The role of T-stress and stress triaxiality combined with the geometry on tensile fracture energy of brittle adhesives

In this study, a new semi-empirical evaluation method is proposed to take into account the effects of substrate stiffness and bondline thickness on the tensile fracture behavior of brittle adhesives. To this end, combined experimental-numerical analyses are conducted on double cantilever beams with various geometries. Two different data reduction approaches including the simple beam theory and the J-integral technique are employed to obtain the fracture energy of the tested joints. The experimental fracture energy and the corresponding numerical results are used to analyze the considered configurations based on the proposed relation. The new parameter is a function of the tensile fracture energy (GIC), the first non-singular stress term of William's series expansion (T-stress), the amount of stress triaxiality and the bondline thickness (t). Based on the proposed method, the role of each factor in the mode I fracture energy of brittle systems is specified. It is found that the T-stress has a critical impact on the GIC obtained by adhesively bonded double cantilever beams (DCBs) where the adhesive bondline is different. It is also shown that the effect of stress triaxiality is less significant but it should be taken into account. The results also show that the new relation can predict the effect of the substrate stiffness on the GIC of the considered adhesives very well. The optimum bondline thickness of DCBs corresponding to the maximum GIC is also predicted based on the proposed relation. Further validations are also performed by applying the method to experimental data previously published in the literature.