Specimen proposals for mixed mode testing of adhesive layer

The experimental methods to determine the fracture properties for adhesives under mixed mode loading is not as well established as compared to such methods for adhesives under pure mode loading. Some controversies exist regarding the decomposition of the mode mixity. For a flexible linear elastic adhesive, the mode mixity of a single-layer adhesive joint is directly related to the deformation of the adhesive layer at the crack tip. The governing equations for linear elastic single-layer adhesive joints show that the mode mixity depends on the external loads, the properties of the adherends and often on the flexibility of the adhesive layer. This implies some fundamental problems that have to be addressed before an experimental method can be established. The purpose of this paper is to investigate different specimen configurations for mixed mode loading. Requirements for the design of a specimen configuration are given. A new specimen configuration is proposed based on the geometry of a semi-infinite symmetric DCB-specimen. According to this study, the proposed test specimen offers exceptional flexibility, variety and stability.