Characterizing damage and fracture of sheet metal materials using large scale test specimen

Several approaches to characterizing damage evolution and fracture behaviour of sheet metal materials are currently in existence. These are based on different testing methodologies and test specimen designs, some of which, when combined with higher sheet thicknesses used for aluminium alloys in the automotive field, can reach and exceed geometrical limits required for the plane stress assumption commonly applied to numerical modelling of sheet metal materials. Furthermore, if shell elements are to be used in modelling of such structures, the characteristic length of the element should be larger than the thickness of the modelled sheet material. In order to allow for element sizes accounting for the two considerations outlined above, new test specimen geometries covering a range of stress triaxialities have been developed with a deformation region significantly larger than that of other commonly used test specimen designs. The geometries have been manufactured and tested on an automotive grade AA6xxx series aluminium alloy with DIC strain measurement to determine failure strains. The results were then applied to finite element models using various element sizes and the behaviour of the numerical models compared to the test results. (paper)