Estimation of surface roughness and modulus degradation due to damage by nano-indentation
The roughness of a surface influences the surface mechanical properties, such as elastic modulus, hardness and so on. In a plain strain condition, a material under deformation does not undergo change in Elastic Modulus, but when it has voids it undergoes a change in Elastic Modulus due to damage caused by indentation or deformation. Past studies have shown how the behavior of hardness changes by surface roughness of the material using spherical indenter on the spherical surfaces. The effect of the elastic modulus changes with the roughness however has not been investigated. The main aim of this thesis is to develop the methodology to estimate the behavior of elastic modulus and hardness of the material with different surfaces and when the material has damage such as voids, cracks, etc. The models used in this thesis are developed using Msc Patran and simulated using finite element analysis code LS-DYNA. In this thesis four models are developed with different surfaces to estimate the behavior of elastic modulus and hardness by nanoindentation using a sharp tip conical indenter. The change in modulus and roughness are estimated by nano-indentation using Oliver and Pharr’s theory. The penetration depths normalized with respect to a roughness scale parameter, and the effective radius encountered by the indenter, a first order model of roughness dependency of hardness is of nano-indentation on a fractal surface. It is shown, as the roughness of a surface increases, the hardness measured at depths comparable with the roughness scale deviates increasingly from the actual hardness. Not only the roughness influences the material properties but also when the material has damage in, it also influence the material properties. For this problem, the models are developed by placing some voids in the material and the behavior of elastic modulus and hardness of material with and without damage are estimated. Finally, the penetration depth estimated from nano-indentation is compared using the classical Hertzian theory and interestingly found that this theory can also be used for nano-indentation of metals and solids. The results from this research can be utilized to estimate roughness and modulus degradation caused by nano-indentation.
Wichita State University, College of Engineering, Dept. of Mechanical Engineering
Includes bibliographic references (leaves 79-81)