Fracture mechanics analysis of stitched stiffener-skin debonding

An analysis based on plate finite elements and the virtual crack closure technique has been implemented to study the effect of stitching on mode I and mode II strain energy release rates for debond configurations. The stitches were modeled as discrete nonlinear fastener elements with a compliance determined by experiment. The axial and shear behavior of the stitches was considered, however, the two compliances and failure loads were assumed to be independent. Both a double cantilever beam (mode I) and a mixed mode skin-stiffener debond configuration were studied. In the double cantilever beam configurations, G\sub{I} began to decrease once the debond had grown beyond the first row of stitches and was reduced to zero for long debonds. In the mixed-mode skin-stiffener configurations, G\sub{I} showed a similar behavior as in the double cantilever beam configurations, however, G\sub{II} continued to increase with increasing debond length.