bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear elastic characteristics of a cast epoxy resin
Authors: Ogorkiewicz R M
Published: July 2007

Behaviour under different types of short-term loading of specimens cast from an epoxy resin shows that in the realm of small strains its deformational characteristics can be regarded as linear elastic.
Bending of fibre-reinforced composite circular plates of non-uniform thickness
Authors: Lakshminarayana H V , Srinath H
Published: July 2007

By use of classical plate theory complete analytical solutions are obtained for the bending of thin fibre-reinforced composite circular plates of radially varying thickness exhibiting rectangular orthotropy. The plate equations are solved for three specific cases of axisymmetric loading and boundary conditions. The solutions are presented in non-dimensional form. Numerical results are presented graphically for glass-epoxy composite plates.
Partially conforming plate bending elements for static and dynamic analyses
Authors: Ross C T F
Published: July 2007

Two partially conforming flat-plate bending elements have been developed for static and dynamic analyses through the principle of virtual work.

One of these elements is triangular and the other quadrilateral and both have corner nodes only, with three degrees of freedom per node. By use of these elements in the matrix displacement method, the natural frequencies of vibration of a square cantilevered plate have been calculated; these calculated results have been compared with experimental results. Agreement has been found to be good, and in general, convergence appears to take place.
Dependence of stress-optical coefficients on the mechanical and optical properties of polymers
Authors: Theocaris P S
Published: July 2007

The internal structure of the stress-optical coefficients, as they are related to various direct interferometric methods, has been analysed and the nature of their components studied. It is shown that the stress-optical coefficients are composed of two parts. The one part depends on the variation of the mechanical properties; the other is related to the variation of the refractive index of the polymer. The influence of the mechanical properties is considerable and comparable to the influence of the optical properties. The study of the mechanical and optical contributions to the values of the stress-optical coefficients included not only the linear, but also the non-linear viscoelastic behaviour of the polymers. It is concluded that the corresponding limits of linearity of these coefficients do not coincide. Furthermore, the influence of the mechanical properties on the stress-optical coefficients is increasing relatively to the influence of the optical properties in the non-linear region.
A finite-element method applied to predicting fatigue-crack growth
Authors: Walton D , Woodman N J , Ellison E G
Published: July 2007

A finite-element analysis is presented to determine the stress and strain fields at and near the tip of a crack in an elastic-plastic material. These results, together with estimates of the crack opening displacement and plastic-zone size, are compared with equivalent values obtained from linear elastic fracture mechanics and the strip-yield model. Finally the finite-element-strain field data are used in a model which predicts the rates of fatigue-crack propagation; these correlate well with experimental results.
Plane-surface strain examination by speckle-pattern interferometry using electronic processing
Authors: Denby D , Leendertz J A
Published: July 2007

The characteristic speckle pattern formed when imaging a scattering surface illuminated by laser light retains phase information, which can be used for interferometric measurement of surface displacement. The application of this principle to measuring in-plane strain resolved in one direction is described, together with the novel use of television equipment to detect and process the information contained in the speckle pattern and display the consequent interferogram. This is faster, and more convenient and versatile than customary photographic methods. Sources of practical error are analyzed, and some results are presented from investigations of strain distributions in fibre-composite tensile specimens.
In-plane strain measurement by speckle photography: A practical assessment of the use of Young's fringes
Authors: Luxmoore A R , Amin F A A , Evans W T
Published: July 2007

A photograph of a laser speckle pattern will diffract light, and a doubly exposed negative, which has been shifted between exposures, will produce a Young's fringe pattern with the fringe spacing inversely proportional to the displacement. This effect is used to detect the in-plane displacements of tensile specimens and cracked specimens, and changes in length of aluminium crystals due to annealing.
An interference technique for the measurement of in-plane displacements of opaque surfaces
Authors: Marchant M , Bishop S M
Published: July 2007

A laser interferometer system is used to record two mutually perpendicular diffraction gratings on a photoresist coated specimen. When either grating is re-illuminated by the fringe pattern used to form it, real-time observations can be made of moiré fringes corresponding to surface displacements which occur as a tensile load is applied to the specimen. The technique has been used to study the in-plane deformations of carbon-fibre composites, and typical results are given.
The technique of holographic interferometry applied to the study of transient stresses
Authors: Robertson E R , King W
Published: July 2007

The paper reports on the technique of holographic interferometry, using a ruby pulsed laser as the coherent light source, applied to the study of a longitudinal transient stress induced in a rectangular bar by an axial impact of a second bar. Reasons for using a holographic technique are given together with ways of alleviating some of the associated problems. Some qualitative results are presented on the work done to date.
Holographic photoelasticity: Influences of inaccuracies of optical retarders on isochromatics and isopachics
Authors: Ajovalasit A
Published: July 2007

In this paper the influence of inaccuracies of the optical retarders on the isochromatic and isopachic fringes obtained by holographic photoelasticity is studied.

