A new constitutive model for ballistic Roma Plastilina no. 1 clay

Abstract

Roma Plastilina No. 1 (RP # 1) clay has been widely used as a backing material in ballistic tests of body armor. However, the constitutive behavior of RP # 1 clay is still not well characterized. In this article, a new constitutive model is proposed to describe the stress–strain relation of ballistic RP # 1 clay, which accounts for the coupled effects of strain hardening, strain-rate hardening, and temperature softening. The model is phenomenological and can be regarded as an extended Johnson–Cook model. The model contains nine parameters, all of which are calibrated using six true stress–true strain curves at two deformation temperatures and three strain rates obtained at the US Army Research Laboratory (ARL). The newly proposed constitutive model with the calibrated parameters is applied to predict six other true stress–true strain curves at another two temperatures, which are compared to the experimental curves that were also generated at the ARL. The non-uniqueness of the fitting parameter values is discussed, and an error analysis is conducted. The results of the error analysis show that the new constitutive model provides a fairly accurate prediction of the stress–strain behavior of ballistic RP # 1 clay.