Correlating Ultrasonic Velocity in DC04 with Microstructure for Quantification of Ductile Damage

The detection of ductile damage by image-based methods is time-consuming and typically probes only small areas. It is therefore of great interest for various cold forming processes, such as sheet-bulk metal forming, to develop new methods that can be used during the forming process and that enable an efficient detection of ductile damage. In the present study, ductile damage in DC04 was examined using ultrasonic testing. First, different grain sizes were set by heat treatment. Subsequently, the sheet metal was formed by cold rolling. A clear correlation between the average void diameter and the measured ultrasonic velocity could be shown. The ultrasonic velocity showed a clear decrease when the average void size increased because of the increasing forming degree. The ultrasonic measurements were finally employed to calculate a damage parameter D to determine the amount of ductile damage in the microstructure for different grain sizes after cold rolling.