Indentation Analysis of Transversely Isotropic Materials
Bhat, Talapady Srivatsa
MetadataShow full item record
Instrumented indentation, as a tool for characterization of mechanical properties, has well been established in the past decades. Studies have been conducted to understand the behavior of isotropic materials under indentation and techniques to accurately predict isotropic material properties have also been reported. Further, within the isotropic regime, work has been done to predict the indentation hardness without having to investigate the area of contact during indentation. Studies have also reported the prospect of utilizing indentation to predict the fatigue behavior of isotropic materials. This dissertation is made with the intent of extending the use of indentation, as a characterization tool, to the anisotropic regime. The effect of transverse isotropy on the indentation response of materials is systematically studied here. Extensive computational analysis is performed to elucidate the underlying deformation mechanics of indentation of transversely isotropic materials. Owing to the anisotropy, indentation may be performed parallel or perpendicular to the plane of isotropy of the specimen. It is observed that the indentation response varies significantly for each of these cases. The two cases are treated as unique and an identical systematic analysis is carried for both. The indentation orientations shall henceforth be referred to as transverse and longitudinal indentation for indentation parallel and perpendicular to the plane of isotropy respectively. A technique is developed capable of extracting the elastic-plastic properties of transversely isotropic materials from interpretation of indentation response in either direction. The technique is rigorously tested for its robustness, accuracy and uniqueness of results. A sensitivity analysis is performed to determine how sensitive the technique is to errors in experimental results. Rigorous studies are performed to understand the variation in pile-up or sink-in during indentation with varying anisotropy in the specimen. As a result of these studies, relations are obtained between the contact area and hardness during indentation and material properties of transversely isotropic materials. Further, utilizing the previously devised technique, relations which directly predict hardness from either known material properties or known indentation response, in either the transverse or longitudinal direction, without actually measuring the area of contact are obtained. Variation of hardness with anisotropy as well as other material properties is thoroughly studied. Fatigue response of transversely isotropic materials to cyclic indentation is studied using computation analysis. Distinct variation in the fatigue response with varying anisotropy is observed and reported. A systematic investigation into the indentation behavior of materials with residual stress is undertaken. Algorithms are developed to predict the residual stress and material properties for elastic perfectly plastic materials from known indentation response for both isotropic as well as transversely isotropic materials. The algorithms are then tested for their accuracy and sensitivity.