Fracture Criterion for Notched Thin Composite Laminates

Abstract

Fracture behavior of fiber-dominated center-notched AS4/3501-6 graphite-epoxy laminates is investigated in this study. Nine laminate configurations are studied to examine flaw size effects, crack tip damage mechanisms, and failure modes under uniaxial tensile loading. Results indicate that a constant value of fracture toughness K Q is a laminate material property. A layup independent failure criterion is proposed, which relates laminate fracture toughness to the fracture toughness K Q 0 of the principal load bearing ply. K Q 0 characterizes the in situ fracture toughness of a notched 0-deg layer in the event of fiber breakage along the plane of the notch. Once its value is estimated from preliminary tests, this parameter can be used to predict fracture toughness, and hence residual strength, of other fiber-dominated laminates of the same material system. The model predictions agree well with current experimental results, as well as with data published by other researchers. The model is further extended to predict residual strength of laminates with inclined cracks (mixed-mode loading). It is demonstrated that the normal projection of the crack to the applied load can be considered as the equivalent crack and governs laminate residual strength.