Fracture characterization of ZEK100 magnesium alloy sheet under monotonic and non-proportional loading histories

In the present paper, a comprehensive investigation was conducted into the fracture response of a rare-earth magnesium alloy sheet, ZEK100-O, under quasi-static conditions. Various types of specimen geometries were fabricated in different orientations with respect to the rolling direction of the sheet to reveal the anisotropic fracture response of the alloy under proportional loading conditions. To visualize directional dependency of the fracture response, experimental fracture loci for different orientations were constructed. Furthermore, non-proportional tests were performed by abrupt changes of stress states to study the role of the loading history on fracture behaviour of the alloy. The non-proportional tests entailed pre-straining the material in uniaxial and equi-biaxial tension up to a prescribed deformation level, followed by extreme changes of stress states to plane-strain tension or shear. Based on the results of the proportional and non-proportional tests, the validity of employing "damage indicator" approaches commonly utilized in phenomenological modelling of fracture is assessed. (paper)