Design optimization for inner core of crash box for vehicle based on NPR/PU structure

Vehicle crashworthiness is a critical aspect of the passive safety domain in passenger cars, and crash boxes play a significant role in vehicle collisions. Currently, the crash boxes predominantly utilized in vehicles are primarily simple thin-walled structures, which exhibit average energy-absorbing capabilities. To enhance vehicle collision safety, this article proposes an inner core filled with negative Poisson's ratio (NPR) structure and polyurethane (PU) material to the design of crash box. Initially, a double-arrow type NPR structure is selected as the framework, with polyurethane (PU) serving as the filling material. This combination forms the inner core of the crash box. A collision analysis is conducted on three types of crash boxes, examining the differences in their performance indicators in detail to demonstrate the superiority of the proposed design. Subsequently, variables that significantly influence the evaluation metrics were identified through extreme value difference analysis, and these variables were designated as the design parameters for the subsequent optimization process. Finally, the Neighborhood Cultivation Genetic Algorithm (NCGA) and Non-dominated Sorting Genetic Algorithm-II (NSGA-II) were employed as optimization algorithms for the optimal design, and the optimal results of the two algorithms are determined separately using Normal Boundary Intersection (NBI) method, and then compared to determine the overall optimal solution. The simulation results indicate that the NSGA-II optimized NPR/PU collision box provides substantial advantages in overall performance. After NSGA-II optimization, the NPR/PU crash box exhibits reduced overall collapse displacement and maximum peak collision force compared to other crash boxes, along with enhanced specific energy absorption capacity. These findings indicate that the designed NPR/PU crash box significantly improves the vehicle's crashworthiness in the event of a collision. This article offers valuable theoretical insights to support the development and exploration of automotive crash boxes.