Experimental study of Mode I and Mode II interlaminar fracture toughness on aerospace structural composite T300/914

Carbon epoxy composite T300/914 which has wide applications in aerospace industries, as a structural material, has been analyzed, to determine the interlaminar fracture toughness. Laminates with a thickness of 4.6 mm, consisting of 48 layers of T300/914, are considered for estimating the inter-laminar fracture toughness. These specimens have been fabricated by hand layup method followed by controlled curing in an autoclave. Tests have been conducted in accordance with ASTM standards, for Mode I by Double Cantilever Beam (DCB) test and End Notch Flexure (ENF) test for Mode II. Pulse-Echo test results and C-Scan images of the specimens were also analyzed to locate the exact position of delamination. During the preliminary tests, it was found that the interlaminar fracture toughness varied, because of bonding of release film with the sides of the laminate. By Modified Beam Theory, Mode I and Mode II fracture toughness values of the prepared specimens were found to be 0.090 kJ/m2and 0.542 kJ/m2, respectively. It was also noted that the fracture toughness of the specimens from the same laminate varied with the degree of compaction.