Modeling, Simulation and Prediction of Rockwell Hardness Indentation
Li Ma, Samuel R. Low III, Richard J. Fields, Roland deWit, Jun-Feng Song, Theodore V. Vorburger, J Zhou
Rockwell hardness test, as a measure of the resistance of a material to localized plastic deformation, is a valuable and widely used mechanical test. However, the accuracy of Rockwell hardness measurement is still in question. The indenter, including both the spheroconical diamond indenter and ball indenter, is a major contributor to Rockwell hardness measurement error. An international effort is being made to establish a world-wide unified Rockwell hardness scale with metrological traceability. The difficulty in manufacturing spheoroconical diamond indenters to the required geometric specifications has resulted in most commercially manufactured indenters to vary in shapes from one to another. A common problem with steel ball indenters is the tendency of the balls to flatten with use, which can result in erroneously elevated HR value. Either steel or tungsten carbide (WC) ball indenter is permitted to be used in the reversed ASTM International and International Organization for Standardization. Significant differences occurred in Rockwell hardness tests depending on whether steel or WC ball are used. In this research, Finite element analysis (FEA) method is used to simulate the Rockwell hardness measurement process. The influences of spheroconical diamond indenter s geometry, including tip radius, cone angle and form error, on Rockwell C hardness tests are analyzed by the FEA model, and further verified by the experimental results. A new method is developed to directly input the Rockwell indenters profiles into the FEA model for hardness performance prediction. The prediction results show good agreement with NIST experimental results. The effects of four different sizes of steel and WC ball indenters on different Rockwell hardness scale are studied and compared with the experiments. Both FEA and experimental study provide important quantities reference for the difference of steel and WC indenters in Rockwell hardness tests.