Hypervelocity impacts on thin brittle targets: experimental data and SPH simulations

The meteoroids and debris environment play an important role in the reduction of spacecraft life time. Ejecta or secondary debris, are produced when a debris or a meteoroid impact a spacecraft surface. These ejecta can contribute to a modification of the debris environment: either locally by the occurrence of secondary impacts on the component of complex and large space structures, or at long distance by formation of small orbital debris. This double characteristic underlines the necessity to model the damages caused by an HVI as well as the material ejection caused by the impact. Brittle materials are particularly sensitive to hypervelocity impacts because they produce features larger than those observed on ductile targets and the ejected fragments total mass including ejectas and spalls is in the order of 100 times bigger than the impacting mass. The main aim of this paper is to study the damaging and ejection processes that occur during hypervelocity impacts on thin brittle targets (dp = 500 microns for velocities ranging from 1 to 5 km/s). The two stage light gas gun “MICA” available at CEA-CESTA has been used to impact thin fused silica debris shields and the impacted samples have been analysed with environmental SEM microscopy and perthometer. Experimental characterization of ejected matter has also been performed on the MICA facility. The severe deformations occurring in any hypervelocity impact event are best described by meshless methods since they offer clear advantages for modeling large deformations and failure of solids as compared to mesh-based methods. Numerical simulation using the SPH method of Ls-Dyna and the Johnson Holmquist material model adapted for fused silica were performed at ENSICA. The results of these calculations are compared to experimental data obtained with MICA. Experimental data include the damage features in the targets (front and back spalled zone, perforation hole and cracks observed in the target) and the clouds and fragments ejected during the impact