Modeling, Simulation and Prediction of Rockwell Hardness Indentation

Li Ma, Sam Low, Richard Fields, Roland deWit, Metallurgy Division, MESL, NIST

John Song, Theodore Vorburger, Precision Engineering Division, MEL, NIST

Jack Zhou, Department of Mechanical Engineering and Mechanics, Drexel University

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.

Category: Engineering

Contact Person: Li Ma, Guest Researcher from Drexel University

Room A117, building 223

Metallurgy Division, Stop 8553

Material Science and Engineering Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899

Tel: (301) 975-2057

Fax: (301) 975-4553


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