Strength prediction of CFRP plates with a hole under biaxial compression-tension

An approximate solution in the form of a polynomial is developed for the in-plane stresses near a circular hole, in an orthotropic composite laminate under biaxial loading. The derived stresses are found to be in good agreement with the exact anisotropic solution, for a series of laminates investigated. However, the degree of accuracy of the approximate stress distribution is strongly influenced by the laminate lay-up and the biaxiality ratio. The resultant stresses are then employed in a fracture mechanics model to estimate the damage initiation, growth and final fracture of carbon fibre-epoxy plates with an open-hole subjected to biaxial compression-tension static loading. Using the independently measured laminate parameters of unnotched strength and in-plane fracture toughness, the model successfully predicts the notched strength of multidirectional laminates under various biaxiality ratios.