Showing papers in "Journal of Strain Analysis for Engineering Design in 1987"
TL;DR: In this article, a finite element formulation for stress analysis under axisymmetric conditions is presented for free and constrained inflation of a flat circular membrane, the latter with respect to inflation against a circular cylindrical surface, a 60 degree conical surface, and a horizontal plate.
Abstract: Thermoforming of a heated polymeric membrane by pressure inflation against a relatively cold mould surface presents a class of large deformation stress analysis problems in which account must be taken of the progressively changing boundary conditions caused by the sheet coming into contact with the mould surface. As a first step towards solving the general problem, the paper presents a finite element formulation for stress analysis under axisymmetric conditions. Analysis results are presented for free and constrained inflation of a flat circular membrane, the latter with respect to inflation against (a) a circular cylindrical surface, (b) a 60 degree conical surface, and (c) a horizontal plate. As reasonable physical approximations, the material is considered to be purely elastic while the contact conditions are idealized to be either friction-less or non-slipping. Analysis results are compared with those obtained by experiments on rubber membranes.
129 citations
TL;DR: In this article, a method for the efficient, rapid determination of stress intensity factors for plane cracks at or near free surfaces, with arbitrary far fields, was described, and the basic technique was well established.
Abstract: We describe a method for the efficient, rapid determination of stress intensity factors for plane cracks at or near free surfaces, with arbitrary far fields. The basic technique is well est...
112 citations
TL;DR: In this paper, the standard boundary element method is modified to take explicit account of the singularity in the stresses at a crack-tip, and the known expansion terms of the crack tip displacement and stress fields are subtracted to remove the numerical difficulties associated with the representation of a singular stress field at the cracktip.
Abstract: In order to compute stress intensity factors accurately, the standard boundary element method is modified to take explicit account of the singularity in the stresses at a crack-tip. The known expansion terms of the crack tip displacement and stress fields are subtracted to remove the numerical difficulties associated with the representation of a singular stress field at the crack-tip. Hence the accuracy of calculation is much improved, without appreciably increasing the amount of computation involved. Furthermore, the stress intensity factor is directly obtained as a part of a solution and no extrapolations are required. The improved formulation is applied to a configuration, which is representative of a part of the wing in a civil transport aeroplane. This configuration consists of a pair of circular cut-outs (supply ports) near to which smaller holes exist; these small holes are particularly susceptible to cracking.
51 citations
TL;DR: In this article, the test results obtained on 24 externally-pressurised torispherical steel shells are given in order to evaluate the buckling/collapse pressures of all the domes.
Abstract: The test results obtained on 24 externally-pressurised torispherical steel shells are given in this paper. The knuckle radius-to-diameter ratio of the domes varied from 0.06 to 0.18 and the spherical cap radius-to-thickness ratios were between 75 and 335. Initial shape and thickness measurements were carried out on all the torispheres and a summary of this information is given. The BOSOR 5 shell buckling program was employed to predict the buckling/collapse pressures of all the domes; both perfect domes and those with axisymmetric imperfections were considered. The correlation between the theoretical predictions and the experimental results was, in general, very good.The main conclusions of the present investigation are: (i) that some of the experimental buckling pressures were lower than those obtained by multiplying the BS 5500 design values by a safety factor of 1.5, and (ii) that those torispheres with sharp knuckle radii failed by plastic collapse in the knuckle region and the collapse pressu...
24 citations
TL;DR: In this paper, the authors describe the formulation and implementation of a semi-analytical procedure for enhancing finite element surface stress predictions, which is demonstrated by application to a variety of test cases.
Abstract: This paper describes the formulation and implementation of a semi-analytical procedure for enhancing finite element surface stress predictions. The efficacy of the process is demonstrated by application to a variety of test cases.
23 citations
TL;DR: In this paper, the effect on the stress levels in axially loaded bolt has been investigated for the case where a nut which incorporated a circumferential groove in its outer surface was used.
Abstract: The effect on the stress levels in an axially loaded bolt has been investigated for the case where a nut which incorporated a circumferential groove in its outer surface was used. It was found from a three-dimensional photoelastic frozen stress study that the modified nut reduced the maximum stress in the bolt by 5 per cent. The addition of a bevel to the load bearing face of this nut further reduced the maximum stress to 74 per cent of its value in a standard connection. It has been established that these modifications reduce the maximum shear stress in the roots of the nut threads, and that the stress concentration associated with the groove was smaller than the maximum stress concentration in both the nut and bolt thread roots. The increase indicated by photoelastic analyses in the strength of the connection produced by these modifications, has also been substantiated by fatigue tests of steel connections, but these results are not reported in this paper.
