Effect of service temperature on static failure of BFRP/aluminum alloy adhesive joints

In order to predict the static failure behavior of BFRP/aluminum alloy adhesive joint under service temperature in the process of vehicle lightweight design, the adhesive joints under three different stress states were manufactured, including tensile stress state, shear stress state and combined tension-shear stress state, five temperature measuring points of-40 ℃, -10 ℃, 20 ℃, 50 ℃ and 80 ℃ were selected according to the characteristics of vehicle service temperature, the change rules of adhesive joint failure strength with service temperature under different stress states were obtained based on the quasi-static tensile test, and the failure forms and failure criteria of adhesive joints were analyzed. Based on the tensile and shear stresses of adhesive joints at different service temperatures, the quadratic stress failure criterion equations of the joints were established to predict the failure strengths of the joints at different service temperatures. Analysis result shows that the failure strength of the adhesive joint is obviously affected by the service temperature, and the failure strength decreases with the increase of the service temperature. The different proportions of shear stress and tensile stress in the adhesive joint will also have a certain impact on the failure strength of the joint, and the failure strength of the joint will decrease more obviously with the increase of the service temperature at greater shear stress proportion. Compared with the service temperature-40 ℃, the failure strengths of tensile and shear joints decrease by 47.77% and 61.49% at 80 ℃, respectively. With the increase of the service temperature, the failure stress and Young's modulus of the adhesive decrease gradually, while the failure strain increases gradually, which shows that the service temperature affects the mechanical properties of the adhesive greatly. The failure mode of the adhesive joint is the mixture failure of cohesion and fiber tearing. Under the action of tensile stress, the joint is more prone to fiber tearing. With the increase of the service temperature, the fiber tearing area decreases. In order to prevent fiber tearing, it is necessary to avoid the effect of tensile stress on the adhesive joint. The fitting accuracies of the quadratic stress failure criterion curves of the adhesive joints at different service temperatures are more than 0.957, therefore, the drawn response surface of failure criterion can reflect the change rule of failure strength of the adhesive joint at the service temperature of vehicle.