Showing papers in "Strain in 1998"

Determination of material constants in creep continuum damage constitutive equations

Abstract: Experimental creep and creep rupture data are presented for copper at 150, 200 and 250°C and for 0.5Cr0.5Mo0.25V steel at 640°C. Creep continuum damage constitutive equations have been shown to be capable of accurately representing the creep behaviour of both materials. A six variable optimisation program, which was developed to efficiently obtain the material constants, is described.

Measurement techniques for buckling sensitive composite shells

Abstract: This paper describes a measurement system that was developed for an experimental study on buckling of glass reinforced composite cylinders. An automated non-contact laser device operating inside the test specimen provided a three dimensional scanning system for measuring the deformation of the shell wall. The measurement system was used to obtain the initial geometric imperfections, as well as the deformation under varying control axial displacement. All loading and data acquisition operations were carried out using advanced computer controlled techniques. Due to the large number of measurements undertaken in each test, data collection was followed by processing and reduction techniques, thus delivering the data in a form suitable for finite element analysis and comparative studies. Typical results are presented in order to demonstrate the reliability, accuracy and versatility of the system.

Optically enhanced tiling (OET) in digital fringe pattern analysis

Abstract: In digital fringe pattern analysis information is usually lost in high fringe density zones due to digitisation and quantisation errors. A generic approach namely optically enhanced tiling (OET) is presented to construct a composite picture from multiple optically zoomed images. The procedure is explained with the help of the problem of data acquisition in digital photoelasticity using phase shifting technique.

Phase shifting method for retroreflective grating analysis

Abstract: A phase shifted retroreflective grating system has been presented for measuring the derivative and contour of quasi flat specular surfaces. The system has been tested with a small indent of maximum depth less than 10 microns. The experiment shows that the system can tell the defect size, shape and polarity (indent/outdent). The method can be developed for industrial application in nondestructive testing and evaluation(NDTE).

Factors affecting the intensity distribution in high stress gradient zones in digital photoelasticity

Abstract: In digital photoelastic analysis it is observed that in high stress gradient zones the fringes become brighter. It leads to erroneous results, if not accounted for, in those techniques which use quantitative values of intensity to evaluate the experimental parameters. In this note, the reasons for the above phenomenon is investigated and suitable recommendations are given.

Theoretical design of calibration beams for strain gauge factor measuring apparatus

Abstract: By starting with theoretical analysis and combining with the needs of practical applications, this article carries out a preliminary theoretical investigation of optimum design of the cross sectional shape and dimensions of calibration beams for strain gauge factor measuring apparatus. A new formula is derived in this paper that shows the quantitative relationship among strains on the beam surfaces, the strain non-uniformity within a certain range of the beam and beam thickness, which provides a theoretical basis for the accuracy improvement of the measuring apparatus and for correct application of the calibration beams, and also for drawing up and improving items concerning with calibration beams in strain gauge standards internationally. It is proven through experiments that the neutral axis of the bent calibration beam of rectangular cross section under pure bending moments is actually not circular but parabolic.

Experimental analysis of acrylic models

Abstract: Strain gauge application has been used to study the mechanical behaviour of shell models. Application has been made directly to acrylic devices designed by means of the homeostatic model technique. The testing procedure of one such model made with the aim of assessing the anticipated membrane status is detailed. This has resulted in an interesting experience of strain gauge application to this type of material.

A hybrid approach to the compliance testing of training shoes

Abstract: There is, as yet, no totally rational method for testing training shoes. The situation is complicated by the coupling that exists between the physical characteristics of the shoes and the biomechanical response to them. This paper sets out to establish a basis for the physical aspects of testing, and shows how the biomechanical response may be integrated into a suitable model. The basic assessment of the compliance properties of training shoes was carried out by the measurement of load-deflection curves. The analysis of these curves was based on the McMahon/Green two mass, two spring model of limb-ground interaction, which defines the tangent modulus of the load-deflection curve as the relevant quality parameter. For a selection of 30 shoe types, the load-deflection curves were analysed to show how a systematic approach may be developed to understanding the variances in the shoe characteristics. It has also been shown how these findings may in part explain why running shoes which have apparently widely differing load-deflection characteristics have been found to perform rather similarly insofar as the measured level of ground reaction is concerned.

