An experimental damage tolerance investigation of CFRP composites on a substructural level

Abstract

The damage tolerance (DT) allowables for the design of a composite structure are typically determined through experiments on the coupon level. The present study examines the transferability of the DT behavior from the coupon level to a structural level. For that purpose, a DT critical panel with two stiffeners was designed and tested. In one quasi-static and two cyclic compression after impact tests, the damage evolution behavior was studied and compared with results achieved on the coupon level. Similar phenomena were found on both scales: a long interval of load cycles, without any detectable damage evolution is succeeded by the sudden propagation of the delamination and the fiber fracture. Afterward, the ultimate failure occurs within few load cycles. Even though the stiffened panel offers a significant possibility to transfer load from the damaged skin, a significant damage stabilization could not be achieved. The no-growth interval was found to be shorter on the structural scale, however, an analytical DT analysis suggests the different damage size as the most likely cause. However, it was found that the stiffeners slow down the damage propagation. Eventually, the study confirms the no-growth design approach as the preferred method to account for the DT of stiffened, compression-loaded composite structures.