Hoon Lee, Ph.D. Candidate
Dr. James Stubbins, Director of Research
November 9, 2023 | 1:00pm - 3:00pm CST
This final examination will be held in 111K Talbot Laboratory.
Tensile behavior analysis on neutron irradiated Fe-Cr-C alloys using in-situ Synchrotron X-ray and micromechanics modeling
ABSTRACT: Ferritic/martensitic steels (F/M steels) exhibit notable resistance to swelling, a low coefficient of thermal expansion, and high thermal conductivity, making them promising advantages as fuel cladding materials. In order to enhance comprehension and provide a comprehensive framework for analyzing the deformation and damage mechanisms in ferritic-martensitic steels, it is important to acquire experimental observations including the influence of irradiation, M23C6 type precipitations, and the evolution of dislocation density.
The in-situ X-ray diffraction (XRD) technique is well-suited for characterizing the distribution of load transfer across different phases, with respect to changes in macroscopic stress or strain. The XRD method is used to precisely determine the inter-planar dimensions of a crystal, hence offering significant insights into the stress-strain states and anisotropic characteristics of various phases. The application of micromechanical modeling is essential in comprehending the progression of lattice strain in polycrystalline materials. Quantitative analysis of the prediction of lattice stresses and their consequences on plastic relaxation provides valuable insights into the mechanics of phase interactions.
The elastic constants of iron/chromium carbide are evaluated by the utilization of in-situ XRD measurements and homogenization calculations using the self-consistent approach. This study presents the matrix equivalent stresses resulting from the interplay between load partitioning and carbide reinforcement. The present study investigates the role of dislocation density in the analysis of material dislocations during the process of plastic deformation. The method of least squares was employed to concurrently compute the dislocation density and the ratio of edge and screw dislocations. The application of Small-Angle X-ray Scattering (SAXS) enables the investigation of the presence of inhomogeneous microstructures in metal alloys, such as irradiation damages and micro cracking. Internal damage, such as the production of micro clusters are produced by irradiation and micro-cracking occurs by applied strains. The data implies that in samples higher dose irradiation the onset of micro-cracking may take place in the matrix. On the other hand, in samples with lower dose or unirradiated, the process of micro cracking begins at the interface between the matrix and carbide.
The investigations of microstructural phenomena occurring during load-partitioning and micro-cracking in materials have significant importance in understanding micro mechanical phenomena and advancing the development of advanced computer models. The application of in-situ X-ray diffraction (XRD) technique and micromechanics modeling can offer valuable insights into engineering approaches assessing the load-bearing capacity and conducting safety evaluations of structural components.
