Investigation of stiffener run-out failure

The interface weakness is of major concern in stiffener run-out regions where the stiffener is terminated due to a cut-out, intersecting rib, or some other structural feature which interrupts the load path. More damage tolerant stiffener run-outs are clearly required and these are investigated in this paper. Using a parametric Finite Element analysis, the run-out region was optimised for stable debonding crack growth. The baseline and modified run-out designs were manufactured and tested. Damage initiation and propagation were investigated in detail using state-of-the-art monitoring equipment including Acoustic Emission and Digital Image Correlation. As expected, the baseline configuration failed catastrophically. The modified run-out showed slightly improved stability, but delamination failure in the stiffener promptly led to catastrophic failure. The FE model was revised to include delamination, and a second design and experimental iteration was carried out, leading to a design with increased damage tolerance.