Effect of notch length and pre-crack size on mode II fracture energy of brittle adhesives

Abstract

In this study, the effects of notch length and pre-crack size on mode II fracture energy of brittle adhesives are investigated. These effects are not considered by the direct beam theory (DBT) and the compliance-based beam method (CBBM) for the end-notched flexure (ENF) specimens. The sum of the lengths of the notch and the pre-crack are known as the pre-crack size in common data reduction schemes. In the current work, experiments were performed on ENF adhesive joints using digital image correlation (DIC) technique. Then, the fracture energy was obtained experimentally based on the J-integral method, the classic beam theory, and the compliance-based beam method. Numerical analyses were carried out to measure the stress distribution ahead of the pre-crack tip. Based on the obtained results, it is shown that there is a specific pre-crack length and notch size in which the pure mode II condition in an ENF test is obtained. Other combinations of the notch to pre-crake size ratio result in mixed mode conditions where the obtained fracture energy significantly changes.