bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of stresses in the wall-ironing of cups
Authors: Dood B
Published: July 2007

The experimentally determined effects of die angle, friction and reduction on the ironing process are briefly described and the limitations of the slab method for the calculation of the ironing load are outlined.

Hill's two-centred fan slip-line field for ironing is discussed and the static inadmissibility of some of the solutions is described. A further limitation on these fields is shown to occur when the hydrostatic pressure at the slip-line cusp at the punch surface is less than or equal to − k. Under these circumstances, it is predicted that thinning of the material at the punch will occur, which in practice would give a product with a reduced wall thickness and an increased internal diameter.
An integrated retardation technique for the determination of thermal stresses in rotationally symmetrical bodies
Authors: Khayyat F A , Stanley P
Published: July 2007

The theory of a non-destructive photoelastic method for the quantitative determination of thermal stress concentrations in rotationally symmetrical bodies with a transverse plane of symmetry is presented. This is a development of Fox's work, in which integrated relative retardation and scattered-light observations are required.
Bending of an incomplete annular plate and related problems
Authors: Barber J R
Published: July 2007

Closed-form solutions and stress-concentration data are obtained for the problem of a sector of an annular plate subjected to moments and transverse forces on its radial edges. Closed-form solutions are also given for a semi-infinite plate or a circular plate subjected to a system of concentrated forces and/or moments at the edge.
An improved method for the determination of mode i stress intensity factors by the experimental method of caustics
Authors: Theocaris P S , Ioakimidis N I
Published: July 2007

A modification of the usual way of determining mode I stress intensity factors at crack tips by using the experimental method of caustics is proposed. In accordance with the proposed modification, both principal diameters of an experimentally obtained caustic should be taken into account so that the influence of the part of the stress field behaving like r1/2 near the crack tip is minimized ( r being the polar distance from the crack tip). This modification makes the method of caustics much superior to the photoelastic and interferometric methods for the evaluation of mode I stress intensity factors, not only from the experimental but also from the theoretical point of view. Some interesting geometrical properties of the caustics formed at crack tips are also deduced in this paper.
Analysis of an annular disc with a concentrated, in-plane edge load
Authors: Srinivasan V , Ramamurti V
Published: July 2007

The static analysis of an annular disc with a clamped inner boundary and a concentrated, in-plane load at the outer boundary is presented. The singularity associated with the concentrated load is isolated and the resulting non-singular problem is solved by the method of complex potentials. The superposition of these two solutions gives the desired solution. Results are presented for various radius ratios.
Contribution of experimental stress analysis to the safety and economy of technical systems
Authors: Meyer M L
Published: July 2007

A report on the Sixth International Conference on Experimental Stress Analysis, held in Munich, Germany, 18th to 22nd September, 1978.
Nonlinear mechanical and thermal responses of a unidirectional carbon-fibre-reinforced plastic
Authors: Ditcher A K , Webber J P H
Published: July 2007

Experimental results for unidirectional carbon-fibre-reinforced plastic (CFRP) are reported which show that the longitudinal stress-strain behaviour of this material is nonlinear elastic up to failure. The tangent modulus is found to reduce with increasing compressive strain, and to increase with increasing tensile strain. In addition, a small variation in Poisson's ratio with longitudinal strain is found.

A specimen width of 5 mm (rather than the usually accepted 10 mm width) is used in order to reduce the likelihood of end effects being transmitted to the centre of the specimen. This is supported, to some extent, by a theoretical plane stress analysis using finite elements.

A relatively simple method of measuring the thermal expansion of CFRP using suitably compensated strain gauges is described, and experimental results are given.
An instrument for the measurement of structural vibrations
Authors: Lewis C P , Ball R
Published: July 2007

A method of measuring structural vibrations by using an accelerometer in conjunction with a specially designed signal processor is described. Test results obtained on a pedestrian footbridge, an inner ring road flyover and a typical industrial floor are used as illustrations of the technique.
Boundary integral equation analysis of elastic stresses around an oblique hole in a flat plate
Authors: Abdul-Mihsein M J , Fenner R T , Tan C L
Published: July 2007

The boundary integral equation (BIE) method for three-dimensional, linear, elastic stress analysis is applied to some stress concentration problems associated with oblique circular holes in flat plates subject to in-plane tensile loading. Satisfactory agreement is obtained with both an analytical solution for a normal hole and previously published experimental results for oblique holes. Computed maximum stress concentration factors are generally higher than those obtained experimentally, and are very sensitive to changes in the angle of obliquity. Results are presented for three relative plate thicknesses, and in one case for two directions of loading. The BIE method is shown to be a very useful tool for solving problems of engineering stress and strain analysis.
Rotating thin cylinder: Effect of small error in circularity
Authors: Holland M
Published: July 2007

The error-modified, circular, mean-line form is represented by an elliptic profile and equations are developed for bending moment, tensile and shear forces resulting from inertia loading. It is shown that the maximum values of tensile force and bending moment both occur at the same location if the ratio of principal axes lengths is less than, or equal to, 1.09.

