Development of a rivet geometry for solid self-piercing riveting of thermally loaded CFRP-metal joints in automotive construction

Due to excellent mechanical properties, carbon fibre-reinforced plastics (CFRP) are often used for lightweight structures in the mobility sector and combined to sheet metals in order to reduce the weight of the structure. Due to different melting temperatures, the use of conventional thermal joining technologies is restricted. Therefore, the demand of efficient mechanical and adhesive joining technologies is increasing. In this publication, the damage behaviour of self-piercing riveted CFRP-metal joints subjected to thermal loading is analysed via computed tomography . Particular attention is paid to the residual stresses introduced in the CFRP, resulting from an interference-fit of the rivet and the laminate. It is shown, that primarily radial compressive stresses are responsible for the observed failure of the CFRP. With regard to these effects, geometric adaptions of the self-piercing rivet are carried out, which prevent damages occurring during the thermal loading. Therefore, a calculation method based on complex valued potential functions to determine stress concentrations in the composite with interference-fit bolts is used. The calculation is validated via optical 3D image-correlation. The damage reduction using the developed rivet is validated by means of micro-sections and single-lap shear tests.