Thermal ratcheting in granular materials with irregular particle shapes

Abstract

Granular materials with irregular particle shapes, such as sands, undergo a myriad of temperature variations in natural and engineered systems. However, the impacts of cyclic temperature variations on the mechanics of granular materials remain poorly understood. In this context, little is known about the mechanical response of such materials to cyclic temperature variations for central variables that characterize granular systems: particle shapes, applied stress levels, relative densities, and temperature amplitudes. This paper presents advanced laboratory experiments to explore the impacts of cyclic temperature variations on the mechanics of sands. The results show that cyclic temperature variations applied to sands induce thermal ratcheting: the cumulative growth of irreversible bulk deformations of such materials due to microstructural rearrangements caused by thermal expansions and contractions of constituting particles. The deformations of granular materials caused by thermal ratcheting strongly depend on particle shape, stress level, relative density, and temperature amplitude. These deformations are limited for individual thermal cycles but accumulate and become significant for multiple thermal cycles. Thermal ratcheting leads to substantial compaction in sands and other granular materials, which can affect various natural and engineered systems.