Papers by Author: Gyu Young Lee

Abstract: In order to establish a reasonable and integrated fatigue design criterion for the long life design of the gas welded body structure, stress distribution around the gas welded joints subjected to tensile load was numerically analyzed. And also, the
P-Nf curves were obtained by fatigue tests. By using these results,
P-Nf curves were rearranged in the
σ-Nf relation with the hot spot stress at the welded joint. And a guideline for fatigue design of gas welded joints was proposed.

Abstract: The cathode protection method is a very useful corrosion protection technology for the underground pipelines. However, it has some problems that hydrogen generated by electrochemical reaction on the wet surface of the pipelines is attacked into the pipe weld, and make degradation of their mechanical properties. Therefore, in this study, welding residual stresses around of the X65 pipe weld, which is generally used as a material of the gas pipelines, were previously calculated. And next, by using the cathode protection method, artificially degraded the X65 pipe weld including base metal, assessed its influence on the mechanical properties of the X65 pipe weld.

Abstract: In order to establish a reasonable and integrated fatigue design criterion for the long life design of the gas welded body structure, stress distribution around the gas welded joints subjected to tensile load was numerically analyzed. And also, the
P-Nf curves were obtained by fatigue tests. By using these results,
P-Nf curves were rearranged in the
σ-Nf relation with the hot spot stress at the welded joint. And a guideline for fatigue design of gas welded joints was proposed.

Abstract: In this paper, as a fundamental study to evaluate fracture characteristics and material degradation by corrosion, evaluated electrochemical corrosion and corrosion fatigue characteristics of CF8A steel using as a material of the piping system in nuclear power plant. CF8A steel was artificially degraded at 400°C for 3 months. The environmental test condition is 3.5wt.% NaCl solution of room temperature. Corrosion rate of degraded CF8A steel in NaCl solution of room temperature increases with concentration of NaCl solution increase. However, concentration of NaCl solution will be more than 4.0wt.%, it shows decreasing tendency. Crack growth rates of degraded and not-degraded CF8A steel in air condition do not show remarkable difference. However, in 3.5wt.% NaCl solution, crack growth rates of them showed higher than ones in air. Particularly, crack growth rate of degraded material remarkably increases compare to one of notdegraded material.

Abstract: CF8A steel is a material of the piping system in nuclear power plant. In order to evaluate its fracture characteristics and degradation by corrosion, electrochemical corrosion and corrosion fatigue characteristics were evaluated. CF8A steel was artificially degraded at 400°C for 3 months. Corrosion rate of degraded CF8A steel in NaCl solution of room temperature increases with concentration of NaCl solution increase. However, concentration of NaCl solution will be more than 4.0wt.%, it shows decreasing tendency. Crack growth rates of degraded and not-degraded CF8A steel in air condition do not show remarkable difference. However, in 3.5wt.% NaCl solution, it showed higher than that of in air.

Abstract: Austenitic stainless steel has a large problem to decrease its corrosion resistance and mechanical properties by sensitization in the welding process. Thus, in this paper, corrosion fatigue characteristics of artificially sensitized STS304 were investigated. According as heat treatment period for sensitization increases, the Cr-carbide deposition in the grain boundary and degree of sensitization (Ia/Ir) increased. From the results, corrosion fatigue strength of sensitized STS304 was remarkably reduced compare to non-sensitized ones.

Abstract: Durability assessment for the suspension system of the vehicle is very important. In order to secure reliability on the results of durability assessment and fatigue design criterion, accurate stresses for the interesting component must be basically calculated. In this paper, numerical stress analyses for the automobile’s coil spring were performed. Residual stresses by shot peening were also analyzed. The effects of the stress analysis results on fatigue strength of the coil spring were discussed. From the results, fatigue durability of the shot peened coil spring could be considerably improved by the effects of compressive residual stress. However, being attacked by corrosive environments, it could decrease by corrosion fatigue degradation.

Abstract: Durability assessment for the suspension system of the vehicle is very important. Particularly, corrosion fatigue strength of coil spring depends on many factors including mechanical and environmental properties. In this paper, residual stresses by multiple shot peening were analyzed using finite element analysis, and evaluated its effect on corrosion fatigue strength. And also, a corrosion fatigue design criterion for coil spring of light commercial vehicle (LCV) based on proving ground response was proposed.