For a cylinder having a mean-diameter-to-wall-thickness ratio of one hundred and with a difference in principal axes lengths of 0.1 per cent, the maximum stress is shown to be 1.33 times that in a perfectly circular cylinder. When the difference in the length of principal axes is increased to 0.4 per cent, this stress intensification factor increases to 1.75.
A semi-analytic finite-element analysis of circular plate bending problems
Authors: Richards T H , Delves B
Published: July 2007

Semi-analytic formulations have previously been used for a number of stressing problems wherein axisymmetric structures have supported non-axisymmetric loads. The approach is here shown to be very useful for circular plates, and to have especial value for design analyses using desk top computers in which the main store is relatively small.
Exact straight-line elements
Authors: Lightfoot E
Published: July 2007

A method of obtaining exact finite element stiffnesses directly from governing differential equations is explained; another method which uses the column analogy is indicated. These can both be modified by matrix manipulation to allow for relaxed restraint conditions. Exact stiffness matrices are given for the straight prismatic beam, the beam-column (or tie), the vibrating beam-column (or tie), the tapered beam and the annular slab. They are compared briefly with matrices obtained from simple polynomial approximations. Further exact finite elements are possible; they minimize convergence problems and their wider usage is advocated.
Method of fracture toughness evaluation of adhesive joints
Authors: Chow C L , Ngan K M
Published: July 2007

This paper presents the development of a testing method for adhesive joints under Mode 1 fracture. The proposed testpiece consists of two slender beans with a ‘blister’ at the centre of each, which are bonded together and loaded in compression. The effect of buckling and the stability of crack propagation is analysed and found to be in satisfactory agreement with experimental observations.

Equations for the evaluation of the fracture toughness based on the energy criteria are derived for the proposed test configuration. The results obtained using the method are checked with those from the DCB specimen and found to be satisfactory.
Least squares computation of the prestrain and work hardening parameters of sheet metal
Authors: Twizell E H , Adak I
Published: July 2007

For most metals the load-extension and stress-strain graphs are too complicated for easy mathematical analysis, and empirical equations must be formed. One such equation, which is especially useful when large strains are experienced, is Swift's equation σ = A( B + ∊) n where ∊ and σ represent logarithmic strain and true stress, respectively. The prestrain and work hardening coefficient are represented by B and n respectively, and A is a constant for the metal being used.

Non-linear least squares optimization methods are more accurate than elementary methods for computing A. B. and n from discrete data pairs (∊i,σi)i= 1,2,…, N (N≥3) determined experimentally, and a model is developed which adapts the Gauss-Newton and Levenberg-Marquardt algorithms for this purpose. Numerical results for a number of specimen sheets are reported, and comparisons of the reliability and efficiency of the two algorithms are made.
Interaction between two equal skew-parallel cracks
Authors: Gdoutos E E
Published: July 2007

A thorough study of the interaction effects between two equal skew-parallel cracks in a plate subjected to a tensile or a compressive uniform stress perpendicular to the direction of the cracks was undertaken. The dependence of the critical stress of fracture and the pattern of initial crack propagation on the geometrical configuration and loading of the plate was analysed. It was found that crack propagation starts from the inner or the outer tips of the cracks depending on their geometry. For the first case, one inner tip propagates either in the direction of the other or in the opposite direction, while for the second case the two cracks always propagate in opposite directions. A comparison between the case when the two cracks act as one and when each acts separately from the other was made and the limits of the horizontal and vertical distances between the cracks, for which their behaviour approaches the one or the other situation, were established.
Stress concentrations at axially loaded projections of flat bars
Authors: Fessler H , Woods P J
Published: July 2007

The effects of shape and position of load application on the magnitude and position of the peak stresses are determined from photoelastic models. Stress concentration factors for any practical application can be quickly determined from the results. Minimum stress concentration factors for loaded projections are compared with published values for (unloaded) shouldered plates in tension. Optimum proportions which give minimum stress in various design situations are also presented.
Variable-stiffness elastic base mechanism for model shear wall structures
Authors: Coull A , Adams N W
Published: July 2007

A description is given of a simple mechanism which was developed to simulate a system of variable-stiffness elastic base supports for a coupled shear wall structure. A system of cantilevers was used to enable both vertical and rotational base flexibilities to be provided, the two being independently variable over the required range of relative stilesses.

