Failure analysis of novel hybrid busbars made by hole hemming for electric vehicle applications

Abstract

This paper focuses on the failure behavior of novel joints between aluminum and copper sheets produced by hole hemming, with potential applications in hybrid busbars for electric vehicle batteries. This technology involves deforming the aluminum sheet to create a mechanical interlock with the copper sheet, eliminating the need for additional elements, heat, or welding. First, the materials are characterized, and the most suitable strain hardening law is determined to model their post-necking behavior. Then, to model their ductile fracture behavior, the Modified Mohr–Coulomb (MMC) fracture criterion is calibrated through uniaxial tension, plane strain, and shear tension tests. Next, hole-hemmed joints are manufactured and subjected to shear tests. A comprehensive numerical model of the hole hemming process and shear test is developed to investigate the joints’ failure mechanisms and study the influence of mechanical interlock and process deformation history on joint performance. The findings show that the created joints achieve a maximum load of 3.56 kN and a displacement of 9.30 mm. The main failure mode predicted is hole bearing, which aligns with the mode observed in experimental tests. Finite element analysis reveals that while no damage occurs in the copper sheet during the joining process, this sheet is damaged during the shear test, leading to joint failure. Additionally, a higher mechanical interlock leads to greater failure displacement and load, although it decreases the initial load level. This research demonstrates that novel hole-hemmed joints can effectively connect aluminum and copper sheets, presenting promising results for battery applications.