The Strength Distribution of 90° Plies in 0/90/0 Graphite-Epoxy Laminates

Graphite epoxy cross ply laminates show multiple cracking in the 90 ° ply before final rupture occurs. By the aid of a piezo-electric load cell crack formation was measured as a function of the applied load in (0 2 /90 2 ) s , (0 2 /90 3 ) s and (0 2 /90 6 ) s laminates. With these experimental results and a shear lag analysis, to account for the non-homogeneous stress distribution in cracked 90° plies, it was possible to estimate the Weibull strength distribution of the respective 90° ply. it was found that at decreasing 90° ply thickness the shape factor increases. This can be attributed to a suppression of defect growth close to the 90°/0° interface. Because of the changing shape parameter at decreasing ply thickness a description of the thickness effect by a Weibull shape parameter is im possible.