Showing papers in "Journal of Strain Analysis for Engineering Design in 1999"
TL;DR: In this article, the authors used the notch stress intensity factors (N-SIFs) to predict the fatigue behavior of mechanical components weakened by V-shaped reentrant corners, where the singularity in the stress distribution makes any failure criterion based on the elastic peak stress no longer applicable.
Abstract: The stress field parameters, namely the notch stress intensity factors (N-SIFs) according to a more recent definition, can be used to predict the fatigue behaviour of mechanical components weakened by V-shaped re-entrant corners, where the singularity in the stress distribution makes any failure criterion based on the elastic peak stress no longer applicable. When the notch root radius is small but different from zero, the N-SIF can still be used, since a comprehensive analytical approach is available for open sharp and blunt notches. The fatigue strength reduction factor can be given as a function both of the elastic peak stress (only if it has a finite value) and of the N-SIF (for every notch tip radius value), by assuming that the fatigue strength of notched elements depends on a mean stress value in the critical zone.The welded joints are an example of practical N-SIF use in fatigue strength prediction. In this case not only the fatigue crack initiation life but also the fatigue crack propagat...
63 citations
TL;DR: In this article, constitutive models based on the plasticity criterion for porous media given by Gurson, and the CDM framework proposed by Lemaitre are reviewed, giving attention to identification procedures for the damage parameters.
Abstract: The possibility of extending fracture mechanics concepts and design criteria to ductile failure is an issue that has attracted the attention of many researchers. Many models that address this are available nowadays. For these, two kinds of approach are widely used: the porosity-based model proposed by Gurson and the continuum damage mechanics (CDM) approach. Any new user that has to deal with these models for the first time is often hindered by the difficulty of finding in the literature, or measuring, the material parameters necessary. In addition, the use of these models, which are often available already built into commercial finite element codes, requires great experience and attention in order to avoid the danger of ‘numerical traps and tricks’. Here, constitutive models based on the plasticity criterion for porous media given by Gurson, and the CDM framework proposed by Lemaitre are reviewed, giving attention to identification procedures for the damage parameters.
56 citations
TL;DR: An iterative gradientless method for shape optimization of stress concentrators, from the context of structural fatigue life extension, has been presented in this article, which is implemented to interface with the finite element code PAFEC, which does not normally have an optimization capability.
Abstract: This paper presents an iterative gradientless method for the shape optimization of stress concentrators, from the context of structural fatigue life extension. The method has been implemented to interface with the finite element code PAFEC, which does not normally have an optimization capability. The key feature of the approach is to achieve constant boundary stresses, in regions of interest, by moving nodes on the stress concentrator boundary by an amount dependent on the sign and magnitude of the local hoop stress obtained from a previous iteration of a standard finite element analysis. The results of example problems are presented which include the optimization of hole shapes in flat plates and the optimization of the design of bonded reinforcements with a focus on minimizing adhesive stress while maintaining the effectiveness of the reinforcement. In all cases, it was found that significant stress reductions were achieved by way of the local shape changes due to the optimization. The method pr...
46 citations
TL;DR: In this article, a finite element model of a seven-wire strand has been developed for the analysis of termination effects, taking full account of frictional effects in the spiral strands.
Abstract: A finite element model of a seven-wire strand has been developed for the analysis of termination effects. The cyclic symmetric and antisymmetric features of the strand have been used to reduce the finite element model size. The effects of a fixed-end termination on the contact forces (pressure) and the resulting relative movements between the wires along the contact lines have been determined, taking full account of frictional effects in the spiral strands. The aforementioned factors are thought to be strongly related to the fretting fatigue, wear and energy dissipation under cyclic loads.
40 citations
TL;DR: In this article, the effect of optical refraction at an interface between optically dissimilar media is modelled in order to apply the principles of three-dimensional digital image correlation (DIC) to measure deformations on submerged objects accurately.