An example is given of the use of the system in a model investigation of a three-dimensional shear wall structure.
A tension—torsion creep-rupture testing machine
Authors: Trampczynski W , Morrison C , Topliss W E
Published: July 2007

The paper discusses the design and construction of a high-temperature creep machine capable of applying combined tension and torsion loadings. The design utilizes an air bearing and pinned universal joints to achieve axiality of loading. An extensometer is described which transmits the deformation of the specimen gauge length outside the furnace and allows the continuous measurement of axial and shear strains to be made using linear variable differential transducers at room temperature. Results of elastic and creep tests are presented which show the performance of the machine to be satisfactory.
Stress distribution in a sharp-edged wedge under boundary conditions similar to those of wedge indentation
Authors: Ghobrial M I , Lancaster P R , Mellor P B
Published: July 2007

Plasticity analysis for orthogonal indentation of plastic rigid material by an acute angled wedge suggests that the faces of the wedge will be subjected to uniformly distributed pressure and tangential stresses over the contact length. In the present work the stress distribution at the tip of an infinitely deep wedges obtained when the wedge is subjected to such a stress distribution. The theoretical results are compared with photoelastic experiments and good agreement is achieved.
The use of vibration measurements for the detection of diffuse creep damage
Authors: Cawley P , Adams R D , Plumbridge W J
Published: July 2007

The feasibility of using measurements of structural natural frequencies for the non-destructive assessment of diffuse creep damage has been investigated for a 1 per cent chromium—½ per cent molybderum—¼ per cent vanadium steel crept at stresses above and below the ductile brittle transition stress. The frequency changes observed during creep were similar to those predicted for constant volume straining of the specimen. Uncertainties arose due to the formation of an oxide layer on the specimen surface but no evidence has been found to suggest that, in either range, significant independent changes of modulus or density occur during creep. It has also been shown that the speed of sound in a material is unaffected by the presence of small voids since the apparent modulus and density are changed in the same proportions. Ultrasonic velocity measurements cannot therefore, be used to detect voiding in its early stages. The results also suggest that natural frequency measurements are unlikely to detect this type of damage.
Non-linear stress-strain behaviour of carbon fibre reinforced plastic laminates
Authors: Ditcher A K , Rhodes F E , Webber J P H
Published: July 2007

An analytical method is proposed which predicts the non-linear stress-strain response of a CFRP laminate. The method uses a secant modulus iterative method and includes thermal effects due to the temperature difference of a laminate from its curing temperature. Details of the basic CFRP non-linear behaviour in transverse and in-plane shear loadings are given. Experimental data on 0°/±45°/0° balanced laminates are presented and compared with theoretical predictions.
Anisotropic hardening theory and the Bauschinger effect
Authors: Rees D W A
Published: July 2007

A review of anisotropic hardening theory is presented with particular reference to the Bauschinger effect in reversed torsion and anisotropic yield loci in σ, τ space associated with plastic shear strain history.

The Bauschinger effect is obtained experimentally from a series of torsion tests on En3B steel tubes prestrained to a maximum of 10 per cent plastic shear strain. The effect, measured from the stress in reversed torsion at the proportionality limit, is analysed from the theory. It is shown to be consistent with experimental observations made on the translation and contraction of an initial yield locus, that are in marked contrast to the rigid translation of kinematic hardening rules.

The degree of shear prestrain is shown to considerably influence the magnitude of the effect, an observation in full support of a theoretical Bauschinger parameter. The present test data together with existing published data for commercially pure aluminium 1100-F and the aluminium alloy Noral 19 S confirm that the controlling parameter is a scalar coefficient of plastic prestrain. The investigation supports a scalar function that is parabolic in the second invariant of plastic prestrain.

The effect of yield point definition is examined and a comparison between theoretical and experimental yield loci is presented.
Coriolis effect on the vibration of flat rotating low aspect ratio cantilever plates
Authors: Sreenivasamurthy S , Ramamurti V
Published: July 2007

The Coriolis effect on the first bending and first torsional frequencies of flat rotating low aspect ratio cantilever plates has been investigated using finite element method. The cantilever plate has been modelled using plane triangular shell elements with three nodes and eighteen degrees of freedom. Three typical skew angles (0, 45, and 90 degrees) and two aspect ratios (1 and 2) are considered in the analysis. In addition to the Coriolis effect other effects, namely the geometric stiffness and the supplementary stiffness, have been considered. The mass and stiffness matrices have been derived using area coordinates. It has been found that the effect of including Coriolis effect is to lower the first two frequencies. This effect is negligible when the skew angle is 90 degrees. In the other two cases, skew of 0 and 45 degrees, there is a noticeable effect on the first torsional mode frequency when the aspect ratio is unity and on the first bending mode frequency when the aspect ratio is 2. An increase in the Coriolis effect is observed when the aspect ratio is increased from 1 to 2, with the skew angles of 0 and 45 degrees and a decrease when the skew angle is 90 degrees. The difference between the two frequencies (with and without Coriolis effect) becomes more and more noticeable as the rotational speed increases.
Experimental determination of crack growth resistance of ductile materials
Authors: Woo C W , Kuruppu M D
Published: July 2007

