MULTISCALE MODELING TECHNIQUES PERTAINING TO COMPOSITIONALLY GRADED MARTENSITIC STEELS

Abstract

The introduction of composition gradients into the already hierarchical structure of martensitic steel leads to difficulties in modeling that arise from events occurring in the material at different length scales. In this thesis we isolate the features that are important to describing the mechanical properties of martensite and constitutively couple them through their respective length scales. The idea of a representative volume element is rigorously explored in which the microstructure is represented through a Masing model as well as more advanced structures akin to a nanocomposite. As such, we are able to keep track of microscopic yielding and internal stress evolution at the smallest scales (nanoscale through microscale). With the use of representative volume elements, we are able to track events at the largest scale as well by freely being able to change scale. As such, macroscopic phenomenon such as: thermal fields, composition fields, macroscopic loads, and the associated macroscopic phase distributions and stress distributions are evaluated. We conclude by demonstrating the power of this modelling technique in the design and optimization of compositionally graded steel structures via virtual prototyping.