Numerical investigation on the quasi-static axial crushing behaviour of square bellows with varying pitch for crash box applications

This study presents a numerical investigation on the quasi-static axial crushing behaviour of square bellows with varying pitch for crash box applications. The primary objective is to reduce the initial peak crushing force (IPCF) while maintaining efficient energy absorption characteristics. Finite element simulations were performed on square tubes with different pitch configurations, and their crashworthiness performance was evaluated in terms of energy absorption (EA), specific energy absorption (SEA), mean crushing force (MCF), and crash force efficiency (CFE). To ensure physical accuracy, the effective deformation length for each configuration was determined individually based on the onset of densification identified from the force–displacement response. The results show that the introduction of pitch significantly reduces the IPCF across all configurations. However, this reduction is accompanied by a decrease in EA and SEA, indicating a trade-off between peak force mitigation and energy absorption capacity. Among the studied configurations, the specimen with a moderate pitch (5 mm pitch) demonstrates a favourable balance by achieving substantial reduction in IPCF while retaining comparatively higher energy absorption than other pitched structures. The MCF and CFE values remain relatively consistent, as they are governed by the progressive deformation behaviour prior to densification. Overall, the findings highlight the importance of optimising geometric parameters to achieve a balanced crashworthiness performance, particularly in applications where reduction of initial impact force is critical.