Flexural and low‐velocity behavior of <scp>GFPP</scp> / <scp>DP980</scp> honeycomb sandwich structure inspired by fiber metal laminates

Abstract With the rapid development of electric vehicles, a hybrid composite structure has been designed for the battery pack bottom guard to enhance impact resistance and reduce weight. The glass fiber‐reinforced polypropylene (GFPP)/DP980 honeycomb sandwich structure consists of GFPP panels with a polypropylene honeycomb core. DP980 advanced high‐strength steel plate is encapsulated within the structure, inspired by fiber metal laminates. A lightweight and high‐strength sandwich composite lay‐up solution was determined through equivalent bending stiffness theory, finite element simulation and experiment. An asymmetric sandwich structure with the steel plate on the impacted side enhanced flexural strength and ductility, demonstrating different failure sequences and a higher bending strength of 77.64 MPa compared to 50.18 MPa when the steel plate was on the unimpacted side. As impact energy increased from 100 to 200 J, the sandwich structure showed higher peak impact load, deeper craters, and increased bulge height, with significant delamination up to 175 J, while gravel impact tests revealed minimal flexural strength reduction (4.92%) even after repeated impacts. This study confirms that the use of thermoplastic sandwich structures is a viable and promising option for crash safety and the lightweight design of battery pack bottom guards. Highlights The thermoplastic honeycomb sandwich structure is polypropylene‐based. The use of advanced high strength steel is inspired by fiber metal laminates. Both thickness and surface density are considered in the structural design. The steel plate placed on the impacted side improves the flexural behavior. The sandwich structure has excellent impact resistance and lightweight level.