In situ quantitative three-dimensional characterisation of sub-indentation cracking in polycrystalline alumina

In-situ X-ray computed tomography characterisation of 3D fracture evolution and image-based numerical homogenisation of concrete

“…2 up to 10.5 kN, gives a modulus of 0.85 GPa which is far lower than the expected elastic modulus of 20-30 GPa of normal-strength concrete; this is largely due to the compliance of the loading rig. The 3D digital volume correlation (DVC) technique Mostafavi et al, 2013a;Mostafavi et al, 2013b;Vertyagina et al, 2014) was therefore applied to measure the full 3D displacement field within the cube, from which the average strain and elastic properties in the loaded volume could then be obtained (Baimpas et al, 2014;Gonzalez et al, 2013;Marrow et al, 2016). In addition, like 2D digital image correlation (DIC), crack opening displacements less than the voxel size can be detected and measured by DVC, and thus cracks that are too narrow to be detected by threshold-based segmentation of the XCT image can also be identified (Marrow et al, 2012;Vertyagina et al, 2014).…”

“…However, in-situ XCT studies, which scan the internal structures of materials under progressive loadings so that the structural damage and fracture evolution can be examined and related to the loading process are now feasible. For example, De Kock et al (2015) have observed the fracture process in rocks under ambient freeze−thaw cycling and Nagira et al (2011) studied semi-solid carbon steels., whilst in recent years some of the authors of this paper have conducted in-situ XCT experiments to examine deformation in metal-metal composites (Baimpas et al, 2014), fatigue cracking in magnesium alloy , indentation cracking in alumina (Vertyagina et al, 2014) and ceramic composites ), tensile deformation in nuclear graphite (Marrow et al, 2016), and polymeric foams (McDonald et al 2011), liquid flow and deformation in semi-solid aluminium alloys (Cai et al, 2016), indentation deformation in a metal-matrix composite 3 (Mostafavi et al, 2015), and fracture of propagation in nuclear graphite (Mostafavi et al, 2013). For such studies to be successful, it is important to consider the experimental constraints of increasing X-ray absorption with sample dimension and density, which limits the maximum dimensions and increases the time to record tomographs, and also for digital volume correlation analysis of deformation, it is necessary that the microstructure contains sufficient "speckle" contrast that can be discerned at the experiment's resolution .…”

Digital Volume Correlation: Review of Progress and Challenges

“…Very early on, various types of foams were imaged via tomography and their behavior was studied thanks to DVC [207,11,197,181,59,15,64]. The degradation mechanisms of such materials in indentation experiments received some attention [231,20,22]. One of the reasons is that tomography reveals their in-situ temporal development, which can only be assessed post-mortem with other investigations.…”

“…Localized phenomena are situations in which full-field measurements make a (huge) difference (e.g., strain localization [127,1,214,49] and cracks [198,231,94]). This is particularly true when kinematic measurements can be performed nondestructively in the material bulk.…”

“…The gray level residuals were also used to detect matrix/nodule debonding in cast iron [93,219,29]. Maximum eigen strain fields enabled multiple microcracking to be quantified in brittle materials [101,231,94,240] and damage in SiC/SiC composites [201]. Other strain descriptors such as the first and second invariants were used to detect cracks [38].…”