APPROXIMATE INTERLAMINAR FRACTURE ENVELOPES FOR UNIDIRECTIONAL E-GLASS/POLYESTER COMPOSITE

Abstract

In this paper an experimental study is performed in order to determine an approximate interlaminar fracture envelope of a unidirectional E-glass polyester composite. First, the pure mode-I fracture toughness is determined by using the standard double-cantilever beam (DCB) specimen. Second, the pure mode-II toughness of the material is evaluated by means of the over-notched flexure (ONF) specimen. Finally, the mixed-mode toughness is determined with the aid of the over-leg bending (OLB) coupon. Both the initiation and propagation fracture toughness are determined within the extended ranges of crack length. The fracture envelopes are determined by using the steady-state values of the fracture toughness at crack initiation and propagation. Two criteria are used to obtain the envelopes: the traditional power expression and the physically more acceptable criterion by Williams. The results are compared with previous envelopes and similarity is established.