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

•Empty and foam-filled AZ31B and DC04 beams were tested in three-point bending.•Both AZ31B and DC04 beams show an effect of strain rate on the energy absorption.•A higher density foam achieves higher bending resistance, but fractures earlier.•AZ31B significantly outperforms DC04 in terms of specific energy absorption.•AZ31B beams reach higher specific energy absorption than steel DC04 beam.

Lightweight magnesium alloys and polyurethane foams have attracted much attention in the automotive industry due to their potential to reduce vehicle weight. This study conducted quasi-static/dynamic three-point bending tests to investigate 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 showed that both deformation/fracture modes and energy absorption capacity of the thin-walled beams subjected to bending loads depend on the strain rate and other parameters, such as the beam material's strength and ductility, foam density and wall thickness. Both the DC04 beams and AZ31B extruded beams showed a positive effect of strain rate on the energy absorption capacity. A beam filled with a higher density foam achieves higher bending resistance, but fractures at a smaller deflection. The experiments demonstrated that AZ31B significantly outperforms DC04 in terms of energy absorption and specific energy absorption for the foam-filled beams, when the beams are subjected to bending loads at a deflection of 250 mm. However, this gain could be weakened when the performance is assessed at a larger fracture deflection because the foam-filled AZ31B beams tend to fracture at smaller deflections. For applications that require limited deformation, there is a possibility to develop lightweight auto-body structures such as rocker rails by substituting foam-filled AZ31B structures for mild steel structures, while maintaining or exceeding their current crashworthiness and safety.