Comparison of lightning strike damage in bolted and bonded CFRP joints using a coupled electro-thermal FE model

Abstract

Carbon Fiber Reinforced Plastics (CFRPs) composite structures are widely used in aeronautical structures. Due to the semiconducting nature of CFRPs, lightning strikes can cause significant damages in aircraft components made from such materials. In CFRP laminates joined by mechanical fasteners or adhesive bonding, the damage induced by lightning strikes is a complex multiphysics coupling process. In the present work, in order to study the effects of the different lightning current components on CFRP joints due to the Joule heat flux phenomenon, a coupled electro-thermal FE model has been developed using the ANSYS commercial FE code. Two case studies are considered, i.e. a bolted single-lap joint and an adhesively bonded single-lap joint of CFRP laminates. The model is based on the SOLID5 coupled field solid element and applies a non-linear, time-transient analysis. The main input to the model are the thermal-electrical properties of the CFRP material which vary with temperature. Three electrical lightning strikes of low, medium, and high peak intensity have been applied according to the SAE ARP 5412 standard. The numerical results reveal the detrimental effect of the lightning strike on the bolted joint of the riveted case as the electro-thermal conditions on the bolt facilitated the through-the-thickness degradation of the CFRP material, as opposed to the adhesively bonded joint where the increase of the peak intensity has led to an escalation of the area and penetration of matrix thermal damage (pyrolysis) as well as to the increase of fiber damage (deterioration and ablation). Through static mechanical analysis, the residual joint stiffness has been also predicted.