bluuebunny/crossref_metadata_2025 huggingface dataset:
An ultrasonic fatigue crack growth monitor and load controller
Authors: Wade E H R , Lee G M C
Published: July 2007

The design of an ultrasonic crack follower which continuously monitors the position of a fatigue crack in a 36 mm thick C.K.S. type specimen is described. An open-bottomed ‘tank’ containing a mobile immersion probe is mounted on the top surface of the sample. The probe is used to measure the position of the crack tip by normal ultrasonic techniques; as the crack grows the probe is automatically advanced to keep the reflected signal intensity constant. The probe drive mechanism is geared to two potentiometers, one of which produces an output proportional to the probe position, the other is used to attenuate the load control signal so as to keep the stress intensity range constant. The unit was capable of detecting crack growth increments of 450 μm. The automatic nature of the measurement greatly simplified the collection of fatigue crack growth data.
A note on special photographic techniques applicable to photoelasticity
Authors: Meyer M L , Mehrotra C L , Pabani S A
Published: July 2007

Equidensity techniques used increasingly in photoelasticity are based on pseudo-solarization effects. These and related photographic phenomena are defined, the classical procedure and improvements described, basic experimental results and calibration methods demonstrated.
An optical method for direct measurements of strain in a torsional Hopkinson-bar apparatus
Authors: Stevenson M G , Campbell J D
Published: July 2007

A method has been developed to measure the related rotation of the flanges of a thin-walled tubular specimen during a torsion test. The method, which is based on the Moiré-fringe technique, is capable of use at the high rates of strain encountered during a Hopkinson-bar test, as well as at low rates of strain. In the application described, the specimen gauge length is very short, but the method could be used for specimens of considerably longer gauge length.

Direct calibration of the system is easily carried out at low angular velocities. The method can then be used to measure directly the specimen strain during a Hopkinson-bar test, and thus to check the value derived from measuremets of torsional waves in the elastic bars. Results of such comparisons are given, and it is found that the values given by the two method agree well, the differnce being attributable largely to inaccuracies in the torque measurement. The new method permits the determination of specimen deformation during the later stages of the test when multiple wave reflections render the wave analysis iaccurate. In particular, it has been found that the specimen may be subjected to reversed plastic straining, so that the total plastic strain connot be determined from the permenent deformation at the end of the test.
A penalty function approach to problems of plastic flow of metals with large surface deformations
Authors: Zienkiewicz O C , Godbole P N
Published: July 2007

An iterative solution permits determination of velocities in plastic flow using a finite element formulation. By updating co-ordinates very large deformation can be followed.
Origins of the stress intensity factor approach to fracture
Authors: Hayes D J
Published: July 2007

The development of energy balance approach to fracture is traced. Limitations of the approach are discussed and the justification for its application to practical problems is indicated.
Yielding fracture mechanics
Authors: Turner C E
Published: July 2007

Yielding fracture mechanics seeks to find a relationship between applied stress, crack size and material toughness that is independent of the geometry of a component when fracture occurs after significant degree of yielding. The crack opening displacement, Δ, and the J contour integral are two proposals for describing the stresses and deformation at the tip of a sharp crack embedded in a region of yielding material. The concepts can be related in the form J = M σ YΔ where σ Y is the uniaxial yield stress, and M a factor with a value between about 1 and 2.5. The concepts are still under development. Either term can be chosen as a measure of the severity of crack tip deformation in a given material with the onset of crack growth in monotonic loading occurring at a critical value, Δ c or Jc, for a given thickness. Experimental evidence so far is in broad support of this picture but there remains uncertainty over the degree to which Δ c or Jc is independent of geometry and the extent to which stable crack growth prevents the usage of one simple criterion of fracture for all structural configurations.
Problems in creep testing under biaxial stress systems
Authors: Kelly D A
Published: July 2007

Two types of creep testing machine, one to apply bi-axial tension to cruciform specimens and the other, torsion to disc-shaped specimens, have been constructed in the course of an investigaton of the behaviour of copper subject to multi-axial stress systems. Problems of bending in biaxial tension and buckling in torsion were encountered subsequent to construction of the machines. In the former case the deficiency was accepted and eccentric loading used to control the bending within acceptable limits. In the latter case microscopic examination was found necessary in order to define creep failure.
New analysis of holophotoelastic patterns and their application
Authors: Ebbeni J , Coenen J , Hermanne A
Published: July 2007

This paper shows that by the use of a new type of diffuser it is possible in photo-holoelasticimetry, without any addition of optical elements or particular preparation of the specimen, to record simultaneously but separately fringe patterns respectively related to the sum and the difference of the principal stresses. The value of intensity of the interfering light reaching the hologram plate is established and hence the equations of the recorded pseudoisopachic fringe patterns are given. Used successfully for the study of particular static problems, where numerical methods are very difficult or impossible, the present interferometer is also suited for dynamic problems.
Finite element analysis of cracked bodies to determine stress intensity factors
Authors: Chow C L , Lau K J
Published: July 2007

