Dynamic Weakening Due to Localized Thermal Softening with Application to the Formation of Hypervelocity Impact Craters

Abstract Introduction The need for a dynamic weakening mechanism to facilitate the collapse of a transient cavity to produce the complex crater shape has been well documented. Several mechanisms have been proposed: acoustic fluidization [1], thermal softening due to shock melting [2] and frictional melting (i.e. thermal softening) along fault planes [3]. Several studies have stressed the potential importance of thermal softening during the impact process [4-10] which is the subject of this work. 2. Methods In prior work, we developed a numerical model of shear failure and frictional heating within faults and demonstrated how this model may play a role in explaining complex crater morphology [9] and in the acquisition of remnant magnetization to help explain the present paleomagnetic state of the lunar surface [10]. The model was based on the damage model of Collins et al. [11] and extended by estimating statistical crack spacing based on strain rate, a determination of shear heating within cracks and heat loss via conduction away from cracks. With this extension, thermal softening can occur as the temperature within a crack approaches the melt temperature. A model incorporating these features was added to CTH [12] as The Brittle Damage with Localized thermal softening (BDL) model. We’ve recently implemented a version of this model into a new hydrocode which we call SPAARC (Shock Physics Accelerated Adaptive Research Code) where it is called the Crater model.