Potential energy as a new approach for detection and monitoring of fatigue damage in scarf adhesive joints modified with nanoparticles

Abstract

In this study, fatigue results of the scarf adhesive joints (SAJs) were extensively analyzed regarding the effect of the adhesive materials (neat epoxy (NE), and SiC and Al₂O₃-nanocomposite), bond thickness (0.17 mm and 0.25 mm) on their dynamic properties, which include loss factor (tan δ), loss modulus (E''), dissipated energy (U _d ), potential energy (U _p ), and storage modulus (E'). Safe fatigue lives of the NE, SiC, and Al₂O₃-SAJs were estimated at different reliability levels. The experimental measurements revelated that reducing the adhesive layer thickness from 0.25 mm to 0.17 mm result in enhancing the tensile strength and stiffness of the SiC-SAJs by 9.6% and 4.4%, respectively, in return of 9.5% and 5.4% for the Al₂O₃-SAJ relative to the NE-SAJ. The strength and stiffness of the SiC-SAJs with 0.17 mm bond thickness are higher than those of the Al₂O₃-SAJ by 15.4% and 3.3%, respectively. The highest improvement of 22.0% in the fatigue strength was occurred for the SiC-SAJ with bond thickness of 0.17 mm in return of 4.8% for the Al₂O₃-SAJ. The U _p was used for the first time (except author works) for monitoring and predicting the damage in the adhesive joints practically the change in the enclosed area of the hysteresis loop is too small to cause a large variation in the tan δ, E'', and U _d . Damping factor of the NE-SAJs is marginally increased with the stress levels compared to the aggravated increase of both SiC and Al₂O₃-SAJs. Zhang model predicts well the potential energy and storage modulus specially at higher stress levels.