The determination of Mode III fracture toughness in thick composite laminates

In this paper we propose a method of determining the Mode ZZZ interlaminar fracture toughness in thick composite laminates. Previous finite element results show that when an edge-cracked composite specimen is subjected to torsion loading, the fracture behavior is dominated by Mode III. In order to simplify the calculation of strain energy release rate, an analytical series solution employing effective moduli is derived to study the fracture behavior of edge-cracked multilayer laminates. This analytical tool is applied for angle-ply laminates to characterize the critical strain energy release rates. Several angle-ply laminates with artificial damage located at arbitrary interfaces have been tested to find the interlaminar fracture toughness under torsion loading. Experimental results show that Gut, ranges from 650 to 850 J/m2 for most cases. Test results reveal that this theory and experimental method can be used to find interlaminar Gmc values for angle-ply composites.