Jason Cheon

Relation of joint strength and polymer molecular structure in laser assisted metal and polymer joining

Abstract The study of laser assisted metal and polymer joining has been conducted to identify the mechanism of the hybrid joint. The bonding mechanism has been revealed to be due to the expansion pressure of pyrolysis fragments. Previous research has dealt with superficial factors without consideration of the polymer thermal decomposition phenomenon, which is the major factor of the joining strength. With experiments and simple chemical analysis for simple structured polymers this paper presents the quantitative relationship among the joint strength, the expansion pressure, the gas fragment composition, and the molecular structure. To verify the relation of the joint strength and the polymer molecular structure, the results were analysed and compared with the results of previous studies. Correlation of the quantified joint strength and the quantified expansion pressure and the monomer yield is also defined. The results confirm that the joint strength is correlated with the polymer structure.

Thermal-Metallurgical-Mechanical Analysis of Weldment Based on the CFD Simulation

A new method of numerical thermal-metallurgical-mechanical analysis was introduced in this paper. The CFD welding simulation is based on the mass and heat transfer analysis solving mass, momentum, and energy conservation equations along with the Volume of Fluid (VOF) method. The VOF method is employed to track the shape of the free surface. The arc and droplet heat source model with electromagnetic force and arc pressure model were used for the arc welding process. Next, the temperature history of CFD welding simulation was transferred to the FEM domain for thermal-metallurgical-mechanical analysis with CFD-FEM framework. The diffusion kinetics considered phase transformation model successfully predicted phase fraction and residual stress distribution of carbon steel weldment. By using the combination of suggested T-M-Me analysis method and CFD welding analysis, it is possible to reproduce a phenomenon closer to reality. Also, the recent CFD-based process analyses and results that can be extended to multi-physical analysis were briefly introduced. However, considerable assumptions and simplified models are different from real welding phenomena. To solve this gap and to use welding simulation as a prediction tool rather than a reproduction, many young researchers will need to challenge.