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T12 - Ultrasonic Pore Measurement

Development of an acoustic measurement methodology for the determination of microstructural damage

Project Status: Active

Last Update: 01.07.2021


In order to produce functional components with complex forming elements, solid forming operations are applied to semi-finished sheet metal parts in processes of sheet-bulk metal forming (sbmf). Due to high and locally varying degrees of forming, the sbmf processes not only cause locally varying degrees of work hardening but also initiate a certain amount of ductile damage in the form of voids in the microstructure, which can have a significant influence on the later fatigue behavior. In addition, the cold forming processes can sometimes result in high residual tensile stresses in the components surface, which have a negative effect on crack formation and crack propagation and thus on the fatigue strength of the components. From the point of view of a future user, testing techniques are therefore required with which the degree of ductile pre-damage on corresponding functional surfaces can be determined locally and non-destructively during production.

Therefore, the focus of the present project is the development of a new testing methodology for the quantification of ductile damage based on the time-of-flight detection of ultrasonic waves. Within subproject C04, complex preparation methods and evaluation routines were developed in preliminary work in order to evaluate the ductile damage associated with the sbmf using scanning electron microscopic images. These evaluation routines are to be used to verify the results of the ultrasonic tests and to assign them to specific defects within the microstructure. With a damage characterization based on the time of flight detection of the sound waves, it is possible to analyze relatively large test areas with short measuring times.

The results are then transferred to an advanced measurement technique such as phased array to reduce measurement times and simultaneously analyze components with complex geometries. Finally, recommendations for a future near production use are to be derived in order to enable an application in different areas of metal forming technology. These include the suitability of measurement setups in terms of detection capability, local resolution and measurement times