Date of Graduation
Statler College of Engineering and Mineral Resources
Mechanical and Aerospace Engineering
Bruce S. Kang.
Conventional material testing methods, such as tensile tests require the preparation of specimens and is not applicable for small-size coupons or on-site, in-situ testing. In this research, a method of determining material stress-strain curve based on spherical indentation is studied. Spherical-indentation process is analyzed by finite element (FE) method and a systematic analysis of relationships between indentation parameters and true stress/plastic-strain (sigmat- epsilonp) curve is performed for a range of material properties. A detailed methodology based on Tabor's empirical formula and Meyer's law is developed to determine the material strain hardening properties, Young's modulus and yield strength. It is noticed that Tabor's empirical formula is valid in the plastic region (deep indentation) with a small percentage error in the calculated values of yield strength. Based on the FE results, strain values have been predicted corresponding to which indentation gives satisfactory output. Steel and aluminum alloys, with same Young's modulus and yield strength but with different strain hardening coefficients, were selected for the simulation. FE simulation of 20 material models was performed. It is observed that the Tabor's constant is not equal to the value of 2.8 but takes different values for different materials. From the results it is concluded that the value of Tabor's constant decreases as the strain hardening value increases.
Konda, Bharath, "Methodology to determine post yield material mechanical properties from spherical indentation" (2005). Graduate Theses, Dissertations, and Problem Reports. 1603.