A method of determining the fracture resistance of ductile materials is presented in this paper. The method employs a renforced DCB test specimen to characterize stable crack growth in a large structure. From the consideration of the quasi-static energy balance during slow stable crack growth, the fracture resistance was measured using the J approach. By repeated partial unloading during slow stable crack growth the need for multiple specimens with virgin crack length was eliminated. The fracture resistance of three different materials was measured for comparison. Results indicated that the fracture resistance increases significantly during the nitial stage of crack growth. When the crack propagation reaches an equilibrium state of stable crack growth the fracture resistance remains fairly constant over a large crack increment.
The yield surface behaviour of pressure vessel steels
Authors: Moreton D N , Moffat D G , Parkinson D B
Published: July 2007

The yield surface response to plastic deformation of a range of pressure vessel steels has been investigated, and the results are presented in the form of families of yield loci, for a range of pre-stress directions and magnitudes. A single empirical relationship is derived which is shown to be representative, within reasonable accuracy, of all materials tested, the only specified material property being the uniaxial yield stress. Use of this empirical model is illustrated in predicting the shakedown loads for three pressure vessel components.
Characterizations of creep crack growth in 1 per cent Cr Mo V steel
Authors: Smith D J , Webster G A
Published: July 2007

Estimates of stress intensity factor, K, reference stress, σref, and creep parameter, C∗, have been made for compact tension (CT) and double cantilever beam (DCB) test-pieces containing side grooves. Limit analysis techniques were used to determine the latter two parameters. It is shown that the expressions developed for σref are sensitive to the collapse mode proposed, whereas those for C∗ are largely independent. Comparisons of predictions of creep crack growth data on CT and DCB specimens of a 1 per cent CrMoV steel in terms of K and σref have revealed different dependences for the two geometries, suggesting that neither parameter gives satisfactory correlations. Better overall agreement is obtained with the C∗ parameter, even though gross creep deformations were not observed. It is suggested that further improvement may be gained with this parameter if more accurate estimates of C∗, which allow the inclusion of elastic terms, are used.
Stresses around large circular holes in uniform circular cylindrical shells
Authors: Bull J W
Published: July 2007

An experimental and finite element analysis of a uniform cylindrical shell with a large circular cut-out is presented. In this analysis three hole sizes are considered, namely μ = 2.037, 4.084, and 6.344 (where μ = {[12(1 - y2)]1/4/2} × [ a/( Rt)1/2]), for loadings of axial compression, torsion and three point bending. The experimental results are the only ones available for cylindrical shells with large values of μ (except for one graph by Savin (1)†), while for three point bending there is no previously published theoretical or analytical results.

Good agreement is found between the calculated and experimental stresses around the holes.
Steady-State stress distributions in circumferentially notched bars subjected to creep
Authors: Al-Faddagh K D , Fenner R T , Webster G A
Published: July 2007

The paper describes a procedure, based on a finite element method, for calculating directly the steady-state stress distribution in circumferentially notched bars subjected to creep without the need for obtaining solutions at intermediate time intervals. Good agreement is obtained with relevant approximate plasticity solutions and with numerical calculations which approach the steady-state over a period of time from the initial elastic stress distribution. Also, the procedure is equally applicable to primary, secondary, and tertiary creep, provided the variables of stress and time are separable in the creep law.

Results obtained for a range of notch geometries and values of the stress index, n, are reported. It is found for each profile that a region of approximately constant effective stress, σ, independent of n, is obtained which can be used to characterise the overall behaviour of the notch throat region when a steady-state is reached sufficiently early in life. An approximate method for estimating the maximum equivalent steady-state stress across the notch throat is also presented which does not require a computer solution.
A new technique for coupled plane thermal stress problems
Authors: Takeuti Y , Tanigawa Y
Published: July 2007

It is well known that the thermoelastic coupling term and the inertia term have to be taken into account for a rigorous treatment of a sudden change of temperature in a elastic body. It is now well understood that the inertia effect may disappear in pure thermal stress problems on the stress distribution for realistic materials. In the present paper, we propose a new technique for the coupled thermoelastic fields by introducing an additive harmonic function. Thus, we can obtain exact solution for all the time period. The effect of thermoelastic coupling on the temperature and the stress distributions is shown in the numerical example.
The design and manufacture of supports for horizontal vessels
Authors: Blenkin R
Published: July 2007

Various types of supports for horizontal cylindrical vessels are reviewed and the use and limitations of BS 5500 examined. Design and manufacturing requirements for saddle supports are discussed and reference made to some in-service problems.
Stresses in horizontal storage vessels - a comparison of theory and experiments
Authors: Tooth A S , Duthie G , White G C , Carmichael J
Published: July 2007

