Digital volume correlation analyses of synchrotron tomographic images

Three-dimensional (3D) images of nodular graphite cast-iron samples obtained with synchrotron tomography are analysed by resorting to digital volume correlation. This technique uses the material microstructure to measure displacement fields within a sample submitted to mechanical loading. Compared to classical two-dimensional (2D) digital image correlation, the reconstructed volumes used by DVC tend to increase the uncertainty in the correlation calculations, yet elastic strains of the order of 10(-3) can be measured. Displacement fields around the front of a fatigue crack have also been measured by an extended version of DVC, and are used to extract stress intensity factors (in modes I, II, and III) along the crack front. The values are in good agreement with finite element calculations when the experimentally measured displacements prescribed on the sample boundaries are considered as input in the numerical simulations.