Elasto-Plastic Failure Analysis of Composite Bolted Joints

Abstract

An elasto-plastic finite element analysis of pin loaded joints in laminated composites has been investigated and comparisons made with both existing 2-D linear elastic plane stress analytical solutions and experimental results for a graphite/epoxy laminate. The finite element analysis included nonlinear material behavior after initial failure by assuming an elastic-perfectly plastic bimodular material model. Laminated plate theory was used to obtain lamina stresses and the Hill yield criterion applied in each layer to create a ply-by-ply failure analysis. The effect of including friction forces along the fastener hole interface on the stress distribution around the hole was also studied. Based upon the results, failure criteria are proposed for each of the basic failure modes, bearing, shearout and net-tension. Failure maps for each ply were developed to characterize the damage progression and identify critical failure strength and mode. For the [0_i/±45_j/90_k] family of laminates the elasto-plastic finite element stress analysis coupled with the developed failure criteria resulted in good agreement with experimental results.