatigue. The inversion of the obtained scattering data provided crack depth and crack length as a function of the number of cycles applied in tension-tension fatigue. Auxiliary experiments were conducted to study the acoustic response of the crack to tensile and compressive loads, thought to open and close the crack. The technique may allow for new insights into the physics of the “crack closure” effect.
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    Journal of nondestructive evaluation 1 (1980), S. 201-206 
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    Keywords: fracture mechanics ; noncircular crack ; fatigue life ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A transfer function that converts an irregularly shaped two-dimensional crack into an equivalent circular crack of equal propagation lifetime is proposed. The methodology extends the exact elliptical to circular crack transfer function to other noncircular cracks with geometries that slightly deviate from the elliptical. Results for rectangular, symmetric dumbbell, and asymmetric dumbbell cracks are presented.
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    Journal of nondestructive evaluation 1 (1980), S. 249-261 
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    Keywords: Ultrasonics ; cracks ; surface roughness ; diffraction ; scattering ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Ultrasonic measurements from rough cracks were carried out using both broad-band and narrow-band methods. An analysis is suggested to determine parameters of the crack quantitatively such as size, shape, rms surface roughness, and distribution function of the surface roughness. Ultrasonic measurements of the parameters compare very well with the actual parameters of the defect.
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    Journal of nondestructive evaluation 1 (1980), S. 287-293 
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    Keywords: Photoacoustic microscopy ; SPAM ; silicon nitride ; surface crack ; turbine vanes ; NDE
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Scanning photoacoustic microscopy (SPAM) was applied to silicon nitride turbine hardware for purposes of detecting fabrication defects. SPAM traces in selected areas of complex-shaped turbine stator vanes were obtained and indicate that surface-crack detection of the order of tens of microns is possible. Means were devised to allow for multiple scans in areas previously inaccessible to other nondestructive techniques capable of detecting defects in the 25- to 100-µm range. The results show that SPAM is applicable to reaction-bonded silicon nitride turbine components and capable of detecting small surface-related defects.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 1-11 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The distribution of the first-passage time is of decisive importance in lift (elevator) design. It yields the easure of performance of the system, the expected number of stops, the interval (i. e. time elapsed between two successive departures from a given floor) and many other parameters and factors determining the required number of lifts in a building. The derivation is based on the transition probability matrix of the operation policy, and consists in solving a system of linear equations.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 55-62 
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    Keywords: Engineering ; Engineering General
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    Notes: Fourier analysis of numerical accuracy has traditionally concentrated on the propagation behaviour of various methods. When systems of equations in more than one unknown are involved, analysis of propagation accuracy alone is shown to be incomplete. A distribution factor is introduced to complement the Fourier analysis in these cases, and application of the concept to two problems commonly encountered in the water resources field is demonstrated. The distribution factor is shown to provide important information which cannot be obtained from the customary analysis of propagation accuracy.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 177-188 
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    Keywords: Engineering ; Engineering General
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    Notes: A simple approximation by nonconforming finite elements is presented that passes the patch test of Irons and Strang but does not yield approximate solutions converging to the solution of the given boundary value problem. It is constructed from continuous piecewise linear functions perturbed by step functions. Further, strange convergence properties of such approximations are explained in all details because they may be typical for the behaviour of nonconforming finite elements violating the basic precondition for convergence.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 209-223 
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    Keywords: Engineering ; Engineering General
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    Notes: The solution of incompressible, viscous flow problems using the primitive variable finite element approach is formulated in a coherent and physically reasoned exposition. In particular, it is shown that terms associated with changes in momentum caused by lack of mass conservation should logically be included in the governing equations. Previous formulations have not considered this possibility. Numerical results are presented to show the effect of inclusion of these extra terms; however, it is concluded from the numerical results for the specific case which was tested that there is no obvious benefit obtained by including these terms.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 237-247 
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    Keywords: Engineering ; Engineering General
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    Notes: A dual load method of truss analysis is presented that allows highly nonlinear member behaviour to be followed. In particular, a brittle type of strut behaviour is considered. The method assumes that the inelastic strut response is known and that piecewise linearization of the behaviour is acceptable. An example is given to illustrate the type of problem that can be handled. The example involves negative stiffness of the members and consequently attention must be given to the equation solving procedure for the structure. A comparison is made with some observed test results.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 291-295 
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    Keywords: Engineering ; Engineering General
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    Notes: A numerical Laplace transform inversion technique is described, which is a modification of the inversion method using an exponential series representation. By adding an auxiliary function and using Erdélyi's inversion formula, the proposed technique provides the inverse approximation with improved accuracy near t = 0. Numerical illustrations shows that this procedure also works in cases when the original method of schapery fails to give satisfactory results.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 308-318 
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    Keywords: Engineering ; Engineering General
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    Notes: A new method for interpolating in triangles is described. Bivariate cubic polynomials are utilized to define an interpolant which assumes arbitrary position and slope on the entire boundary of a triangular domain. Some examples and applications are discussed.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 351-360 
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    Keywords: Engineering ; Engineering General
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    Notes: Numerical convergence of first- and second-order plate-bending elements is investigated. Using iso-parametric formulation, general bilinear and biquadratic quadrilaterals, with the three moment components and the transverse deflection as dependent variables, are obtained. The same elements are also used as degenerate triangles by collapsing one side. A constant bending moment patch test, applied numerically to the elements, indicated poor performance for linear triangles, while the bilinear, quadratic and biquadratic elements behaved well, with exact results in uniform meshes. Further numerical examples showed the same general trend as the patch test. Although bilinear, quadratic and biquadratic elements were always able to yield the correct solutions with mesh refinements, the linear triangles were in general unable to do so.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 381-404 
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    Keywords: Engineering ; Engineering General
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    Notes: The complete two-dimensional partial differential equations for developing laminar flow in a circular tube have been treated by a finite difference analysis. Property variation with temperature, especially that of viscosity, is allowed for in a flexible manner. The continuity and momentum equations, and then the energy equations, are solved by direct elimination at each axial step, and marching procedure used in the axial direction. A new technique is that the stepwise energy balance is rigidly satisfied throughout by using it as a constituent equation in place of the ‘explicit’ wall thermal boundary condition normally used.The analysis predicts the complete developing hydrodynamic and thermal fields, together with friction factors and heat transfer coefficients. It has been tested for a range of fluid velocity and thermal boundary conditions and for various fluids, including high viscosity oils, water and air.Data for constant wall heat flux have already been published. 1,2 Predictions for constant wall temperature presented here are for forced and combined convection and are compared with experimental data of Test3 and Zeldin and Schmidt4.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 464-469 
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    Keywords: Engineering ; Engineering General
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    Notes: A numerical method for solving two-point boundary value problems associated with systems of first-order nonlinear ordinary differential equations is described. It needs four function evaluations at each point and is of order h6, where h is the space chop. Results of computational experiments, which include perturbation of the initial conditions, comparing this method with other known methods are given.
