Non-Speckle-based DVC for Measuring Large Deformations in Homogeneous Solids using Laboratory X-ray CT

Abstract: X-ray computed tomography (XCT) has become a reliable metrology tool for measuring internal flaws and other microstructural features in engineering materials. However, tracking of material points to measure three-dimensional (3D) deformations has hitherto relied on either artificially adding tracer particles (speckles) or exploiting inherent microstructural features such as inclusions. This has greatly limited the spatial resolution and magnitude of the deformation measurements. Here we report a novel Flux Enhanced Tomography for Correlation (FETC) technique that leverages the inherent inhomogeneities within nominally homogeneous engineering polymers to track 3D material point displacements without recourse to artificial speckles or microstructural features such as inclusions. The FETC is then combined with a Eulerian/Lagrangian transformation in a multi-step Digital Volume Correlation (DVC) methodology to measure all nine components of the deformation gradient within the volume of complex specimens undergoing extreme deformations. FETC is a powerful technique that greatly expands the capabilities of laboratory-based XCT to provide amongst other things the inputs required for data-driven constitutive modelling approaches.