Failure mechanism at stiffener runout in stiffened composite panels

In an aircraft structure, it is often necessary to runout some of the stiffeners to satisfy detailed design requirements. Depending on the structural design, stiffeners for a wing structure may terminate at a chord-wise splice, at the forward or rear spar, at a rib, or at a structural discontinuity, such as an access hole. But an abrupt stiffener termination can cause highly localized bending gradients due to stiffness discontinuities and load-path centricities. In this paper, both experiment tests and FEM models relating to three different stiffener runout specimens were presented and the failure modes of these specimens were discussed in detail. In tension, the failure is deduced by peel stress and interlaminar shear stress. In compression, the failure is deduced by interlaminar shear stress only.