Showing papers in "Journal of Strain Analysis for Engineering Design in 1979"
TL;DR: In this article, a method of non-destructively assessing the integrity of structures using measurements of the structural natural frequencies is described, where measurements made at a single point in the structure can be used to detect, locate and quantify damage.
Abstract: A method of non-destructively assessing the integrity of structures using measurements of the structural natural frequencies is described. It is shown how measurements made at a single point in the structure can be used to detect, locate and quantify damage. The scheme presented uses finite-element analysis, since this method may be used on any structure. The principle may, however, be used in conjunction with other mathematical techniques. Only one full analysis is required for each type of structure.Results are presented from tests on an aluminium plate and a cross-ply carbon-fibre-reinforced plastic plate. Excellent agreement is shown between the predicted and actual damage sites and a useful indication of the magnitude of the defect is obtained.
1,379 citations
TL;DR: In this paper, the authors derived stress intensity factors for a crack at the edge of a sheet subjected to localized fretting forces and used them as a Green's function to derive stress intensity for arbitrary distributions of tensile and shear stresses at the edges of the sheet.
Abstract: Solutions are derived for mode I and mode II stress intensity factors for a crack at the edge of a sheet subjected to localized fretting forces. Both normal and tangential forces are considered. These solutions are approximated by a polynomial function of crack length, which is then used as a Green's function to derive stress intensity factors for arbitrary distributions of tensile and shear stresses at the edge of the sheet.
76 citations
TL;DR: The hole-drilling method is a semidestructive technique which allows the measurement of residual stresses as discussed by the authors, but it is prone to misalignment between the hole and the hole.
Abstract: The hole-drilling method is a semidestructive technique which allows the measurement of residual stresses. In this method, a source of error is due to the misalignment between the hole and ...
56 citations
TL;DR: In this article, a multiple image-shearing camera with coherent light illumination is proposed to measure the derivatives of surface displacements with respect to three directions simultaneously, and flexural strains in bent plates are investigated.
Abstract: This paper describes a multiple image-shearing camera. By incorporating coherent light illumination, the camera serves as a multiple-shearing speckle interferometer which measures the derivatives of surface displacements with respect to three directions simultaneously. The application of the camera to the study of flexural strains in bent plates is shown, and the determination of the complete state of two-dimensional strains is also considered. The multiple image-shearing camera uses an interference phenomenon, but is less demanding than holographic interferometry with respect to vibration isolation and the coherence of the light source. It is superior to other speckle techniques in that the obtained fringes are of much better quality.
53 citations
TL;DR: In this article, simple relations for the plane strain and axisymmetric compression moduli for blocks of compressible soft elastic material bonded to rigid end plates were developed based on simplifying assumptions.
Abstract: Using simplifying assumptions based on a theoretical solution for incompressible materials, simple relations are developed for the plane strain and axisymmetric compression moduli for blocks of compressible soft elastic material bonded to rigid end plates. The approximate theoretical solutions compare well with finite-element analysis data for materials with Poisson's ratios between 0.125 and 0.499 83 and blocks having width-to-thickness or diameter-to-thickness ratios between 0.25 and 128.
50 citations
TL;DR: In this paper, a beam-on-elastic-foundation (BEF) model is used for the determination of crack-opening-displacements (COD) and their application to aluminium-Araldite joint systems.
Abstract: A method of analysis is presented for the determination of crack-opening-displacements (COD) and their application to aluminium—Araldite joint systems. Use is made of a beam-on-elastic-foundation (BEF) model, which is extended to represent the physical system. It is seen that, in conjunction with this, the Dugdale ‘strip-yield’ model solution may be combined to characterize interfacial or cohesive fracture cases.Fracture toughness values, based on both load and displacement control testing conditions, are examined and show that the equation derived for the load-control model yields greater accuracy. Results of the proposed method are compared with those obtained by a two-dimensional, finite-element analysis and are found to be in good agreement. The validity of the proposed analysis is further verified by experimental observations employing conventional compliance methods for both interfacial and cohesive fracture modes.
