Due to efficient material utilization and reproducible high-quality level, metal forming processes, such as forward extrusion, meet the requirements of economical and resource-saving production. However, the capability of the workpieces is considerably affected by the occurrence of forming-induced damage. So far, there are only few investigations available on the influence of process-induced damage on fatigue properties. With the knowledge of damage influence on the component durability, components can be designed specifically and enable optimization of loading capability and lightweight construction. Also, the degree of process-induced damage after forming is currently measured by time- and cost-intensive destructive electron microscopic analysis. Direct current potential drop (DCPD) could offer the opportunity for an efficient non-destructive assessment of ductile damage.
The aim was to develop and validate a method for damage characterization that allows conclusions to be drawn about the expected lifetime of components. Therefore, a highly accurate electrical resistance-based sensor system for the assessment of forming process-induced damage and loading-induced cyclic damage, and for the analysis of their interaction has been qualified. In the very high cycle fatigue (VHCF) range, fatigue failure occurs starting from the interior of the volume, e.g. due to damage in form of pores. Therefore, adapted VHCF fatigue tests (up to 2·10\textsuperscript{8} cycles) were performed to investigate the influence of forming-induced damage. During the fatigue tests, DCPD, high-speed DIC and temperature measurement were applied to allow a non-destructive characterization of the ductile damage, to separate application-related fatigue damage mechanisms and to analyze their interaction. The results of the non-destructive characterization were confirmed by light and electron microanalysis. Round specimens of case-hardened steel AISI 5115 (16MnCrS5, 1.7139) with different process-induced damage states were studied.
A significant influence of deformation-induced damage on the electrical resistance measurement was validated with the sensor system. The values of electrical resistance were according to the damage quantity and validated by scanning electron microscopy. In VHCF fatigue tests, a significant influence of the degree of forming-induced damage was observed. The time- and cost-effective non-destructive method for forming-induced damage analysis provides the capability for process monitoring in future.