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  • 90
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 470-476 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An algorithm is given to discretize a polygon or curved surface into triangular arrays. The method first involves the manual division of the array into quadrilaterals with specified numbers on rows and columns. The individual points are then filled in automatically and elements are automatically generated. A point of particular importance is that the number of columns or rows may be made to change. A subroutine is given to perform this task.
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  • 91
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 483-494 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An approximate analysis method for calculating local and system geometric imperfection influences on the displacements, stresses and buckling load of imperfect truss structures, is developed. The structural response, as a function of the design variables, is expressed in this approximate analysis which is much faster and cheaper than the ‘accurate’ analysis. The accurate analysis for a particular design is used as a base for each approximate analysis which then gives the response information needed for other designs in the neighbourhood about the base point design. Comparison of the approximate behaviour predictions with accurate results based on the more refined analysis methods shows that the quality of the proposed approximate analysis procedure is adequate for guiding a structural design procedure. It is evident that the approximate analysis is capable of describing the nonlinear behaviour of the structure, but when nonlinearity increases, the quality of the approximate analysis tends to deteriorate.
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  • 92
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 575-582 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The usual linear shape function for approximating axial displacement in beam finite elements used as eccentric stiffeners leads to an inconsistency which can result in large errors in the deflection of plates or composite beams. The introduction of an additional degree-of-freedom for these elements circumvents this problem.
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  • 93
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 639-648 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A boundary-location method is developed for finite element simulation of steady, two-dimensional flows of Newtonian liquid with free boundaries. In the method, boundary shape and position and the velocity and pressure fields are determined simultaneously. Inertial, viscous, gravitational, and surface tension effects are included in the development. The complete set of nonlinear finite element equations is solved by a modified frontal method combined with Newton-Raphson iteration to speed convergence. The finite element used to illustrate the method approximates the pressure as a piecewise constant function and the velocity and free boundaries as piecewise linear functions. Example calculations for flow from a slit show that the method can be effective.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 685-699 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The choice on an efficient direct integration procedure for linear structural dynamic equations of motion is discussed. It is suggested that as accuracy parameter the truncation error on the exponential terms contained in the modal contributions of the exact solution be assumed. This error does not always coincide with the local truncation error. These considerations were used to design an unconditionally stable one-step method whose accuracy is 0(h4). Numerical comparisons with some well-known integration schemes showed the efficiency of the proposed method.
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  • 95
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 713-731 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a generalized method which generates linear, triangular, quadrilateral and pentahedral elements for the finite element method. Depending on geometrical and material variations, the region to be discretized is manually divided into blocks such as lines, triangles, quadrilaterals, pentahedrons and hexahedrons in several appropriate co-ordinate systems. However, no connectivity information of the adjacent blocks is required by the user as input. The continuity of the generated nodal co-ordinates and element configurations at the block interface are automatically maintained to describe the geometry of structures, no matter how these five types of blocks are connected. Furthermore, a mesh grading algorithm which generates reliable mesh grade distributions in the interior of the triangular and quadrilateral blocks is established corresponding to the arbitrarily defined subdivision numbers for each edge line of blocks. This algorithm is extended to the mesh grading in the interior of the hexahedral and pentahedral blocks. Element numbers are also renumbered in this scheme, in addition to node numbers, in order to increase the computational efficiency of the global matrix assembly. Additional facilities, i.e. loading data generation, boundary condition data generation and so on, are also discussed. An illustrative and a practical example are given to demonstrate the capabilities of this scheme.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 773-778 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The shape functions of serendipity rectangular elements had originally to be found by inspection. More recently an algorithm has been developed to formalize the construction of these shape functions. Here a simple expression is found for the interpolation function of the most general serendipity element. The shape functions can be derived immediately.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 955-980 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A series of finite element algorithms for the calculation of the post-buckling behaviour of structures are proposed. The algorithms represent a finite element implementation of a variational principle for nonlinear eigenvalue problems. Incremental amplitude solution schemes are defined. Numerical results are presented for the post-buckling behaviour of specific structures with linear and nonlinear pre-buckling states.
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 1041-1052 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Additional Material: 7 Ill.
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 15 (1980) 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    International Journal for Numerical Methods in Engineering 15 (1980), S. 935-942 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Additional Material: 8 Ill.
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