Impact Behavior and Residual Strength of Sandwich Structural Elements Under Static and Fatigue Loading

Abstract

The extent of impact damage in sandwich structures depends on the core material and the stacking sequence of the sandwich skin laminate, the size, mass and velocity of the impactor and on the ability of the component to absorb the shock at the impact point. Because of the complex interaction between these parameters the forecast of the damage and the progress under Tension-Tension (T-T), Tension-Compression (T-C) and Compression-Compression (C-C) fatigue loading is difficult to conduct. Impact damage is most critical, when the skin remains intact. Except of a small dent or blister in the skin surface the impacted zone is often barely visible. Nevertheless, the damage may grow under fatigue loading to a critical size, where the component is endangered. In sandwich structures with foam core a delamination will be detected most likely around the impacted zone between skin and core. The damage progress is triggered by the local buckling of the delaminated skin layer. In structures with Honeycomb core delaminations are hardly detected after impact (see Figure 1). The core is crumpled in the vicinity of the impacted zone and the elastic support of the skin layers is reduced. Under compressive loading the core shrinks in thickness direction and the skin layer may buckle in core direction