Abstract: The effect of optical refraction at an interface between optically dissimilar media is modelled in order to apply the principles of three-dimensional digital image correlation (DIC) to measure deformations on submerged objects accurately. Using an analytical formulation for refraction at an interface, a non-linear solution approach is developed to perform stereo calibration. The proposed method incorporates a simplified parametric representation for the orientation and position of an interface(s), accounting explicitly for the effects of refraction at all such interfaces in the path of each stereo camera. Separating the calibration process into two parts, a modified bundle adjustment process with an updated Levenburg–Marquardt (LM) non-linear optimization algorithm is employed to determine (a) intrinsic and extrinsic stereo camera parameters without interface refraction and (b) orientation and position of each planar interface. Detailed simulations demonstrate the efficiency, accuracy, and stabili...
30 citations
TL;DR: In this article, the known solutions for contact problems in which partial slip arises are reviewed and how these may, in some cases, be readily extended. The objective is to prov...
Abstract: In this paper the known solutions for contact problems in which partial slip arises are reviewed and how these may, in some cases, be readily extended is indicated. The objective is to prov...
24 citations
TL;DR: In this article, a finite element analysis of the punch and bulge test has been undertaken and validated by comparison with results from experiments, giving good agreement for the punch force for two differing specimen materials.
Abstract: The punch and bulge test provides a technique for the determination of material properties from small specimens. Although the test has been in use for a number of years, the behaviour of the specimen is not fully understood. A finite element analysis of the test has thus been undertaken and validated by comparison with results from experiments, giving good agreement for the punch force for two differing specimen materials. The finite element analysis has enabled punch force-displacement curves, von Mises stresses, equivalent plastic strains and vertical deflections for the upper and lower surfaces of the disc to be obtained.The finite element model has also been used to determine the relationship between the specimen yield stress and the punch force for elastic-perfectly plastic specimens. It is shown that a linear law applies over a 6:1 range of yield stresses and thus the punch and bulge test represents an effective method of yield stress measurement from small specimens.The effect of experiment...
23 citations
TL;DR: In this article, three formulations of a single region dual boundary element method for dynamic crack problems are presented, and the dynamic stress intensity factors are calculated by crack opening displacement, which is derived from the dynamic behavior of stationary cracks in threedimensional analysis.
Abstract: In this paper, three formulations of a single-region dual boundary element method for dynamic crack problems are presented. The dynamic stress intensity factors are calculated by crack opening displacement. These methods are developed to study the dynamic behaviour of stationary cracks in threedimensional analysis. Formulations of the methods and computational efficiency characterized by memory and central processing unit time are discussed. In order to compare these three approaches, they are applied to pure mode and mixed-mode crack problems in infinite and finite domains.
20 citations
TL;DR: In this paper, the Coulomb's law of friction is applied to three-dimensional frictional contact problems using a quadratic boundary element formulation, where the contact variables are defined with respect to each of the surfaces using local coordinate systems.
Abstract: This paper is concerned with the development of advanced algorithms for three-dimensional frictional contact problems using a quadratic boundary element formulation. The contact variables are defined with respect to each of the surfaces using local coordinate systems. Equilibrium conditions, displacement continuity requirements and Coulomb's law of friction applied to three-dimensional contact are used to derive the contact equations. These equations are directly coupled at the contact interface to form a reduced set of determinate simultaneous equations. Four three-dimensional frictional contact applications covering stationary and advancing contact surfaces are presented in which boundary element solutions are compared with the corresponding finite element solutions. The results are presented in the form of normal contact stresses, shear stresses, relative tangential displacements and the stick-slip partitioning of the contact interface.
20 citations
TL;DR: In this article, the least squares method, in conjunction with a Laurent series representation of the stress functions and local collocation, is used to evaluate reliable stresses on the boundary of holes in loaded composites from measured data away from the hole.