This paper presents the salient features of the experimental work carried out on a series of horizontal storage vessels. These include a 3.66 m diameter gas receiver and two smaller vessels each of 0.91 m diameter. The saddles used to support the vessels represent the two extremes of saddle design where the cantilever section is either of ‘flexible’ or ‘rigid’ construction and in both cases welded to the vessels. All the vessels were extensively strain gauged in the region of the saddle supports and at the centre of the vessel. Hydraulic, pressure surcharge and pneumatic tests were carried out on the vessels. Typical experimental results have been compared with the theoretical analysis described in (1)†. It is found that a satisfactory measure of agreement is obtained for both the flexible and more rigid results for the water fill tests, but that the pressure results are sensitive to vessel imperfection which are not considered in the theoretical analysis (1).
Elastic stresses due to torque transmitted through the prismatic part of keyed connections part II: Effect of shape with usual fits and friction
Authors: Fessler H , Eissa M
Published: July 2007

Models of 25 different shapes of keyed connections have been loaded by a large range of torques, using ordinary and frozen-stress photoelasticity.

Empirical formulae have been derived for five contact points where the stresses are concentrated. These formulae give good predictions over the complete shape range of the metric and inch standards. The latter is consistently better than the former.
Applications of the white light speckle method to interior displacement measurement
Authors: Asundi A , Chiang F P
Published: July 2007

The white light speckle method is used to obtain the interior displacement at different planes of a block with a central idented load, and of a prismatic bar of square cross section under torsion. The problem of decorrelation of speckles due to tilt is not encountered in this method, resulting in reasonable fringe patterns, and good agreement between the displacements obtained with this method and that predicted by the theory of elasticity is found.
Vibration tests on spherical shell caps
Authors: De Souza V C M , Croll J G A
Published: July 2007

Fabrication and testing of vibrations in small-scale, electroplated nickel, spherical shell caps which are clamped on their open boundaries, are briefly described. Comparisons with theoretical predictions show that with low levels of excitation energy, for which displacements in the resonant response are considerably less than the shell thickness, classical thin shell theory provides a close description of observed resonance in both axisymmetric and non-axisymmetric modes. For larger excitation energies, for which resonant displacements are of the same order as the shell thickness, tests are reported to show the possible need to include in analysis the effects of geometric non-linear, modal interactions.
An elastic-plastic finite element analysis of a compact tension specimen
Authors: Kfouri A P
Published: July 2007

Results from an elastic-plastic finite element analysis of a compact tension specimen (CTS) are presented and provide information on the growth of crack tip plastic zones, crack tip opening displacements, stresses and strains in the region of the crack tip, and Rice's J integral. The elastic-plastic crack separation energy rate GΔ is also evaluated when the crack extends at various loads by applying a crack tip node release technique.
Experimental and theoretical correlations for elastic buckling of axially compressed ring stiffened cylinders
Authors: Ellinas C P , Croll J G A
Published: July 2007

Re-examination of some 85 past experiments on the elastic buckling of axially loaded ring stiffened cylinders shows the existence of two distinctive behavioural regimes. Lightly stiffened cylinders, like isotropic cylinders, buckle into non-axisymmetric modes having long axial wavelengths at loads that are sensitive to the precise magnitudes of small initial imperfections. Heavily stiffened cylinders are characterised by snap buckling into axisymmetric modes which, for elastic behaviour at least, show only limited sensitivity to initial imperfections.

Each of these characteristics is shown to be predicted by the recently developed ‘reduced stiffness analysis’ method, which, despite the relatively perfect nature of test specimens, predicts reliable lower bounds to the experimental scatter. Taken together with the previously demonstrated empirical validity of the reduced stiffness analysis for the prediction of buckling modes and lower bounds to buckling loads for both isotropic and stringer stiffened cylinders, the present comparisons provide further support to the recommendation that this method be considered as an alternative basis for future design.
An analysis of shot peening
Authors: Hills D A , Waterhouse R B , Noble B
Published: July 2007

It is shown that the residual stresses obtained during shot-peening are directly proportional to the treated material's hardness, and that the depth of material influenced depends on the velocity of approaching shot. The relationship between the shot size and depth hardened is developed, and experimental evidence is provided to verify the major points of the analysis. Useful curves, enabling the variation of residual stress with depth to be estimated, are included, and this enables the shot-peening treatment to be matched to alleviate any subsequent contact-pressure loading that the material may experience during service.
Some useful results in the tangentially loaded hertzian contact problem
Authors: Sackfield A , Hills D A
Published: July 2007

Results available in the literature for the problem of two contacting bodies, suffering Hertzian contact and with an assumed proportional shear, are reviewed. The general case of the problem, when the axes of the contact patch are unequal, is studied, and the resulting stresses deduced in their most convenient and closed form. An example of the use of these results, in deducing the elastic limit, is given.
Model studies on plate girders
Authors: Narayanan R , Adorisio D
Published: July 2007

Tests on eighteen small scale models which simulate the elastic and post-buckling behaviour of plate girders when subjected to shear loading are reported and discussed. The models were fabricated of steel and Araldite; the major aim was to assess whether small scale models can be employed to study shear buckling problems. A secondary object was to examine whether araldite could be used for predicting the structural behaviour and ultimate loads of plate girders.

