Design optimization of a multi-material, fiber-reinforced composite-intensive body-in-white of a mid-size SUV

Abstract

Transportation accounts for almost a third of all energy consumption and emissions in the U.S. With an emphasis on improving the energy efficiency of vehicles and transitioning to electrified vehicles, lightweighting has become relevant to compensate for the added complexity of battery packs and hybrid powertrains. Lightweight materials such as aluminum, magnesium, and fiber-reinforced plastic (FRP) composites can reduce the vehicle’s structural mass, the body-in-white (BIW), by up to 50%. However, the higher proportion of large sports utility vehicles (SUVs) and trucks in the North American fleet poses a challenge, as the larger size and high production scale of the structural components for this segment can significantly increase material costs. Thus, a multi-material approach to deploy FRP composites at select locations in an existing metal BIW can help advance composites design, integration, and manufacturing technologies. Furthermore, these designs can be translated for future EV structures. This study utilizes a systems approach to 1) establish design targets through structural analysis of the baseline SUV BIW design under various static and dynamic load cases, 2) conceptualize multi-material designs, and 3) assess the designs to meet lightweighting, cost, and sustainability objectives. Sustainable recycled carbon fiber-reinforced composites and other cost-effective FRP composite materials manufactured using state-of-the-art high-pressure resin transfer molding (HP RTM) technology were assessed for use in structural elements. An ultrasonic additive manufacturing (UAM) technique was implemented to produce mechanically interlocked metal-fiber transition joints to serve as a joining mechanism between fibers and metals in the multi-material design. To incorporate the transition joint design into the topology optimization scheme, a high-fidelity model of the fiber-metal transition joints that describes the fiber-oriented interactions between the fibers, cured-epoxy matrix, and metal components was developed. This model's results accurately represented the behavior from experimental testing. They can be transferred to the FEA solver as a computationally efficient material card specifically for use at the metal-composite transition regions in the proposed designs. The results from this system-level multi-material composites integration study have been presented.