Effect of hygrothermal aging on transverse impact mechanical properties of BFRP adhesive joints

NA Jing-xin;TAN Wei;MU Wen-long;LUAN Jian-ze

Journal of Traffic and Transportation Engineering,2020,Vol 20,No. 04

The BFRP was selected to make single lap joints in order to provide a reference for crash safety of vehicle adhesive structure. According to the service environment of vehicle, the joints were aged for 0, 5, 10, and 15 d in two environments with the temperature and humidity of 80 °C/30% (GWCS) and 80 °C/95% (GWGS), respectively. The change rules of failure load and failure mode with time were tested by the quasi-static tensile test. The glass transition temperatures of BFRP and adhesive before and after aging were analyzed using the differential scanning calorimetry. The transverse impact tests with the impact energies of 0, 20, 40, and 60 J were carried out for the joints which were unaged or aged for 15 d. The trends in energy absorption, maximum impact load, and maximum deformation with impact energy were analyzed, and the change rules of joint failure load and failure mode were also tested. The analysis result shows that after GWCS aging, the failure loads of joints decrease slightly, and the post-curing reaction of adhesive and the molecular chain fracture of BFRP occur, which makes the joints more prone to matrix cracking or fiber tearing. GWGS aging can obviously accelerate the degradation of joint performance and easily cause hydrolysis and expansion of the interface between adhesive and BFRP. After 15 d of aging, the failure loads drop by 54.99%, and the mixed failure of interface and cohesion occurs. After GWCS aging, the joints have a good ability to bear the impact load and resist deformation, and the failure loads change little after impact. After GWGS aging, the joint is obviously affected by the transverse impact, and its ability to bear the impact load and resist deformation is poor. Impacted by 60 J, the joint surface damages seriously, and the failure load tumbles by 58.71%. The mixed failure of interface and cohesion occurs, and the damage crack is obvious. It can be seen that in vehicle service, the adhesive structure should avoid the effect of high-temperature and high-humidity environment, especially the influence of transverse impact on the aging adhesive structure.