Experimental comparison of energy absorption characteristics of polyurethane foam-filled magnesium and steel beams in bending

Abstract

Lightweight magnesium alloys and polyurethane foams have attracted much attention in automotive industry due to their potential to reduce vehicle weight. This study conducted quasi-static and dynamic three-point bending tests to acquire preliminary knowledge of the energy absorption characteristics and deformation behaviour of empty and polyurethane foam-filled magnesium alloy AZ31B thin-walled beams, and to make comparisons with mild steel DC04 beams. The results suggested that both deformation/fracture modes and energy absorption capacity of the thin-walled beams subjected to bending loads depends on loading rate and other parameters, such as the beam material’s strength and ductility, foam density and wall thickness. It was found that both the steel and magnesium thin-walled beams reach higher energy absorption under dynamic bending condition. There is a clear tendency showing that a foam-filled beam with a higher foam density achieves higher load carrying capacity, but it fractures at a smaller deflection. The experiments demonstrated that AZ31B may significantly outperform DC04 in terms of Energy Absorption (EA) and Specific Energy Absorption (SEA) for foam-filled thin-walled beams subjected to bending loads, when the fracture deflection is constrained to a medium value. However, this outperformance could be weakened when the performance is assessed at a larger fracture deflection because foam-filled AZ31B beams tend to fracture earlier. For applications with limited deformation, there is a possibility to develop lightweight auto-body structures such as rocker rails by substituting AZ31B for mild steels, while maintaining or exceeding their current crashworthiness and safety.