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Numerical assessment of strain rate in an adhesive layer throughout double cantilever beam and end notch flexure tests

The increasingly larger use of adhesive joints in the automotive industry demands a full comprehension of the adhesive behaviour when subjected to dynamic loadings. So far, some authors studied the effect of the strain rate regarding the adhesives performance, usually for the range of approximately 0–105/s; nevertheless, few studies are clear regarding the method used to calculate strain rate, especially when fracture mechanics analysis is the focus of study. Those who present approaches to assess the values of strain rate usually consider a constant value for each test. In this paper, a numerical approach is proposed to assess the strain rate in modes I and II in double cantilever beam and end notch flexure tests, respectively. The results of this study demonstrate that the strain rate in the adhesive bondline along the crack propagation in the double cantilever beam and end notch flexure tests is not constant when loaded at a constant cross-head speed. This finding also helps to justify why experimental R-curves of double cantilever beam tests, when loaded at speeds above quasi-static conditions, do not have a perfect plateau contrasting with those, usually presented by numerical simulations, that do not take into account the effect of the strain rate.