21 citations
TL;DR: In this article, a micropolariscope has been developed for the automatic analysis of photoelastic data, which can take readings of isoclinic angles and fractional fringe orders, repeatable to within ±0.08 degrees and ± 0.001 fringes.
Abstract: A micropolariscope has been developed for the automatic analysis of photoelastic data. It will position frozen stress slices mounted on its stage to within ±0.002 mm, and takes readings of isoclinic angles and fractional fringe orders, repeatable to within ±0.08 degrees and ±0.001 fringes. A rectangular grid of up to 3 × 50 points can be read automatically, taking about 1¼ minutes per point; the readings are stored on a floppy disc and printed out.The original slice is itself sliced, and the subslice is viewed again in the orthogonal direction to produce a second set of readings. Software has been devised to analyse the two sets of readings. It makes use of Tesar's modification of Frocht's Shear Difference method to calculate five cartesian stresses, which may be plotted and printed in tabular form. Flexible facilities are provided for editing, correcting, plotting, and printing intermediate stages in the analysis, and for storing results in data files
19 citations
TL;DR: In this article, a new method for determining the stresses in a finite element analysis on the surface of a body is proposed, where the body is meshed using standard quadratic isoparametric elements and the nodal displacements determined in the normal way.
Abstract: A new method for determining the stresses in a finite element analysis on the surface of a body is proposed.The body is meshed using standard quadratic isoparametric elements and the nodal displacements determined in the normal way. The stresses are then determined within any surface element by letting the quadratic become a cubic element, applying the corner nodal displacements and known boundary stresses as penalty functions, and then performing a finite element analysis on the single element.The solution then yields a further set of displacements from which the stresses can be determined.The method is applied to various two-dimensional bodies and the improvements in the predicted boundary stresses shown.
18 citations
TL;DR: In this article, the authors describe a recently developed technique used for the fabrication of small scale welded steel models with plate thickness as low as 0.6 mm while maintaining fabrication geometrical tolerances to scaled equivalents of those found in full scale fabrication and within the ranges dictated by relevant design guidance documents.
Abstract: This paper describes a recently developed technique used for the fabrication of small scale welded steel models. The extensive use of jigging has allowed stiffened cylindrical models to be manufactured with plate thickness as low as 0.6 mm while maintaining fabrication geometrical tolerances to scaled equivalents of those found in full scale fabrication and within the ranges dictated by relevant design guidance documents.These models have been successfully loaded to destruction, with their performance correlated against that of larger scale models and the results of advanced non-linear numerical techniques.
14 citations
TL;DR: In this article, the measurement of initial geometric imperfections of stringer-stiffened cylindrical shells on a laboratory scale is reviewed and recent results are presented, and the concept and purpose of an international imperfection data bank is outlined and the activity of the Technion branch is described.
Abstract: The measurement of initial geometric imperfections of stringer-stiffened cylindrical shells on a laboratory scale is reviewed and recent results are presented. Buckling loads are predicted by the multimode analysis and are compared with experimental results. The concept and purpose of an international imperfection data bank is outlined and the activity of the Technion branch is described. An evaluation of the characteristics of shells from their measured imperfection record is attempted.
14 citations
TL;DR: In this paper, the authors considered the same loading situation, but obtains the plastic strain loop width in the alternating plasticity and ratchetting regimes, and the result of this analysis is found to be in agreement with numerical studies.
Abstract: A previous paper by the authors (1) obtained expressions for the ratchetting rates of a Bree cylinder subjected to a cyclic internal pressure load together with a cyclic through-wall thermal gradient The two cases of these loads varying in-phase and out-of-phase were considered The work reported here considers the same loading situation, but obtains the plastic strain loop width in the alternating plasticity and ratchetting regimes The result of this analysis is found to be in agreement with numerical studies
TL;DR: In this paper, the finite element method has been used to determine stress concentration factors due to axial loading applied to axisymmetric, external projections on hollow tubes, for any shape within the range covered by the investigation.
Abstract: The finite element method has here been used to determine stress concentration factors due to axial loading applied to axisymmetric, external projections on hollow tubes. A range of tube and projection dimensions have been covered by the investigation. There is good agreement between the present results and previously published data. The results are presented in a manner which allows stress concentration factors to be quickly determined, for any shape within the range covered by the investigation.
TL;DR: In this article, detailed surface displacement measurements have been made on the surface of a thermally deformed cylinder using a real-time holographic interferometry technique to measure the cartesian components of surface displacement at any surface point in the field of view.