A method for the computation of the stress intensity and associated geometrical correction factors by use of the finite element analysis is presented. The lack of ability to represent crack tip stress conditions has been the shortcoming of the conventinal techniques in finite-element solutions of problems of cracked bodies. The proposed method provides the representation of crack tip stress conditions with elliptic displacement functions which lead to the direct computation of stress intensity factors. The method is applied to several crack configurations with relatively coarse finite-element networks and the accuracy is found to be satisfactory when compared with results of previous workers.
Load increment ratios in the elastic—plastic analysis of anisotropic materials by the variable-stiffness finite-element method
Authors: Tayal M , Budney D
Published: July 2007

One important decision is involved in the variable-stiffness approach to the solution of elastic-plastic problems by the finite-element method - namely the size of the load-increments that should be employed. This paper presents a very simple method of estimating ‘load-increment ratios’ which can be used to determine the size of these increments. If, however, a pre-determined constant load-increment size is employed, the load-increment ratios can be used to proportion appropriately the elastic and plastic stiffnesses of transition finite elements which go from the elastic to the plastic state during the load-increment.
Stress concentrations in anisotropic plates by the method of caustics
Authors: Theocaris P S
Published: July 2007

The optical method of caustics has been extended to study, theoretically and experimentally, the stress fields developed around discontinuities or singularities in anisotropic plates. The equations of the caustic to be expected from illuminating the anisotropic plate by a coherent light beam were derived in terms of the two complex stress functions used in the complex formulation of the plane anisotropic stress problem, the coefficients of the optical anisotropy of the material and the characteristics of the optical arrangement. The particular case of the singular stress field developed at the tip of a crack in an orthotropic plate was studied in detail. A series of experiments was then undertaken with slotted plates taken from the neck region of a polycarbonate plate which had been necked in tension and therefore showed a significant amount of anisotropy. The experimental data corroborated the theoretical predictions. It was concluded that singular or discontinuous stress fields can be successfully studied by the method of caustics.
Silicone rubber models for design and stress analysis of large components
Authors: Meyer M L
Published: July 2007

Relatively large models of soft silicone rubber sprayed with enamel paint are used successfully for initial estimates of stresses in side plates of winder drums. Results are compared with established formulae, and extended rules are indicated for initial design based on model test results.
The influence of Bauschinger effect on overstrained spring strip
Authors: Swift W A C
Published: July 2007

A theoretical Bauschinger chart has been constructed, the data being based on experimental results. This chart is used to predict the resisting moment of the strip whilst determining the residual-stress distribution using a layer-removal technique.
Limitations of the Westergaard equations for experimental evaluations of stress intensity factors
Authors: Evans W T , Luxmoore A R
Published: July 2007

The full equations for stresses and displacements around a central crack, in an infinite plate subjected to uniaxial and biaxial tension, are determined using the Westergaard stress function. These are compared quantitatively with the usual approximate forms, in order to assess the range of validity of the latter for use in experimental measurements of stress intensity factors.
Repeated use of frozen-stress photoelastic models
Authors: Fessler H , Litewka A , Perla M
Published: July 2007

A fairly large, somewhat complicated model was used to study systematically the errors involved in the repeated use of such a model, made possible by cementing inserts into the gaps left in the model when slices have been removed. To obtain accurate results it is necessary to keep the thickness of cement as small as possible and to cure the cemented joint at elevated temperature before loading. It is also desirable to subject the insert material to the same temperature history as the model.
Bending stresses in thin circular plates with single eccentric circular holes
Authors: Ollerton E
Published: July 2007

The bending stresses in thin circular plates having a single eccentric circular hole and small deflections are reported. The plates can have any mixture of clamped and simply supported boundaries, and can be subjected to a concentrated force uniformly distributed round the inner boundary, moments about two perpendicular axes, or uniform pressure on the plate surface. A previous paper (1)∗ has described the method of analysis using bipolar co-ordinates, and has given values for deflection and slope coefficients for varying diameter ratios and eccentricities under the loads described above. The present paper discusses the stresses found in the plates under the same conditions.
Elastic-plastic fatigue crack growth under load cycling
Authors: Branco C M , Radon J C , Culver L E
Published: July 2007

An analytical solution based on non-linear beam theory has been derived to compute the variation of total cyclic potential energy in fatigue crack growth under conditions of gross plasticity. It was assumed that the variation in total potential energy with crack length was equal to the cyclic value of J, written as Δ J = Jmax - Jmin where Jmax and Jmin are the maximum and minimum values of the contour integral J in the loading cycle. The solution is applicable to any geometry, providing fully tensile loading and cyclic creep occurs. It was applied to the contoured double-cantilever-beam (d.c.b.) geometry and Δ J was found to be dependent upon load P, crack length a, number of cycles N and the strain hardening and cyclic creep properties of the material. The results obtained may be applied in the study of crack propagation at relatively small deflections.

