Energy absorption mechanisms and capabilities for magnesium extrusions under impact

•Crushing and cutting of AM30 magnesium tubes, quasi-static and up to 20 m/s impacts.•Brittle sharding of crushed tubes, superior CFE and stable deformation for cutting.•Cutting force immune to reductions under dynamic loading, unique to magnesium.•Fully analytical model for the force-displacement response proposed and validated.•High speed photography at 20 000 fps with photron SA4 and SEM images collected. There is significant interest in replacing conventional materials with novel, lightweight alternatives. Magnesium alloys are favorable candidates since magnesium is the lightest structural metal available. The impetus of this investigation was to examine the mechanical performance for AM30 magnesium extrusions subjected to quasi-static and dynamic progressive crushing and axial cutting with impact velocities up to 18 m/s investigated. These magnitudes replicated high speed, transportation-related impacts in a range where experimental data is crucial but absent from the literature. The collected data was compared in terms of total energy absorption, force efficiency and overall deformation stability to assess the feasibility of this novel material as a potential substitute for vehicular safety systems which are traditionally composed of steel. Axial cutting was generally outperformed in terms of energy absorption capacity when compared to crushing, except for the case of 10-bladed cutting. However, the degree of fracture observed and corresponding lack of stability under crushing was unacceptable for a safety system while every cutting test proceeded with a highly repeatable, near-constant force response which successfully mitigated fracture. The average cutting force efficiency was approximately 85%, compared to 30% for the progressively crushed specimens. A fully analytical model to predict the complete force-displacement response under a cutting deformation mode was derived and validated, based upon experimental observations, with an average error of 4% for a series of geometries, alloys, loading rates and cutting tools. Additionally, this revised model possesses a stronger theoretical basis than the original by considering the influence of strain energy release rate per unit area (J-integral) and a brittle cutting membrane rather than empirical correction factors. The influence of mechanical leverage on the axial cutting force, by radial clamping of the flared sidewalls, was also considered in the revised analytical model and validated for an expand