For the single-exposure hologram it is shown that the isochromatic visibility decreases as for light- and dark-field configurations, whereas the isochromatic fringes are distorted only for the dark-field configuration.

For the double-exposure hologram it is shown that the isopachic fringes are generally distorted; with the isochromatics there is a decrease of fringe visibility.

Experimental results confirming the theory are reported.
Plane-Stress yielding of cantilevers in bending due to combined shear and axial load
Authors: Johnson W , Chitkara N R , Ranshi A S
Published: July 2007

A plane-stress slip-line field analysis has been made of the possible plastic deformation modes of a built-in cantilever beam of rectangular cross-section subjected to a shear force at the free end with or without an axial load. Plastic-collapse loads for the several types of deformation patterns suggested are computed and the results presented in detail in the form of curves. Some simple upper- and lower-bound estimates to the collapse load have also been determined and are compared with both the plane-stress slip-line results and those presented by Green (1), plane-strain conditions being assumed. The agreement between the plane-stress slip-line fields and the assumed lower-bound results is found to be excellent.
Stress concentrations at dimples in crankshafts
Authors: Diver P , Fessler H
Published: July 2007

Photoelastic tests have been carried out to determine stress-concentration factors for spherical and elongated dimples which may be machined into the bearing surfaces of crankshafts to remove cracks or inclusions. The shapes and sizes are based on the proposed British Standard.

The effects of proximity of dimples to one another and to a radiused shoulder are also studied. The results show that the stress concentrations at dimples are much smaller than those at circumferential grooves on which the proposed British Standard is based.
Numerical stress concentrations for stepped shafts in torsion with circular and shaped fillets
Authors: Battenbo H , Baines B H
Published: July 2007

A computer programme has been developed to solve for torsion of solids of revolution by numerical solution of an exact boundary integral equation which is valid for any shape and any degree of connectivity. The programme gives solutions directly at the boundary and requires only simple boundary data defining the contour to be input. The basic integral equation has been differentiated to give internal stresses directly, when required.

The computed results have been checked experimentally by photoelastic techniques and are compared with analytical solutions for the circular cylinder and the cone.

Comprehensive charts are given for stress concentrations in stepped shafts with circular fillets and fillets constructed of two blending radii. Fillets giving stress concentrations close to unity have also been investigated.
A two-dimensional photoelastic study of steam-turbine casing flanges with interface relief
Authors: Wilson I H
Published: July 2007

The efficiencies of various full-face and face-relieved flanges in producing a steam-tight seal for split-casing turbine designs have been determined with two-dimensional photoelastic models. Checks on the results carried out on a few of the flange geometries by means of finite-element techniques of analysis showed good agreement between the two. It was concluded that within the scatter of experimental results no difference in the effectiveness of sealing exists between full and relieved flanges.
Buckling of a viscous strut loaded eccentrically
Authors: Ellington J P
Published: July 2007

A solution to the problem of buckling of a viscous strut with eccentrically applied end loads has been found previously as an infinite trigonometric series having poor convergence for small values of time. An alternative series solution has been found, using powers rather than exponentials of time, which provides not only rapid convergence but simple closed forms for bounds on the maximum deflection.
Determining the contact area in elastic-indentation problems
Authors: Barber J R
Published: July 2007

A general relationship is established, determining the contact area in the indentation of an elastic half-space. Contact pressure is shown to increase monotonically with load throughout the contact area.
Creep characteristics of an experimental model composite
Authors: Lomax A B
Published: July 2007

A simple experimental model is proposed to simulate the creep properties of composite materials with aligned continuous reinforcement. A complete programme of testing, covering the full range of percentage reinforcements at three test temperatures, is described.

The experimental results are compared with predictions based on various theoretical methods; for this comparison incremental techniques devised by the author are used. Digital-computer programmes have been written to make the latter methods tractable. Quantitative allowance for material scatter is included in the analyses.

