Visco-damage tension model for rocks in ground-shock applications

A simple rate-dependent tension model, tailored primarily for rocks in ground-shock calculations, has been constructed. It is formulated as an internal state variable theory with spherical void development taken to approximate the underlying dissipative micromechanism. This simplifying assumption of ductile, rather than brittle, damage growth has been made to enhance the practicality of the model for large-scale problems. The model has been restated within the fromework of (strain-softening) viscoplastcity to associate it with the desirable mathematical properties of the latter theory. The tension option, extended to include healing in the post-damage compressive phase, has been implemented in a standard cap constitutive routine and is referred to as the visco-damage tension model. Model parameters are selected for a shale-like material. Results of uniaxial shock-loading strain-rate calculations exhibit desired characteristics in tension. Damage-related hysteretic effects are illustrated through cyclic loading calculations. It is planned to develop more effecient computational procedures to facilitate adoption of the model into large-scale ground shock calculations. Anisotropic extensions of the model will then be considered.