Failure Prediction of Composite Lugs Under Axial Loads

An approach to predict failure of composite lugs under axial loading is presented. The approach relies on superposition of the solution for an infinite plate with a pin-loaded hole and an infinite plate with an unloaded hole corrected for finite width effects based on methods presented in the literature. A relatively simple equation for the net section stress is derived. For failure prediction the maximum net section stress is equated to the first-ply failure of the laminate. The approach was used to determine analytically the optimum lug configuration. For a wide variety of layups, it was found that the optimum pin-diameter-to-lug-width ratio is approximately 0.41. A test program was executed to verify the predictions of the approach with three different lug configurations with tape, fabric, or combinations of tape and fabric materials with quasi-isotropic and orthotropic layups. The specimens were tested in tension, and in all cases the test results were within 10% of the failure predictions.