Abstract: Determining stress raisers necessitates accurate knowledge of the stresses on the edge of the geometric discontinuity. Recognizing difficulties in obtaining measured stresses at the edge of a hole or notch, the least-squares method, in conjunction with a Laurent series representation of the stress functions and local collocation, is used to evaluate reliable stresses on the boundary of holes in loaded composites from measured data away from the hole. Advantages over previous such hybrid analyses include the fact that few measured input data are required, that they can be arbitrarily located and that only a very few terms are needed in the stress function representation. The approach is illustrated for stress input as well as moire-measured displacements. Application to each of the three classes of orthotropy is deliberately addressed.
18 citations
TL;DR: In this article, a new definition of the strain-concentration factor (SCNF) has been proposed for circumferentially notched cylindrical bars under static tension.
Abstract: A new definition of the strain-concentration factor (SCNF) has been proposed for circumferentially notched cylindrical bars under static tension. The average axial strain used in the definition of this new SNCF takes into consideration the triaxial state of stress at the net section. This is very different from the definition of the conventional average axial strain, which has been defined under uniaxial state of stress. This new average axial strain approaches rapidly 2 In(d 0 /d) as plastic deformation develops from the notch root; this 2 In(d 0 /d) is the average axial strain at the net section at deformation levels where elastic deformation is negligible compared with the plastic one. The value of the new SNCF increases with plastic deformation from the notch root and then decreases gradually. It becomes less than its elastic value at large deformations; however, it is larger than unity at any deformation level. This is consistent with the concave distributions of axial strain at the net section. On the other hand, the value of the conventional SNCF becomes less than unity after plastic deformation develops from the notch root. This is contradictory to the concave distributions of axial strain. The new SNCF is greater than the conventional value at any deformation level. The new SNCF approaches the conventional SNCF as the stress triaxiality decreases at the net section. The proposed SNCF is more reasonable than the conventional SNCF.
TL;DR: In this article, a high-speed photographic film record of a Taylor impact experiment was analyzed to determine the strain, strain rate and stress of the Taylor impact, and the stress was calculated on the basis of an interpretive a...
Abstract: A high-speed photographic film record of a Taylor impact experiment was analysed to determine the strain, strain rate and stress. The stress was calculated on the basis of an interpretive a...
TL;DR: In this article, a three-layer technique based on the two-dimensional finite element method for adhesively bonded composite patch repair of cracked structures is presented, which is capable of characterizing the crack growth and debond growth behavior, as well as predicting the fatigue life extension of the repaired structure with a perfectly or imperfectly bonded patch.
Abstract: Adhesively bonded composite repair of metallic structures is one of the candidate technologies that has enormous potential in the ageing aircraft. A computational tool to analyse the repaired aerospace structure using an adhesively bonded composite patch is presented. This involves the three-layer technique based on the two-dimensional finite element method for adhesively bonded composite patch repair of cracked structures. This technique is capable of characterizing the crack growth and debond growth behaviour, as well as predicting the fatigue life extension of the repaired structure with a perfectly or imperfectly bonded patch. Also, the thermal effects which may develop during bonding or during service and the non-linear material behaviour of the adhesive are incorporated in this technique. The results from the three-layer technique show good agreement with experimental results as well as a previous investigator's published numerical results. Besides the accuracy of the technique, the advantag...
TL;DR: In this article, the authors used the distributed dislocation (or displacement discontinuity) method for the analysis of strains in the neighborhood of a slot of finite width, which is of particular significance for the crack compliance method of residual stress measurement.
Abstract: This paper describes the use of the distributed dislocation (or displacement discontinuity) method for the analysis of strains in the neighbourhood of a slot of finite width. The results are of particular significance for the ‘crack compliance’ method of residual stress measurement which calculates residual stresses in a component from measured strain changes during the introduction of a slot. Two cases are analysed here: a flat-bottomed slot and a slot with a semi-circular bottom. Both cases are compared with a thin slot approximation (i.e. a crack). It is shown that the effect of the slot width is quite small for practical strain gauge locations, provided that the slot has a flat bottom. The effect of bottom profile is more significant and it is demonstrated that previous empirical results reported in the literature do not appear to account correctly for the effect of the bottom profile.
