A dynamic bounding surface plasticity damage model for rocks subjected to high strain rates and confinements

Abstract

A dynamic bounding surface plasticity damage model is developed for rocks with the consideration of high strain rates and confinements. This is achieved through adopting the strength surface of Holmquist-Johnson-Cook (HJC model)/ Johnson-Holmquist-ceramic (JH2 model) model as bounding surface, and employing the critical state concept for brittle-ductile transition. In addition, a simple continuum damage evolution law is taken for strength degradation and a simple vertical mapping rule is adopted to link current stress state with its corresponding strength state. A series of hardening rules that account for both plasticity and strain rate, and damage evolution law, etc., are proposed within the framework of consistent condition of dynamic model. A ‘S’ shape dynamic increase factor (DIF) function is adopted to consider the strain-rate effect of dynamic loadings, which aims to adjust the size of bounding surface with the consideration of radial enhancement. The proposed model is validated through modeling conventional triaxial compression tests under different confining pressures, dynamic triaxial tests, and Split Hopkinson Pressure Bar (SHPB) tests with various strain rates. Good agreement between modeling results and experimental data indicates that dynamic characteristics of rock, including rate and confinements dependency, are captured well by the proposed model. The proposed model is then implemented into a commercial software, GDEM, to simulate the stress wave propagation problem. Simulation results by the proposed model and two benchmark models are compared, which further validate the capability and applied potential of the proposed model.