Study on the elasto-plastic localized damage constitutive model of raw coal

Due to the heterogeneity of raw coal, the initiation, propagation, and aggregation of internal microcracks lead to the formation of local macroscopic cracks, ultimately causing instability and failure. Based on the Mohr-Coulomb failure criterion and considering the localized damage effect, this study establishes a constitutive model for raw coal with coupling elasto-plastic localized damage. Damage evolution is used as an internal driving variable to control the expansion and contraction of the yield surface, describing the strain hardening and softening behavior of the coal rock. An exponential function form of damage criterion is employed to describe the damage evolution during the rock fracturing process and establish the relationship between the changing localized band size and the damage variable. By comparing numerical simulation results with raw coal triaxial test data, the effectiveness of the proposed model is demonstrated. The results show that the model can adequately capture the main nonlinear deformation characteristics during the loading process of raw coal, and post-peak strain softening phenomenon is attributed to the rapid increase in localized damage. Therefore, the proposed constitutive model can reflect the mechanical characteristics of localized deformation and failure of raw coal, providing new research ideas for theoretical model studies in deep rock engineering.