Effects of temperature and increasing amplitude cyclic loading on the mechanical properties and energy characteristics of granite

Abstract

Increasing upper limits of cyclic loading tests at different temperatures were carried out to reveal the influence of temperature and stress level on the mechanical properties and energy characteristics of granites. The mechanical properties of granite were altered by temperature and cyclic loading, which is manifested by the observation of rock hardening, i.e., the elastic modulus increases gradually in an approximately logarithmic relationship with increasing stress levels and the relative residual strain shows a decreasing trend. The energy evolution of granite changes from nonlinear characteristic to linear characteristic with increasing temperature. The input energy density and elastic energy density, at 25 °C and 100 °C, both increase nonlinearly with increasing stress levels as an approximately exponential relationship, whereas those, in the range of 200 to 600 °C, increase almost linearly as the unloading stress level is less than 0.9. The energy distribution of granite subjected to cyclic loading was revealed, i.e., the energy accumulation is dominant in the pre-peak stage. The mathematical model of elastic energy density and input energy density at different temperatures was proposed, which is critical for the energy-based brittleness index that can be used to evaluate the stability and compressibility evaluation of the reservoirs. This generalized equation of different types of rocks merits further study.