Critical mechanical properties and FEA simulation for crashworthiness assessment of a coarse-grained cast AM50 alloy

A coarse-grained AM50 alloy was used as a model alloy for investigation of constitutive behaviour, Charpy toughness and effect of stress state on deformation and failure of cast Mg alloys. The results provide critical mechanical properties of a cast AM50 alloy for crashworthiness assessment and development of finite element simulation techniques. For cast Mg alloys, the effect of strain rate and temperature is larger on tensile strength than on compressive strength because twinning is more extensive in compression than in tension. The effect of strain rate on compressive strength is negligible because twinning activity of the cast Mg alloy is dominant. The load vs. deflection of Charpy specimens were measured for modelling, and the effect of loading rate and temperature on load of Charpy specimens is very small because part of the specimen is in compression. The equivalent strain to fracture of the cylindrical round notched tension specimen decreases with increasing stress triaxiality; though for the flat-grooved plane strain specimen, the equivalent fracture strain remains constant over the range of stress triaxiality investigated. Because the two different specimen geometries give rise to different Lode angle values, the test results show that the Lode angle parameter is an important parameter for deformation and fracture of Mg alloys. Finite element simulations of loading of the cylindrical notched-tension and Charpy specimens were carried out using a Lode-angle dependent von Mises model, and were found to provide a reasonable description of the load–displacement curves measured in the tests. For the flat-grooved plane strain specimens, the computations under-predicted the force–displacement response measured.