In-Situ Imaging of Spall Fracture

Abstract Spall failure is a dynamic fracture process commonly observed during hypervelocity impact and is of particular concern in application areas such as ballistics and spacecraft shielding. Standard methods to investigate spall include plate impact experiments on a gas gun, explosive loading, laser-driven shocks, and laser-driven flyer plates. Despite the number of options available to induce spall failure, options for experimental diagnostics are extremely limited. Experiments are generally restricted to interferometric techniques to measure the free surface velocity as well as post-mortem analysis of the damage. Here, we demonstrate an experimental technique for imaging spall failure in-situ during plate impact experiments on polycarbonate. Imaging is achieved by aiming a high-speed camera at the rear surface of the target by way of a turning mirror such that the camera is viewing down the impact axis. Our experiments show that this technique has sufficient spatial and temporal resolution to extract specific time-resolved information on the damage development process. Overall, our work demonstrates that in-situ imaging of spall fracture can generate valuable information on the spall failure process in transparent materials and can easily be achieved in most existing facilities.