The implications of the author's results for composites, and also for more complex structural creep, are indicated. It is found that the effects of scatter are so predominant that it is not appropriate to resort to methods more complex than those based on the mechanical equation of state.
Optimization of shape to minimize stress concentration
Authors: Francavilla A , Ramakrishnan C V , Zienkiewicz O C
Published: July 2007

The problem of minimizing stress concentrations in machinery components is formulated as one of unconstrained minimization by incorporating all ‘side’ constraints on design variables by use of penalty functions. Design parameters describing the transition are determined for an optimal fillet in a tension bar, as well as for a piston-rod ‘eye’. The procedure is generally applicable.
Analysis of strain-gauge data from thin-walled structural members subjected to eccentric longitudinal loading
Authors: Randolph M F , Lightfoot E
Published: July 2007

In full- or reduced-scale tests on skeletal structures, several cross-sections are usually strain-gauged to enable strain distributions to be obtained and stress resultants to be deduced. This paper explains how such measurements are best analysed, with special emphasis on the proper inclusion of longitudinal stresses associated with warping. Two examples are included.
Design of shrunk-fit pressure vessels: A short graphical method
Authors: Enahoro H E
Published: July 2007

A short graphical method is developed from the existing standard graphical technique for the solution of problems on shrunk-fit pressure-vessel design. Examples are provided to illustrate the versatility of the new method and the great saving in time as compared with both the tedious anlytical solutions that are readily available in text books and the existing graphical method with its complex pattern of lines.
Stresses in high-pressure taper-hub flanges with recesses for nut facings
Authors: Fessler H , Perry D A
Published: July 2007

Frozen-stress photoelastic analyses were carried out to determine the elastic stresses, due to initial bolting only, set up in a British Standard 250 mm taper-hub flange rated at 250 bar and in 15 different shapes of flange in which recesses were used to reduce the diameter and the peak stresses.

It was found that stress concentrations occur at the recess fillets as wel as at the flange fillet. Two shapes were determined which are smaller and lighter and have lower peak stresses than the B.S. shape without recesses.
A single hologram technique for the determination of absolute retardations in holographic photoelasticity
Authors: Ajovalasit A
Published: July 2007

A method for the determination of the absolute retardations families in photoelasticity.

The method, which use real-time holographic interferometry, requires only one hologram for the observation of the absolute retardations over the whole model.

This is achieved by viewing in the reconstruction process the loaded model through a polarizer. Where the polarization direction is parallel to one of the principal stresses, only the corresponding family of absolute retardations is observed.

As an example of application the absolute retardations and stresses in a deep beam centrally loaded are determined.
Buckling of beams and plates onto an intermediate support studied by the dynamic relaxation method
Authors: Hook P M , Rushton K R
Published: July 2007

Problems involving beams or plates which deflect until contact is made with internal restraints are examined using a modified form of the dynamic relaxation method. Three particular problems are considered in detail. The first a concerned with a laterally loaded beam restrained by an internal point support. Next the effect of a restraint surface positioned parallel to and a short distance away from an axially loaded strut is considered. Finally a study is made of the postbuckling of a square plate onto a line support positioned parallel to the loaded edges.
Origins of the energy balance approach to fracture
Authors: Hayes D J
Published: July 2007

The basic philosophy of the stress intensity approach to fracture is scrutinized. The limitations of the approach are discussed and its application to the solution of practical problems is indicated.
The fracture toughness of metals
Authors: Knott J F
Published: July 2007

Problems in applying LEFM to the fracture of metals are discussed. Fracture toughness values for cleavage and fibrous modes are related to the micromechanics of fracture.
Evaluation of stress intensity factors
Authors: Cartwright D J , Rooke D P
Published: July 2007

Some of the more useful methods of evaluating stress intensity factors are presented in a concise form. The stress intensity factor is defined and compared with the more familiar stress concentration factor. The shape factor, the parameter which characterizes the shape of the crack, the orientation of the crack and the proximity of other boundaries, is introduced; the techniques for determining the shape factor are divided into theoretical and experimental. Each method is described with a minimum of mathematical detail; references are given to papers where the methods are more fully described and used to solve specific crack problems. The accuracy and usefulness of the methods is summarized.
Analysis and application of fatigue crack growth data
Authors: Pook L P
Published: July 2007

The phenomenon of metal fatigue has been studied for a long time, but it has only relatively recently been appreciated that most structures, particularly welded joints, contain crack-like flaws, so that virtually the whole fatigue life is occupied by fatigue crack growth. The fracture mechanics concept of stress intensity factor has proved particularly convenient for the analysis of fatigue crack growth data in a form which can be applied directly to engineering problems, and its use has led to a much better understanding of the fatigue behaviour of structures. The effects of interaction between different load levels are not yet fully understood; this is not necessarily a serious drawback as servo-hydraulic fatigue testing equipment permits the application of virtually any load history to structures or fatigue crack growth specimens.
Environmental effects in crack growth
Authors: Parkins R N
Published: July 2007

The interdependence of material structure, electrochemical parameters and the response of a material to the application of stress can produce slow crack growth by a number of different mechanisms. The recognition of the importance of such factors as environment composition, especially within the confines of a pit or crack, and of plasticity, especially in relation to the rate at which deformation presents bare metal at the tips of cracks, is vital if reproducible data are to be obtained.
A computer-aided method for calculating the distributions of strain-rate and strain from an experimental flow field
Authors: Farmer L E , Oxley P L B
Published: July 2007