TL;DR: In this article, a systematic approach is presented for the stress analysis of shell intersections made of composite materials, and the finite element method used is based on a modified mixed for mixed for...
Abstract: In this study, a systematic approach is presented for the stress analysis of shell intersections made of composite materials. The finite element method used is based on a modified mixed for...
TL;DR: In this article, a 6 × 41 wire rope of 76 mm diameter was used with axial loads ranging up to 1.4 MN and axial stiffnesses were measured, both for large load ranges and for small load perturbations superimposed on larger mean loads.
Abstract: Some recent tests on a 6 × 41 wire rope of 76 mm diameter are reported. A specimen 7 m long whose ends were prevented from rotating was used with axial loads ranging up to 1.4 MN. Axial stiffnesses were measured, both for large load ranges and for small load perturbations superimposed on larger mean loads. The torque generated in the rope by axial load was measured, as was the response of the axially preloaded rope to external torque applied at the mid-point of the rope. These experimental data are reported and compared with new theoretical predictions, and with other theoretical results and a range of manufacturers' rules. Some encouraging correlations have been found.
TL;DR: In this article, the authors investigated the plastic upsetting of a disc with spherical dies to determine points on a forming limit curve and found that fracture occurs at the free surface of the specimens.
Abstract: The plastic upsetting of a disc with spherical dies is investigated experimentally and theoretically to determine points on a forming limit curve. For steel specimens of various dimensions, it is found from experimental study that fracture occurs at the free surface of the specimens. Simple theoretical calculations based on the obtained experimental results are performed to determine the state of stress and strain leading to fracture initiation. An advantage of the theoretical approach proposed is that considerations of friction on the die-workpiece interface are excluded. The fracture conditions obtained are used to predict the shape of the forming limit curve at large values of the triaxiality factor.
TL;DR: In this paper, a plane analysis of a peg or beam, located in a shrink-fit recess within an elastically similar halfplane, is carried out, and conditions of separation and slip along the peg-halfplane interface are analysed.
Abstract: A plane analysis is carried out of a peg or beam, located in a shrink-fit recess within an elastically similar half-plane. The peg is subject to transverse tip forces, and conditions of separation and slip along the peg-half-plane interface are analysed. This permits design curves for the avoidance of separation to be established, as well as conditions for the avoidance of interfacial slip. The former is a requirement for the maintenance of full stiffness of the joint, while the latter are needed in order to avert the possibility of fretting.
TL;DR: The integration of the resultant methodology for spectral analysis with phase stepping is used to achieve automatic analysis of photoelastic fringe patterns containing a minimum fringe order of no greater than four, and without the requirement for a zero-order fringe order to be present in the pattern.
Abstract: The theoretical description of spectral contents analysis is extended to red-green-blue (RGB) photoelasticity. The integration of the resultant methodology for spectral analysis with phase stepping is used to achieve automatic analysis of photoelastic fringe patterns containing a minimum fringe order of no greater than four, and without the requirement for a zero-order fringe order to be present in the pattern.
TL;DR: In this paper, a mixed variational principle is suggested for electromechanical analysis, in which the displacements, the transverse stresses and the electric potential are the primary variables, and a three-dimensional hybrid element approach is built on the principle.
Abstract: A mixed variational principle is suggested for electromechanical analysis, in which the displacements, the transverse stresses and the electric potential are taken as the primary variables, and a three-dimensional hybrid element approach is built on the principle. Two kinds of specific element, namely the bimaterial interface element and the surface element, are developed so that the interlayer traction-continuity and surface traction-free conditions of transverse stresses can be imposed exactly. Two numerical examples of intelligent laminates with piezoelectric layers bonded to the upper and lower surfaces are presented to demonstrate the efficiency of the present approach.
