High strain rate constitutive modeling of aluminum nitride including a first-order phase transformation

This work presents a computational constitutive model for materials exhibiting a first-order phase transition. The model can represent both recoverable and non-recoverable volume loss characterized by first-order phase transitions. Aluminum Nitride (AIN) is used to demonstrate the model. AIN has a first-order phase transition from the wurtzite (hexagonal) structure to the rock salt (cubic) structure. This phase transformation has been observed under static high pressure testing and inferred to be occurring under high strain rate shock wave loading. The phase transition begins at an approximate hydrostatic pressure of 16GPa where a 20% volume loss commences. The volume loss has been inferred to be non-recoverable. The model used for this study was previously developed for crushable materials, but is demonstrated herein that it can be straightforwardly applied to materials that exhibit a first-order phase change. Constants are obtained for the model using AIN test data. Plate impact experiments are simulated using the model, demonstrating the ability of the model to capture the material behavior. The model is also used to evaluate the recoverability of the volume loss and implies that the volume loss is non-recoverable