Modeling, simulation and prediction of Rockwell hardness indentation.

摘要

Rockwell C hardness (HRC) test, which measures a material's resistance to localized plastic deformation, is a valuable and commonly used mechanical test for evaluating mechanical properties of steels and other high-strength metals because of its simplicity, low cost and non-destructivity. However, the accuracy of HRC measurements is still in question. An international effort is being made to establish a world-wide unified Rockwell hardness scale with metrological traceability. A key factor affecting Rockwell hardness testing and standardization is the Rockwell diamond indenter. The National Institute of Standards and Technology (NIST) proposed a metrological approach using high accuracy standard Rockwell indenters to reduce the HRC measurement uncertainty. The difficulty of manufacturing diamond indenters to the required geometric specifications has resulted in most commercially manufactured indenters, to vary in shape from one to another. This difference in shapes is thought to be a major contributor to Rockwell hardness measurement uncertainty.; In this study, HRC hardness tests and influence quantities are investigated. The mechanical models for Rockwell hardness indentation are established and analyzed for both elastic and inelastic materials using self-similarity simplification approaches. It is shown that by using principles of similarity and cumulative superposition, the complicated moving boundary condition problems could be simplified to that of an intermediate stationary one for a flat indenter. A Finite Element Analysis (FEA) model for Rockwell hardness measurement is established and analyzed. The specimen size, element type and mesh selection are studied to obtain high efficiency and accuracy of the FEA model. Different FEA simulation results including the force-depth relation, stress strain distribution and geometrical effects of the Rockwell indenter (tip radius, cone angle and form error) are discussed, analyzed and verified by the experimental results. A new method is developed to input the Rockwell indenter profiles into the FEA model for HRC prediction directly. The prediction results show good agreement with NIST experimental results. In order to obtain the test material properties, a reverse computation method is introduced. In this method, the reverse computations are conducted based on different loading conditions. The method is further verified by NIST experimental results.