a b s t r a c tThe interfacial fracture of adhesively bonded structures is a critical issue for the extensive applications to a variety of modern industries. In the recent two decades, cohesive zone models (CZMs) have been receiving intensive attentions for fracture problems of adhesively bonded joints. Numerous global tests have been conducted to measure the interfacial toughness of adhesive joints. Limited local tests have also been conducted to determine the interface traction-separation laws in adhesive joints. However, very few studies focused on the local test of effects of adhesive thickness on the interfacial traction-separation laws. Interfacial toughness and interfacial strength, as two critical parameters in an interfacial traction-separation law, have important effect on the fracture behaviors of bonded joints. In this work, the global and local tests are employed to investigate the effect of adhesive thickness on interfacial energy release rate, interfacial strength, and shapes of the interfacial traction-separation laws. Basically, the measured laws in this work reflect the equivalent and lumped interfacial fracture behaviors which include the cohesive fracture, damage and plasticity. The experimentally determined interfacial traction-separation laws may provide valuable baseline data for the parameter calibrations in numerical models. The current experimental results may also facilitate the understanding of adhesive thicknessdependent interface fracture of bonded joints.

The hydrodynamic behavior of a squirmer swimming in the flow of power-law fluid is studied numerically with an immersed boundary-lattice Boltzmann method. The power-law fluids with three typical power-law indexes (n = 0.5, 1, and 1.5) are selected for embodying the characteristics of non-Newtonian fluid. The results show that, at zero Reynolds number, the squirmers swim slower in the shear-thinning fluid (n = 0.5) than in the Newtonian fluid (n = 1). The speed of squirmer swimming increases monotonically with the Reynolds number in the shear-thickening fluid (n = 1.5). When the fluid inertia is taken into account, the speed of a pusher (a kind of swimmer type) increases monotonically with the Reynolds number, while the speed of a puller (another kind of swimmer type) shows a non-monotonic increasing tendency. Some critical points, beyond which the pullers swim with lateral displacement, are obtained. The flow field and force distribution around the squirmer are calculated and analyzed. The power expenditure of squirmers in different kinds of flow is also studied. It is found that, as the Reynolds number increases, the power expenditure generally decreases in shear-thinning fluid, which is different from the case in Newtonian fluid and shear-thickening fluid. Finally, the hydrodynamic efficiency is introduced to compare the power expenditure of squirmers with that of a counterpart particle towing in the same type of fluid. Results show that the hydrodynamic efficiency of pushers increases with the Reynolds number, while the hydrodynamic efficiency of pullers shows non-monotonic behavior when the Reynolds number is varied.

a b s t r a c tThe nonlinear analytical solutions of an end notched flexure adhesive joint or fracture test specimen with identical or dissimilar adherends are investigated. In the current study, a cohesive zone model (with arbitrary nonlinear cohesive laws) based analytical solution is obtained for the interface shear fracture of an end notched flexure (ENF) specimen with sufficiently long bond length. It is found that the scatter and inconsistency in calculating Mode II toughness may be significantly reduced by this model. The present work indicates that the Mode II toughness G IIc under pure shear cracking condition is indeed very weakly dependent on the initial crack length. And this conclusion is well supported by the experimental results found in the literature. The parametric studies show that the interface shear strength is the most dominant parameter on the critical load. It is also interesting to note that with very short initial crack length and identical interface shear strength, higher Mode II toughness indeed cannot increase the critical load. Unlike the high insensitivity of critical load to the detailed shape of the cohesive law for Mode I peel fracture, the shape of the cohesive law becomes relatively important for the critical load of joints under pure Mode II fracture conditions, especially for joints with short initial crack length. The current study may help researchers deepen the understanding of interface shear fracture and clarify some previous concepts on this fracture mode.

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