Analysis of Delamination Arrest Fasteners in Bolted-Bonded Composite Structures
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Delamination is one of the most critical damages in carbon fiber composites, which are being employed in primary aircraft structures. One common solution to prevent a delamination from propagating is to install fasteners, clamping the laminate together and partially arresting the delamination. In this thesis, the effectiveness of multiple fasteners installed in series to arrest the mixed-mode interlaminar failure in composite structures is investigated analytically. An accurate finite element model for predicting delamination propagation behavior of bolted-bonded structures was developed and validated by experimental test data. The finite element results showed that the presence of fasteners can slow down propagation of the crack by compressing the lamina together and transferring load via Mode II shear engagement of the fastener. Compared to the single-fastener case, damage tolerance of the structure was improved by the inclusion of the second fastener. Additionally, if the tensile modulus of the lamina is not high enough, laminate failure would occur before the delamination past the second fastener. Parametric studies were also performed to evaluate the influences of friction and laminate stiffness, fastener stiffness, fastener spacing and specimen width. Numerical results were discussed and a conclusion on the effectiveness of delamination arrest was drawn.