Internal Deformation Measurement of Polymer Bonded Sugar in Compression by Digital Volume Correlation of In-situ Tomography

A polymer bonded sugar (PBS) cylindrical specimen, in which caster sugar grains are embedded in hydroxylterminated polybutadiene (HTPB) binder matrix, was compressed up to −31.5 % of compressive strain without confinement, while its internal microstructures were determined by X-ray micro-computed tomography. The reconstructed volumetric images were analyzed to determine three-dimensional (3D) morphologies and to investigate the damage and failure mechanisms. The image grayscale was filtered by threshold values to identify individual material constituents, and determine grain volume fraction. An incremental digital volume correlation (DVC) technique was developed to determine the internal deformations and to track the movement of individual sugar grains. The evolution of the internal 3D deformation of PBS is correlated to its microstructures, as well as debonding and void formation. The side length of a cubic representative volume element (RVE) for the PBS is determined as 10 times of the average grain size, based on the analysis of sugar volume fraction; it is consistent with the RVE size determined from convergence analysis of the average and the standard deviation of strain distribution. Image analysis indicates that void ratio can be used as an indicator to quantify the extent of damage. Debonding occurs at first in the inner core region, and then propagates to the outer annular region. Debonding is also determined as the primary mechanism for damage formation and evolution. Grain fracture was not observed during the uniaxial compression of this PBS specimen under a nominal strain of −31.5 % without confinement.