TL;DR: In this paper, the mathematical difficulties associated with the determination of interior point stresses for an anisotropic domain with body forces using the boundary element method (BEM) are discussed and overcome, and the corresponding Somigliana's identity for strains is derived, from which the stresses at the interior point may be obtained.
Abstract: The true boundary integral equation, based on the so-called direct formulation of the boundary element method (BEM), for two-dimensional anisotropic elasticity with body forces has only recently been reported in the literature. It involved transforming a volume integral term associated with the body forces into integrals around the surface of the domain. In the general case, this transformation for anisotropic elasticity gives rise to a series of line integrals along paths which traverse the domain, but their numerical evaluation does not pose any difficulties for the solution of the unknown boundary displacements or tractions. Similarly, the displacements at interior points of the anisotropic domain can be directly calculated using Somigliana's identity for displacements. However, because of the presence of the extra line integrals in this identity as well, the strains, and hence the stresses, at these points cannot be obtained by simple direct differentiation of the identity. In this paper, the mathematical difficulties associated with the determination of interior point stresses for an anisotropic domain with body forces using the BEM are discussed and overcome. The corresponding Somigliana's identity for strains is derived, from which the stresses at the interior point may be obtained. The veracity of the formulation is then demonstrated by three examples.
Abstract: The aim of the paper is to propose appropriate numerical methods and constitutive models for solution of the gear dynamic contact problem. This has been done through comparison with international gear standards. Such solution techniques are necessary for an accurate analysis of stress state and resultant design improvement of the complex gear configurations. This paper consists of two parts. The first part presents a solution of the general transient contact problem when the stress state of the tooth is studied. This has been carried out in two phases, initially using a coarse multiple-tooth finite element model to establish contact conditions and subsequently using a refined single-tooth-pair finite element model. Differences of up to 163 per cent were found between various international gear standards and the computed results. Various reasons for this have been discussed. The second part of the paper presents results from two types of local analysis which model viscoplasticity in the surface layer and defect generation respectively. These studies achieve a fuller understanding of the stress distribution in the contact zone, its deviation from the classical Hertzian closed-form solution and provide a firm basis for modelling the effect of gear dynamics on local damage, wear and failure. All the computations are made for single-tooth contact and procedures for optimizing the integration time step are used.
TL;DR: In this paper, the authors considered the problem of plane elasticity of a confocal elliptic ring subject to external and internal pressure and derived the general equations based on the Muskhelishvili method.
Abstract: The classical problem of plane elasticity, namely a confocal elliptic ring subject to external and internal pressure, is considered. The general equations based on the Muskhelishvili method...
TL;DR: In this paper, a dynamic fourth-order partial differential equation for one-dimensional torsion, based on the Barr's equation, is proposed to account for axial inertia associated with cross-sectional warping and the axial stresses which arise when warping is constrained.
Abstract: The double torsion fracture test has been widely used in the past for measuring resistance to crack growth under static loading and, more recently, under high-loading-rate conditions. Specimen deformation in this test is conventionally analysed on the basis of a one-dimensional torsion equation. Under dynamic conditions, it is imperative to establish an accurate torsion equation which can be used to model the double torsion test. The present paper describes the development, in this context, of a dynamic fourth-order partial differential equation for one-dimensional torsion, based on Barr's equation. The equation obtained in this paper accounts for the axial inertia associated with cross-sectional warping and the axial stresses which arise when warping is constrained. The equation can also accommodate non-linear elasticity. The equation is validated, using Barr's own data, for the torsional resonance problem which he studied and, using finite-element analysis, for a problem of constrained static torsion analysed by Timoshenko.
TL;DR: In this article, an experimental and finite element investigation of the non-linear elastic-plastic force-displacement response of a simply supported tubular YT-joint under a range of ratios of the T- to Y-brace applied loads, in order to develop an understanding of the dependence of the joint response on loading path is described.
