Fatigue behaviors and mechanism-based life evaluation on SPR-bonded aluminum joint

Abstract

Fatigue behaviors of hybrid joint, the combination of cold-formed mechanical fastening with adhesive bonding, are yet to be understood comprehensively even though they have been widely used in industries. The lack of understanding is mainly attributed to the complicated load transfer path and possible interactions between the two types of joining techniques, namely mechanical interlocking and adhesive bonding. In the present work, fatigue tests are performed on self-piercing riveted (SPR) joint, adhesive-bonded joint, and the SPR-bonded joint under lap shear and 45° loading conditions. Failure mechanisms are evaluated based on terminated fatigue test and numerical analysis. Periodical and asymmetric failure mode can be identified in SPR-bonded joint. Although both crack pinning and asymmetric failure mode induced by SPR suppress the crack growth in adhesive bonding, the effect of crack pinning is significant only when crack approaches SPR. The asymmetric failure also leads to load transfer path evolution, intensifying damage on SPR joining. A mechanism-based fatigue life evaluation method is proposed by characterizing the interactions with crack growth method and structural stress method. The calculated results are compared with the experimental ones, and good correlations are observed for both lap shear and 45° loading conditions.