Strength of Tensile Loaded Graphite/Epoxy Laminates Containing Cracks, Open and Filled Holes

Most methods currently used for predicting tensile strength of composite laminates containing holes and cracks adopt a characteristic distance approach such as the Point Stress Criterion (PSC) or the Average Stress Criterion (ASC). These and similar ap proaches are attractive to designers since they are simple to apply. The limitation of such approaches, however, is that the characteristic distance is not a physical parameter but is an empirically determined constant, dependent on the geometry of the specimen. The Damage Zone Criterion (DZC) presented in this paper is based on fundamental physical principles. A damage zone is assumed to be present in the maximum stress region of the laminate when the tensile stress reaches the tensile strength of the unnotched laminate. Taking into account the stress redistribution followed by a damage development, a closed form analytical expression of the strength is derived from the equilibrium conditions of the specimen. The strength of laminates with holes and cracks is then predicted on the basis of two fundamental parameters, the unnotched tensile strength (σ ₀ ) and the critical damage zone length ( d* _I ). The DZC is simple to apply, makes excellent predictions of the strength of specimens made from laminates of different configurations, and provides significantly improved accuracy compared with the PSC.