Extension of JIS K7086 for Evaluation of Fracture Toughness Value of CFRP Joint Using High Toughness Adhesive

Abstract

Two extensions were developed for the modified compliance method in JIS K7086 double cantilever beam (DCB) test to accommodate recent high-rigidity CFRP bonded with tough adhesive. First, shear bending in the short crack condition was considered for the approximation of polynomial in the estimation of energy release rate. Second, sample thickness was set as a variable to maintain a crack length-to-crack opening ratio of 0.4, which is specified in the current JIS K7086 standard with a fixed sample thickness of 3 mm. In the case of the DCB, test was conducted on the T800S/3900-2B (TORAY) unidirectional CFRP specimen bonded with AF555 (3M) tough epoxy adhesive, the extended methods showed a stable energy release rate in the short crack conditions. Conversely, the current method specified in JIS K7086 showed a decreasing value as the crack length increased. In contrast, both methods showed identical energy release rates when compared to the present JIS K7086 standard for the general-use Araldite 2015 （Huntsman） adhesive.