Papers by Keyword: Eigenstrain

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Authors: Alexander M. Korsunsky
Abstract: The sin2ψ technique for near-surface and bulk stress evaluation is frequently considered to be the method of reference, largely due to the historical reason of being established early on in the development of experimental study of residual stress, and due to the widespread availability of laboratory X-ray facilities equipped with goniometers allowing ψ-tilting to be carried out. In recent years other diffraction-based techniques of residual strain and residual stress evaluation have been developed, some of them based at large facilities such as synchrotrons, neutron reactors or spallation sources, and others becoming available in the laboratory setting. It is therefore perhaps relevant and timely to review the strengths and shortcomings of the sin2ψ technique in today’s context. In the present study this task is addressed through the use of polycrystal elasto-plastic modelling that allows the determination of equivalent average elastic lattice strains following complex deformation history, and by post-processing of the model results in order to extract the parameters measurable in diffraction experiments. In particular, it is possible to extract the simulated strain values that would be measured at different tilt angles, and to build a family of sin2ψ plots for different reflections. It then becomes possible to assess the degree to which the hypotheses underpinning the principle of this method are enforced or violated; to select the most suitable reflections; and to discuss how the method could be improved or varied to provide more reliable residual stress measurement procedures.
Authors: Min Yu, You Wen Liu
Abstract: The interaction between a screw dislocation and a reinforced lip-shaped crack embedded in an infinite matrix subjected to a remote longitudinal shear load is investigated in this paper. By combining the sectionally holomorphic function theory, Cauchy singular integral, singularity analysis of complex functions and Riemann boundary problem, the problem is reduced to solve an elementary complex potentials equation. The general expressions of complex function in the matrix and the reinforcement layer are derived explicitly in series form for the case when the screw dislocation is located in the matrix. The image force acting on the screw dislocation and the stress intensity factor are also calculated. Some numerical results are provided to discuss the effects of dislocation position, material parameters, geometric configurations and eigenstrain on the image force.
Authors: Tea Sung Jun, Fabio Rotundo, Lorella Ceschini, Alexander M. Korsunsky
Abstract: Linear friction welding (LFW) is a solid state joining process for bonding of two flatedged, complex geometry components through relative reciprocating motion under axial (compressive) forces. Although the proof of principle has been obtained some time ago, recently a number of studies have been published aimed at optimising the joining operations to obtain best joint strength and reduced distortion and residual stress. The present paper is devoted to the study of linear friction welds between components made from aluminium alloy 2124 matrix composite (AMC) reinforced with 25vol% particulate silicon carbide (SiCp). Neutron diffraction was used to measure interplanar lattice spacings in the matrix and reinforcement, and to deduce residual elastic strains and stresses as a function of distance from the bond line. Significant asymmetry is observed in the residual stress distribution within the two components being joined, that may be associated with the difference in the microstructure and texture.
Authors: Shu Yan Zhang, Jordan Schlipf, Alexander M. Korsunsky
Abstract: A traditional approach to increasing fatigue resistance of many assemblies involves the creation of regions of compressive residual stress. For example, riveting holes used in modern passenger aircraft are currently subjected to cold expansion using split mandrel tools. The method is relatively expensive and not entirely problem-free. In the present study we consider a method of creating residual stresses around drilled holes referred to as ‘dimpling’, that itself is a variation of a novel technique known as the StressWaveTM process. An experimental procedure is described for the creation of localised regions of significant plastic deformation and residual stress by ‘dimpling’, allowing the production of cold-worked and residually-stressed specimens. The overall aims of this study were to determine thickness-average residual stresses by two different techniques, namely, one destructive technique (Sachs boring) and one non-destructive (high energy X-ray diffraction); and to compare the results. In Sachs boring experiments the variation of strain gauge readings with increasing diameter of the central hole was recorded. A classical elastic-ideally plastic axisymmetric model for plane stress conditions was used in the analysis. Energy dispersive synchrotron X-ray diffraction experiments were performed for non-destructive assessment of residual elastic strains. The two different stress evaluation techniques used in this project led to consistent results. Good correlation was found between the stresses obtained from X-ray diffraction results and those deduced from Sachs boring experiments.
Authors: Stefano Coratella, M. Burak Toparli, Michael E. Fitzpatrick
Abstract: Residual stresses play a fundamental role in mechanical engineering. They can be generated by manufacturing processes or introduced purposely by surface treatment technologies. One of the most recent technologies developed to introduce residual stresses is Laser Shock Peening. Since it is a relatively expensive technology, a fundamental role is played by the Finite Element Analysis approach to predict the final residual stress profile. The FEA approach consists of either direct simulation of the LSP process or the application of the eigenstrain approach. The application of the eigenstrain theory in predicting residual stresses after LSP treatment in curved edges is the subject of this research.
