Search Results

Use of ultra high strength steel (UHSS) sheet in automotive components has potential to simultaneously reduce weight and increase crashworthiness. For crashworthiness design and simulation, constitutive equations are required; however, these are scarce for UHSS. Also, UHSS sheets may suffer unexpected fracture such as shear fracture, and toughness data for UHSS sheets is very limited. In this work, effects of strain rate and temperature on flow stress of two UHSS sheet steels (a dual-phase ferritic/martensitic DP980 and a martensitic boron (B) steel) are experimentally investigated and compared to a simple constitutive equation for structural steels based on thermal-activation theory of dislocation motion. The flow stress of the two UHSS steels obeys a constitutive equation similar to that of structural steels of other microstructures (ferrite, ferrite/pearlite, pearlite, ferrite/bainite, and bainite).

Effects of strain rate and temperature on tensile, compressive and toughness properties were investigated for an extruded Mg alloy AM30 in both extrusion (ED) and transverse (TD) directions. The effects of strain rate and temperature on uniaxial flow stress were reported elsewhere but will be briefly described to facilitate the understanding of Charpy results (i.e., load, deflection and absorbed energy). The effects of loading rate from quasi-static to 5.1 m/s on un-notched and V-notched Charpy load-deflection curves up to maximum load were negligible, but load up to maximum load increased with decreasing temperature. The deflection at rapid load-drop in un-notched Charpy tests increased with decreasing loading rate and increasing temperature between -50°C and 100°C for un-notched ED and TD specimens (i.e., L-T and T-L specimens according to ASTM E 1823 terminology).