Experimental analysis of damage propagation in riveted CFRP-steel structures by thermal loads

This paper focuses on the description of damage propagation around rivets in multiple joined single lap carbon fiber reinforced plastics (CFRP)-steel structures due to loads as a consequence of different coefficients of thermal expansion. Materials and rivets were chosen according to automotive body shop applications. Specimens were evaluated non-destructively in ultrasonic C-scans to characterize damage behavior of blind and self-piercing rivets in CFRP-steel-connections before and after the application of thermal loads. An algorithm for an automated detection of damage size on ultrasonic C-scan images was developed as the basis for further damage classification. The results show that blind riveting (BR) causes crack-like initial damage that broadens to roundish plane defects due to heating. Initial extensive damage due to self-piercing riveting (SPR) propagates in elliptic shape. Additionally, tension tests revealed a loss in ultimate load by 10–15 % induced by thermal loads and associated with damage propagation. A correlation between initial damage, relative displacement, and thermal loads was observed.