AbstractsEngineering

The effectiveness of shifting the failure mode away from delamination by the installation of multiple fasteners in series which arrests and stabilizes mixed mode interlaminar failure in composite structures has been demonstrated through analytical and experimental investigation. Based on the novel mixed mode axially loaded specimen, a multi-fastener specimen was manufactured using a quasi-isotropic layup. Testing showed that the damage tolerance of the structure was improved by the inclusion of a second fastener in the crack arrest feature, with laminate failure occurring before significant delamination propagation past the second fastener. Concurrently, finite element models were developed with good agreement of the results. Parametric studies were performed which aid in the optimization of the feature by studying the relative effect of various parameters such as fastener spacing and stiffness as well as laminate thickness and layup. Additional modeling investigated the crack curvature caused by the installation of a fastener, and the possibility of modeling the system with one dimensional elements. It is recommended that the finite element solution be used to aid in the design of alternate specimen configurations which would increase the crack length prior to total laminate failure.