A General Methodology for Full-Field Plastic Strain Measurements Using X-ray Absorption Tomography and Internal Markers

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 30 μm. 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.

In Situ Experiments with X ray Tomography: an Attractive Tool for Experimental Mechanics

“…Two different strategies have been employed so far for dealing with the markers. One is to introduce them artificially in the studied material [59][60][61][62], the other is to directly use the materials microstructure [31,[63][64][65][66][67][68][69]. The first method can in principle be applied to a variety of materials, provided a suitable technique for distributing homogeneously the markers is found.…”

“…The first method can in principle be applied to a variety of materials, provided a suitable technique for distributing homogeneously the markers is found. However, the question of how much the presence of those features affect the deformation process remains an issue [61]. From that point of view, natural markers appear more attractive but the number of materials presenting a relevant microstructure is restricted.…”

The Evolution of the Field of Biomechanics Through the Lens of Experimental Mechanics

“…The extension of DIC into DVC, and its use in the study of bone mechanics, was first published in EM in a landmark 1998 paper by Bay et al [75] that has received more that 75 citations to date. Since then, several EM publications have investigated the improvement and optimization of DVC [76] and its application to three-dimensional strain mapping [77,78]. Other biologically relevant imaging approaches that are related to DVC include the use of microcomputed tomog- raphy and ultrasound to study the microstructure of bone [79].…”

Quantitative 3D X‐ray Imaging of Densification, Delamination and Fracture in a Micro‐Composite under Compression

“…Methods for tracking fiducial markers using X-ray computed tomography (CT) or magnetic resonance imaging (MRI) [11] have been developed to measure the complete strain tensor in three dimensions. [12] Diffraction-based methods can map strain in three dimensions on a per-crystallite basis in polycrystalline materials, [13] with recent developments in X-ray scattering techniques beginning to address strain mapping of amorphous materials in two dimensions. [14] It has recently been demonstrated that techniques based on coherent diffractive X-ray imaging can image the displacement field inside perturbed crystals.…”