Creep mechanical characteristics and nonlinear viscoelastic-plastic creep model of sandstone after high temperature heat treatment

This work studies the creep mechanical characteristics and nonlinear viscoelastic-plastic creep model of sandstone treated at different temperatures. The peak strain, uniaxial compressive strength (UCS), and Young's modulus of sandstone treated at different temperatures are discussed as well as creep strain and long-term strength. The conventional uniaxial compression curves and uniaxial creep curves of sandstone treated at different temperatures are compared. Moreover, a nonlinear generalized Kelvin model is developed to simulate the decay creep deformation; a time-triggered nonlinear viscoplastic model is proposed to simulate the accelerated creep deformation. By combining the time-triggered nonlinear viscoplastic model with the nonlinear generalized Kelvin model, plastic element, and viscous element, a nonlinear viscoelastic-plastic creep model that can well reflect the entire creep process of sandstone treated at different temperatures is established. According to the results of model validation and parameter inversion, the new nonlinear creep model can be employed to predict the creep instability of rocks under high temperature environment.