Mixed mode I/III fracture behavior of adhesive joints

Abstract

In this paper, the mixed mode (I/III) fracture behavior of an epoxy based adhesive is investigated using a modified mixed mode I/III apparatus. The fracture tests are performed on adhesively bonded aluminum rectangular specimens with different adhesive thicknesses. Based on the obtained experimental data, the critical stress intensity factors (SIFs) of the adhesive are calculated by performing a 3D finite element analysis (FEA). Then, the fracture energy of modes I and III of the adhesive were extracted using SIFs. To verify the obtained fracture energy, an extended finite element model (XFEM) was employed. The obtained numerical results were in good agreement with the experimental data. It shows that the proposed apparatus can be applied for measuring the mixed mode I/III fracture energy of brittle or semi brittle adhesives where a small scale yielding around the crack tip is observed. The crack propagation path was also analyzed and the out-of-plane angle of crack propagation in the adhesive layer was estimated using XFEM. By comparing the experimental fracture surfaces with the crack propagation path obtained out of the numerical results, it is observed that the XFEM can provide an appropriate estimation of the crack propagation path in adhesive joints under mixed I/III loading.