30 citations
TL;DR: In this article, 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, where 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 r 1/2 near the crack tip is minimized.
Abstract: 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.
23 citations
TL;DR: In this article, the longitudinal stress-strain behavior of carbon-fibre-reinforced plastic (CFRP) is investigated and it is shown that the material is nonlinear elastic up to failure.
Abstract: 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.
15 citations
TL;DR: In this article, a simple relation was developed for the plane strain rotation moduli for blocks of soft elastic material bonded to rigid end plates, and the deformation arises when one plate rotates relative to the other plane about an axis along the centre of its width.
Abstract: Making assumptions similar to these used to obtain compression moduli, a simple relation is developed for the plane strain rotation moduli for blocks of soft elastic material bonded to rigid end plates. The deformation arises when one plate rotates relative to the other plane about an axis along the centre of its width. The approximate theoretical solution compares well with finite-element analysis data for materials with Poisson's ratios of 0.333, 0.483 87 and 0.499 83 and blocks having width-to-thickness ratios between 0.25 and 64.
14 citations
TL;DR: 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.
Abstract: 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.
13 citations
TL;DR: In this paper, the static analysis of an annular disc with a clamped inner boundary and a concentrated, in-plane load at the outer boundary is presented, and the singularity associated with the concentrated load is isolated and the resulting non-singular problem is solved by the method of complex potentials.
Abstract: 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.
TL;DR: In this article, a simplified, two-dimensional, mathematical model of a coupling between flexible beams is solved by a Legendre expansion procedure, and its main application is in the field of arthroprostheses.
Abstract: A simplified, two-dimensional, mathematical model of a coupling between flexible beams is solved by a Legendre expansion procedure. Its main application is in the field of arthroprostheses.
TL;DR: In this paper, closed-form solutions and stress-concentration data were obtained for a sector of an annular plate subjected to moments and transverse forces on its radial edges.
Abstract: 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.
TL;DR: In this paper, an alternating-current electrical-potential system for measuring crack growth is described, where the positions of the current supply and potential sensing leads can be optimized using two-dimensional finite-element and boundary integral equation methods.
Abstract: This paper describes an alternating-current electrical-potential system for measuring crack growth that is more sensitive than a corresponding direct-current system and which is capable of a discrimination in crack length of approximately 20 μm. It shows how the positions of the current supply and potential sensing leads can be optimized using two-dimensional finite-element and boundary integral equation methods. Both methods give calibrations which are in good agreement with optical measurements of crack growth and with measurements made using a graphitized electrical analogue paper technique. The boundary integral equation approach is shown to he the more efficient to use for a range of geometries, since it is only necessary to specify the shape of the boundary and redundant information at internal nodes need not be obtained.
TL;DR: In this paper, a nondestructive photoelastic technique, requiring integrated retardation and scattered light measurements, is used for the determination of thermal stress concentrations in hollow cylinders with an internal and an external curcumferential groove, subjected to a steady-state radial temperature gradient.
Abstract: A non-destructive photoelastic technique, requiring integrated retardation and scattered-light measurements, is used for the determination of thermal stress concentrations in hollow cylinders with (i) an internal and (ii) an external curcumferential groove, subjected to a steady-state radial temperature gradient.
TL;DR: A method of measuring structural vibrations by using an accelerometer in conjunction with a specially designed signal processor is described, using a pedestrian footbridge and a typical industrial floor as illustrations.
Abstract: 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.
TL;DR: In this paper, 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.
Abstract: 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.
TL;DR: In this article, 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.
Abstract: 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.
TL;DR: In this article, a semi-graphical method is presented for the determination of the St Venant torsion constant and maximum shear stress in a prismatic bar of any solid cross-section, intended for use in the trial and error process of design.
