Multi-Material Hybrid Rocker Panel Structures for EV Battery Protection

Multi-material solutions for the light weighting of electric and internal combustion engine (ICE) vehicles is an emerging trend to replace structural components made of steel/aluminum. Automotive chassis consists of structural members such as rails, posts and rockers which form frames that need to meet stringent crashworthiness requirements such as frontal, side (IIHS & Pole) and rollover impacts. The high strength steel and aluminum used in these structures are often heavy and require several secondary steps to complete the frame. In the present paper, we discuss the design and optimization of multi-material hybrid rocker panel solutions to meet pole impact requirements and decrease weight with an emphasis on structural battery protection in electric vehicles. Rocker panel structures are situated at the bottom of the lateral edges of the vehicle and extend longitudinally along the length of the vehicle, between the front and rear wheels. Most Electric Vehicles (EVs) have batteries below the floor at various locations along the length of the vehicle. Reinforced rocker panel structures are intended to absorb the energy during a crash, protecting the battery from intrusion and shock. Conventional steel/aluminum rocker panel structures are made with multiple reinforcements (sandwich/extruded tubular steel structures) and a sequence of assembly processes are involved to attach them onto the vehicle frame. Key challenges for the rocker panel design are low packaging space and control of energy absorption to minimize intrusion and shock all along the battery pack during pole impact. In addition, the design has to be customizable to adapt to the different stiffness and dynamic response from the surrounding parts along the vehicle length. Honeycomb-based NORYL GTX™ rocker panel structures were designed to optimize the impact absorption energy in the available package space for pole impact requirements. Various design elements are introduced to enable local tuning of energy absorption at different locations along the length of the vehicle. Material models (MAT 24 & MAT187) were developed using high strain rate data, and simulations were performed to optimize the design, created using LSDyna1 software. The rocker panel solution developed is up to 40% lighter in weight with similar crushing behavior when compared with the steel/aluminum solutions.