Authors: Andrew M. Venter, O. Philip Oladijo, L.A. Cornish, Natasha Sacks
Abstract: Residual strains and stresses associated with the processing steps of the industrial high-velocity oxygen-fuel (HVOF) thermal spray technique, was non-destructively characterised in both the coatings and substrates. A range of substrates, having coefficients of thermal expansion different to that of the as-coated WC-Co material, have been considered to assess the potential role of the thermal misfit associated with the coating procedure. Surface and depth resolved studies of the in-plane and normal components of residual strains have been investigated by exploiting the penetrating capabilities of high energy synchrotron X-rays in conjunction with micron sized gauge volumes to enable strain gradient determination with high positional resolution. Results reveal the presence of large residual strain/stress mismatches at the interface region in all the substrate materials, whereas the strains/stresses in the as-coated material are small, seemingly independent of the substrate material. The different contributions due to the HVOF process are qualitatively assessed in terms of an eigenstrains (plastic deformation) approach.
Authors: Hai Wen Wang, Xue Jun Chen
Abstract: The interfacial stresses of a segmented Cr coating by the hybrid technique of laser pre-quenching steel substrate plus post-deposition have been investigated. The discrete laser quenched zones (LQZs) were modeled as multiple inclusions, each of which is embedded with a prescribed uniform eigenstrain. Based on the failure criterion of the adhesion strength, the interfacial stresses are considered to be responsible for interfacial debonding. The interfacial stresses were evaluated by using the finite element (FE) method. Dimensional analysis was utilized to identify the scaling variables affecting the stresses. The dependence of a range of dimensionless variables of interest on the interfacial stresses has been assessed through a detailed parametric study.
Authors: Xu Song, Solène Chardonnet, Giancarlo Savini, Shu Yan Zhang, Willem J.J. Vorster, Alexander M. Korsunsky
Abstract: The aim of the study presented here was to evaluate the residual stresses present in a bar of aluminium alloy 2124-T1 matrix composite (MMC) reinforced with 25vol% particulate silicon carbide (SiCp) using X-ray diffraction and 3D profilometry (curvature measurement using Mitutoyo/Renishaw coordinate measurement machine) and comparing these results with numerical models of residual strain and stress profiles obtained by a simple inelastic bending model and Finite Element Analysis (FEA). The residual strain distribution was introduced into the test piece by plastic deformation in the 4-point bending configuration. At the first stage of this study the elasticplastic behaviour of the MMC was characterized under static and cyclic loading to obtain the material parameters, hardening proprieties and cyclic hysteresis loops. Subsequently, synchrotron Xray diffraction and CMM curvature measurements were performed to deduce the residual stress profile in the central section of the bar. The experimental data obtained from these measurements were used in the inelastic bending and FEA simulations. The specimens were then subjected to incremental slitting using EDM (electric discharge machining) with continuous back and front face strain gauge monitoring. The X-ray diffraction and incremental slitting results were then analysed using direct and inverse eigenstrain methods. Residual stresses plots obtained by different methods show good agreement with each other.
Authors: Min Yu, You Wen Liu
Abstract: The paper is aim to investigate the interaction of a screw dislocation in strained reinforcement with a lip-shaped crack under remote longitudinal shear load using complex variable method of Elasticity. The exact solution of complex function of the matrix and the renforcement layer are obtain in series form; then, the expressions of stress field, image force and stress intensity factor of crack tip can be derived; finally, numerical disccusions are pesented and the results shows that the lip-shaped crack in reinforcement layer has interference effect on the interaction of dislocation and reinforcement layer, and the eigenstrain in x-direction has little effect on image force; however, the eigenstrain in y-direction has great influence on image force.
Authors: Adrian T. DeWald, Michael R. Hill
Abstract: This paper describes a method for extending the capability of the contour method to allow for the measurement of spatially varying multi-axial residual stresses in prismatic, continuously-processed bodies. Currently, the contour method is used to determine a 2D map of the residual stress normal to a plane. This work uses an approach similar to the contour method to quantify multiple components of eigenstrain in continuously-processed bodies, which are used to calculate residual stress. The result of the measurement is an estimate of the full residual stress tensor at every point in the body. The methodology is presented and the accuracy is assessed for a representative test case using a numerical experiment. Finally, a measurement is performed on a thick laser peened plate of 316L stainless steel to show that the approach is valid under real experimental conditions.
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