Further validation of the Jain and Mai models for interlaminar fracture ofstitched composites

Micromechanical models proposed by Jain and Mai to predict the improvement in Modes I and II interlaminar fracture toughness (G(R)) Of polymer composi tes when reinforced by through-thickness stitching have been further valida ted against a large number of measured G(R) values. Experimental G(R) value s were obtained from the literature for a variety of carbon- and glass-fibr e-reinforced polymer composites stitched over a wide range of densities wit h different yam materials (polyester, carbon, glass, Kevlar(R)) of varying thickness. Good agreement was found between the measured and theoretical in terlaminar fracture toughness values for both the Modes I and II conditions , despite some major assumptions having to be made about the failure mechan ism and mechanical properties of the stitches. An assessment of the experim ental Mode II G(R) data reveals that the commonly used end-notched flexure method is not suitable for the interlaminar fracture toughness testing of s titched composites. It is recommended that Mode II delamination resistance should be measured by using the end-notched cantilever method. (C) 1999 Els evier Science Ltd. All rights reserved.