Showing papers in "Strain in 1992"
TL;DR: A survey of the stress separation techniques available with a view to incorporating the most suitable method into an automated full field polariscope can be found in this paper, where the authors provide a survey of different techniques for stress separation.
Abstract: Current developments in the automation of photoelastic analysis have enabled the fast and accurate collection of the isochromatic and isoclinic parametersl from photoelastic specimens. Since the isochromatic parameter yields the difference in the principal stresses then a suitable procedure has to be used for their separation. This paper provides a survey of the stress separation techniques available with a view to incorporating the most suitable method into an automated full field polariscope.
24 citations
TL;DR: In this paper, the ratchetting behavior of pipe components under internal pressure and simulated seismic loading has been investigated using special fixtures and a standard laboratory universal testing machine fitted with a fatigue module.
Abstract: The ratchetting behaviour of piping components under internal pressure and simulated seismic loading has been investigated using special fixtures and a standard laboratory universal testing machine fitted with a fatigue module. Experimental arrangements are presented for testing plain pipes with or without thinned sections, elbows and tee branch junctions under in-plane dynamic bending; similar fixtures and arrangements could be used for reducers and flanged connections and other types of loadings. Input accelerations up to 5g have been achieved and the results demonstrate that a great deal can be learnt about piping component behaviour from such simple arrangements and without resorting to sophisticated or expensive experimental techniques. The necessary instrumentation and algorithms for the analysis of results are described. Some sample results are included and discussed in terms of overall piping component behaviour. Two recommendations are suggested to more realistically simulate typical earthquake input spectra.
13 citations
TL;DR: In this article, a large scale model analysis using embedded strain gauges of the strain distribution in the cement mantle surrounding a femoral prosthesis is underway, where a loose fitting rectangular steel insert inside a surrounding rectangular epoxy sheath was used to model an extreme case of the torsional and bending components of hip joint load.
Abstract: A large scale model analysis, using embedded strain gauges, of the strain distribution in the cement mantle surrounding a femoral prosthesis is underway. In order to predict, and so avoid, positions of locally high strain gradients in this model, a finite element and experimental analysis of a similar problem was undertaken. For this purpose, a loose fitting rectangular steel insert inside a surrounding rectangular epoxy sheath was used to model an extreme case of the torsional and bending components of hip joint load. The axial component of joint load was modelled using an axisymmetric finite element model of a tapered shaft. The finite element results were used to determine suitable positions for embedding gauges in the experimental model. Results showed that the finite element analysis failed to adequately model the close sliding fit between the steel insert and epoxy. Altering the experimental model to artificially replicate the finite element contact conditions produced good correlation in bending, with experimental strains agreeing with simple bending theory to within 6%. Satisfactory correlation under torsional loading was not obtained, but strain magnitudes were low. Predicted positions for embedding gauges give conservative results, lessening the possibility of strain gradient induced error in the large scale model test of the cement mantle and prosthesis.
11 citations
TL;DR: In this article, the reliability of calibration constants derived from finite element calculations, the choice of basic stress calculation formulations, and methods used to compute the residual stress variation with depth from the specimen surface are discussed.
Abstract: A recent paper by H L Pang and S R Pukas1 touched on some important aspects of non-uniform residual stress measurement by the hole drilling method. This note discusses three significant issues raised in that paper, and presents a dissenting viewpoint. The three issues concern: the reliability of calibration constants derived from finite element calculations, the choice of basic stress calculation formulations, and methods used to compute the residual stress variation with depth from the specimen surface.
10 citations
TL;DR: In this article, a theoretical and photoelastic static contact stress analysis was performed on the design of the plastic tibial plateau in an orthopaedic knee prosthesis, which was based on a review of existing theoretical analyses concerned with the contact mechanics of layered elastic systems.
Abstract: This study is based on a theoretical and photoelastic static contact stress analysis, relevant to the design of the plastic tibial plateau in an orthopaedic knee prosthesis. It involves the review of existing theoretical analyses concerned with the contact mechanics of layered elastic systems and, where possible, the validation of any relevant findings using two dimensional photoelasticity. Significant findings include the identification of a general minimum recommendable design thickness for the plastic tibial plateau, the endorsement of using the Hertzian contact theory to predict contact stress levels in the tibial plateau of certain knee implants and the slight improvement in contact conditions in the plastic when the plateau is perfectly bonded to its supporting metal tray.
