A methodology is presented to investigate and improve the strength and damage tolerance of stiffened composite panels used in aerospace structures subjected to postbuckling deformation. These structural panels have the capability to operate in the postbuckling field, but the possible interaction between the postbuckling deformation and the damage initiation and propagation is yet to be fully understood. The developed methodology considers single-stringer specimens representative of stiffened panels to analyze skin-stringer separation. In this paper single-stringer specimens are studied in a four-point twisting configuration in order to investigate the region of maximum twisting, where the separation between the skin and the stiffener can initiate. A new test set-up is presented that recreates the four-point layout that can trigger separation due to twisting. The applied methodology shows that it is possible to mimic the out-of-plane buckling deformation of a large panel and study this numerically and experimentally through a single-stringer specimen.
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