A method of calculating strain-rates and strains from an experimental flow field is developed using simple geometry with polynomials used to represent small segments of the experimental streamlines and the corresponding distance/time along streamline curves. The method is applied to an experimental flow field for plane strain extrusion obtained using printed grids (0.002 inch square), the input to the computer program being the co-ordinates of the grid intersection points and the punch velocity.
Crack closure at positive stresses during random load fatigue crack growth
Authors: Dover W D , Boutle N F
Published: July 2007

Fatigue crack closure at positive stresses during broad band, random load fatigue crack growth, has been investigated. Tests were performed on centre-notched specimens made from an aluminium alloy (B.S. 2L 71).

The closure stress was found to be dependent upon the material thickness, the mode of fracture and the stress ratio Q. Under plane strain fracture mode conditions it was found that the closure stress for 22 mm thick specimens was greater than that found with 6 mm thick specimens. This difference in closure behaviour produced a slower fatigue crack growth rate for the thicker specimens. In addition it was found that for a given r.m.s. stress the fatigue crack closure level only impinged upon the dynamic range at low mean stress levels.
The effects of cross-section deformations on the displacements of a multiple-shell roof composed of π-shaped elements
Authors: Gambarova Pietro , Giuriani Ezio
Published: July 2007

The subject of this paper is the analysis, by means of an optical-interferometric method, of the displacements of a multiple-shell roof, composed of π-shaped elements, mutually connected by linear hinges.

The first part deals with both the warping of the section (due to combined bending and torsion) and plane cross-section deformations: two different theoretical approaches (‘rigid section’ and ‘deformable section’) are considered, so that experimental and theoretical results can be compared; a linear load is applied to each hinge in turn, In the second part, the effects of diaphragm spacing on the section distortion are analysed in the case of a single prismatic element.
Corners in the yield locus
Authors: Svensson N L , Metcalfe R
Published: July 2007

A relatively simplified model is developed which confirms the prediction that corners should be identified in the yield locus following prior plastic straining. The model predicts the shape of the corner associated with different types of combined stress prestrain. Comparison with a limited number of experimental investigations indicates that the model may be sufficiently accurate to quantitatively predict the nature of the corner.
The effect of differential thermal expansion on residual stresses in a welded connection
Authors: Procter E , Beaney E M
Published: July 2007

Two tests were conducted on a welded joint between a forging and a pipe adaptor, to investigate the effect of differential thermal expansion in the various parts of the joint, on the residual stress. The first test was carried out with the weld in the approved manufacturing stress relieved condition. The second test was carried out following normalizing and extended stress relief heat treatments.

Strain gauge measurements were made on the heat affected zones and at various positions across the weld as the forging was heated and cooled through approximately 250° C. The apparent strain outputs of the gauges used at each location were determined from gauges attached to ‘stress free islands’ machined in the weld at the required postions Since the tests could only be carried out over a 250° C range the results were linearly extrapolated to cover the range of stress relief temperatures.

It is shown that differential expansion can have significant effects on residual weld stresses as the structures are temperature cycled.
Model studies of the elastic buckling of a stiffened plate
Authors: Tulk J D , Walker A C
Published: July 2007

The paper reports on an experimental investigation of the elastic buckling behaviour of a small-scale model of a stiffened plane. The model was made from epoxy resin to allow large buckle deflections within the elastic strain range. These tests are part of a programme aimed at proving the feasibility of using small-scale models to elucidate the behaviour of large stiffened plates such as are used in marine or civil engineering structures.

It is shown for the geometry examined here that, although the component stringer and plate elements of the panel would individually exhibit stable post-buckling, together they interact to give unstable behaviour. The effects of imperfections are systematically studied and it is shown that the load-carrying capacity of such a structural configuration is sensitive to initial geometric deformations.

A simple mathematical analysis is developed which indicates the parameters governing the physical problem and which could form the basis for future rational studies of the level of imperfections at which sensitivity may be considered slight.
Large deflections of beams in four-point bending
Authors: Paolinelis S I , Ogorkiewicz R M
Published: July 2007

Equations are derived for large deflections of slender prismatic beams of linearly elastic materials in four-point bending - and are solved numerically.
Fracture toughness measurement of mild steels with reinforced-double-cantilever-beam specimen
Authors: Chow C L , Owen R C
Published: July 2007

