Pull-Through Failure of Bolted Composite Joints

摘要

The design and certification of composite aircraft structures requires extensive and costly testing of bolted joints since no robust predictive tools are available. The majority of investigations in this field focused on the shear loading of bolted carbon fibre-reinforced polymer matrix composites, while studies on the behaviour of pull-through loading are limited. Thus, this paper presents an investigation of the factors affecting bolted composite laminates subjected to out-of-plane loading with the objective to develop an empirical predictive model for the pull-through failure load. An experimental investigation is presented where the influence of fastener head geometry, size and laminate thickness was systematically studied. Specimens manufactured from out-of-auto clave carbon-epoxy prepregs were transversely loaded in a servo-hydraulic testing machine. The load-displacement response was measured and the failure mechanisms were examined by optical microscopy. The results showed that failures were dominated by inter-ply delamination and through-thickness shear failure of the laminate. A conical damage zone was found under the fastener head with damage spreading from the fastener hole in the radial direction. The opening angles of the cones varied with the fastener head geometry. Transverse deformation and inter-laminar shear caused the final failure in the form of inter-ply delamination. Finally, an empirical equation for the prediction of the pull-through resistance that includes the joint characteristic factors was developed.