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

Abstract

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.

DCB tests at constant strain rate using crash-resistant epoxy adhesives: A numerical and experimental approach

“…These results are compared with simulations of the strain rate evolution for the same adhesives at constant velocities of 150 and 15 mm/s, some of which were performed in a previous work. 19 For all the cases shown, it is possible to notice that the values of strain rate are pretty much constant throughout the tests. The biggest deviation, around 20% of the target value, was found for the case of the Nagase XNR6852 E-3 at constant strain rate of 100 s -1 .…”

“…As mentioned before, the authors first assessed how the strain rate changed as the crack propagates along the specimens of DCB and ENF tests in a previous study. 19 One of the main conclusions of that study was that the variation of strain rate could be significant for the determination of the energy release rate in mode I, since it was found that the strain rate in the final part of the test was around three times lower than that measured at the beginning of the test.…”

“…The procedure to calculate the strain rate is described in detail in a previous study. 19 To create the mesh of the substrates, represented in Figure 1(b), the authors employed biasing techniques with element dimensions varying from 5 to 1 mm in the direction of the adhesive thickness and a constant distance of 1 mm along the bondline. In the areas of the substrates that were not bonded by the adhesive (namely the loading and pre-crack zones) a rougher mesh was used.…”

“…In a previous study 19 the authors assessed how the strain rate changed with the propagation of the crack along the bonded area of specimens being loaded in DCB and ENF tests. It was found that while the variation of strain rate was minimal for the ENF test, at least for the duration of the testing stage were the energy release rate in mode II could be measured, for the DCB test it was found that the strain rate changed drastically, being around three times lower in the final stages in the test than the initial value measured at the beginning of the test.…”

Effects of impact fatigue on residual static strength of adhesively bonded joints

“…Nunes et al. 11 studied the influence of strain rate on modes I and II fracture energy. Their results showed that when a DCB specimen is loaded at a constant cross-head speed, the strain rate is not constant ahead of crack tip.…”