The fracture toughness of mild steels was successfully determined under monotonic and cyclic crack propagation. The conditions governing the valid measurement of fracture toughness were satisfied by r.d.c.b. (reinforced-double-cantilever-beam) specimens, and photomicrographic evidence and compliance measurements verified the yielding of the specimens during cracking confined to the crack tip. Measurements of fracture toughness of EN 24 (BS 970 817M40) steel were made on the r.d.c.b., c.o.d. (crack-opening displacement) and c.k.s. (standard tension testing) specimens and the results verified the validity of the r.d.c.b. testing method. The compliance measuring approach was used to determine the rate of fatigue crack propagation and was found satisfactory using the graphical representation based on change in crack extension force Δ G. It was observed that the grain size of the steel has definite effects on its fracture toughness.
Variables affecting the strength of balsa wood
Authors: Soden P D , McLeish R D
Published: July 2007

Tests have been carried out to determine the strength of balsa wood and its variation with density. Particular attention is paid to the tensile strength of balsa loaded at different angles to the grain and a simple theory of failure is derived from the results. The compressive strength and modulus of elasticity are also reported. Similarities between the mechanical behaviour of balsa wood and unidirectional fibre-reinforced composites are discussed. Adequate data are presented for the design of balsa wood structures.
Influence of a zero-load rest period in elevated-temperature fatigue
Authors: Miller K J , Plumbridge W J
Published: July 2007

A preliminary investigation of the influence of rest periods on Stage I crack growth has been performed on a 2½ per cent Ni Cr Mo steel by testing cylindrical specimens under high-strain reversed torsion conditions at 20, 100, 200, 300 and 400°C. Increases in lifetime of up to 100 per cent are observed, and their magnitude is a function of temperature and the rest-period duration, with maximum lifetime occurring at 300°C and a total rest period of 20 hours. Strain ageing is cited as the dominant process, which explains the dependence of optimum lifetime conditions on both temperature and total rest period duration.

Since components are frequently rested and/or subjected to variable strain-rate conditions over a range of temperatures, it is suggested that results obtained from uninterrupted laboratory tests may be conservative unless overageing occurs leading to cyclic softening.
A statistical appraisal of the measured deformations in several steel box girder bridges
Authors: Ellis L G
Published: July 2007

This paper summarizes the results obtained from an exhaustive survey of the imperfections in the component parts of steel box girder bridges. An appraisal is made of compliance with the Merrison Interim Design Rules, and tolerances are suggested.
Measurement of residual stresses and distortions in stiffened panels
Authors: Somerville W L , Swan J W , Clarke J D
Published: July 2007

Methods for measuring residual stresses and distortions in welded structures are described and initial results are given of a survey being carried out during manufacture of warship hull sections. The stresses are determined by measuring the elastic strain induced in the plate and stiffeners due to contraction of the stiffener welds, and profiles of the stiffener and plating after welding have been obtained. The survey is intended to provide information for use in future design calculations of the buckling strength of ship hulls.
Effects of residual stresses on the ductile strength of plane welded grillages and of ring stiffened cylinders
Authors: Faulkner D
Published: July 2007

Structural engineers have for a long time accepted the importance of residual stresses when considering fracture modes of failure. It is only in the last quarter-century that attention has been focused on their adverse effect on ductile modes of failure and, in particular, on buckling collapse. The last decade has seen increased research activity, spurred on by recent failures in box-girder bridges.

The nature and distributions of locked-in-stresses during hot and cold forming and during welding are outlined. The effect these have on inelastic buckling collapse of flat plated grillages and ring-stiffened cylinders is examined for all likely modes of failure. Experimental data are scarce, but they confirm that both forming and welding stresses can reduce the stiffness and strength of both types of structure very significantly. This is caused by a direct reduction in buckling stresses (as usually supposed), but equally important is the loss in stiffness due to early yield and other effects. In particular the cold-bending of ring-frames can have very serious adverse effects, as shown by recent finite-element programmes.

Cold-cambering, and certain other corrective measures adopted by fabricators, seem more likely to weaken the structure than to improve it.
Shrinkage stresses in a thin plate with a central weld
Authors: Kamtekar A G , White J D , Dwight J B
Published: July 2007

A study was made of the residual stresses caused by weld shrinkage in a plate containing a central longitudinal weld. A theoretical analysis was developed in which the weld was treated as a moving concentrated heat source, through-thickness variations in temperature and stress being ignored. The equations were solved in finite-difference form and the stresses were computed at discrete stages during welding and cooling. Allowance was made for the variation of yield stress with temperature. Computed results were obtained for the bead-on-plate and butt welded cases.

Residual stresses were measured in 40 flat plate specimens containing a central butt weld, with thicknesses ranging from 6 to 16 mm. The results led to proposed values for the factors H and C in the simple Moxham formula, which are in reasonable agreement with theoretical predictions.
Allowance for imperfections in ship structural design
Authors: Goodman R A , Mowatt G A
Published: July 2007

The development of quality standards in shipbuilding is reviewed, and the need for an analytical assessment of standards identified.

