Strain rate-dependency of thermal infrared radiation of sandstone subjected to dynamic loading: Insights from a lab testing

Abstract

Rocks are generally deformed and fractured upon various scales of strain rates. Understanding the strain rate effects on the thermal infrared radiation (IR) characteristics of rock materials is crucial for predicting and detecting rock failure. In the study, uniaxial compression experiments were conducted on sandstone samples at different strain rates using an Instron hydraulic servo testing machine and a split Hopkinson pressure bar (SHPB) system. Meanwhile, a thermal infrared camera was utilized to capture and record the changes in the IR temperature on the rock surface. The spatial and temporal evolution of thermograms, IR temperature distribution histograms, and average IR temperature (AIRT) during testing were obtained and analyzed. A quantitative correlation between strain rate and the variation in AIRT (ΔT) was established. Furthermore, the dissipation of heat energy (Q) in the sandstone samples during SHPB tests was estimated. Results indicated that at relatively lower strain rates (ranging from 10−6 to 10−2 s−1), the ΔT of rock sample exhibited slight dependence on strain rate. However, a significant rate sensitivity emerged when the strain rate exceeded a specific threshold (approximately 137.09 s−1 for the tested sandstone). The rate-dependent behavior of ΔT across the investigated range of strain rate (up to 102) can be characterized by an allometric power model. Notably, during SHPB testing, the proportion of Q was negligible despite the pronounced rate dependency of heat energy. The abrupt rises in ΔT and Q under dynamic loading conditions can be elucidated by the increasing occurrence of shear cracks and energy-level jumps stimulated by impact disturbance.