Finite element analysis of the asymmetric ENF test specimen

The objective of this article is to investigate the asymmetric end notched flexure (AENF) test. The AENF test specimen consists of two sublaminates with different stiffnesses (dissimilar elastic properties and/or thicknesses). A key observation in this test is that AENF test specimens exhibit different fracture behaviour depending on their positioning in the test. Depending on the position of the stiffer sublaminate, ‘local contact’ or ‘global contact’ may occur along the cracked arms giving rise to different contact pressure distribution. This variation in the contact pressure distribution leads to different fracture behaviour at the crack tip: mixed-mode I/II or pure mode II. This work demonstrates that a straightforward experimental or numerical compliance calibration (CC) procedure can effectively determine the total energy release rate (ERR) in mixed-mode conditions (G​=G_I​+G_II​) or the mode II component (G_II​) when pure mode II is present, depending on the positioning of the specimen. The criterion established by other authors under which the AENF test configuration exhibits pure mode II at the crack tip was also reviewed. In this case, analytical formulations developed by other authors were compared with the CC procedure and the virtual crack closure technique (VCCT). Finally, this article examines the influence of several test parameters on the mode mixity. These parameters include the specimen degree of asymmetry, the initial crack length, and the degree of the deformation applied during the test. The entire investigation was conducted using the finite element method (FEM).