Fatigue Life Prediction of Adhesive Joints Based on Initial Stiffness and Stiffness Degradation

Use of adhesively bonded joints in structures has been increased in recent years because of their advantages. In structural applications, fatigue is generally considered to be the most important form of loading in respect to long-term service life. In this paper, experimental tests have been performed in order to examine the fatigue damage process of double lap adhesive joints, composed of E-glass laminates and epoxy adhesive with TiO2 particles, under fatigue loading and then a method was proposed for fatigue life prediction based on initial stiffness. The scatter in results shows that the fatigue life is mostly dependent on initial stiffness. According to this, an exponential equation based on the initial stiffness has been proposed to have an initial estimation of fatigue life of the adhesive joints. In addition to the initial stiffness, stiffness degradation of the joints under fatigue loading influences on their final performance and therefore the initial estimation of fatigue life based on the initial stiffness could be modified. Also to have an online control of the fatigue damage process during the fatigue loading, a damage index using stiffness degradation was introduced.