The use of a probabilistic approach in the form of a reliability analysis is recommended, and a description of a system suitable for this task given. The various levels of complexity which may be involved are described, and the problems of implementation outlined. The method is illustrated by an application of the system developed at Lloyd's Register of Shipping to assess suitable quality standards for initial imperfections in ship plating.

To correlate the mathematical simulation of reliability with actual experience, use is made of technical information on structural damages from Lloyd's Register of Shipping Technical Records database.
Radial loading of a cylindrical shell through plate brackets
Authors: Kitching R , Hughes J F , Saedi F
Published: July 2007

The elastic behaviour of a cylindrical shell subjected to radial load applied through two circumferential plate bracket attachments positioned diametrically opposite each other at the mid length of the cylinder has been investigated experimentally. An existing theoretical analysis, based on the assumption of a uniform distribution of load across a bracket, was modified in the light of the experimental observations which indicated that the assumption was not valid for the size of bracket used.

Experimental stress distributions and maximum values of stress in the cylinder are compared with those calculated from the modified analysis in the text, which showed an improvement on the existing analysis for the proportions of the shell and bracket considered.
A comparison of finite-element and experimental studies on plane stress crack geometries
Authors: Luxmoore A R , Light M F , Evans W T
Published: July 2007

The load-deformation behaviour of thin plate crack specimens has been studied in detail using the moiré technique, and this behaviour has been modelled by plane stress finite-element calculations. Agreement between experimental and numerical results suggests that behaviour of thin plate crack specimens can be modelled by the plane stress finite-element programme, and hence this programme can be used to calculate fracture data for plane stress crack geometries.
Deformed boundaries determined by the method of caustics
Authors: Theocaris P S , Razem C
Published: July 2007

The caustics formed by illuminating straight deformable boundaries by a parallel, convergent or divergent light beam were used to determine the load distribution along these boundaries. A universal method based on the characteristic geometric elements of the corresponding caustics (pseudocaustics) was developed. This method leads to a system of singular integral equations, which was solved numerically by a collocation method of successive approximations. The singular points of the integrals were removed by integrating along regular paths determined by the optically obtained pseudocaustics. This procedure constitutes a new combined numerical-experimental method for solving singular integral equations with singularities of the Cauchy type. Several examples are given to show the potentialities of the method.
Torsional buckling at the limit state of collapse in braced multi-storey i-section steel column design
Authors: Wood R H , Chakrabarti B
Published: July 2007

Following full-scale tests the column design method of the Joint Committee on Fully-Rigid Multi-Storey Steel Frames (1971) was superseded by a new variable-stiffness design method. The controls for torsional-buckling were, however, retained in their original form and their derivation is now published for the first time. Since they were based on limiting stresses, a revision is required to put torsional buckling on the correct basis of vanishing stiffness at collapse. Torsional buckling results in a gradual reduction of permitted slenderness, due to axial load and plastic bending, which affects warping and beam restraint, all of which the designer can determine graphically. Worked examples illustrate how this method can supplement the revised draft code. New light is thrown on controversies concerning the governing equations in torsion.
High-Temperature cumulative damage for stage I crack growth
Authors: Miller K J , Gardiner T
Published: July 2007

The effects of cyclic shear strain-range, shear strain-rate and temperature on the accumulation of damage during constant and variable shear strain range fatigue tests on a 1 per cent Cr-Mo-V steel are reported.

The hypothesis of linear accumulation of damage and the summation of cyclic fractions to unity are shown to be incorrect for interactions of time, cyclic and environmental processes which are considered in detail. Stage I cracks may be accelerated, retarded or stopped and new cracks nucleated. Nevertheless only 8 per cent of the cumulative damage tests in the high strain fatigue regime gave unsafe linear summation factors less than 0.8. None fell below 0.7.
Cumulative damage laws for fatigue crack initiation and stage i propagation
Authors: Miller K J , Zachariah K P
Published: July 2007

A simple model for the demarcation of the initiation and stage I fatigue crack growth phases is introduced. Experimental cumulative damage data are used to determine the phase boundary between these two régimes, and an exponential accumulation of damage theory is invoked for each; here, damage is equated to crack length. Using both the model and the data, predictions are made of lifetime in double, treble and multilevel strain range tests. The theory successfully accounts for the load sequence effect, which is a consequence of the initiation period, and the effect of the difference between successive strain range levels. It is suggested that the Palmgren-Miner expression be replaced by individual expressions for the accumulation of damage in the separate phases of initiation and stages I and II fatigue crack propagation.
A numerical investigation of post-yield fracture
Authors: Light M F , Luxmoore A R
Published: July 2007

