Effects of hygrothermal ageing and temperature on the mechanical behavior of aluminum-CFRP hybrid (riveted/bonded) joints

Hygrothermal ageing and temperature significantly affect the mechanical properties of joints, but the research on their coupling effect in hybrid joints is insufficient. In this work, the combined effects of the long-term factor of hygrothermal ageing and the short-term factor of temperature on the mechanical properties of Al/CFRP hybrid (riveted/bonded) joints (HJs) are investigated by quasi-static tensile experiments and an advanced simulation method. The mechanical properties of HJs with four kinds of ageing degrees are tested at four temperatures (-40 degrees C, 20 degrees C, 50 degrees C, and 80 degrees C). Experimental results show that the joint strength is mainly affected by temperature, while the breaking elongation is sensitive to the degree of ageing. Although the joint stiffness and strength decrease significantly under the combined action of the increase in temperature and the deepening of the ageing degree, the three-stage characteristics of failure (first, the adhesive bond and the rivet share the load; and then the adhesive bond gradually fractures and loses its load-bearing capacity; finally, the rivet bears the load alone) do not change. Furthermore, by integrating the change information of moisture absorption and Fourier transform infrared spectrum into the material model, the simulation shows new light on the failure mechanisms of the HJs on the coupling effect of temperature and hygrothermal ageing. In conclusion, this research helps deepen the understanding of the changing laws of mechanical behavior of Al/CFRP hybrid joints under actual service conditions.