6 citations
TL;DR: In this paper, a semi-empirical model for the evaluation of the critical sections of the interlock tube as it responds to the overall pipe loading and configuration is presented. Results of a finite element analysis and radiographic tests are incorporated to verify and supplement the model.
Abstract: Interlock tubes are one of the key structural layers of most flexible pipes of composite construction for offshore oil and gas transmission and water injection applications. The design and manufacture of such a tube based on a good understanding of its deformation mechanics are undoubtedly of significance to the integrity and safety of flexible pipes and pipe systems. This paper describes a semi-empirical model for the evaluation of the deformations in the critical sections of the interlock tube as it responds to the overall pipe loading and configuration. Results of a finite element analysis and radiographic tests are incorporated to verify and supplement the model.
5 citations
TL;DR: In this article, a new method for the measurement of three dimensional residual stresses in a multi-pass butt welded joint is presented, which involves measuring the strain changes at a through hole surface as a coupon of material with the hole is separated from the body of interest and split.
Abstract: In this paper, a new method for the measurement of three dimensional residual stresses in a multi-pass butt welded joint is presented. The method involves the measurement of strain changes at a through hole surface as a coupon of material with the hole is separated from the body of interest and split. The finite element calculations are used to relate the strain changes at the measurenent points to the initial residual stresses at the hole location. The accuracy of the method is demonstrated by using it to measure a known stress field in a bent beam. The method has been used to measure the through thickness distribution of three dimensional residual stresses in a multi-pass butt welded joint. It could also be applied to the measurement of residual stresses in other welded joints.
4 citations
TL;DR: Gauge heating effects were examined for the case where an electrical resistance foil gauge is bonded to a low thermal diffusivity material in this paper, and the effectiveness of a temperature compensating gauge, the influence on localized creep and relaxation behaviour in the material and the relative order in which the bridge is energized and the testpiece loaded.
Abstract: Gauge heating effects were examined for the case where an electrical resistance foil gauge is bonded to a low thermal diffusivity material These include i) the effectiveness of a temperature compensating gauge, ii) the influence on localized creep and relaxation behaviour in the material and iii) the relative order in which the bridge is energised and the testpiece loaded Calculated temperature distributions are confirmed from experiment This has enabled recommendations to be made for the allowable specific power corresponding to a given temperature rise in a gauge grid of known configuration © 1992 Blackwell Publishing Ltd
3 citations
TL;DR: In this article, an experimental technique developed for the establishment of the basic fatigue characteristics of interlock tubes is presented, which can be used to obviate the necessity for expensive full scale composite pipe testing, provided that an accurate description of the loading conditions imposed on components of the composite is available.
Abstract: An interlock tube, usually made of stainless steel, is one of the key structural components for both bonded and unbonded flexible pipes of composite construction. The fatigue performance of this component is an important factor in determining the long term integrity of the entire pipe.
This paper presents an experimental technique developed for the establishment of the basic fatigue characteristics of such interlock tubes. Details of the fatigue testing method, the specimen design, preparation and calibration procedures will be described in conjunction with tests carried out on 254 mm interlock tube samples.
One of the most important results from this work is that, by careful design and machining of the specimen, the mode of failure seen in full scale pipe samples can be reproduced on small specimens in a laboratory using a fatigue machine. The significance of this is that it is possible to obviate the necessity for expensive full scale composite pipe testing, provided that an accurate description of the loading conditions imposed on components of the composite is available.
2 citations
TL;DR: In this article, a simple technical device has been proposed suitable for exercising strain gauge measurements in introductory courses in tensometry, which is followed from a theoretical strain analysis of the circular thin steel plate loaded by a concentrated central force.
Abstract: A simple technical device has been proposed suitable for exercising strain gauge measurements in introductory courses in tensometry. Its conception has followed from a theoretical strain analysis of the circular thin steel plate loaded by a concentrated central force. The analysis has taken into account a non linearity of the studied strain field and has used a strain tensor for original expression of Poisson's ratio and Young's modulus of the material of the plate. The derivation of analytic expressions of both these constants enabled one to estimate their values by means of the strain gauge measurements. In this way the proposed device demonstrates further application possibilities of the strain gauge method.
