Papers by Author: Dong Ho Bae

Abstract: In order to develop a fatigue design method for the actual railroad car body structures using the fatigue data on simulated single spot welded lap joints, firstly, evaluated fatigue strength on the spot welded t-type member which is a component of the actual railroad car body structure. And next, possibility of fatigue design for spot welded T-type member using the fatigue data of single spot welded lap joints was investigated. From the results, it was found that, even though there is some difference in fatigue strength between single spot welded joint and the actual members under the same fatigue life, the fatigue design criterion could be predicted by correction between them.

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: The vehicle suspension system is directly influenced to ride and handling. Therefore, the major components of the vehicle suspension system should have enough fatigue strength during its lifetime to protect passenger from the traffic accident. Spring is one of the major suspension part of vehicle. Thus, in this paper, a fatigue design method for leaf spring was proposed. At first, numerical stress analysis for leaf spring assembly was performed. On the base of the analysis results, fatigue strength of leaf spring was assessed. And next, after studying numerically on geometrical parameters of leaf spring assembly, an economical prediction method of fatigue design criterion for leaf spring assembly using the theory of artificial neural network was developed and certified its usefulness. Without performing a lot of additional fatigue test for a long time, fatigue design criterion for a new leaf spring assembly having different geometry can be predicted on the base of the already obtained fatigue data.

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: Austenitic stainless steel is a useful material for various industrial facilities such as the nuclear and steam power plant and the heavy chemical industry due to its good corrosion resistance and mechanical properties. However, it has also a large problem that austenitic stainless steel is sensitized in the welding process and its corrosion resistance and mechanical properties decreases by sensitization. Thus, in this paper, corrosion fatigue characteristics of artificially sensitized austenitic STS304 were investigated through corrosion fatigue test. From the results, corrosion fatigue strength of sensitized STS304 was remarkably reduced compare to non-sensitized ones. And it is expected that corrosion fatigue life of TMCP steel can be nondestructively predicted using the DCPD method.