Fatigue crack growth rates were investigated experimentally under tensile cyclic conditions, leading to generalized plasticity. Tests were performed on mild steel d.c.b. specimens at room temperature in laboratory air, 50 per cent r.h. at a loading frequency of 0.1 Hz. Load-deflection loops were monitored during the lifetime and it was found that the experimentally measured variations in potential energy were 5-10 per cent above the theoretical Δ J values. The difference is explained in terms of the shear force effect and also rotation at the crack tip not considered in the theoretical analysis. When the crack growth rate, d a/d N, was plotted against Δ J, a good correlation was obtained. These results offer supporting evidence to the thesis that crack growth rate at high strains is substantially controlled by Δ J.
The influence of mean stress on fatigue crack propagation in a quenched and tempered alloy steel
Authors: Wade E H R , Lee G M C
Published: July 2007

A series of tests are reported which support the proposal that fatigue crack growth rates are retarded by crack closure at low values of applied mean stress intensity. In particular, the evidence presented indicates that closure occurs most readily at the specimen's free surfaces. This leads to dramatic changes in crack front profile under certain loading conditions.
Biaxial buckling of moderately thick laminated plates
Authors: Turvey G J
Published: July 2007

An approximate analysis is presented for the computation of buckling loads of biaxially compressed, simply supported, rectangular, moderately thick, laminated plates. The analysis is based on the use of reduced plate stiffnesses as well as shear correction factors. By comparing the approximate buckling loads with those obtained from a full 3-dimensional analysis, it is demonstrated that the approximate analysis is sufficiently accurate for design purposes. A computer programme based on the approximate analysis is then used to derive a reasonably comprehensive set of dimensionless buckling-load vs plate-thickness-ratio curves.
Shape imperfections in cylinders and spheres: Their importance in design and methods of measurement
Authors: Kendrick S B
Published: July 2007

Most design codes require stiffened cylinders to be made circular to within ½ per cent on radius, and large penalties are incurred by exceeding the shape tolerance. The methods specified for checking on circularity vary greatly and they are vague in some cases and illogical in others.

Two methods of measuring shape are presented, and it is shown that extreme care must be used in analysing the results obtained from chord gauge readings which are often the most convenient to take. The accuracy of the two methods is compared.
Residual stresses and distortions measured during construction of the Milford Haven Bridge
Authors: Cullington D W , Beales C
Published: July 2007

Residual stresses and distortions were measured during various stages of fabrication and erection of the Milford Haven Bridge. Welding caused compressive residual stresses in the plate panels and tension in the stiffeners. The panels distorted in the direction of the stiffened side of the plate. Grit blasting and transporting caused an apparent reduction in the plate stress accompanied by a small increase in this distortion. These processes affected the magnitude of the stresses but not their distribution within a plate panel. Fabrication caused rather larger stresses than those estimated using the Merrison Rules, but distortions were kept within Merrison tolerances.
Control of distortion due to welding and the additional cost involved
Authors: Thompson J D
Published: July 2007

This paper details various aspects of distortion, how these faults occur, how they may be avoided, and if not avoided, how they may be most easily alleviated.

The costs of avoiding or alleviating distortion are most difficult questions to discuss in that the records of many manufacturing shops do not list them separately, and they are often included in normal fabricating shop costs.

Finally, the author tries to lay down some general principles of good practice that will minimize distortion and the consequent residual stress which would be detrimental to the finished structure.
The use of the C∗ parameter in predicting creep crack propagation rates
Authors: Harper M P , Ellison E G
Published: July 2007

The applicability of the C∗ parameter for the prediction of creep crack propagation rates is considered. A new method for estimating C∗ is presented, the results from which show good agreement with those from an existing technique. Experimental results from creep crack growth tests, conducted on a 1 Cr Mo V steel using both compact tension and single edge notch bend specimens, indicate that good correlation with C∗ is obtained once the effects of stress redistribution become negligible. Finally, comparisons are drawn between C∗ and other possible correlating parameters, and the limitations of each approach are discussed.
On non-uniform illumination in a lens polariscope and remedies
Authors: Mehrotra C L
Published: July 2007

Non-uniform illumination originates from (1) non-uniform transmission of light by model and polariscope elements, (2) diffraction and obstruction of light by the edges of elements and camera shutter, and (3) internal reflections of light from lenses and covering glasses. Effects appear as (1) a locally non-uniform background intensity distribution on the viewing screen or camera film, (2) a peripheral zone of generally reduced intensity, and (3) a bright central spot.

