Thoughness determination in composite multimaterial closed corners

Abstract

In the present work, a general procedure for the experimental evaluation of the generalized fracture toughness in multimaterial corners is defined. The proposed method is suitable for closed corners (all material wedges being bonded) having two singular terms in the asymptotic stress representation at the corner tip. For a particular corner configuration, the method finds the load configuration at which one of the singular terms vanishes, thus the main stress contribution being controlled by the other nonvanishing singular term. The experimental test, until failure, using the previously defined load configuration allows the generalized fracture toughness associated to each singular term to be evaluated. The whole procedure has been applied to a bimaterial CFRP-Adhesive bimaterial corner and the generalized fracture toughness values have been obtained. The testing of mixed modes has permitted a failure envelope based on the generalized fracture toughness values at the corner tip to be defined. Previously published results, with different geometries, but involving the same corner, have shown that the failure envelope can predict accurately the failure initiation at these corners.