Papers by Author: Il Sup Chung

Abstract: A pressure plate, a component of the clutch system, was analyzed by two-dimensional and three-dimensional finite element method under three major load conditions of thermal loading due to temperature distribution, centrifugal force and contact pressure of diaphragm spring. The results show that the effects of thermal loading and contact pressure of diaphragm spring are important, which suggests the direction of design improvement. A hub plate was also analyzed with finite element modeling. A stress concentration occurs around the fillet region around the window in the plate where the fracture analysis is executed to find the stress intensity factors. These results will be used as the fundamental data for design improvement of the shapes of pressure plates and hub plates.

Abstract: Mechanical breakdown often comes from the fatigue in many structural parts and nuclear power plants. Among the fatigue phenomenon, especially fretting fatigue occurs in mechanical joints showing small relative movements between contact surfaces. Although the research was developed for one hundred years, occurrence mechanism is not clearly identified yet. INCOLOY alloy 800 is a iron-nickel-chromium alloy having excellent resistance to many corrosive aqueous media and high-temperature atmospheres. This alloy is used extensively in the nuclear power plants industry, the chemical industry, the heat-treating industry and the electronic industry. In this paper, the effect of fretting damage on fatigue behavior for INCOLOY alloy 800 was studied. Also, various kinds of mechanical tests such as tension and plain fatigue tests are performed. Fretting fatigue tests were carried out with flat-flat contact configuration using a bridge type contact pad and plate type specimen. Through these experiments, it is found that the fretting fatigue strength decreased about 50% compared to the plain fatigue strength. In fretting fatigue, the oblique micro-cracks at an earlier stage are initiated. These results can be used as basic data in a structural integrity evaluation of heat and corrosion resisting alloy considering fretting damages.

Abstract: Studies on the strength and fatigue life of machines and structures have been conducted in accordance with the development of modern industries. In particular, fine and repetitive cyclic damage occurring in contact regions has been known to have an impact on fretting fatigue fractures. INCONEL alloy 600, 690 and INCOLOY alloy 800 are iron-nickel-chromium alloy having excellent resistance to many corrosive aqueous media and high-temperature atmospheres. These alloy are used extensively in the nuclear power plants industry, the chemical industry, the heat-treating industry and the electronic industry. In this paper, the effect of fretting damage on fatigue behavior for INCONEL alloy 600, 690 and INCOLOY alloy 800 were studied. Also, various kinds of mechanical tests such as tension and plain fatigue tests are performed. The objective of this study is to guarantee reliability of the facility applied in a power plant by comparing three materials in respect to fretting fatigue.

Abstract: Analysis of structures including periodically arrayed in-homogeneities, whether they are microscopic or macroscopic, can be simplified by using homogenized properties. If the unit structure is repeated in a longitudinal direction, the whole structure may be regarded as a beam with effective flexibility. This study proposes a kinematical periodicity constraint to be imposed on the FE model of the unit structure for beams, which improves the accuracy of the effective flexibility along with reduction of the model size. The method is applied to a beam-in-space containing repetitive un-symmetric holes, and it is demonstrated that the deformation behavior of the homogenized beam agrees well with that of the real structure.

Abstract: In the analysis of materials containing regularly placed in-homogeneities, the evaluation of homogenized properties is an important issue. Common procedure for the homogenization is to define a unit cell, load it somehow, and investigate its structural response. A periodic variation of strain appears when the periodically heterogeneous material is under uniform macro-stress, and therefore, the implementation of this characteristic behavior would be essential to the material characterization based on a unit cell analysis. With the method proposed here, conventional finite element analysis tools can be used with no modification, and it is applicable to the skew-arrayed in-homogeneity problems. The orthotropic elastic and creep properties of materials with voids are examined, and the accuracy and effectiveness are demonstrated.

Abstract: The liquid oxidation behavior of Mg-Ca base alloys containing Be has been presented in this paper. The ignition temperature test and microbalance measurement indicated that the oxide film formed at elevated temperature was protective, resulting in the improved oxidation resistance and ignition-proof properties. A Ca-rich zone was found at the very near surface of oxide layer. With Be addition the oxide layer became dense and compact, which was impermeable for the rapid diffusion of oxygen and magnesium through the oxide layer. It was concluded that the formation of BeO in the oxide layer suppressed the continuous growth of the oxide layer.