The strength and post-buckling characteristics exhibited by steel models were found to be similar to those observed by earlier investigators on full scale girders. The test results of steel models have been compared with the theoretical predictions obtained by using some ten design methods developed in different countries. Most of these methods are shown to give conservative but satisfactory predictions of the ultimate shear capacity of the model steel girders.

Tests on Araldite models demonstrated that post-buckling behaviour can be observed visually on account of the large elastic deformations which the material is capable of, before collapse. However, they were found to be unsuitable for the prediction of the ultimate shear capacity. As Araldite is brittle, collapse would occur prematurely by sudden fracture before the full development of the tension field.
The uniaxial and biaxial, monotonic and cyclic plasticity behaviour of a lead alloy model material
Authors: Hyde T H
Published: July 2007

A chill-cast, antimony-arsenic-lead alloy model material has been used to investigate the monotonic and cyclic loading, uniaxial and biaxial plasticity behaviour of a metal at elevated temperature, i.e., T/ Tm ≈ 0.5.

For the lead alloy used, a post-machining heat treatment of 96h at 100 C considerably reduced the scatter in the material behaviour. Uniaxial monotonic loading tests showed that the behaviour is relatively independent of temperature and strain-rate for strains less than about 1 per cent.

Under cyclic loading conditions, between fixed strain limits, a stable hysteresis loop is obtained after the first cycle for both uniaxial and biaxial stress systems. By taking into account the biaxiality ratio and the increase in yield-range caused by cyclic hardening, the uniaxial and biaxial, cyclic plasticity behaviour was reasonably accurately predicted from the uniaxial, monotonic loading behaviour.
Reduction of stress concentration around a hole in a uniaxially loaded plate
Authors: Jindal U C
Published: July 2007

The stress concentration around a circular hole in a plate can be reduced by up to 21 per cent by introducing auxiliary holes on either side of the original hole. But this approach of auxiliary holes creates two more regions of stress concentration in the plate.

In the present study, the hole geometry has been modified to effect stress reductions as high as 22 per cent. The problem has been analysed numerically by the finite element method and experimentally by two-dimensional photoelasticity. It has been observed that by making the hole oblong in the direction of loading, a high order of reduction in stress concentration around the hole can be obtained.
Analysis for inversion load and energy absorption of a circular tube
Authors: Kinkead A N
Published: July 2007

The basic theoretical approach in the mechanics of external or inside-to-outside inversion of circular tubes is examined and extended by the introduction of two additional and previously unperceived sub-structural mechanisms. It is shown that these refinements when applied to published results for ductile aluminium tubing inverted, in a non-frictional process, furnish very encouraging correlations. Since this analysis is made on an ‘engineering plastic strain’ basis a supplementary calculation is made employing ‘pure plastic strain’ or ‘natural strain’ in the predominant sub-structural processes. The resulting comparisons have shown that for rigid/plastic material characteristics the simplification derived in the use of engineering strain does not introduce serious errors in the evaluation of the inversion load. Here it might be mentioned that in many of the cited papers on external inversion, although the initial equations are set up in pure plastic strain terms, frequently the ensuing analysis is simplified by expressing the logarithmic strain as a series and eliminating all but the first term. This reverts the analysis to an engineering strain type. Hence the work described in this connection validates these previously adopted simplifications.

In view of the satisfactory correlations achieved by introducing the above theoretical refinements for the external inversion process, the same procedure has also been applied to the case of internal or outside-to-inside tube inversion. Published analysis of the internal inversion process has previously neglected the pronounced thickening effect clearly demonstrated in all experimental results. (Tube-wall thickness change is not at all evident during external inversion and in fact this also assists in simplifying that analysis). In the present approach the effects of friction and work hardening in a compressive die process of internal inversion have been included in the manner already deduced in other research but in addition a further sub-structural process explaining and quantifying the associated thickening of the tube wall has been formulated. Here it should be mentioned that some uncertainty exists in relation to the application of strain hardening based on average plastic strains. However, since the four published experimental results available have been made with materials exhibiting strain hardening characteristics, the total newly developed and previously evolved analyses have been combined to enable some correlation to be made. The predicted internal inversion loads for two separate sets of results in three different materials are in very reasonable agreement with experimental values.
A note on the hertz contact problem: A correlation of standard formulae
Authors: Sackfield A , Hills D
Published: July 2007

