Experimental and numerical investigations of residual strength after impact of sandwich panels

Sandwich panels with a foldcore are of interest to the aerospace industry due to their promising properties. There is an increasing interest in the basic properties of such a core and response of these panels to low energy impact loading. In this paper experiments to determine quasi-static properties of such a core and a sequence of impact experiments using a drop tower and 4-point bending tests are presented. The aim of the latter is to assess the damage tolerance of sandwich panels with aramid paper foldcores and carbon fibre reinforced plastic (CFRP) skins under impact loading. The impact energy range in these experiments was chosen to investigate a variety of damage scenarios from barely visible damages (BVID) to fibre fractures in all plies of the impacted face sheet. 4-point bending tests were performed with the panels previously damaged by impact loadings to assess the residual bending strength of these samples. A numerical procedure has also been developed to reproduce these experiments (the impact as well as the 4-point bending tests). The method can also be employed to predict the results of the residual strength in other experiments like compression (CAI) or edgewise compression after the impact.