| Plastic anisotropy in rolled sheets has traditionally been analyzed by conducting tensile tests on strips cut at different angles from the rolling direction and measuring the contraction ratios during testing. This method is tedious, yet sufficient for sheet metals but the application to other material systems is limited. For example, if one were to seek the properties of a coating-substrate system, such an analysis would be impractical due to the combined effects of the coating and the substrate on which it lies. Indentation-based experiments are a great candidate for evaluation of such properties in various material systems for a few, main reasons. Indentation testing machines are readily available commercially and in material characterization laboratories world-wide and are currently being used for the classification of various material properties. Second, the systems in which indentation can be used are far from limited; indentation testing is notorious for its large-scale applicability. Finally, indentation provides a means of inducing localized plastic deformation, which can ultimately serve as a great analysis tool for anisotropy in these properties for a given material. It is shown that examination of material flow in the contact region serves to uniquely characterize the degree of anisotropy. Therefore, the work presented in this dissertation pertains to the development, design, and testing of a set of virtual experiments using Finite Element Modeling with the specific aim to uniquely characterize the anisotropic plastic property of a material in all normal directions given minimal material data prior to testing. Current characterization methods and yield criteria are reviewed, and results suggesting anisotropic yielding in coatings are presented. Further, indentation stress-strain behavior of plastically anisotropic materials is examined, and finally, characterization methods involving indentation-based techniques are presented. |