The values of stresses resulting from point or line Hertzian contact (including frictional traction) are deduced as a special case of the general elliptical geometry problem, and are compared with known solutions.
The boundary integral equation (boundary element) method in engineering stress analysis
Authors: Fenner R T
Published: July 2007

The principles of the boundary integral equation (BIE) or boundary element method (BEM) are discussed in a non-mathematical way. The technique is compared with other numerical methods, particularly the finite element method (FEM), on the basis of computational efficiency, and the main advantages and disadvantages of the BIE approach are outlined.
Some boundary integral equation solutions for three-dimensional stress concentration problems
Authors: Abdul-Mihsein M J , Fenner R T
Published: July 2007

The boundary integral equation (BIE) method for three-dimensional linear, elastic stress analysis is applied to some stress concentration problems associated with transverse circular holes in either hollow or solid circular cylinders subject to axial tension or torsion, also offset-oblique holes in cylinders subject to internal pressure. Satisfactory agreement is obtained with some previously published experimental results, although computed maximum stress concentration factors are generally higher than those obtained experimentally. The BIE method is shown to be a very useful tool for solving three-dimensional problems of engineering stress analysis.
Boundary integral equation evaluation of compression moduli of bonded rubber blocks
Authors: Fenner R T , Remzi E M
Published: July 2007

The boundary integral equation (BIE) method for two-dimensional, linear, elastic stress analysis is applied to two plane strain problems involving either incompressible or nearly incompressible materials. One of these is a test problem with a known analytical solution, which facilitates checking of the accuracy of the numerical results. The other is the determination of compression moduli of bonded rubber blocks, for which some finite element (FE) solutions have been published previously. Comparison of the BIE and FE results suggests that the latter are increasingly inaccurate as the material behaviour approaches incompressibility. Unlike displacement-based FE methods, the BIE method is not subject to singularity problems when applied to incompressible materials.
Boundary integral equation analysis of axisymmetric thermoelastic problems
Authors: Bakr A A , Fenner R T
Published: July 2007

The boundary integral equation (BIE) numerical method for linear elastic stress analysis is applied to axisymmetric problems which also involve temperature variations due to steady-state thermal conduction. The boundary of the two-dimensional solution domain is discretized into isoparametric quadratic line elements, which provide an excellent modelling capability. Satisfactory agreement is obtained with both exact analytical solutions for test problems and numerical results obtained by the finite difference and finite element methods. The BIE method is applied to the problem of a hollow cylinder with an external semi-circular groove, subjected to axial tensile loading and a temperature difference across the cylinder wall. The results emphasise the very high stress concentrations which can be obtained when the effects of thermal and mechanical loading are superimposed. An important practical advantage of the BIE method is the small amount of labour involved in preparing the mesh data.
On angled crack initiation under biaxial loading
Authors: Woo C W , Ling L H
Published: July 2007

The angled crack problem has been of growing interest to both designers and researchers for the prediction of the structural integrity of components under complex loading conditions. In the study of angled crack growth behaviour, it is invariably of interest to predict the initial crack growth direction θ0 and the fractures stress σc at which crack initiation occurs.

In this paper the merits of the various proposed fracture criteria are reviewed. The biaxial loading effect on the parameter used in each criterion for the prediction of the fracture behaviour is studied. It is observed that the popular testing method employing uniaxial loading of a test specimen is inadequate to demonstrate the suitability of fracture criteria in the prediction of θ0 and σc. It is suggested that with the biaxial loading of a test specimen with an angled crack, a better appraisal of the fracture criteria can be obtained. The experimental results obtained in this study seem to support the maximum stress criteria for both uniaxial and biaxial loading conditions. Both tensions and compression biaxial loading effects have been considered.
Whole-field strain determination by moiré shearing interferometry
Authors: Weissman E M , Post D , Asundi A
Published: July 2007

Whole-field patterns of normal strains are produced by optical shearing. The two warped wavefronts generated in the moiré interferometric system are separately sheared to produce two interference patterns. Superposition of these yields the normal strain contours. The shearing apparatus in an adjustable air wedge located near the common focal point of a telecentric lens system. By successively interrogating gratings in three directions and applying the strain rosette equation, the normal and shear strains over the entire surface can be calculated. Excellent experimental verification was obtained.
Stress intensity factors for cracks at loaded holes-effect of load distribution
Authors: Rooke D P , Hutchins S M
Published: July 2007

