Papers by Author: Ki Weon Kang

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Authors: Ki Weon Kang, Byeong Choon Goo, J.H. Kim, Heung Seob Kim, Jung Kyu Kim
Abstract: This paper deals with the fatigue behavior and its statistical properties of SM490A steel at various temperatures, which is utilized in the railway vehicle. For these goals, the tensile ad fatigue tests were performed by using a servo-hydraulic fatigue testing machine at three temperatures: +20°C, -10°C and -40°C. The static strength and fatigue limits of SM490A steel were increased with decreasing of test temperature. The probabilistic properties of fatigue behavior are investigated by means of probabilistic stress-life (P-S-N) curve and they are well in conformance with the experimental results regardless of temperature. Also, based on P-S-N curves, the variation of fatigue life is investigated and as the temperature decreases, the variation of fatigue life increases moderately.
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Authors: Cheol Woong Kim, Dong Joon Oh, Ki Weon Kang, Young Ho Ko
Abstract: If Fiber Reinforced Metal Laminates (FRMLs) were delaminated, the decrease of stiffness and fiber bridging effect would result in the sudden aggravation of fatigue characteristics. It was reported that the delamination of FRMLs resulted from the crack of Al alloy layers and that it depended on the crack growth. When FRMLs with circular holes was un-cracked but was delaminated, it was impossible to analyze them by conventional fracture parameters expressed as the function of cracks. Therefore, a new analytical model called Pseudo Crack Model (PCM) was suggested to compare the delaminations whether cracks were made or not. The relationship between the crack consumption rate (Ccrack) and the delamination consumption rate (Cdel) was discussed and it was also known that the effect of the Ccrack was larger than that of the Cdel.
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Authors: Ki Weon Kang, B.J. Lee, Kyung Young Jhang, Jung Kyu Kim
Abstract: This study was aimed at identifying failure mechanism and strength of brazed copper pipe used in household air conditioner. For these ends, the brazed joints with various brazing length were manufactured according to manufacturer’s recommended methods. The 3-dimensional X-ray technique was used to identify internal flaws and their failure mechanism in brazed joints. And, strength of brazed joint was evaluated by static tests. To evaluate the effect of heat on the brazed joints, the micro-Vickers hardness is measured. Also, bursting tests were performed for burst pressure of brazed joints by using of self-designed internal pressure bursting tester.
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Authors: Ki Weon Kang, Hee Jin Shim, C.M. Kim, Jung Kyu Kim
Abstract: The study aimed at the failure analysis and strength evaluation of brazed joints used in household air conditioner. For these goals, the failure modes were investigated through the fractographic analysis and micro-Vickers hardness test. The failure modes were classified into two different types and their mechanism was influenced by heat and internal flaws such as incomplete penetration and pin holes. Also, a finite element analysis was performed to evaluate the strength behavior of the brazed joints according to the heat and internal flaws.
1043
Authors: Ki Weon Kang, Jung Kyu Kim, Yong Su Kim, Young Min Do
Abstract: The paper presents the fatigue behavior of carbon/epoxy laminates with impact-induced damage under 2-stage block loading. The impact damage parameter is proposed to evaluate the effect of impact damage on fatigue life. Based on this parameter, the model is developed to predict the residual life at second block. Also, the model for equivalent stress is proposed to estimate the fatigue life under 2-stage block loading based on the S-N curves under constant amplitude loading. For these models, the 2-stage block loading fatigue tests were performed on the impacted composite laminates. The effect of impact damage on fatigue life under 2-stage block loading can be characterized by the impact damage parameter. Additionally, the results by the present residual life prediction model agree with experimental results regardless of applied impact energy. Also, the equivalent stress and corresponding fatigue life by the present model agrees well with the experimental results.
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Authors: Ki Weon Kang, Jung Kyu Kim, Heung Seob Kim
Abstract: The goals of this paper are to identify the impact damage behavior of plain-weave E-glass/epoxy composites and predict the fatigue life of the composites with impact-induced damage under constant amplitude loading. To identify these behaviors, the low velocity impact and fatigue after impact tests are performed for glass/epoxy composites having two types of fiber orientations. The impact damage behavior is dependent on the fiber orientation of the composites. The fatigue life of the impacted composites can be identified through the prediction model, which was proposed on the carbon/epoxy laminates by authors regardless of fiber orientations.
1291
Authors: Cheol Woong Kim, Dong Joon Oh, Kee Joo Kim, Ki Weon Kang
Abstract: The diverse studies on Al/GFRP laminates with the circular holes, therefore, have been carried out recently. The recent studies just focused on the behavior of the fatigue crack propagation and the delamination when the shape and the size of the notches were changed. Therefore, this study evaluated the location effect of the defects in the vicinity of the circular notch of the high strength monolithic aluminum and Al/GFRP laminates on the initiation life (Ni) of the fatigue cracks, the relationship between the crack length (a) and the fatigue life (N). In addition, the fatigue crack behavior of Al/GFRP laminates was studied when the fatigue loading and the interlaminar delamination took place at the same time during crack propagation. In conclusions, (1) for the monolithic aluminum, 10% of the failure life at θ2=30° was more increased than that at θ3=60°. (2) The crack length and the fatigue life behavior of Al/GFRP laminates according to the location of the artificial defect were different from those of the monolithic aluminum. Namely, the fatigue life of θ1=0° and θ2=30° were remarkably shorter than those of θ3=60° and θ4=90°.
693
Authors: Jung Kyu Kim, Ki Weon Kang, Hee Jin Shim, Bum Seok Shon
Abstract: The study aimed at the fatigue life estimation for leakage of refrigerant used in household air conditioner. The leakage of brazed joints was affected by the manufacturing faults with flaws and service condition which is at the internal pressure and at the excitation. Therefore, the four point bending tests were performed to estimate effects of internal pressure and excitation for the fatigue life of brazed joints. In addition, to investigate effect of internal pressure and excitation on the fatigue life, the orthogonal array table in Design of Experiment is adopted.
150
Authors: Ki Weon Kang, Jong Kweon Kim
Abstract: This paper presents the fatigue behavior of plain-weave E-glass/epoxy composites with impact-induced damage under constant and variable amplitude loading. The constant amplitude fatigue life of the impacted composites can be identified through the prediction model, which was proposed on the carbon/epoxy laminates by authors. Also, the models are derived to calculate the equivalent stress of the composites under variable amplitude loading, considering the impact damage. These models allow fatigue data of the unimpacted and impacted composites under variable amplitude loading to be correlated with constant amplitude data of the unimpacted composites.
1079
Authors: Jung Ho Hwang, Heung Seob Kim, Young Choi, Seong Beom Lee, Ki Weon Kang
Abstract: In automotive applications, a particular area of concern is the relation between thermoelastically induced hot spots and noise and vibration in brake system. The finite element methods have been extensively used for thermal analysis applied to brake components. The two-dimensional model has been extended to an annular three-dimensional disc model in order to consider more realistic braking condition. In a conventional braking analysis, the interface pressure is assumed either constant or inversely proportional to radius. However, under the dynamic braking conditions, the frictional heat generated during braking causes thermoelastic distortion that modifies the contact pressure distribution. This paper describes the thermo-elastic instability arising from friction heat generation in braking and proposes the finite element methods to predict the variation of temperature and thermal deformation under single braking and repeated braking mode.
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