Recent uptake in the use of lithium-ion battery packs within electric vehicles has drawn significant attention to the selection of busbar material and corresponding thickness, which are usually based on mechanical, electrical and thermal characteristics of the welded joints, material availability and cost. To determine joint behaviour corresponding to critical-to-quality criteria, this study uses one of the widely used joining technologies, ultrasonic metal welding (UMW), to produce tab-to-busbar joints using copper and aluminium busbars of varying thicknesses. Joints for electrical and thermal characterisation were selected based on the satisfactory mechanical strength determined from the T-peel tests. Electrical contact resistance and corresponding temperature rise at the joints were compared for different tab-to-busbar joints by passing current through the joints. The average resistance or temperature increase from the 0.3 mm Al tab was 0.6 times higher than the 0.3 mm Cu[Ni] tab, irrespective of busbar selection.

The mechanical response of steel auxetic structures manufactured using laser-powder bed fusion was explored. The level of control exerted by the key design parameters of vertical strut length (H), re-entrant strut length (L), strut thickness (t) and re-entrant angle (ϴ) on the mechanical response was examined through a design of experiment approach with ANOVA statistical analysis methods applied. The elastic modulus in directions normal to (E_x) and parallel to (E_y) the vertical strut was found to be primarily dependent upon t and L, respectively, whereas yield strength in both test directions (σ_x and σ_y) was strongly dependent on t and L. A large variation in modulus was found between the two test directions (E_x / E_y – 1.02 ± 0.07 GPa/ 4.4 ± 0.1 GPa), whereas, yield strength showed little anisotropy (σ_x / σ_y–45 ± 6 MPa/ 45 ± 9 MPa). Poisson’s ratio parallel to the vertical strut varied considerably with geometry but not in a direction normal to the vertical strut. Deformation mechanisms were found to be different of compression in the x and y directions, being a combination of stretching of the vertical strut; compression, bending and hinging of the re-entrant strut (x); and vertical strut compression and re-entrant strut stretching and bending (y).

To assist in light weighting of electric vehicles by improving the volumetric and gravimetric energy density and the structural performance of the battery pack, a modelling methodology based on a macro finite element model of a pouch cell has been developed. This model treats the core cell structure as a homogeneous orthotropic honeycomb block with the pouch material being defined as an orthotropic fabric with compressive stress elimination. The model considers five compression and bending load cases simultaneously and allows a level of element discretisation that is computationally efficient and appropriate for inclusion in full vehicle and sub-system simulations. The methodology is scalable in that it can be applied to a range of chemistries, external geometries and internal cell constructions. When considering stacks of cells, the model is predictive for both lateral compression and three-point bend, but further work is required to improve the confined compression response.

Traditionally, prediction of the dimensions of an assembly has concentrated on the variation of the constituent components and fixtures. Although recent methods have accounted for both statistical variation and flexibility of sheet metal components, the impact of the joining process has largely been ignored for riveted and spot-welded assemblies. The self-piercing rivet (SPR) has been used increasingly in the automotive industry for joining lightweight aluminium body structures, but the localized distortion around an SPR has been shown to be greater than that associated with the spot weld commonly used in steel body constructions. Consequently incorporation of such distortion into the simulation process for predicting the overall distortion of assemblies would be useful. This paper presents a simulation method based on a local/global approach where the distortion occurring around a single SPR is projected on to a global assembly at each rivet location. The results for both flat sheet assemblies and a simple top-hat assembly are presented for comparison and show that the method can be valuable in the early design stages by predicting the distortion from the joining process. Some suggestions for improving the method are also discussed.

Laser micro-welding is increasingly being used to produce electrically conductive joints within a battery module of an automotive battery pack. To understand the joint strength of these laser welds at an early design stage, micro-joints are required to be modelled. Additionally, structural modelling of the battery module along with the electrical interconnects is important for understanding the crash safety of electric vehicles. Fusion zone based micro-modelling of laser welding is not a suitable approach for structural modelling due to the computational inefficiency and the difficulty of integrating with the module model. Instead, a macro-model which computationally efficient and easy to integrate with the structural model can be useful to replicate the behaviour of the laser weld. A macro-modelling approach was adopted in this paper to model the mechanical behaviour of laser micro-weld. The simulations were based on 5 mm diameter circular laser weld and developed from the experimental data for both the lap shear and T-peel tests. This modelling approach was extended to obtain the joint strengths for 3 mm diameter circular seams, 5 mm and 10 mm linear seams. The predicted load–displacement curves showed a close agreement with the test data.

This paper investigated various aspects of replacing existing micro-resistance spot welding (micro-RSW) with micro-laser spot welding for joining Inconel 718 thin foils to thick 410 steel stack-up to allow faster, non-contact joining together with flexibility in spot positioning and removal of tip dressing required for RSW electrodes. The joint quality was evaluated based on the mechanical strength, microstructural characteristics and joint strength at elevated temperature as these joints are often used for high-temperature applications. Experimental investigations were performed using micro-RSW and micro-laser spot welding to obtain the 90° peel and lap shear specimens, each comprising four spots. The obtained strength from laser joints was significantly higher than that of micro-RSW joints due to larger weld nugget formation and interface width. The process map for obtaining good quality welds was also identified, and about a 17% reduction in joint strength was obtained when welded specimens were subjected to elevated temperature (i.e., 500 °C) in comparison with room temperature. This reduction was compensated for using the flexibility of laser welding to add two extra spots. The overall performance of the micro-laser spot welds was found to be better than the micro-RSW considering joint strength, flexibility in placing the spots and time to produce the welds.