Failure Analysis of Bolted Joints in Composite Laminates

An investigation into the bolted joint strength of Kevlar/epoxy and graphite/ epoxy [0/45/90/-45]_2s composite laminates is presented. The fundamental problem of a single bolt hole loaded symmetrically in tension is considered. The first objective of the study was to generalize the relationships between width, edge distance, hole size, thickness, washer diameter, and degree of lateral constraint with bolted joint strength based on experimental observations. The second objective, which is the focus of this paper, was to numerically predict the same observation using only the composite's lamina properties. The effective laminate behavior is calculated using a nonlinear laminate analysis based on lamina properties and ply orientations. The effective laminate properties are then input into a nonlinear finite-element analysis computer code to model the bolted joint. The predicted bolted joint failure regions and strengths were consistent with the experimental data, although improved nonlinear constitutive finite-element models are needed. The analysis is useful in predicting critical width, edge distance, and washer sizes needed to optimize bolted joint strength.