Abstract: A semi-graphical method is presented for the determination of the St Venant torsion constant and maximum shear stress in a prismatic bar of any solid cross-section, intended for use in the trial-and-error process of design. Comparison is made with standard results for a wide range of shapes of cross-section.
TL;DR: In this article, the effect of die angle, friction and reduction on the ironing process is discussed and the limitations of the slab method for the calculation of the load are outlined.
Abstract: 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.
TL;DR: In this article, a method of concentric Mohr's circles for correcting transverse sensitivity errors in bonded resistance strain-gauge readings in a biaxial stress field is explained and its use illustrated.
Abstract: A method of concentric Mohr's circles for correcting transverse sensitivity errors in bonded resistance strain-gauge readings in a biaxial stress field is explained and its use illustrated. A coaxial gauge pair with one element of negative and one of positive transverse sensitivity is proposed for corrected evaluation of readings.
TL;DR: The view, that competence in the use of a finite-element package takes the sting out of structural design, pales when it is realized that the true role of the stress analyst is to create simplified models of the engineering problem and to use the solutions of the model problems, accurate or otherwise, as a basis for predicting the behaviour of the real.
Abstract: In recent years, the finite-element method has come into widespread use as a tool for the structural design engineer. Of course, in its infancy, it met with considerable opposition from a broadly traditionally-minded engineering profession but, with the ready availability of powerful digital computers, two factors were of overriding importance in its acceptance. Firs.tly, such is the power of the method to furnish an accurate solution to a large class of engineering structural problems, involving considerable geometrical complexity and varying load types, that many design programmes, which formerly required the design, manufacture and testing of several prototypes before a satisfactory design could be achieved, can now be effected with the production and test of a single prototype; the iteration to a satisfactory design being carried out purely on numerical models. The saving on expense and time has frequently been considerable. Secondly, again because of the powerful modelling capacity and the availability of adequate computer power, much simpler design problems can be solved reliably, quickly, and at low unit cost. In either case, market forces compel a manufacturer to adopt a finite-element approach once it has made significant inroads into his product area. Not unnaturally, the dramatic achievements of the method have led to a certain air of euphoria and to the not uncommon belief of the newcomer that, not only is the method omnipotent, but a passing knowledge of the use of some finite-element package will reduce most structural problems to banality. Nothing could be further from the truth. While the finite-element method is, in principle, capable of solving accurately a very large class of structural problems its ability to d o so in practice is limited by economic considerations and by the user’s ability to specify the given problem adequately. Thus, while simple two-dimensional static problems are economically feasible, three-dimensional, dynamic and nonlinear problems are all, usually, prohibitively costly. Furthermore, in many cases, particularly those involving plasticity or creep, adequate experimental constitutive data are not available so that accurate models just cannot be created. The view, that competence in the use of a finite-element package takes the sting out of structural design, pales when it is realized that the true role of the stress analyst is to create simplified models of the engineering problem and to use the solutions of the model problems, accurate or otherwise, as a basis for predicting the behaviour of the real
TL;DR: In this paper, a computer program is developed to undertake the elastic stress analysis of a limpet-coil vessel consisting of a cylindrical shell and part-circular coils, when the coils are at a different average temperature to that of the main shell.
Abstract: A computer program is developed to undertake the elastic stress analysis of a limpet-coil vessel consisting of a cylindrical shell and part-circular coils, when the coils are at a different average temperature to that of the main shell.Results of the analysis are used to present data on maximum stresses for a wide range of practical geometries for the vessel.
TL;DR: In this article, the equations governing the torsion of a prismatic bar of visco-plastic material with Bingham characteristics were derived and solved using the pseudo-functional finite-element method.
Abstract: The equations governing the torsion of a prismatic bar of visco-plastic material with Bingham characteristics are derived and solved using the pseudo-functional finite-element method. Results are presented for a square bar, in the form of stress trajectories, for Bingham numbers of 2.0 and 0.33.