Thermoelastic Couplings and Interparticle Friction Evidenced by Infrared Thermography in Granular Materials

Infrared (IR) thermography was used to analyze the thermomechanical response of a two-dimensional non-cohesive granular assembly. Two constitutive materials with different types of thermoelasticity were chosen: thermoplastic polyurethane (TPU) and polyoxymethylene (POM), which feature entropic and isentropic elasticity respectively. Cylinders of each material were mixed together. Analysis was performed under confined compression at two observation scales. Thermoelastic couplings and interparticle friction were separately evidenced. First, the strong thermal effect of entropic coupling was revealed at the contacts, in the stress concentration zones. Second, image processing enabled us to clearly extract the thermal signature of the interparticle friction zone, a quantity that cannot be identified by the other full-field measurement techniques available today. It can thus be claimed that IR thermography provides two distinct routes for the analysis of granular materials by distinguishing the reversible and irreversible parts from the global thermomechanical response. The study also opens prospects for the experimental analysis of soft granular media.