The stress fields around cracks have been calculated for general yield conditions using two- and three-dimensional elasto-plastic finite-element programmes. These programmes were used to evaluate the Rice J-integral, and compare the values with published data obtained by experimental techniques.
Pressure distribution and bulging profiles during compression of non-circular prismatic blocks between parallel frictional platens
Authors: Daneshi G H
Published: July 2007

An analysis is presented of the axial compression of non-circular prismatic sections, based on the existence of velocity discontinuity lines. Equilibrium equations are written along the ‘flow lines’, and theoretical pressure distribution curves are calculated in different directions and compared with experimental measurements. The theoretical pressure hills and lateral deformations are in good agreement with the experimental observations.
Force and displacement influence functions for the circular ring
Authors: Barber J R
Published: July 2007

A set of influence functions is developed for the complete, uniform, circular ring, subjected to concentrated forces or moments. Equilibrium is satisfied by the introduction of fictitious supports that are self-cancelling when the applied force system is in equilibrium. The method provides a general solution for the circular ring on a statically determinate support.
A three-parameter method for determining stress intensity factors from isochromatic fringe loops
Authors: Etheridge J M , Dally J W
Published: July 2007

Methods for determining the stress intensity factor, K, from isochromatic fringe loops obtained from photoelastic models with sharp cracks are briefly reviewed. A new three-parameter method is introduced which follows the two-parameter approach developed previously by Irwin. In the three-parameter method, three different terms in an analytical solution are adjusted to obtain a suitable match between the theoretical and experimental isochromatic loops. The three parameters are: K/√2πz, which describes the crack-tip singularity, ( b) β K/√z, to account for variations in the stress field removed from the crack tip and ( c) σoa = α1 K/√2πa, which is added to the σ x component of the stres field to account for the biaxiality of the far-field stresses.

A relationship is derived for the maximum shear stress, τm, in terms of the three fitting parameters ( K, α, and β) and the two geometric parameters ( rm and θm) associated with the isochromatic fringe loops. A method of solution based on measurements of rm and θm from any two independent fringe loops is given.

The accuracy of the three-parameter method was determined by using exact results from the central crack problem for a standard. It was found that the error was within ± 1 per cent for 69° < θm < 145°. Comparison with the two-parameter method shows that the three-parameter method is more accurate and is applicable over a wider range of θm.
A unified interpretation of interferometric and holographic fringe patterns in photoelasticity
Authors: Theocaris P S , Gdoutos E E
Published: July 2007

A unified interpretation of interferometric and holographic fringe patterns obtained from birefringent materials is presented by using physical concepts only. The two fundamental fringe systems, corresponding to the individual stress-optical retardations along the principal stress directions, are considered to recombine mechanically for the formation of isochromatic and isopachic fringe patterns. This mechanical interference is shown to be more pronounced only when certain conditions concerning the position and the spatial frequencies of the original systems are satisfied. It is shown that only one of the isochromatic and isopachic fringe patterns, corresponding to the shorter diagonals of the individual quadrangles, formed by the two initial fundamental fringe systems, is obtained under normal experimental conditions, and that it is possible to have in one region of the pattern one system and in another region the other. Both isochromatics and isopachics can be obtained only when special precautions are taken during the application of the particular experimental method. The factors influencing the formation of either the isochromatics or the isopachics, or both, are indicated and analysed. The existing confusion in the literature concerning the interpretation of holo-interferometric patterns is thoroughly discussed and clarified. Two simple examples—that is, the circular disc in diametral compression and the infinite plate with a circular hole in tension—are selected to show the main features in this interpretation.
The influence of mean stress and thickness on the fatigue crack growth behaviour of the aluminium alloy BS2L71
Authors: Dover W D , Boutle N F
Published: July 2007

A series of fatigue crack growth tests have been conducted on sheet specimens of thicknesses 3, 6, 16 and 22 mm. These tests have been under both random and constant amplitude loading for a number of different mean stress levels.

The results from these tests have shown that the resistance to fatigue crack growth increases as the thickness increases at low growth rates. In contrast, at high growth rates this behaviour is reversed. Both random and constant amplitude data showed this feature. Crack-closure measurements have been used in an attempt to explain these differences in behaviour for high and low growth rates.

