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 (19 91) 1683) concluded that, similar to the situation in homogeneous solid med ia, the directional stability of cracks in adhesive bonds is also significa ntly influenced by the magnitude of the T-stress. Cracks tend to be directi onally 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 experi mentally in this study using double cantilever beam (DCB) specimens with va rious levels of the T-stress. The technique reported to vary the T-stress i nvolves a mechanical stretching procedure of the specimens and is able to c ontinuously alter the T-stress level over a fairly wide range. Using the fi nite element analysis (FEA) method, the T-stress for DCB specimens is calcu lated and comparison is made with the analytical solution obtained by Fleck et al. (Int. J. Solids Structures 27 (1991) 1683) for the bi-material sand wich 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 differen t thickness adherends. (C) 2001 Elsevier Science Ltd. All rights reserved.