Papers by Author: Alexander M. Korsunsky

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Authors: Tan Sui, Si Qi Ying, Nikolaos Baimpas, Gabriel Landini, Alexander M. Korsunsky
Abstract: The dentine-enamel junction (DEJ) is an important biological interface between the highly mineralized hard out layer (enamel) and the comparatively softer tooth core (dentine) of teeth. The remarkable performance of this interface provides the motivation for investigation into the detailed structure and function of the DEJ. In this study, synchrotron X-ray diffraction measurements of the DEJ subjected to the in situ uniaxial loading were carried out to capture the structure-property relationship between the DEJ architecture and its response to the applied force. The knowledge of the architecture and properties of the natural DEJ will hopefully help in biomimetic engineering of superior dental restorations and prostheses, and the development of novel materials to emulate the DEJ.
Authors: Alexander M. Korsunsky, Karen E. Wells, Brian A. Shaw
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: Aghasi R. Torosyan, Jonathan R. Tuck, Alexander M. Korsunsky, Svetlana A. Barseghyan
Authors: D. G. Leo Prakash, Willem J.J. Vorster, Shu Yan Zhang, Alexander M. Korsunsky
Abstract: This paper presents a study of the residual strain field within a high pressure die cast (HPDC) AZ91 Mg alloy bar subjected to four point bending. The technique employed for this purpose is high energy synchrotron X-ray diffraction. Strain scanning using polychromatic X-ray beam allows the collection of multiple peak diffraction patterns and monitoring of small peak shifts as a function of beam position. These shifts allow collective interpretation in terms of the equivalent macroscopic residual elastic strain. Residual elastic strain distributions were studied in the sections subjected to pure bending and also in sections of contact between the sample and the rollers. These experimental results are compared with the predictions from a finite element analysis of contact and deformation. Good agreement is found between the modelled and measured results. It is hoped that these results help improved understanding of complex deformation behaviour of thin-walled HPDC AZ91 components and provide useful background information for lifing assessment of such structures.
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: Lorella Ceschini, Alessandro Morri, Fabio Rotundo, Tea Sung Jun, Alexander M. Korsunsky
Abstract: The aim of the present work is to evaluate the possibility of using the Linear Friction Welding (LFW) technique to produce similar and dissimilar joints between a 2024 Al alloy and a 2124Al/25vol.%SiCP composite. In this solid state joining process the bonding of two flat edged components is achieved through frictional heating induced by their relative reciprocating motion, under an axial compressive force. Microstructural characterization of the welds was carried out by optical and scanning electron microscopy, to investigate the effect of LFW both on the aluminium alloy matrix and the reinforcement particles. The mechanical behaviour of the welded specimens was studied by means of hardness and tensile tests. The mechanisms of failure were investigated by SEM analyses of the fracture surfaces. LFW joints in MMCs resulted substantially defect free, with a uniform particle distribution, while a partial lack of bonding at the corners was observed in the others welds. The hardness decreased by approximately 10% in the welded zone, with some data fluctuations due to the complex microstructural modifications introduced by the LFW process. The joint efficiency, evaluated in respect to the UTS, was 90% for the Al alloy joints and 80% for the MMC joints. A decrease in the elongation to failure was measured in all the LFW specimens, probably related to the orientation of the plastic flow in the TMAZ, where the fracture generally occurred.
Authors: Alexander M. Korsunsky, Karen E. James
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: Daniele Dini, Alexander M. Korsunsky, Fionn P.E. Dunne
Abstract: Microscopic and macroscopic deformation of a polycrystal due to an applied load can be modelled using crystal plasticity implemented within the Finite Element (FE) framework. However, while macroscopic predictions can readily be validated against conventional monotonic and cyclic stress-strain curves, verification at the microscopic level is harder to achieve, since it involves calibrating the predictions for stresses and strains in individual grains, or in grains grouped by certain criteria (e.g., orientation). In this paper an elasto-plastic polycrystal finite element model is introduced, and its calibration is performed at a mesoscopic level via comparison with neutron diffraction data obtained experimentally. Time-of-flight (TOF) neutron diffraction experiments carried out on ENGIN-X instrument at ISIS involved in situ loading of samples of C263 nickel-based superalloy. In order to compare the numerical predictions of the FE model with these experimental data, the corresponding mesoscale average elastic strains must be extracted from the results of the simulation by employing a ‘diffraction post-processor’. This provides a much improved technique for the calibration of FE formulation and enhances the confidence in the model. The FE diffraction post-processing procedures are discussed in detail, and comparison between the model predictions and experimental data are presented.
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