Characterization of damage in forward rod extruded parts

In addition to strain hardening and residual stress, damage influences the product performance of forward rod extruded parts. Damage is usually neglected and difficult to quantify. The evolution of ductile damage in metal forming is closely correlated to the load path. An experimental approach using automated energy dispersive X-ray spectroscopy (EDX) particle analysis in scanning electron microscopy (SEM) is used to successfully quantify the void area fraction and obtain information on ductile damage. The method is performed on forward rod extruded 16MnCrS5 workpieces with varying extrusion strains and shoulder opening angles (and thus varying underlying load paths). The quantified damage is directly correlated to the load path, which can be described by the stress triaxiality evolution during forming. Density measurements were performed to further validate the results. By observing the change of strain-weighted stress triaxiality and maximum stress triaxiality, it is shown, that the maximum stress triaxiality is the decisive parameter enabling void nucleation.