# Experimental Investigation of the Dynamic Responses of Thin-Walled and Foam-Filled Steel Tubes Subjected to Repeated Impacts

## TL;DR

This study examines how steel tubes filled with foam respond to repeated impacts, showing that foam improves energy absorption and reduces contact force.

## Contribution

The study introduces a new understanding of how foam-filled steel tubes perform under repeated impacts, including pseudo-shakedown behavior.

## Key findings

- Foam-filled tubes increased energy absorption by 33.6–43.5% compared to thin-walled tubes.
- Crush curves matched across multiple impacts and single impacts with equivalent energy.
- Foam-filled tubes showed pseudo-shakedown behavior after repeated impacts.

## Abstract

In this study, a horizontal impact setup was used to measure the dynamic responses of specimens fixed on a reaction wall and subjected to repeated impacts generated by a large-tonnage impactor. The contact force, deformation process, energy absorption, and other properties of two specimens (a thin-walled steel tube and foam-filled steel tube) were thoroughly investigated. The results demonstrated that the thin-walled tube’s properties were consistent with the four-phase and six-phase deformation models and that the foam-filled tube’s properties were consistent with the two-phase deformation model. In the early stages of the experiment, the foam-filled and thin-walled tubes were similar in terms of the contact force and energy absorption. However, when the polyurethane (PU) strain reached 0.8, the PU significantly increased the support of the tubes, reduced the contact force (by extending the contact time), and increased the energy absorption capacity by 33.6–43.5%. The crush curves of the specimens were in agreement for cases involving multiple impacts, as well as for one impact with the same impact of kinetic energy. The crush curves can be used to assess the actual performance of crashworthy devices. Furthermore, after repeated impacts, the foam-filled tube exhibited a pseudo-shakedown behavior.