Abstract: Detailed surface displacement measurements have been made on the surface of a thermally deformed cylinder using a real-time holographic interferometry technique to measure the cartesian components of surface displacement at any surface point in the field of view. No assumptions were made as to the type and direction of displacements being measured and the resulting equations were analysed using a computer analysis package (I)† developed at the Polytechnic of Wales. For comparative purposes, elastic finite-element programs working on experimental temperature distributions were used in a theoretical model of the experiments.
TL;DR: In this paper, the standard method generally used to determine the strength coefficients in the tensor polynomial failure criterion is re-examined and alternative methods for calculating these strength parameters are proposed and compared using previously published experimental data for paperboard.
Abstract: The standard method generally used to determine the strength coefficients in the tensor polynomial failure criterion is re-examined. Alternative methods for calculating these strength parameters are proposed and compared using previously published experimental data for paperboard. For this material it is shown that the proposed alternative methods can lead to better analytical descriptions of the experimentally-determined failure envelopes.
TL;DR: In this paper, the boundary integral equation (BIE) method is used to solve two elastostatic problems involving complex toroidal geometries, and results are presented for the stress concentration factor, and are compared with numerical work for thick-walled cylindrical pipes.
Abstract: The three-dimensional boundary integral equation (BIE) method is used to solve two elastostatic problems involving complex toroidal geometries. The first problem concerns a thick-walled 180 degree pipe bend connected to tangent pipes, subjected to in-plane bending and internal pressure. Results are presented for stresses and are compared with results from previous numerical and experimental work. The second problem concerns a thick-walled pressurized torus, with cross bores situated in the toroidal plane. Separate solutions are given for cross bores located at the intrados and extrados of the torus. Results are presented for the stress concentration factor, and are compared with numerical work for thick-walled cylindrical pipes.
TL;DR: In this article, the defect is assumed to be an axisymmetric circumferential slot of uniform depth on the outer surface of a spherical shell, and the material was assumed to obey the von Mises yield criterion and a nonlinear programming method was used to give optimum lower bounds.
Abstract: One of the requirements of the two criteria method of safety assessment of a pressure vessel with a defect is an estimate of the plastic limit pressure. Here the defect is in a spherical shell close to its junction with a protruding radial cylindrical branch. The defect is assumed to be an axisymmetric circumferential slot of uniform depth on the outer surface of the shell. Lower bounds to the limit pressure are calculated for a wide range of geometries. The material is assumed to obey the von Mises yield criterion and a non-linear programming method is used to give optimum lower bounds. Data is supplied for spherical shell radius to thickness ratios from 25 to 100, nozzle radius to vessel radius ratios from 0 to 0.4, nozzle to vessel thickness ratios from 0.25 to 1.0 and ligament thickness to vessel thicknesses (ligament efficiencies) of 0 to 1. Slot widths vary from the significant to the infinitesimal, where it becomes a crack. Vessels of some proportions were shown to have their limit pressure...
Abstract: The elastic stress concentrations in an infinite plate with a circular central hole which is loaded uniaxially, is a classical problem in the theory of elasticity. The aim of this work is to investigate the stress concentration phenomena in a uniaxially loaded square plate with a large central circular hole. Various load distributions on the external boundary are discussed. As a result of the numerical method and the experimental work, carried out on photelastic models, interesting stress distributions were found. (1) Both compressive and tensile stresses were found in the minimal section perpendicular to the direction of the acting load in the cases of either tensile or compressive loading. (2) In the case of a nearly concentrated load, the maximal stress appears at the intersection of the hole with the loading axis. The numerical method used here can easily be generalised for the study of other problems of plane elasticity and thermoelasticity of either isotropic or anisotropic bodies.
TL;DR: In this paper, the maximum stresses measured in a cylindrical shell subjected to a radially applied local load were higher than BS 5500, Appendix A, Section 2.1.
Abstract: In a recent paper, two of the present authors showed that the maximum stresses measured in a cylindrical shell subjected to a radially applied local load were higher than BS 5500, Appendix ...
TL;DR: In this paper, a technique for predicting the load distribution and local stress distribution in threaded tether connections is presented for predicting both load and stress in threaded-tethered tether connections by modelling the connection as a system of springs and beams and then using the appropriate stress concentration factors derived by the finite element method.
Abstract: A technique is presented for predicting the load distribution and local stress distribution in threaded tether connections. The load distribution is derived by modelling the connection as a system of springs and beams. This distribution is then used in conjunction with the appropriate stress concentration factors derived by the finite element method to obtain the local stress distribution.A comparison is made between the theoretical predictions of local stress and published experimental results obtained from a photoelastic model.
TL;DR: In this article, a novel end face seal assembly composed of a rubber load ring, a metal stiffening ring, and a rubber seal ring serially connected together is presented, and the design procedures adopted to achieve good operational effectiveness and long wear life are discussed in detail.
