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ABSTRACT: Probing the strain locally and throughout the bulk of various materials has long been of interest in Materials Science. This
article presents a general methodology for assessing the plastic strain in terms of the displacement gradient tensor throughout
the bulk of opaque samples. The method relies on a homogenous distribution of marker particles throughout the bulk of a sample,
markers which are detected through the application of synchrotron X-ray tomography. Making use of the morphology of individual
markers, motion of individual markers is tracked during deformation allowing the local displacement field to be determined
throughout the bulk. The local displacement gradient tensor is derived from the displacement field. Spatial resolution is
directly related to marker particle density in the sample, here 30μm. The accuracy of the displacement gradient tensor calculation
is dependent on the accuracy with which each marker position is determined and is shown to be in the range from 0.005 to 0.012.
Experimental Mechanics 04/2012; 48(2):199-211. · 1.52 Impact Factor
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ABSTRACT: The recent developments in X-ray detectors have opened new possibilities in the area of time-resolved pump/probe X-ray experiments; this article presents the novel use of a PILATUS detector to achieve X-ray pulse duration limited time-resolution at the Advanced Photon Source (APS), USA. The capability of the gated PILATUS detector to selectively detect the signal from a given X-ray pulse in 24 bunch mode at the APS storage ring is demonstrated. A test experiment performed on polycrystalline organic thin films of alpha-perylene illustrates the possibility of reaching an X-ray pulse duration limited time-resolution of 60 ps using the gated PILATUS detector. This is the first demonstration of X-ray pulse duration limited data recorded using an area detector without the use of a mechanical chopper array at the beamline.
Journal of Synchrotron Radiation 06/2009; 16(Pt 3):387-90. · 2.73 Impact Factor
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ABSTRACT: By combining a synchrotron X-ray source and the microtomography technique, the displacement gradient tensor components can be measured directly throughout the volume of a metal sample containing highly absorbing marker particles to detect material flow. The present article describes application of these techniques to compression of a rectangular Al-W specimen with a central hole. The results show that the externally imposed axial displacement gradient is accommodated mainly in two 45 degrees shear bands passing through the hole. A simple deformation analysis provides insight into shear band formation.
Journal of Microscopy 05/2006; 222(Pt 1):28-35. · 1.63 Impact Factor
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ABSTRACT: Newly developed experimental methods allow the extension of surface strain measurements into three dimensions throughout the bulk of opaque materials. By comparing two specimens with different geometries but consisting of similar materials under compression deformation, the ability of one of these new methods to distinguish between homogeneous and heterogeneous response to identical macroscopic boundary conditions is illustrated. Extending a previous study of a specimen deforming homogeneously to the entire specimen volume rather than a small subvolume, the effect of the marker particles on the material properties is discussed.
Materials Science and Technology 11/2005; 21(12):1428-1431. · 0.77 Impact Factor
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ABSTRACT: A recently developed marker-based technique for mapping of the displacement gradient tensor and the strain throughout the bulk of optically opaque specimens is presented and applied to an aluminium alloy multicrystal. Through investigations at 4%, 10% and 14% axial strains, the internal strain field is observed to be non-homogenous with the observed patterns present throughout the range of strains investigated. The morphology of the strain field is visualized with a resolution better than 50μm and variations are tentatively associated with the grain structure as recorded by EBSD. Future applications of the technique in combination with other 3-dimensional approaches are discussed with respect to comparison with Finite Element modelling approaches.
Materials Characterization.
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Mater. Character. 50(2008)7,842-851.