Abstract: This paper describes an experimental and finite element investigation of the non-linear elastic-plastic force-displacement response of a simply supported tubular YT-joint under a range of ratios of the T- to Y-brace applied loads, in order to develop an understanding of the dependence of the joint response on loading path. The experiments consist of the static testing of simply supported tin-lead alloy models of tubular YT-joints under combined, proportionally applied T- and Y-brace-end axial forces. A number of different finite element approaches are presented and discussed via comparison with the test results. An improved version of the energy-based elastic-plastic prediction procedure of the present authors is presented; this is shown to represent a framework for the determination of the non-linear local joint T- and Y-brace force-displacement responses to arbitrary radial loading paths in the load space. The work is considered relevant to the simplification of tubular framework analysis method...
TL;DR: In this paper, an experimental examination of the fatigue crack growth in pin-loaded tubes was carried out and the results obtained from this examination were correlated with numerical results provided by the finite element method.
Abstract: This paper details results obtained from an experimental examination of the fatigue crack growth in pin-loaded tubes. Initially, various methods of acquiring crack growth data, which can present particular difficulties for this geometry and type of connection, are briefly reviewed. The nature of crack growth in this particular pin-loaded joint is classified in terms of its trajectory, tilt and twist; crack geometric data are analysed within these categories. The work is then correlated with numerical results provided by the finite element method given in the companion paper, Part 1. The crack growth rate is also compared with published data and a satisfactory correlation found. This will enable an analyst to have more confidence in predicting the remaining life of a pin-loaded cracked tube.
TL;DR: In this paper, a boundary element is used to improve the accuracy and complex stress intensity factors are determined by several techniques, namely the one point stress formula, the one-point discontinuity displacement formula and an energy technique.
Abstract: In this paper, three-dimensional interface crack problems are analysed by the boundary element method. A special crack tip element is used to improve the accuracy and the complex stress intensity factors are determined by several techniques, namely the one-point stress formula, the one-point discontinuity displacement formula and an energy technique. Stress intensity factors are presented for single-edge, double-edge and centre cracks in bi-materials.
TL;DR: In this article, a numerical analysis of a cracked pin-loaded tube was carried out and the relationship between various methods of calculating "total" or "equivalent" stress intensity factors was discussed and the reliability of using J contour integral results was shown.
Abstract: This paper contains a numerical analysis of a cracked pin-loaded tube. The relationship between the various methods of calculating ‘total’ or ‘equivalent’ stress intensity factors is discussed and the reliability of using J contour integral results is shown. Trends in the stress intensity factors K1, KII, KIII and Ke are found and the changes in these factors for changes in the profile and length of the crack are explained. A set of ‘best-case’ curves reflecting the profile of the crack in the experimental work and the method of selecting these cases is shown; these will be used for comparison with experimental data in a companion paper, Part 2, which follows.
TL;DR: In this article, experimental and computational activities aimed at supporting the development of a press-pack insulated gate bipolar transistor (IGBT) are reported, and a testing rig for accelerated testing of single IGBT chips under controlled contact pressure conditions is presented.
Abstract: Product development in the power electronic industry is characterized by the short time-to-market and high-reliability requirements. Improved design methods and advanced modelling techniques are therefore required to support package design selection and to arrive at lifetime prediction algorithms for failure prevention. In this work, experimental and computational activities aimed at supporting the development of a press-pack insulated gate bipolar transistor (IGBT) is reported. A testing rig for accelerated testing of single IGBT chips under controlled contact pressure conditions is presented. Then, thermomechanical simulations of accelerated tests by the finite element method provided stress-strain evolution in the device and insight into the sources of local degradation.
TL;DR: In this paper, a procedure for modifying finite element predictions of equivalent stress and equivalent total strain in order to obtain equivalent stress/total strain ranges for lowcycle fatigue life estimates is described.
Abstract: The paper describes a procedure for modifying finite element predictions of equivalent stress and equivalent total strain in order to obtain equivalent stress and equivalent total strain ranges for lowcycle fatigue life estimates.