Microscopic insights into thermal cycling effects in granular materials via X-ray microtomography

The mechanics of granular materials at the macroscopic scale inherently depends on the particle interactions occurring at the microscopic scale. In recent decades, growing investigations have explored the mechanics of granular materials subjected to thermal cycles, as they involve complex responses that bear significance for science, engineering, and technology. However, the fundamental understanding of the mechanics of granular materials subjected to thermal cycles remains hindered by the absence of empirical evidence into the microscopic particle interactions that govern the macroscopic response of such materials. For the first time, this study presents direct experimental evidence obtained via synchrotron X-ray microtomography to reveal the behavior of the particles that constitute granular materials during thermal cycling. This work experimentally confirms the existing theory by which thermally induced particle interactions drive a macroscopic volumetric expansion and contraction of granular materials upon heating and cooling, respectively, and the development of irreversible volumetric deformations upon the completion of thermal cycles. The results uncover the evolution of particle non-uniform translations, rotations, and contact variations during thermal cycling, which all inherently depend on particle shape.