Impact damage resistance and tolerance of stringer stiffened composite structures

Abstract

This paper describes an investigation into the resistance and tolerance of skin– stringer panels to impact damage. The effect of panel geometry and impact location on the damage extent and compressive strength were studied. When the impact site approached the stringer or the bay aspect ratio increased, the impact resistance was increased; more energy was absorbed elastically through structural response. In the strength tests, impact damage beneath a stringer was less detrimental than damage in the bay. In five of the six panels tested, failure was precipitated by a combination of bay buckling and skin–stringer detachment, except in one panel where massive lateral delamination growth led to a large reduction in strength. For impact damage in a bay, a wide bay, thick skin design was the most damage tolerant while for impact damage beneath a stringer, a high buckling strain design was the most tolerant. The results suggest that, at current in service strain levels, impact damage may be tolerated in some cases.