Determination of the fracture toughness by automatic image processing

We determine the fracture toughness of a duplex stainless steel using the COD-concept (crack tip opening displacement). The COD sub i values are obtained by stereophotogrammetric reconstruction of fracture surfaces. This is done by analyzing stereoscopic scanning electron microscope (SEM) images of the surfaces with an automatic image processing system. This system allows the automatic generation of a digital elevation model (DEM) with approx50 000 points for each fracture surface image. Height-profiles at the point of crack initiation can be obtained from this DEM. The examination of corresponding profiles from both specimen-halves leads to COD sub i .