Characterization and evolution of complex 3D materials by digital image analysis and correlation

The aim of this thesis is to present a methodology to utilize spatial density visualization capabilities of X-Ray Microtomography (μCT) to characterize, and to capture the deformation in complex materials. μCT is a versatile technique, which has been used to non invasively visualize, investigate and quantitatively analyze materials and works on the principle of attenuation of X-Rays as they pass through them. In the first part of this dissertation, we have attempted to employ this 3D imaging technique to study the influence of local density variations along the length and width of a roller compacted Micro Crystalline Cellulose (MCC) ribbon on the local ribbon strength which in turn, potentially alter the mechanical properties (such as tensile strength and hardness) of its end product - a solid pharmaceutical dosage form. Density variations in three cases of ribbons produced a) with no lubrication b) by including Magnesium Stearate lubricant in the excipient and c) by lubricating rolls and screws have been investigated. Heckel and elastic recovery analysis indicate that the local density variations in the roller compacted ribbons drastically impact the mechanical properties of the solid dosage form. The rest of this dissertation involves the study of micromechanical behavior of open-cell solid foams. Metallic foams are cellular materials of very low densities in comparison to their parent material and are capable of large deformations owing to cellular collapse. Our understanding of their mechanical behavior is restricted to their heterogeneous deformation under uniaxial compression because of its architecture. Even though high speed photography combined with Digital Image Correlation techniques, capture the whole field strain map, they are limited by their capacity to visualize the surface deformation. Since the boundary conditions inside the volume of the sample are different, the surface deformation may or may not be a representative of the deformation pattern in the complete volume of the sample. Assuming plane strain along the direction of applied uni-axial deformation, the full field strain in the sample volume is measured by Digitally Correlating average images extracted from volumetric μCT data (which capture spatial material information from a thin section of the sample volume) with a similar successive image through progressive steps of applied deformation. Strain fields at slices at the surface and those at the interior are compared. It has been found that regions closer to the free surface are susceptible to higher deformation values in comparison to the core. A foundation has been created to expand this methodology to capture the out of plane deformation in the entire volume.M.S.Includes bibliographical referencesby Srinivas Iye