A Perspective on Materials Selection for Body Structure Lightweighting in Battery Electric Vehicles

Automotive body structure light-weighting for internal combustion engine vehicles is constrained by simultaneous and increasingly challenging vehicle cost, fuel economy and passenger safety standards. Mass optimization via materials selection in internal combustion engine vehicles, therefore, is ultimately dependent on the normalized cost of mass reduction solutions and the associated implications on passenger safety and vehicle performance metrics. These constraints have resulted in development and implementation of increasingly high specific-strength solutions for metallic components in the body structure and chassis. In contrast, mass optimization in battery electric vehicles is subject to alternative performance metrics to fuel efficiency, although considerations for vehicle safety and cost naturally remain directionally similar. In this study, an analytical model adapted from constrained optimization methodologies for battery electric vehicle mass optimization is employed for determination of target glider mass under fixed performance requirements. Results for cost minimization indicate an increase in total vehicle weight with increasing battery energy density and decreasing unit cost. By utilizing a marginal cost function for automotive structural material lightweighting, it is demonstrated that the marginal cost of body materials - or the cost allowance per unit weight reduction - is accordingly reduced with fixed performance requirements, i.e., power and range, and increasingly efficient and cost-effective powertrains. The developed model further highlights that the reduced, although still substantial, benefit of body structure lightweighting favors adoption of advanced steel solutions with current and projected electric vehicle battery and powertrain technologies due to reduced marginal cost. Materials selection considerations are then discussed with an emphasis placed on next-generation steel solutions for cost-effective occupant and battery protection.