FRACTURE CRITERION FOR NOTCHED THIN COMPOSITE LAMINATES

Fracture behavior of fiber-dominated center-notched AS4/3501-6 graphit e-epoxy laminates is investigated in this study. Nine laminate configu rations are studied to examine flaw size effects, crack tip damage mec hanisms, and failure modes under uniaxial tensile loading. Results ind icate that a constant value of fracture toughness K-Q is a laminate ma terial property. A layup independent failure criterion is proposed, wh ich 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 bre akage along the plane of the notch. Once its value is estimated from p reliminary tests, this parameter can be used to predict fracture tough ness, and hence residual strength, of other fiber-dominated laminates of the same material system. The model predictions agree well with cur rent experimental results, as well as with data published by other res earchers. The model is further extended to predict residual strength o f laminates with inclined cracks (mixed-mode loading). It is demonstra ted that the normal projection of the crack to the applied load can be considered as the equivalent crack and governs laminate residual stre ngth.