Despite existing studies on the effects of temperature on the behavior of bonded joints, the role of loading mode and test type (strength, fatigue, and fracture tests) on the rate of degradation of adhesive/joint properties at high temperatures has not been adequately investigated. The aim of the current study is to determine if adhesives experience the same rate of degradation at high temperature when they are subjected to different mode mixities. To do so, an epoxy adhesive was subjected to strength, fracture, and S–N fatigue tests, for modes I and II, at different temperatures. The results show that there is a significant difference between the rate of degradation in mode I/tensile and mode II/shear loading conditions. It was also found that the rate of degradation in adhesive properties is a function of test type. Based on the results, by increasing the temperature, a less reduction in tensile strength was found in the Arcan joints (almost 50% reduction) compared with the dogbone specimen (where the strength was reduced by less than 40%). According to the results, for all the considered tests, temperature sensitivity was more noticeable in tensile loading conditions compared with the shear mode. It is shown that despite the reduction in tensile fracture energy with temperature (by around 23%), the shear fracture energy was improved (by over 20%) at 50°C. Based on these results, an S–N model was also developed to create a master S–N curve, plotted as a function of temperature.
The strength and the performance of adhesive joints can be significantly influenced by the ageing procedure. However, the role of aging in the failure mechanism of adhesive joints as a function of loading conditions has not been studied yet. The current research aims to investigate the effect of mode mixity on the failure mechanism of aged adhesive joints using Arcan samples. Based on the results loading the tested joints in shear led to a higher percentage of interfacial failure than in tensile. However, it was also found that the shear loading mode is less sensitive (compared to tensile loading) to the ageing conditions.
Hygrothermal aging has a significant impact on the performance of adhesives and bonded joints. However, despite extensive investigations into the aging effect of bonded structures, there is still limited knowledge on how aging affects joint performance as a function of the loading type and the load angle.Accordingly, in this study, an epoxy adhesive was tested under different loading types/angles including tensile and shear standard strength tests, mode I and mode II fracture tests, and fatigue and static Arcan tests. All these experiments were performed for both aged and unaged conditions. To understand the influence of loading angle on the failure response of aged bonded joints, Arcan samples were subjected to mixed mode loading conditions as well. A fractography analysis was conducted to provide a better understanding of the failure mechanism of aged samples loaded at different modes. Based on these results, it was found that mode I (tensile loading conditions) is more sensitive to the aging conditions than mode II (shearing) for all loading types (strength, fracture, and fatigue tests). The influence of moisture on fracture toughness was however less relevant than the strength. The results also showed that for the same loading mode and for the same Arcan joints, the fatigue strength is significantly more degraded by the aging conditions than the static strength.
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