The random and constant amplitude test results have been correlated successfully for square-mode growth, using a ‘weighted’ average range approach.
Experimental and computer-aided investigations and optimization of stress-relieving notches
Authors: Steinchen W P
Published: July 2007

In many designs, it is desirable to economize in weight and minimize stress concentration. After a general demonstration of the effect of additional notches or holes in relieving the maximum concentration of stress in notched machine elements, extensive quantitative investigations were made for bars and shafts of circular cross-section subjected to tensile, bending and torsional loadings.
Full-field numerical differentiation
Authors: Rowlands R E , Winters K D , Jensen J A
Published: July 2007

The numerical representation and differentiation of experimental information is extended to full-field capability involving two independent variables. Bicubic spline, regression analysis and finite-element concepts are employed. Smoothing of the experimental data is accomplished mathematically. The technique are demonstrated by analysing loaded plates.
Techniques for investigating the yield surface behaviour of pressure-vessel materials
Authors: Moreton D N , Moffat D G , Hornby R P
Published: July 2007

The Mises shear strain energy model has long been accepted as satisfactory for defining initial yield in the general three-dimensional stress state. For materials which strain-harden after initial yield, the situation is complex and subsequent yield surfaces will depend on the direction and level of pre-stress. This paper describes experimental techniques for investigating general yield surface behaviour, and presents illustrative results for a 2 1/4 per cent Cr, 1 per cent Mo pressure-vessel steel.
A correlation study of finite-element modelling for the stress analysis of composite-material laminates
Authors: Lakshminarayana H V , Viswanath S
Published: July 2007

A correlation study has been made to evaluate the effectiveness of finite-element modelling for the stress analysis of composite-material laminates. The specific problems studied are: a boron—epoxy composite laminate with a circular hole under axial tension; a boron—epoxy composite laminate with an elliptical opening under axial tension; a glass-fibre-reinforced plastic plate subjected to line load; and a glass-fibre-reinforced plastic annular disc under diametrical compression. Correlations of finite-element predictions are made with analytical solutions and experimental data. The study has demonstrated the accuracy of finite-element modelling employing a quadratic strain traingular (QST) finite-element for the stress analysis of composite-material laminates.
Three-dimensional stress analysis by the boundary integral equation method
Authors: Tan C L , Fenner R T
Published: July 2007

The principles and development of the boundary integral equation (BIE) method for solving engineering problems are reviewed, with particular emphasis on applications in three-dimensional stress analysis. Its use in problems of this type is illustrated with the aid of three examples, one a classical stress concentration problem, the other two involving cracked components. Compared with a finite-element method, the BIE approach is shown to be capable of being both more accurate and more economical to use in terms of competing resources required and the cost of data preparation. These advantages may, however, be less clear-cut when predictions of stresses and displacements at a large number of points within a component are required, or when the component concerned has a relatively high surface-to-volume ratio.
The state of stress near the singularities created by a plane punch
Authors: Andrianopoulos N P , Theocaris P S
Published: July 2007

An attempt is made to obtain photoelastically the stress distribution in the near vicinity of singular points, when a punch is indenting an elastic half-plane. The punch is to be assumed flat and rough so that friction is developed between the contact surfaces. By expanding the complex stress function into a Taylor series, an extrapolation law is obtained, which allows the calculation of stresses at the vicinity of the singular points by means of photoelastic measurements at positions remote from these points. The error limits of this technique are defined and, finally, a relation between the order of singularity and the parameters of the photoelastic pattern is established.
A simplified general method of analysis of the elastic torsion of non-circular solid sections
Authors: Dooley J F
Published: July 2007

A semi-graphical method is presented for the determination of the St Venant torsion constant and maximum shear stress in a prismatic bar of any solid cross-section, intended for use in the trial-and-error process of design. Comparison is made with standard results for a wide range of shapes of cross-section.
Plane strain rotation moduli for soft elastic blocks
Authors: Lindley P B
Published: July 2007

Making assumptions similar to these used to obtain compression moduli, a simple relation is developed for the plane strain rotation moduli for blocks of soft elastic material bonded to rigid end plates. The deformation arises when one plate rotates relative to the other plane about an axis along the centre of its width. The approximate theoretical solution compares well with finite-element analysis data for materials with Poisson's ratios of 0.333, 0.483 87 and 0.499 83 and blocks having width-to-thickness ratios between 0.25 and 64.
On the determination and application of cod to epoxy-bonded aluminium joints
Authors: Chow C L , Woo C W , Sykes J L
Published: July 2007

A method of analysis is presented for the determination of crack-opening-displacements (COD) and their application to aluminium—Araldite joint systems. Use is made of a beam-on-elastic-foundation (BEF) model, which is extended to represent the physical system. It is seen that, in conjunction with this, the Dugdale ‘strip-yield’ model solution may be combined to characterize interfacial or cohesive fracture cases.

Fracture toughness values, based on both load and displacement control testing conditions, are examined and show that the equation derived for the load-control model yields greater accuracy. Results of the proposed method are compared with those obtained by a two-dimensional, finite-element analysis and are found to be in good agreement. The validity of the proposed analysis is further verified by experimental observations employing conventional compliance methods for both interfacial and cohesive fracture modes.