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Methodology to Determine Post Yield Material Mechanical Properties from Spherical Indentation Bharath Konda 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/plasticstrain (σ t-ε p) 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. Acknowledgements I would like to thank Dr.Bruce Kang for providing me with an opportunity to work with him, and for his guidance and technical advice. His support and patience during the course of my research work deserve a special mention. I would also like to thank Dr.Jacky C.Prucz, and Dr.Charles F.Stanley, for their technical guidance and advice. I wish to express my sincere thanks to Ziheng Yao. Without his help it would have been very difficult to accomplish the amount of work that I have been able to in the last few years. Ziheng Yao had provided me invaluable analysis knowledge and for this I thank him. Finally, I would like to thank my parents and brother for their moral support and encouragement throughout my graduate studies. I dedicate my research thesis to them.

Methodology to determine post yield material mechanical properties from spherical indentation