This paper shows how local non-uniformities can be detected by photography. The peripheral zone may be avoided by use of a reduced size of field. Remedies for the deleterious bright spot may include a suitably chosen distance between first field lens and model, a small camera aperture and, in extereme cases, a translucent screen between light source and first field lens.
Replacement of quarter-wave plates by photographic double exposure for controlled density evaluation
Authors: Mehrotra C L , Meyer M L
Published: July 2007

Isoclinics are eliminated by double exposure of a film in the camera of a plane polariscope and by rotation of the coupled polaroids through 45° between the two exposures of equal duration. The resultant photographic isochromatic pattern can be evaluated by interpreting and calibrating as lines of constant fractional fringe orders the sharp boundaries between dark and bright regions seen in a developed high-contrast film negative or the narrow equidensity lines obtained in a developed Agfacontour film negative. Alternatively a developed low-contrast film negative may be copied by contact or enlargement on high-contrast or Agfacontour film.

The fractional fringe orders of the lines on any photograph depend on the exposure time, or copying exposure time, and on the coupling angle of the polaroids. Monochromatic light, or white light with blue-sensitive or orthochromatic film, may be used. An evaluated example and error analyses show that discrimination of fractional orders is about the same as in conventional compensation methods.
Thin annular plates having an inner clamp carrying bending moments
Authors: Ollerton E
Published: July 2007

The problem considered here concerns a thin annular plate having an inner clamp which provides a simple support and an outer clamp which provides either a simple support or a built-in edge. The inner clamp supports a bending moment which tends to tilt it out of plane.

A complete theoretical solution to the problem is presented for small deflections of the plate. Equations are derived for the deflections and stresses in terms of the applied bending moment, the plate geometry and the elastic constants of the plate material.

Calculated results are compared with the trends of known values for plates with eccentric inner clamps.
Stress concentration factors around the intersection of two cylindrical holes in an infinite elastic body
Authors: Hooke C J , Demunshi G
Published: July 2007

The paper presents an approximate solution for the stress distribution around two cylindrical holes intersecting at right angles in an infinite homogeneous, isotropic, elastic body, when the body is subjected to uniform tension at an infinite distance from the holes. Stress concentration factors for a range of ratios of the hole radii are presented, both for the case when the two holes are infinitely long and for when the smaller hole is semi-infinite.
Stationary creep prediction from model tests using reference stresses
Authors: Fessler H , Hyde T H , Webster J J
Published: July 2007

The theoretical basis of the experimental determination of reference stresses from model tests is established for one-dimensional and complex stress systems. A graphical method of obtaining the experimental reference stress is presented and used to determine reference stresses for the strain in beams in pure bending and the tip deflection of cantilever beams from room-temperature tests of lead-antimony-arsenic models. The results are compared with theoretical values.

It is shown how prototype deformation can be predicted from a test of a model of the component, model material creep data and the strain of a uniaxial prototype material specimen tested at the reference stress. Errors in the prediction of prototype deformations are considered.
Fracture studies of point-loaded centre-cracked plates
Authors: Chow C L , Lau K J
Published: July 2007

This paper describes the development of a point-loaded, centre-cracked (P.L.C.C.) plate in fracture studies. The methods used to determine a satisfactory geometry for the specimen, in terms of the stability of cracking, are discussed, and the results agreed well with those obtained experimentally. The stress intensity factor ( KI) of the plate is presented for a wide range of H/W values, using a finite-element method based on a displacement-function approach. Fracture-toughness ( Gc) tests, involving the use of a quasistatic energy concept, are conducted and used to check the accuracy of the computed KI-values. Good correlation is obtained between the stress and energy approaches.
Crack extension forces in elasto-plastic stress fields
Authors: Light M F , Luxmoore A R
Published: July 2007

A finite-element method has been used to calculate crack extension forces for experimental fracture specimens which failed after general yield. The results are compared with the values of the J-integral for the same specimens, and a significant discrepancy is noted. The crack extension forces at failure for a centre-notch and bend specimen of the same material were found to be almost identical, but did not agree with the plane strain GIC value reported for thick-section specimens.
Inextensional collapse of thin-walled tubes under axial compression
Authors: Johnson W , Soden P D , Al-Hassani S T S
Published: July 2007

Inextensional collapse modes are presented for the axial compression of thin-walled tubes. Shortening is achieved by folding about fixed hinge lines to form a number of flat triangular planes. A new mechanism is propounded by which collapse proceeds progressively from one end of the tube, following the passage of a travelling hinge.

Simple expressions are developed for mean collapse load and the energy absorbed during collapse of rigid-perfectly plastic tubes.

