Crashworthiness Evaluation of Empty and Foam-Filled AZ31B Magnesium Beams under Three-Point Bending

Kurzfassung

Magnesium alloy as the lightest structural metal has recently been suggested as a promising candidate material to reduce vehicle weight and emissions by lightweight design in automotive industry. In order to assess the energy absorbing capability of AZ31B magnesium extruded and continuously cast-rolled sheet metal parts, the German Aerospace Centre (DLR) – Institute of Vehicle Concepts has carried out experimental and numerical study on the mechanical properties and material characterisation of these magnesium alloys. Both empty and foam-filled rectangular section beams were constructed and tested subjected to quasi-static/dynamic three-point bending using DLR’s component crash facility. High speed tensile tests using servo-hydraulic high rate testing machine were carried out to establish strain rate dependent material constitutive model for AZ31B magnesium alloy. Finite element simulation utilising material models MAT_024 and MAT_124 in LS-DYNA explicit FEA package was performed to investigate strain hardening behaviour, tension-compression asymmetry and their relations with plastic deformation modes and energy absorption. The same experiment and simulation procedures were also applied on cold rolled carbon DC04 steel beams to make comparisons with magnesium beams. The experimental results show that foam-filled beams have much higher specific energy absorption than empty beams for both magnesium and steel profiles. The foam-filled AZ31B magnesium beams with proper foam density exhibit higher specific energy absorption compared to foam-filled DC04 steel beams. In addition, finite element simulation results indicate that using calibrated stress-strain curves and failure parameters, material model MAT_124 yields a good agreement with the experimental results.