EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Tool materials like cemented carbide, high-speed steels (HSS) etc. with enhanced strength and hardness possess low ductility. Therefore, it is practically not possible to attain their stress, strain and strain-rate dependent properties using established test methods since a brittle fracture develops after reaching their yield strain. However, such properties at ambient and elevated temperatures are necessary for assessing the reliability of tools subjected to high dynamic and impact loads during manufacturing processes.
To overcome this problem the repetitive impact test was employed. During the loading phase of this test, a cemented carbide ball via an adjustable impact force penetrates a specimen surface at strain-rates up to several hundreds of s-1. Herein, only a restricted material region is compressively loaded over its yield strength. Thus, the propagation of cracks is avoided, and the material is plastically deformed without failure. Consequently, remaining imprints are formed featuring smooth surfaces. Such imprints can be accurately measured and evaluated implementing FE analysis methods to determine stress, strain, and strain-rate material data at ambient and elevated temperatures.
In this paper, a FE analysis method is introduced to assess impact test imprints created by K05 ball indenters at various temperatures and impact durations. Based on an iterative procedure and appropriate FE calculations, the strength data of cemented carbide and HSS specimens at various temperatures were determined and analytically described dependent on the strain-rate. Quasi-static specimen stress-strain material data were proportionally adjusted by the stress augmentation ratio (SAR) until the calculated imprint depths converged with the measured ones at various temperatures and impact times. Hence, equations were developed describing SAR depending on the strain rate and temperature. By implementing these equations, the stress-strain curves, and their characteristic data points such as of the yield stress at various temperatures and strain rates were determined and relevant diagrams created.