Fractal behavior throughout stretch zone of 15-5PH steel under elastic-plastic loading conditions

The topography of the fracture surface along the stretch zone of 15-5PH steel is analyzed for a range of specimen thicknesses, providing information on the changes in elastic-plastic behavior. The relationship between the stretch zone width, as a local toughness measurement, and fractal dimension is discussed along with the restrictions imposed by the stress field evolution. Image stacks for extended depth-of-field 3D reconstructions of the stretch zone region were acquired using a reflected light microscope. Significant correlations between the stretch zone width and fractal dimension with specimen thickness were found from measurements on elevation maps, especially at the center regions. This demonstrates that the stretch zone has heterogeneous topographic behavior depending on thickness and is more homogeneous under plane strain states. Finally, a general equation is suggested to describe the stretch zone width dependence on both the fractal dimension and material thickness.