2 citations
TL;DR: In this article, an electric discharge machining (EDM) technique was used to obtain a stress free sample from the bulk material and compared to annealing heat treatment method for obtaining a stress-free sample, it was found that the EDM technique does not cause the changes of the structures and machining properties of the parent material.
Abstract: This paper aims at the improvement of the accuracy of the centre hole method of residual stress measurement by reducing the error caused by the drilling itself. Based on the results of an intensive experimental investigation, a new approach is proposed for the determination of the induced drilling stresses caused by the mechanical drilling process. In this study, the electric discharge machining (EDM) technique was utilised to obtain a stress free sample from the bulk material. As compared to the annealing heat treatment method for obtaining a stress free sample, it was found that the EDM technique does not cause the changes of the structures and machining properties of the parent material. Thus, the induced drilling stresses in centre hole method can be evaluated more accurately by using a stress free sample obtained by EDM technique than by using an annealed one.
TL;DR: In this paper, a calibration procedure for strain gauges under cyclic, four point bending was presented. But the calibration procedure was not applied to the elastic and plastic components of strain.
Abstract: A plastic sensitivity calibration procedure is outlined for strain gauges under cyclic, four point bending. Tests show that the gauge resistance changes in an approximately linear manner with longitudinal strain for the first quarter cycle of loading. Calibration curves for subsequent reversals to the direction of deformation display zero-shift and non-linearity. Under balanced strain cycling, there is evidence of a cyclically-stable, sensitivity calibration loop. Theoretical considerations are given in which it is proposed that separate sensitivity factors apply to the elastic and plastic components of strain. It is shown that the plastic sensitivity factor is a function of (i) plastic strain induced hardening and softening in the gauge foil and (ii) any apparent change to the gauge resistivity due to imperfect bonding. The elastic component sensitivity factor equals the manufacturer's value only in the absence of hardening. The two sensitivities may be combined to give a total sensitivity factor when a post-yield strain gauge suffers elastic-plastic straining.
TL;DR: In this paper, the basic relations in linear isotropic photoviscoelasticity have been discussed theoretically in detail and a new routine to solve the time dependent principal stress without the measurement of isoclinics has been found.
Abstract: In this paper the basic relations in linear isotropic photoviscoelasticity have been discussed theoretically in detail. A new routine to solve the time dependent principal stress without the measurement of isoclinics has been found. As a proof of the method, examples are illustrated at the end of this paper.
TL;DR: In this article, a straightforward method is described whereby the magnitudes and directions of the principal stresses and strains in two or three dimensions may be derived using the matrix methods of elementary linear ulgebra.
Abstract: A straightforward method is described whereby the magnitudes and directions of the principal stresses and strains in two or three dimensions may be derived using the matrix methods of elementary linear ulgebra. The ideas are extended to simplify the classical derivation of the extreme values of shear stress and of the octahedral stresses. After a description of several visual aids, the work concludes with a definition of the von Mises yield surface consistent with the foregoing procedures.
TL;DR: In this article, a retrographic imaging method was developed which uses retroreflected light for visualising minute irregularities in reflective opaque surfaces, and the experimental setup required for such imaging, and an experiment was devised to determine how this type of imaging can be correlated to actual surface topography.
Abstract: A new experimental method called retrographic imaging has been developed which uses retroreflected light for visualising minute irregularities in reflective opaque surfaces. This paper provides a qualitative explanation of this phenomenon, the experimental setup required for such imaging, and describes an experiment which was devised to determine how this type of imaging can be correlated to actual surface topography. Results indicate that grey level intensity is proportional to an average between the surface contour and its rate of change of slope.
TL;DR: In this article, the authors present a balanced view of the role of experimental stress analysis, identifying areas where there are clear benefits and concluding comments regarding education, training and vocational qualifications.
Abstract: A key requirement for most engineered items is the ability to withstand the various loads that may be applied under conditions of use and of abuse that may reasonably be foreseen. To ensure that the strength requirement is satisfied, the designer must evaluate the levels of applied stress using appropriate calculation methods or by physical experiment. This paper considers the respective roles of computational and experimental methods of stress analysis, discussing the impact of changes in functional capability. Reference is made to the modern certification environment and the requirements of quality assurance, particularly related to the training of engineers and technicians in the necessary skills.
The paper aims to present a balanced view of the role of experimental stress analysis, identifying areas where there are clear benefits. Some concluding comments are made regarding education, training and vocational qualifications.