Comparison of collapse modes and predicted loads with those obtained from experiments on rigid P.V.C. tubes of various thickness, diameter and length give encouraging agreement.
Some finite-element stress analyses of simulated diffusion-bonded lap joints
Authors: Gurney T R
Published: July 2007

A series of finite-element analyses have been carried out on lap joints between similar materials and between two materials with Young's moduli in the ratio 3:1. The main objectives of the work were to determine the influence of the ratio between the overlap distance and the plate thickness on the stress concentrations at the ends of the plates, and to examine the influence of tapering the ends of the plates. In the course of the work, comparisons were made between various loading conditions.
Ovalization of cylindrical tanks as a result of foundation settlement
Authors: Malik Z , Morton J , Ruiz C
Published: July 2007

A method of assessing the effect of foundation settlement upon the ovalization at the top of floating roof storage tanks is presented. The accuracy of the method is tested by comparison with field measurements and experiments on model tanks. Current design specifications for the permissible foundation settlement are reviewed and the extent to which they limit tank ovalization is assessed.
Third international conference on pressure vessel technology—a critical review of papers on analysis, design and creep
Authors: Stanley P
Published: July 2007

This conference, held in Tokyo in April 1977 and organized by the Japanese Organizing Committee, with the support of A.S.M.E., I. Mech E. and a European Participation Committee, attracted 400 delegates from all over the world. More than 100 papers were presented in parallel sessions on a wide variety of pressure-wessel topics; there were also ‘panel sessions’ for the discussion of specific topics. The classification of the numerous and diverse topics covered in the papers was not easy and there were inevitably omissions and misfits in the contents of the sessions. This review covers the papers presented in the sessions on Analysis and Design, Seismic Analysis and Dynamics, and Creep; some of the original groupings have been retained, but an attempt has been made to bring the papers more effectively together into well-defined sets.
Strain-energy release rate for a single-edge-cracked circular bar in tension
Authors: Daoud O E K , Cartwright D J , Carney M
Published: July 2007

The strain-energy release rate is determined for an edge crack in a uniformly stressed bar of circular cross-section. Values of the strain-energy release rate, obtained using a finite-element representation of the bar and by measuring the compliance of the bar experimentally, are shown to be in close agreement. For crack depths of less than one-half diameter, the strain-energy release rates are found to be lower than existing results on rectangular bars having the same relative crack length.
A design exercise for a ceramic turbine disc subjected to centrifugal stresses
Authors: Stanley P , Sivill A D , Fessler H
Published: July 2007

A general procedure for the assessment of the failure probability of a stressed ceramic component is illustrated by a detailed study of a proposed turbine disc design. The procedure is based on a statistical approach using the Weibull probability distribution, and requires the evaluation of a stress integral over the volume or suface area of the component. The stress distributions in this case are obtained from a three-dimensional analysis of a photelastic model of the disc. The proposed design is critically appraised in the light of the derived stress integrals. The variation of failure probability with speed is illustrated and the effects of changes in the material properties of the prototype disc are quantitatively assessed.
Quasistatic energy analysis of a slender D.C.B. specimen
Authors: Chow C L , Ngan K M
Published: July 2007

This paper presents a method of quasistatic energy analysis for characterizing the fracture behaviour of a slender D.C.B. specimen having two parallel beam arms of low bending stiffness. Examples chosen are in-plane tension and anti-plane shear problems, which exhibit linear and nonlinear load-displacement relationships, respectively. The results derived analytically agree well with those obtained experimentally for both examples, thus successfully demonstrating the versatility of the quasistatic energy analysis in fracture studies.

Stability of crack propagation for the geometries considered is analysed and found to be favourable unless there is a large negative value of d G/d a. Negative d G/d a was attained by contaminating portions of an uncracked specimen, and unstable crack propagation was observed experimentally in the contaminated regions.
Experimenal analysis of in-plane strain on curved surfaces using transferring techniques
Authors: Buitrago J , Durelli A J , Parks V J
Published: July 2007

A new grid-transferring technique is introduced that allows the strain analysis of flat or curved surfaces of single or double curvature. The technique consists of transferring a grid from the structure to a flat surface by means of a thin, adhesive, transparent ribbon. Information is obtained along a strip, or point-by-point when circles or rosettes are used. The technique is specially suitable for the solution of problems of finite deformation of flexible structures, and its threshold strain is about 0.004. As a verification of the new method, strains obtained on a disc under diametral compression are compared with results already given in the literature. As a general example of application, strains on the anticlastic surface of tubes with and without perforation, and turned inside out, are determined. The method is not influenced by rigid-body motions.
Theoretical and experimental stress analyses of centrifugal fan impellers
Authors: Bell R , Benham P P
Published: July 2007

Brittle-lacquer and strain-gauge methods and a finite-element analysis are used to determine stress distributions in a simplified model and an actual centrifugal fan impeller.
On the measurement of residual shear stress in scragged torsion bars
Authors: Swift W A C
Published: July 2007

The layer-removal method for determining the residual shear stress destribution in scragged torsion bars is examined.

