A constitutive elastoplastic model with multiple hardening variables for modeling material degradation

Abstract This work proposes a constitutive model based on a composite yield envelope with two smooth branches and three hardening variables to simulate the mechanical behavior of porous materials. The formulation extends the SR4 framework, which follows critical state theory and blends elements of the SR3 and modified Cam-Clay models, by introducing a nonlinear hardening–softening law that depends on plastic volumetric and deviatoric strain increments. The degradation of three geomechanical variables—the tensile intercept of the yield surface with the hydrostatic axis ( p t ), the preconsolidation pressure ( p c ), and the friction angle ( ϕ )—is used to assess different post-peak deformation mechanisms. Stress integration is performed with a generalized substepping algorithm that preserves numerical stability. Numerical tests show that the degradation of each proposed geomechanical variable satisfactorily reproduces the evolution of the yield surface under different stress paths. A Morris-based global sensitivity analysis provided an efficient screening of the model’s high-dimensional parameter space across hydrostatic, triaxial, and yield surface response metrics, guiding a balanced calibration strategy across volumetric and deviatoric deformation mechanisms. Calibration using laboratory tests confirms the model’s ability to accurately reproduce stress–strain curves, capture the evolution of yield surfaces, and simulate the brittle–ductile transition with minimal parameter adjustment. This demonstrates the model’s robustness and computational efficiency for simulating rock deformation.