Experimental and Numerical Study of Submillimeter-Sized Hypervelocity Impacts on Honeycomb Sandwich Structures.

This paper deals with hypervelocity impacts of submillimer-sized debris on honeycomb sandwich panels. These debris, which are mostly present within the low Earth orbit, indeed represent a real threat for spacecrafts and satellites. In fact, for debris large enough to be tracked, pre-determined debris avoidance manoeuvre is usually conducted to prevent any damage. Submillimer-sized debris, however, are too small to be identified and therefore spatial structures must be protected against such threat. Honeycomb structural panels and whipple shields have been used as primary shielding against orbital debris impact. The protection capability is usually estimated using Ballistic Limit Equations (BLE). These data have been built from experimental tests on whipple shield protection and transposed to honeycomb sandwich panels. In the case of Whipple shield, the debris cloud generated at the impact on the bumper sheet expands until reaching the rear wall. BLE for Whipple shields only depends on materials properties, protection geometry, angle of incidence and impact velocity. For honeycomb sandwich panels, the debris cloud is partially channelled within honeycomb cells, thus limiting its radial expansion. The channelling effect is thus a function of the honeycomb cell geometry. The honeycomb BLE presented by the Centre d’Etudes de Gramat (CEG) in 2008 has been introduced in order to take into consideration such effect. The present study proposes to extend the results of the CEG. The main approach is to consider the relative dimensions between the projectile diameter and the honeycomb geometry in order to evaluate the perforation risks of submillimer-sized hypervelocity impacts. The impact process on honeycomb sandwich panel has first been modelled using commercial hydrocode LS-Dyna using hybrid Lagrange and Smooth Particle Hydrodynamics (SPH) solvers. The numerical model has been validated through several hypervelocity impacts experiments carried out at Thiot Ingenierie Shock Physics Laboratory at velocities up to 9.3 km/s. This model has then been used to define a ballistic curve which defines the critical projectile diameter of a specific sandwich panel subjected to submillimer-sized debris impact. The results are finally compared to the ones obtained by the CEG leading to an updated estimation of the protection capability of honeycomb sandwich panels. [ABSTRACT FROM AUTHOR]