It is found that thickness of the layer removed is restricted if the ‘mean stress at mean radius’ assumption is to be valid. Also, it is shown that the modulus of rigidity used in the Fuchs-Mattson equation is not the conventionally accepted modulus, the use of which can lead to large errors in the calculation of the residual shear stress in the outer layers of material.
Square box sections—experimental behaviour under combined bending and compression
Authors: Little G H
Published: July 2007

A series of tests was performed in which short lengths of square thin-walled steel box section to a model scale were tested to failure under combined bending and compression in a stiff loading rig. The design of the rig, the method of manufacture of the specimens, and the nature of the instrumentation are all discussed. The results illustrate the weakening effect of local buckling at large width/thickness ratios, and are compared with an approximate theoretical analysis recently presented by the author. A surprising result is that ten of the twenty-two specimens tested were stronger than predicted by simple plastic theory.
Residual stresses in cold-formed tubes
Authors: Kato B , Aoki H
Published: July 2007

Residual stresses in cold-formed, circular, steel tubes are analysed on the basis of mathematical plasticity. The correlation between this analytical prediction and test results is satisfactory.
Flexural anisotropy of glass-fibre-reinforced thermoplastics injection mouldings
Authors: Smith G R , Darlington M W , McCammond D
Published: July 2007

The anisotropy of flexural stiffness has been examined at low strain using ASTM bar and 3-mm and 6-mm thick edge-gated disc injection mouldings for two glass-fibre-reinforced thermoplastics (GFTP). Experimentally determined values were obtained under three-point bending and compared with theoretical prediction: which took account of the fibre orientation and length distributions in the mouldings. The flexural stiffness of the discs was also studied as a function of direction of test.

The prediction of the resulting anisotropies in flexure compares well with experiment, but these anisotropies are markedly different from those measured previously in tension. It is concluded that it is necessary to have a knowledge of the fibre distribution of a GFTP moulding in order to predict successfully its mechanical properties, or to interpret measured data.
Stress intensity factors in fretting fatigue
Authors: Rooke D P , Jones D A
Published: July 2007

Solutions are derived for mode I and mode II stress intensity factors for a crack at the edge of a sheet subjected to localized fretting forces. Both normal and tangential forces are considered. These solutions are approximated by a polynomial function of crack length, which is then used as a Green's function to derive stress intensity factors for arbitrary distributions of tensile and shear stresses at the edge of the sheet.
Compression moduli for blocks of soft elastic material bonded to rigid end plates
Authors: Lindley P B
Published: July 2007

Using simplifying assumptions based on a theoretical solution for incompressible materials, simple relations are developed for the plane strain and axisymmetric compression moduli for blocks of compressible soft elastic material bonded to rigid end plates. The approximate theoretical solutions compare well with finite-element analysis data for materials with Poisson's ratios between 0.125 and 0.499 83 and blocks having width-to-thickness or diameter-to-thickness ratios between 0.25 and 128.
Transverse sensitivity correction of strain-gauge readings by a method of Mohr's circles
Authors: Vasudevan M
Published: July 2007

A method of concentric Mohr's circles for correcting transverse sensitivity errors in bonded resistance strain-gauge readings in a biaxial stress field is explained and its use illustrated. A coaxial gauge pair with one element of negative and one of positive transverse sensitivity is proposed for corrected evaluation of readings.
Analytical estimate of stresses in bones and prosthesis stems
Authors: Gola M M , Gugliotta A A
Published: July 2007

A simplified, two-dimensional, mathematical model of a coupling between flexible beams is solved by a Legendre expansion procedure. Its main application is in the field of arthroprostheses.
The location of defects in structures from measurements of natural frequencies
Authors: Cawley P , Adams R D
Published: July 2007

A method of non-destructively assessing the integrity of structures using measurements of the structural natural frequencies is described. It is shown how measurements made at a single point in the structure can be used to detect, locate and quantify damage. The scheme presented uses finite-element analysis, since this method may be used on any structure. The principle may, however, be used in conjunction with other mathematical techniques. Only one full analysis is required for each type of structure.

Results are presented from tests on an aluminium plate and a cross-ply carbon-fibre-reinforced plastic plate. Excellent agreement is shown between the predicted and actual damage sites and a useful indication of the magnitude of the defect is obtained.
Simultaneous measurement of three displacement derivatives using a multiple image-shearing interferometric camera
Authors: Hung Y Y , Durelli A J
Published: July 2007

This paper describes a multiple image-shearing camera. By incorporating coherent light illumination, the camera serves as a multiple-shearing speckle interferometer which measures the derivatives of surface displacements with respect to three directions simultaneously. The application of the camera to the study of flexural strains in bent plates is shown, and the determination of the complete state of two-dimensional strains is also considered. The multiple image-shearing camera uses an interference phenomenon, but is less demanding than holographic interferometry with respect to vibration isolation and the coherence of the light source. It is superior to other speckle techniques in that the obtained fringes are of much better quality.
The photoelastic determination of thermal stress concentrations in grooved cylinders with a radial temperature gradient
Authors: Khayyat F A , Stanley P
Published: July 2007