Abstract: A novel end face seal assembly composed of a rubber load ring, a metal stiffening ring, and a rubber seal ring serially connected together is presented. The design procedures adopted to achieve good operational effectiveness and long wear life are discussed in detail. Particular attention is focused on obtaining a load ring exhibiting a linear load-deflection relationship, and a seal ring capable of producing a semi-elliptical pressure profile at the sealing lip. These requirements are met by acting on the cross sectional shape of the rings. A comparison between well-correlating theoretical, numerical, and experimental results is given for both the elastomeric components.
TL;DR: In this article, the stress concentration factor, SCF, as determined using the semi-empirical formulae which are applicable for planar joints are not appropriate for space, grouted joints.
Abstract: This paper presents studies carried out on grouted and ungrouted space tubular joints, with K in one plane and T in the orthogonal plane. Three models have been tested for different load cases adopting T, K, and both T and K (STK) configurations.The tubular joints used in offshore structures, especially in jacket platforms, are multiplanar and some are grouted and hence their study is essential. The stress concentration factor, SCF, as determined using the semi-empirical formulae which are applicable for planar joints are not appropriate for space, grouted joints. The results of the present study indicates that the SCF as determined by formulae for simple joints is unsafe in the plane of K and conservative in the plane of T for the space joint. The effect of the grout is to reduce the stress concentration.
TL;DR: In this paper, a test procedure has been developed and used for determining the flexibility of tubular joints, and the method of testing these joints and the analysis of the test results to obtain flexibility matrices are described.
Abstract: A test procedure has been developed and used for determining the flexibility of tubular joints. The manufacture of Araldite model joints, the method of testing these joints, and the analysis of the test results to obtain flexibility matrices are described.
TL;DR: In this article, a model for estimating the maximum allowable number of broken tensile members in a bonded composite plate before catastrophic failure is presented. But the model has application to the analysis of steelcord and Kevlar-cord elastomer belts containing broken edge cords as the result of impact damage.
Abstract: The tensile strength of composite plates with unidirectional cords depends on the way the load is distributed within the matrix by the cords. Of particular interest is the effect of a broken edge cord or a number of in-line fractured edge cords on the breaking strength of the plate when it is subjected to axial loading. This paper describes a model for estimating the maximum allowable number of broken tensile members in a bonded composite plate before catastrophic failure occurs. The model has application to the analysis of steel-cord and Kevlar-cord elastomer belts containing broken edge cords as the result of impact damage.
TL;DR: In this paper, the Von Mises equivalent stress distribution is used to predict notched bar stress rupture behavior. But this method is not suitable for the case of semi-circular notched specimens.
Abstract: Methods of predicting notched bar stress rupture behaviour are reviewed. Two very different types of notched specimens are analysed using the finite element method; one being a circumferentially V-notched test piece, the other having two semi-circular notches in a plane section.A prediction based on the Von Mises equivalent stress distribution is proposed. Predictions using this method are compared with notched specimen test results in a commercially available titanium alloy, Ti5331s, tested at 600°C. The correlation is good for the semi-circular notched specimen and for the V-notched specimen at low stress, long life and can be improved at high stresses by making allowance for time independent plasticity and for the initial high rate of creep strain accumulation at the notch root.
TL;DR: In this article, the effectiveness of the length by which a radial branch pipe extends within a spherical pressure vessel is discussed with reference to the plastic limit pressure of the vessel and the design rules of BS 5500.
Abstract: The effectiveness of the length by which a radial branch pipe extends within a spherical pressure vessel is discussed with reference to the plastic limit pressure of the vessel and the design rules of BS 5500. Lower bound limit pressures are calculated using a non-linear programming method, the stress resultants being expressed in polynomial form. The material was assumed to be rigid-plastic and to obey the von Mises yield criterion.
TL;DR: In this article, the static linear response of circular cylindrical shells to a radial loading applied halfway along the shells is examined, with shells in which the loading is applied by way of a circular pad containing a small concentric hole.
Abstract: Examination is made of the static linear response of circular cylindrical shells to a radial loading applied halfway along the shells: the chief concern is with shells in which the loading is applied by way of a circular pad containing a small concentric hole. The examination comprises tests on physical models, in which point displacements and strains are measured, and numerical studies based on the use of the finite element method. In the numerical studies two markedly different types of element are used and particular attention is paid to the modelling of the pad region of the cylinder pad combination. Good correlation between test measurements and numerical results is exhibited for radial displacement and for stresses, even when the pad itself is removed from the finite element models by appropriate specification of boundary conditions which reflect full pad rigidity.