13th International Conference on Fracture June 16–21, 2013, Beijing, China damage evolution from a cut-edge during in-situ tensile bending test. The method, in contrast to computed tomography which is for axisymetric objects, allows to image in three dimensions a region of interest (for instance the crack tip) inside a sheet-like sample without cutting it. The laminography set-up used here is located at the ID19 beam line at the European Synchrotron Radiation Facility (ESRF) in Grenoble (France). The acquisition was performed with a voxel size of 0.778 μm3. Applications in the study of damage of an aluminum grade can be found in the literature [12]. More details about the laminography technique are also given elsewhere [12,13]. 2. Material and experiment 2.1. Studied material The material used in this study is a laboratory dual phase steel with a ultimate tensile strength of approximately 600 MPa and a fracture strain of around 17 % at the as-received condition. The material was supplied as a 0.8mm thick cold rolled sheet. The chemical composition and microstructure are given in figure1. (a) C Mn Si Cr 0.08 0.8 0.23 0.68 (b) Figure 1: (a) DP microstructure visualized by scanning electron microscopy (after nital 0.2% etching). (b) Chemical composition of DP600 steel (weight %) The martensite islands appear to be aligned along the rolling direction. In the following the rolling direction will be referred to as L, the long transverse direction as T and the short transverse direction as S. 2.2. The cut-edge profile The shearing, which is a cutting in a straight line over the entire width of the sheet by the action of a moving blade perpendicular to the plane of the sheet, is the most widely used and least expensive process for separating metal panels. In this study, we assume that the shearing and punching have the same effects on the cut edge as the 2D descriptions of these processes are identical. Figure 2 shows an optical micrograph of the polished surface of a sample after the cutting process. The sheared surface profile is characterized by the existence of 4 characteristic zones: rollover, fracture, burnish and burr (figure2). This observation is consistent with the results found in the literature [1,3]. -2-
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