A non-destructive photoelastic technique, requiring integrated retardation and scattered-light measurements, is used for the determination of thermal stress concentrations in hollow cylinders with (i) an internal and (ii) an external curcumferential groove, subjected to a steady-state radial temperature gradient.
A finite-element solution for visco-plastic torsion
Authors: De Vries G , Norrie D H
Published: July 2007

The equations governing the torsion of a prismatic bar of visco-plastic material with Bingham characteristics are derived and solved using the pseudo-functional finite-element method. Results are presented for a square bar, in the form of stress trajectories, for Bingham numbers of 2.0 and 0.33.
Thermal stresses in cylindrical vessels with limpet coils
Authors: Kitching R , Zarrabi K
Published: July 2007

A computer program is developed to undertake the elastic stress analysis of a limpet-coil vessel consisting of a cylindrical shell and part-circular coils, when the coils are at a different average temperature to that of the main shell.

Results of the analysis are used to present data on maximum stresses for a wide range of practical geometries for the vessel.
Measurement of residual stresses by the hole-drilling method: Influence of hole eccentricity
Authors: Ajovalasit A
Published: July 2007

The hole-drilling method is a semidestructive technique which allows the measurement of residual stresses. In this method, a source of error is due to the misalignment between the hole and rosette centres.

This paper presents a theoretical analysis of the influence of such misalignment on the strains measured by the rosette.

Formulae which give the residual stresses taking account of the hole eccentricity are derived. Finally, the errors, which affect the residual stresses when the eccentricity is neglected, are evaluated for some commercial strain-gauge rosettes especially developed for the hole-drilling method.
Optimization of electrical-potential methods of measuring crack growth
Authors: Klintworth G C , Webster G A
Published: July 2007

This paper describes an alternating-current electrical-potential system for measuring crack growth that is more sensitive than a corresponding direct-current system and which is capable of a discrimination in crack length of approximately 20 μm. It shows how the positions of the current supply and potential sensing leads can be optimized using two-dimensional finite-element and boundary integral equation methods. Both methods give calibrations which are in good agreement with optical measurements of crack growth and with measurements made using a graphitized electrical analogue paper technique. The boundary integral equation approach is shown to he the more efficient to use for a range of geometries, since it is only necessary to specify the shape of the boundary and redundant information at internal nodes need not be obtained.
Bond of tube in semi-infinite elastic solid
Authors: Ivering J W
Published: July 2007

The analysis of the bond stress of a thick-walled tube embedded at the surface of an elastic, isotropic, semi-infinite medium is presented. The condition of three-dimensional compatibility between the tube and the anchorage medium is taken into account. An equilibrium equation for a segment of an embedded tube is derived, from which bond stresses acting on the tube can be computed. The general solution obtained relates to the vector function for a uniform lineal load acting perpendicularly to the surface of an elastic half-space. The solution is in agreement with equations derived independently for cases of one-dimensional (lineal) compatibility.

The equation of equilibrium derived for a tube segment embedded at the surface of an elastic half-space is transformed to a form suitable for solving the bond stresses of a tube anchorage embedded at some distance from the surface. A numerical solution of bond stresses obtained by elastic analysis is compared to the bond stress curve along the anchorage obtained experimentally.
Crack stability in fracture toughness testing
Authors: Mai Y W , Atkins A G
Published: July 2007

The significance of crack stability in fracture toughness testing is discussed and the roles played by testing machine stiffness, testpiece geometry and material rate dependence are described. A compilation of the stability factors for more than twenty testpiece geometries under different loading conditions is given and compared with experimental results. Supplementary experimental methods of promoting crack stability for inherently unstable materials are discussed and illustrated with examples.
Calculation of gravitational strains and stresses in a solid of revolution by a mixed point-matching technique
Authors: De Wilde R J , Clement J , Hellemans J M , Boving R
Published: July 2007

This paper presents a point-matching method for solving axisymmetric body-load problems. It can be used for both linear and nonlinear elasticity problems. The change of boundary shape and boundary conditions requires only a few program modifications. The validity of each solution is evaluated by error analysis. The present method is compared with a finite-element technique.
Elastic stress parameters in simply supported skew plates in flexure
Authors: Cusens A R , Besser I I
Published: July 2007

This experimental study was undertaken with the aim of examining the flexural behaviour of a skew slab bridge deck with particular regard to the obtuse corners and the boundaries of the structure. The investigation considered bending and twisting moments, and reactive and shearing forces under concentrated point loads.

