Thermodynamics of continuum damage and fragmentation models for hypervelocity impact

General numerical models of hypervelocity impact problems must account for finite strain deformation, isochoric rate dependent plasticity, volumetric and deviatoric damage, and complex energy domain coupling. Incorporating all these effects into current damage and fragmentation models is difficult, given their limited thermodynamic framework. An alternative, systematic approach to the material model formulation process results in a general thermodynamic framework which can incorporate a variety of constitutive assumptions. Application of the method is illustrated by formulation of an elastic-viscoplastic damage model with finite strain kinematics, Grady-Kipp volumetric damage, Johnson-Holmquist deviatoric damage, and thermodynamic coupling through an entropy state. Hypervelocity impact simulations using the developed model show that predictions of fragment size and fracture surface area based on Grady-Kipp fragmentation theory vary significantly with the extent of plastic deformation, over a velocity range of five to ten kilometers per second.