Investigation of Fatigue Behavior of Steel and GFRP Double-Strap Joints under Varied Cyclic Loading at Given Temperatures

This paper examines the fatigue behavior of steel/glass fiber reinforced polymer (GFRP) double-strap joints under a variation of cyclic shear loading at different given temperatures. Initial experiments were performed at a constant amplitude force, which demonstrated a reduction in fatigue strength at increasing temperatures. The results were used for cumulative relative damage calculation purposes. Subsequent tests were then performed under two-stress level fatigue (TSLF) tests with a given temperature. The TSLF tests demonstrated the following: (1) relative to results at 20 degrees C, the damage was retarded at lower temperatures (-10 degrees C and 0 degrees C), and the damage accelerated at higher temperatures (40 degrees C); and (2) linear damage accumulation models, such as the Palmgren-Miner model, are not appropriate and tend to overpredict fatigue life. By using the nonlinear strength wearout and linear cycle mix models for bonded joints, an improved prediction method is proposed, and the fatigue results of the TSLF tests were discussed in which it was found that the proposed method can accurately predict the fatigue lifetime.