Tests were carried out on a simply supported asbestos-cement slab, with a 45° skew angle. Experimental results are compared with finite element solutions.
Dynamic stress analysis of rotating twisted and tapered blades
Authors: Ramamurti V , Sreenivasamurthy S
Published: July 2007

In this paper the finite element method has been used to determine the stresses and deformations of pre-twisted and tapered blades. Three-dimensional, twenty-noded isoparametric elements have been used for the analysis. Extensive analysis has been done for various pre-twist angles, skew angles, breadth to length ratios, and breadth to thickness ratios of the blades. Experiments were carried out to determine the stresses for the verification of the numerical results and they were found to be in good agreement.
Triaxial fatigue testing machine for polymeric materials
Authors: Lawrence C C
Published: July 2007

Part 1 of this paper is concerned with the design and development of a multiaxial fatigue testing machine. The machine structure is considered in some detail to emphasize the dynamic as well as the static stability essential in machines applying fatigue loading. The machine is capable of testing specimens of the same geometry in torsion, push-pull, and internal pressure (if hollow), either statically or dynamically. These test modes can be operated independently or in combination, both in phase and out of phase. Each mode can be stress or strain dependent.

Part 2 deals with the associated extensometry, test procedures, and preliminary tests on polymethylmethacrylate. These preliminary tests, originally undertaken to test the capability of the machine, whilst not extensive enough to be considered rigorous, are included to illustrate some of the interesting potentialities of multiaxial testing.
Stress analysis of webs of rimmed wheels
Authors: Ramamurti V , Srinivasan V
Published: July 2007

This paper deals with the static stress analysis of the web portion of a spur gear wheel after idealizing the web as a thin annular disc and the rim as a thin uniform ring. Design charts are included giving the stresses and deflections in non-dimensional form.
Crack propagation in thin plates under double torsion
Authors: Chow C L , Ngan K M
Published: July 2007

A method of analysis for characterizing non-linear crack propagation in thin plates under double torsion is presented. Quasistatic energy method is used to derive the fracture toughness and to study the stability conditions of crack propagation within the subcritical crack growth range.

Non-linear relationship between the torque and angular deflection of a thin rectangular bar is well known. A thin rectangular plate containing a central longitudinal crack and acted upon by a system of four-point loading (two opposite forces on each side of the crack) causes non-linear structural response to this loading mode.

The stability of crack propagation in thin plates under double torsion is examined for both the linear (thin plates) and non-linear (thick plates) cases. It is shown that improved stability can be attained if the specimen geometry and loading mode display a non-linear load-displacement relationship at constant crack area, as compared with the corresponding linear case.

A series of experiments is conducted to measure the fracture toughness of PMMA material of different thicknesses. It is observed that the fracture toughness values evaluated analytically using the quasi-static energy method compare favourably with those measured experimentally.

For the range of PMMA plate thicknesses considered, the effect of thickness on the fracture toughness of PMMA material is negligible. Finally, the validity of employing the double torsion specimen for fracture studies is examined by comparing the fracture toughness of thin plates of different thicknesses loaded separately by double torsion and by tension. No significant difference between the two sets of results is observed.
Stress intensity factors from reflected caustics in birefringent plates with cracks
Authors: Theocaris P S , Papadopoulos G A
Published: July 2007

In the present paper the method of reflected caustics is used for the evaluation of stress intensity factors in plates made of birefringent materials with a crack submitted to the opening mode of loading. It has already been established that due to the optical anisotropy of the material the rays reflected from the rear face of the plate form a double caustic. In this paper the influence of the optical anisotropy factor ξ of the material on the relative position and sizes of the two constituent branches of the caustic is studied. Nomograms are given for the accurate evaluation of mode I stress intensity factors from the geometrical characteristics of the two branches of the caustic. A series of tests, undertaken on plates made of polycarbonate of bisphenol A with ξr = 0.153, showed that the accuracy of evaluation of κI is the same as with the same method applied to optically inert materials.
Effects of anisotropy and diaphragm size on biaxial stress—strain curves for sheet metals
Authors: Ilahi M Fazli
Published: July 2007

When a circular diaphragm clamped at the edge is deformed by unilateral hydrostatic pressure the pole is under balanced biaxial tension if the absence of edge effects is assumed. The diaphragm test is an excellent way of obtaining the work-hardening characteristics of sheet metals to fairly high strains. Some previous investigators have tried to correlate the experimental and theoretical stress-strain characteristics of the pole of a diaphragm. In this present work 10 in. and 4 in. diameter dies and sheet metals with an average thickness of 0·040 in. have been used. Previous investigators used diaphragms of smaller sizes; but if the thickness—diameter ratio can be kept small the bending stresses will be negligible.

All sheet metals are anisotropic and for simplicity anisotropy in the plane is neglected, so that an average R value can be adopted. Hill's theory of yielding and plastic flow for anisotropic materials has been used together with the uniaxial tension test values to predict the stress—strain characteristic at pole. The effects of the diameter of the die and the normal anisotropy of the sheet metals on the stress—strain characteristics at pole are discussed.