The design of advanced aircraft structures to resist acoustic fatigue; work in progress

Abstract: Details of the current research activities in the Department of Aeronautics and Astronautics, on the response of advanced aircraft structures to acoustic loading, are presented. Both box type and sandwich structures, employing aluminium alloy, carbon fibre reinforced plastic, and GLARE composite materials, are being investigated. In order to develop design guidelines for these complex structures, it is necessary to combine theoretical predictions, using the finite element method, with experimental measurements of the structural response to random acoustic loading. Both types of structure will be tested in the Progressive Wave Tube facility at Southampton. In addition, it is hoped that a more comprehensive damping guide will be produced for the type of structure used in advanced aircraft design.

Modelling of unbounded media for fluid‐structure interaction applications ‐ a review

Abstract: Many structures used at sea must be able to withstand the occasional extreme weather conditions and the risk of underwater explosions. This applies not only for military ships and submarines but also for tankers and civil exploration and extraction platforms. An understanding is therefore required of the effects of shock induced water waves and unbounded fluid-structure interaction on floating and submerged structures. For modelling purposes these structures may be considered as a system of five components: the structure itself, any fluid within it, the surrounding fluid including the effects of cavitation, the farfield fluid medium and the effect of shock waves. The first two are sufficiently well understood, the remaining three are the subject of continuous research. Recent developments have created new possibilities for treating the farfield fluid medium. Hence, this paper which discusses the various methods used in the modelling of this problem.

Laminated beams subjected to transverse load

Abstract: A simple elastic solution has been developed for predicting the shear stress distribution in a laminated beam subjected to a variety of transverse loading conditions. Photoelastic tests on composite models involving a single bonding layer have been used to validate the theory, and also to comment upon the significance of these results in interpreting the interlaminar shear strength and bending modulus of the simplest form of laminated strip.

Shear stress distribution on a solid circular plate embedded in an elastic halfspace

Abstract: The present investigation deals with the analysis of an axisymmetrically loaded elastic halfspace containing a solid circular plate. The elastic halfspace and the embedded plate has been idealised together as a layered system. Layered theory has been used to determine the shear stress distribution on the embedded plate. Results have been presented for the shear stress distribution on the embedded plate for different values of the relative rigidity parameter.

Experimental analysis of surgically corrected knee joint

Abstract: Holographic interferometry, speckle photography and photoelasticity have been employed in the experimental investigations of the knee joint in four conditions -anatomically normal joint, varus joint, joint after Coventry popliteal osteotomy and joint after correction made using a new variety of the Coventry procedure 1 . The studies included the investigations of the displacements of the bone in the sagittal plane, the displacements of points on the bone 's surface in the frontal plane and the three dimensional state of stress. The obtained results show to what degree changes in the lower limb geometry affect the knee joint and in particular, its stability, functionality and the way in which it carries loads.

Evaluation of stress intensity factor under pure shear stress in orthotropic material

Abstract: Various types of composite materials are currently being developed and used for automobiles, airplanes, ships and other structures in response to required service conditions which are getting increasingly more severe. Of growing importance under such circumstances is the study of stress analysis and fracture mechanics for these composite material structures. Particularly, the primary concern in design of structures and machines should be the initiation of cracks due to excessive deformation, delamination in material or other material defects. In evaluating safety, it is indispensable from the structural design point of view that K value should be known by an analysis conducted in advance. In this study, stress intensity factor (mode II) under a pure shear stress was obtained using the photoelastic method and caustic method and applying an isotropic material and orthotropic material (copper fibre epoxy composite (CFEC) developed by the authors), each containing the crack. Results were compared with theoretical values. As a result, this method was found useful and the effect of the direction of the primary axis of this material on the stress intensity factor was clarified.

Splice jointing behaviour in glulam portal frames

Abstract: The need for effective structural connections in glued laminated timber portal frames is discussed and the design of a flitch plate form of joint is outlined. Tests on the connection are described and its performance under flexure and shear is assessed. The influence of glueline thickness on joint performance is examined.

Symbolism and the bridge

Abstract: An account is given of the formation of a symbolic figure representing hope for the development of the human race and the ecosystem of which it is a part.