Showing papers in "Strain in 1979"

Optimised inner boundary shapes in circular rings under diametral compression

Abstract: Using a method developed by the authors, the configuration of the inside boundary of circular rings, subjected to diametral compression, has been optimised, keeping cleared the space enclosed by the original circular inside boundary The range of diameters studied was 033ID/OD07 In comparison with circular rings of the same ID/OD, the stress concentrations have been reduced by about 30%, the weight has been reduced by about 10% and coefficients of efficiency of about 0–96 have been attained The maximum values of compressive and tensile stresses on the edge of the hole, are approximately equal, there are practically no gradients of stress along the edge of the hole, and sharp corners exhibit zero stress The geometries for each ID/OD design are given in detail

Separation of principal stresses in photoelasticity by means of a computer

Abstract: It is shown that a separation of principal stresses with different types of experiments using computers is more valid and economical for methods based on the condition of compatibility than for those based on the conditions of equilibrium. This means that first the sum of the principal stresses is determined which combined with their differences gives their values separately. In this method several equations are used of the finite difference type and all can be solved by means of an iteration procedure in computer program form.

Interactive control for an automatic polariscope

Abstract: The problems of interpreting and analysing photo-elastic data have deterred non-specialists from making use of this technique when undertaking detailed design studies. Practical difficulties in understanding complex fringe patterns and in making the necessary optical measurements with sufficient precision have implied that considerable experience is necessary to obtain reliable stress values at internal points or across critical sections. By interconnecting two minicomputers it has been possible to develop an interactive polariscope control system which will allow the design engineer, with minimal prior knowledge of photoelastic techniques, to employ relatively sophisticated methods for evaluating the stresses in both two and three dimensional models. The data acquisition sequence involves new procedures for determining both the isoclinic angle and the isochromatic fringe number, and the interactive nature of the control system allows the desired analysis to proceed in response to the replies to a series of simple questions posed by the machine. The application of the system will be illustrated by examples of its use to determine boundary stresses at critical locations, where the high stress gradient presents problems, and in evaluating the separate stress components across the critical section of a grooved cylindrical rod.

Stress distribution around holes in wedges

Abstract: This paper deals with the study of stress distribution around holes in wedges. Ling and Hsu have reported a theoretical analysis for an infinite wedge of uniform thickness and variable depth (with a circular hole), using stress functions. In the present investigation, a large number of electrical resistance strain gauges of small gauge length (3 mm) were used for obtaining the distribution of stresses in a cantilevered wedge of uniform thickness and variable depth, with a circular hole subjected to end loading. The wedge was made of perspex. The results obtained indicate a maximum stress concentration factor of 1.7 using Timoshenko's method of calculating the nominal stress in the wedge at the hole boundary (using his theory of calculating stresses in a wedge without a hole). The experiments on the cantilevered wedge indicate a lower stress-concentration factor compared with the results obtained theoretically by Ling and Hsu for an infinite wedge. In addition to vertical loading, stress distribution with a load inclined to the vertical was also obtained.

An investigation of the dynamic and static stresses in universal bearing H-piles

Abstract: As part of continuing research on steel bearing piles, an investigation was carried out by British Steel Corporation in an attempt to gather data which will illuminate the areas of contention for limiting stress levels to be raised, thereby allowing economies to be made and customers' confidence to be increased in selecting steel bearing piles for a particular application. To assess the characteristics of dynamic and static loading, a strain gauge measurement technique was used. Blow by blow stress analyses were carried out. In total 700 blows were examined. The full record of 700 blows and static observations can be obtained from The We/ding Research Department, of BSC's Teeside Laboratories, Middlesbrough. The results reveal that during the course of driving the pile through hard strata, the impact stresses were 0.6 to 0.7 times the minimum yield stress, at the last blow. These impulsive stresses had no discernable effect on the structure of the piles. Results obtained suggest that considerable increase in design stresses might safely be adopted for steel bearing piles. One of the aims of this long term research is to produce a dynamic testing system which gives more accurate results than can be obtained from traditional methods.

A three dimensional photoelastic study of the stress distributions in double helical epicyclic gears

Abstract: This paper reports on part of a research programme which was carried out using two- and three-dimensional photoelastic model techniques in order to analyse the stress distributions in a double-helical epicyclic gear design incorporating typical features of production gear units. The paper describes the testing of two three-dimensional models, one subjected to torque loading, i.e. tooth forces; the other to combined rotational and torque loading. Note is made of some of the problems inherent in the design and loading of complex models such as those used in the tests and of the solutions developed to overcome the difficulties. Attention is devoted to the analysis of contact loads and load distribution, maximum sub-surface stresses, maximum root fillet bending stresses and the geometry of the lines of contact. General conclusions are drawn and an indication given of the subsequent extensive two-dimensional test programme which was carried out.

Determination of intensity factors at an arched crack tip by the method of caustics

Abstract: Perpendicular sections of caustic surfaces reflected by the constrained zone around the tip of an arched crack in a perspex plate under plane tension, were measured and analysed. The experiments corroborated the theory, the Theocaris' method of Caustics and also show that the intensity factors are functions of the curvature of the crack and the subtended angle.

Simplification of the axisymmetric photoelastic problem

Abstract: The axisymmetric photoelastic problem is reformulated in such a way that data taken from only the meridional plane is sufficient to obtain a solution.

An image‐Moiré method for the direct determination of partial slopes in fixed plates

Abstract: A new image-Moire method yielding directly the partial slope distribution in bent plates is proposed. The fringes are formed by the interference between the grating on the front face of a transparent plate with its reflected image through it on the other face. In illustration of the applicability of the method, results for a centrally loaded simply supported circular plate are presented.

Deflection measurement of a cantilever plate by holographic interferometry

Abstract: Holographic interferometry has been applied to the analysis of a square cantilever plate subjected to a corner load. Whole field deflections were obtained from a reconstructed hologram and compared with theoretical results. Good agreement was obtained indicating thereby the precision with which even complicated structural engineering problems can be solved using the holographic technique.

A technique to determine the load distribution in human feet

Abstract: The human foot supports the body weight at 11 points on the foot, namely the five toes, the five metatarsal heads and the heel. The need arose to determine the load carried by each of the 10 load bearing points on the forefoot. A rig developed to satisfy this need is described, together with typical results obtained. The load distributions of a total of 44 ‘clinically normal’ feet were obtained and a statistical presentation is given which results in the definition of a ‘normal’ load distribution.