A Mechanism-Based Model for the Impact Response of Quartz

The mechanical response of geomaterials to extreme dynamic conditions is essential to understanding planetary impacts, other geological and seismic events, and underground explosions. In this study, we present a multimechanism constitutive model to describe the dynamic response of polycrystalline quartz (e.g., nonporous quartzite), and implement it using a large scale computational analysis to simulate impact events. The active deformation mechanisms within quartz under dynamic loading consist of amorphization, fracture and granular flow. All of these mechanisms are integrated within the model in terms of their competition, evolution, and interaction during a complex loading history. A generalized amorphization model is introduced within a thermodynamically consistent framework on the basis of earlier work in Zeng et al. (2019a, https://doi.org/10.1016/j.jmps.2019.06.012), and accounts for the kinematics of finite deformation inside amorphization bands and the distinct physical properties of the amorphous phase. Fracture in the form of microcracking emanating from internal defects is also considered. Once the material is fully fragmented, the behavior transitions to granular flow. After determining the model parameters for polycrystalline quartz, we illustrate the model response using a representative volume element, where the competition of mechanisms is revealed under several typical loadings. Plate impact experiments and dynamic compression on a polycrystalline quartz foil are then simulated. The simulation results are compared with experiments to prove the predictive capability of the model in capturing the key features of quartz during impact events.