Investigations on low-energy impact and post-impact fatigue of adhesively bonded single-lap joints using composites substrates

This paper presents an extensive investigation on the low-energy impact damage and post-impact fatigue of composite/steel and composite/composite adhesive joints experimentally and numerically. Using carbon-fiber and glass-fiber reinforced plastics (CFRP and GFRP) as well as high-strength steel (HSS), four kinds of adhesive joints were fabricated, i.e., CFRP/CFRP, CFRP/HSS, GFRP/GFRP and GFRP/HSS single-lap joints (SLJ). The impact damage of the joints under different energy impacts was analyzed and introduced into the fatigue simulation. A multi-step coupling numerical method was proposed and validated to predict the post-impact fatigue life of the adhesive joints cost-effectively and conveniently. The effects of the impact energy density and the adherend/adhesive stiffness ratio were studied. The results show that the post-impact fatigue life decreases with the increasing impact energy density. The life decrease percentage of 1275 mJ/g impact condition is approximately more than seven times that of 425 mJ/g impact condition. The post-impact fatigue life of composite/steel joints is more susceptible to low-energy impact damage than that of the composite/composite joints. Reducing the flexural stiffness difference between two adherends as well as the adhesive can improve the post-impact fatigue life of the adhesive joints in composites.