Stress intensity factors are evaluated for a radial crack at the edge of a circular hole subjected to a localized radial or tangential force on its perimeter. These factors can be used as Green's functions to determine the stress intensity factor when an arbitrary load distribution acts on the hole perimeter. Both the accuracy and ease-of-use of this Green's function technique are demonstrated by comparing some test cases with known results. The strong dependence of the stress intensity factor for short cracks upon the detailed load distribution on the perimeter of the hole is discussed, and the importance of fricitional forces is demonstrated in the determination of fatigue lifetimes in the presence of fretting
In-plane thermal stresses in elastic plates
Authors: Wah T
Published: July 2007

A method is proposed for the solution of in-plane stresses and displacements in quadrilateral plates under thermal loads. The procedure employs eigenfunctions for angular regions together with a least squares technique. An electronic computer is a necessary adjunct to the proposed method of solution. Numerical results are given.
Stress analysis of some unsymmetric screwed connections
Authors: Fessler H , Jiong-Hua Wang
Published: July 2007

Unsymmetric shapes and loadings were studied using four frozen-stress photoelastic models. Pure tension was applied to all bolt heads. All the bolt shanks were necked. Three of the blocks were rectangular in cross-section, one was circular with a flat. Two tests represented clamping only; two tests modelled clamping and an offset separating force on a bolted joint causing bending. Results from two previously published tests with axisymmetric blocks are included as a basis for comparisons.

The maximum stresses in screw and block always occur near the start of contact. Their values depend on thread configuration at the start of contact, not on the block cross-section.

Using pitch-average curves as datum allowed analysis of the maximum variations from these curves. In the tests carried out, RMS values of these variations are doubled by making the block unsymmetric and quadrupled by introducing bending.
A note on the influence of residual stress on measured hardness
Authors: Simes T R , Mellor S G , Hills D A
Published: July 2007

The influence of uniform residual stresses on measured hardness value is investigated experimentally, using samples containing a known cylindrical stress value. It is shown that realistic values of this stress have a first order effect on the hardness number obtained in a Vickers pyramidal indenter test.
Interior warping measurement by holographic interferometry
Authors: Juckenack D
Published: July 2007

Holographic interferometry is used to obtain the interior displacement (warping) at different planes of a prismatic shaft of square cross-section in torsion. It can be shown that the fixed-end displacement is not equal to zero.
Biaxial test facility for creep crack growth in damaged material
Authors: Jansson S
Published: July 2007

In order to study creep crack growth at elevated temperatures, a biaxial test system and a method to achieve well-defined damage to material in a purely mechanical way have been developed. Results from two preliminary tests are reported.
Theoretical analysis of a segmented locking ring for shell-bottom connection in pressure vessels
Authors: Strozzi A
Published: July 2007

The internal forces and deflections of a segmented locking ring inserted in an annular slot in a cylindrical vessel, and supporting its bottom while the vessel is subjected to high internal pressure, are studied.

The behaviour of the ring sectors is described in terms of a curved beam of rectangular cross section resting on elastic foundations.

A closed form solution is obtained. The results presented show that the reaction force between the ring sectors and the cylindrical vessel exhibits peaks at the sector ends, and that the maximum value of the bending moment for the ring sectors is moticeably higher than that for a complete ring.
Notch sensitivity of angle-ply carbon fibre composites
Authors: Davies G A O , Zhen Shen
Published: July 2007

The notch sensitivity of carbon composite angle-ply is investigated experimentally. It is found unexpectedly that these laminates are notch insensitive for almost all ply angles, except in those cases when the fibres are inclined at more than 70 degrees to the loading axis.
Evaluation of creep crack C∗ integrals
Authors: Wu D , Christian E M , Ellison E G
Published: July 2007

Numerical contour integrations of the creep crack C∗ integral were carried out for two types of specimen. The results agree reasonably well with C∗ evaluations using limit analysis methods; path-independence of C∗ is shown. A realistic definition of the creep pseudo-stationary state is proposed and various forms of creep data input are discussed.
Analysis of a proposed method for toughness measurments using torsion testing
Authors: Sweeney J
Published: July 2007

A method of fracture toughness testing is proposed in which cylindrical surface-notched specimens are tested in torsion. Analyses are presented which show that the values of K1 which are induced are not sensitive to the precise shape of the notch. Also, the existence in the torsion specimen of a non-constant remote stress, and a curved specimen surface, are shown by finite element modelling to have only a small effect on the K1 values. These findings are used to justify the use of simple models to analyse results from the proposed test.
The plastic behaviour of components subjected to constant primary stresses and cyclic secondary strains
Authors: Cocks A C F , Ponter A R S
Published: July 2007

Some structural situations encountered in the design of the liquid metal fast breeder reactor (LMFBR) can be reduced to problems where an element of material is subjected to a constant primary load and a cyclic secondary strain. Three simple material models are used to calculate the amount of primary plastic strain accumulated in this type of problem. The analyses lead to closed form solutions that overestimate the amount of strain accumulated in experiments performed by Lebey et al. (2)† to model these situations.