The effect of the T-stress on crack path selection in adhesively bonded joints

This paper investigates the effect of the T-stress on crack path selection in adhesively bonded joints. Fleck et al. (Int. J. Solids Structures 27 (1991) 1683) concluded that, similar to the situation in homogeneous solid media, the directional stability of cracks in adhesive bonds is also significantly influenced by the magnitude of the T-stress. Cracks tend to be directionally stable when the T-stress is negative (compressive) and directionally unstable when the T-stress is positive (tensile). This T-stress dependence of crack path selection in adhesively bonded joints is demonstrated experimentally in this study using double cantilever beam (DCB) specimens with various levels of the T-stress. The technique reported to vary the T-stress involves a mechanical stretching procedure of the specimens and is able to continuously alter the T-stress level over a fairly wide range. Using the finite element analysis (FEA) method, the T-stress for DCB specimens is calculated and comparison is made with the analytical solution obtained by Fleck et al. (Int. J. Solids Structures 27 (1991) 1683) for the bi-material sandwich geometry with semi-infinite adherends. The FEA results show that the T-stress increases as the thickness of the adherends decreases, indicating a mild effect of adherend thickness on the directional stability of cracks. This prediction is verified in this paper using DCB specimens with different thickness adherends.