Modeling of Fracture Behaviours of Ultrasonically Welded Cu-Cu Joints Under Different Loading Conditions

A lithium-ion battery pack for electric vehicles may consist of several hundreds of battery cells joined together. Each cell contains joints of multiple thin sheets of electrodes of different conductive materials such as nickel coated copper, copper and / or aluminum. These within-cell and cell-to-cell joints must withstand static and dynamic mechanical loading. Determination of their maximum loading capacity is a very important task in order to predict the life of a battery pack. The standard procedure is to apply mechanical tests, such as lap shear and pull test to each joint. This procedure is time consuming and costly. There is a strong interest nowadays in developing validated models which can predict the actual behavior of the joints under different loadings and the associated failure modes. In this paper, two finite element models are developed to predict the strength of ultrasonically welded two-, three- and four layer joints of 0.2 mm thickness copper tabs with a 1mm thickness busbar. These models have the ability to predict three modes of failure of these joints depending on the weld quality, e.g., interfacial fracture, combined interfacial-circumferential fracture, and circumferential failure. These models are experimentally validated with very good agreement between experimental and predicted results.