Effect of hygrothermal and alternating load coupled aging on CFRP/Al bonded joints

Abstract The fracture failure of bonding structures is closely related to aging environment, so it is of great significance to study the effect of hygrothermal and alternating load coupled aging on bonding structures. Referring to the actual service environment of the vehicle, we formulated three kinds of artificial accelerated aging conditions, including temperature cycle, high temperature and high humidity and hygrothermal cycle. CFRP (Carbon Fiber Reinforced Plastic)/Al butt joints were selected as research object. Under these conditions, after aging for 0 day, 5 days, 10 days, and 15 days, respectively, quasi-static tensile tests were carried out to analyze the failure strength and failure modes of the joint. Through FTIR (Fourier Transform Infrared Spectroscopy) and DSC (Differential Scanning Calorimeter) tests of the CFRP and adhesive before and after aging, the change law of material chemical properties after environment aging was studied, and the influence mechanism of hygrothermal environment on joint was discussed. All three environmental aging conditions were coupled with alternating load, and the accelerated aging tests of joints were carried out to obtain the aging law. Combined with the two factors analysis of variance, the influence degree of different factor on joint strength in coupled aging was quantitatively studied respectively. The results showed that the failure strength of the joint will decrease rapidly and then slowly as aging time went by. Furthermore, with the introduction of alternating load, the decrease of joint failure strength became faster, which was mainly due to the degradation of the adhesive layer and the damage of the adhesive/substrate interface. Under the conditions of hygrothermal coupled with alternating load, the damage mainly occurred in the adhesive layer. Among these three coupled aging conditions, the condition of hygrothermal cycle coupled with alternating load has the worst influence on the joint strength, followed by the high temperature and high humidty coupled with alternating load, and the temperature cycle coupled with alternating load has the least influence on the joint strength.