This paper presents experimental results for validation of exascale simulations of the mechanical response of particulate composites, which are commonly used in inert experiments of high explosives (HE) or mock materials. Idoxuridine (IDOX) crystals were blended with the Estane matrix. Unconfined uniaxial compression experiment was conducted at both low and high strain rates to investigate the mechanical behavior of the composite. At high strain rate tests, we employed a 29-foot-long split Hopkinson pressure bar to compress the specimen, simultaneously recording the surface images with an ultra-high-speed camera to determine the surface deformations using digital image correlation (DIC). Our findings provide insight into both internal and surface deformations of the particulate composite under various loading conditions, establishing correlations between mechanical responses and internal microstructures. These results are crucial for the validation of exascale simulations related to particulate composites.