A damage tolerance study conducted with structure relevant specimens

A preliminary investigation is reported of the development of a Structure Relevant (SR-) specimen, which maintains the essential features of a stiffened panel configuration, in order to study damage growth behavior at limited cost. Several SR-specimens were fabricated, damage was applied, either through impacts or by the insertion of artificial delaminations, compression loads were applied, and C-scan damage areas and internal damage configurations were determined. The failure mode of one series of SR-specimens consists of three phases: a first phase of stable delamination buckling with increasing amplitude but no growth, a second phase of rapid delamination growth until the delamination jumps across the stiff doubler area, causing a significant load redistribution, and a final phase with slow delamination growth in the base skin zones at the edges of the specimen, until total failure occurs at a gross strain of 0.006. The failure mode of another series of specimens could not be described in sufficient detail, due to a lack of instrumentation. In this case the failure mode probably consists of failure due to bending, at a gross strain of 0.006, while the artificial delaminations did not grow until final failure. Delamination growth was observed to follow preferred interfaces, adjacent to 90-degree layers. It is concluded, that the SR-specimen proposed can be used for damage tolerance studies.