A modified Cochran-Banner spall model

The original Cochran-Banner spall model was modified to suit the usual definition of damage and to abandon the simplifying approximation as unnecessary. The strength function given by Cochran-Banner was maintained using the redefined damage and the correction concerning the volume of the mesh cells was realized considering it unnecessary to expect that it is much easier to open microcracks once they are formed than to strain the solid further. In the case of abandoning the simplifying approximation made by Cochran-Banner to calculate the damage, the redefined damage also does not become a new independent variable for which new dynamic laws would need to be specified. Once the spall strength was reached, the damage would be only determined by a series of closed equations including the stress.relaxation relationship given by the strength function, the energy conservation equation, the equation of state and the constitutive equations for the damaged aggregate. The modified Cochran-Banner spall model also included only two parameters: the spall strength and the critical damage, which relate to material properties and specific loading conditions. Comparison of theoretical and experimental results for some spall tests was performed. It was found that the computed free surface velocity profile of target or stress profile of interface between target and soft buffer in plane spall tests was sensitive to the spall strength and the critical damage in the modified Cochran-Banner spall model.