A Research on Microscopic and Macroscopic Mechanics in Melting/Solidification Processes Incorporating Moving Boundary/Interface, and Its Application to Welding and Bonding

点击翻译按钮获取中文摘要

Analyses on melting and solidification processes are carried out by microscopic, macroscopic and mesoscopic viewpoints, in order to reveal the mechanism and to build up thermo-mechanical theory on the phase transformation processes incorporating moving boundary and interface, such as welding and joining. Molecular dynamics method and the finite element method are used as microscopic and macroscopic method, respectively, while phase-field method and crystal plasticity theory are applied to mesoscopic analysis. The summary is as follows :(1) Microscopic Analysis by Molecular Dynamics Method : The motions of atoms around the interface of solid and liquid are analyzed and the stability of the interface, anisotropy in the interface energy depending on crystal orientation are evaluated. And the preferred orientations of crystal growth are determined from the relation between the orientation and interface energy.(2) Mechanical Properties of Welded Heat Affected Zone : Deformation in the micro … More scopic area in the weld metal, heat-affected zone, and parent material of Mo.9Cr-1Mo steel is measured by the micro-grid method, and the relation between hardness, structural change and strain is revealed to be clear.(3) Analysis of Crystal Growth Process by Phase-Field Method : Crystal growth process is analyzed by the phase-field method in which mechanical and thermophysical properties and anisotropy based on the molecular dynamics simulation are introduced. Various modes of dendritic crystals are obtained by the combination of the parameters. These results made it possible to observe the dynamic process of the pattern formation, and some phenomena such as initial stage of crystal growth, which is difficult to experimentally observe, are demonstrated.(4) Finite Element Analysis Based on Crystal Plasticity Theory : Deformation behavior in the heat-affected zone was simulated by the finite element method, and the results obtained by the model in which grain size and anisotropy was introduced were revealed to be corresponding to experimental results. These results are supporting the relation obtained in (2). Less