An Approximate Theory for Predicting the Moduli of Uni-Directional Laminates with Non-Linear Stress/Strain Behavior

Abstract

An approximate theory for predicting the non-linear behaviour of long fibre composites is presented. The theory combines linear elastic fibre properties with non- linear elastic matrix properties to determine the stress/strain behaviour of a uni-directional laminate. On comparison with experimental data for the stress/strain behaviour of a uni directional Carbon fibre/PEEK laminate, predictions agree well with measurement. For on-axis loading, fibre effects dominate and non-linear effects are unimportant. For off-axis loading, matrix effects dominate and consequently non-linear effects are significant, par ticularly the non-linear shear stress/strain behaviour.