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정달우(Dal-Woo Jung),최낙삼(Nak-Sam Choi),김정석(Jung-Seok Kim),서승일(Sueng-Il Seo),조세현(Se-Hyun Jo) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Fatigue fracture behavior of a hybrid bolted joint was evaluated in comparison to the case of static fracture. Two kinds of specimens were fabricated for fatigue assessment; hybrid composite joint specimen with bolted joint for shear test and hybrid joint part specimen applied in the real tilting train for bending test. Characteristic fracture behaviors of those specimens under cyclic loads were obviously different from the case under static loads. For hybrid composite joint specimen, static shear caused the fracture of a pure shear mode in the bolted body, whereas cyclic-shear loading brought about the fracture at the site of local tensile stress concentration. For hybrid joint part specimen, static loading caused the shear deformation and fracture in the honeycomb core region, while cyclic loading did the delaminationat the interface between composite skin layer and honeycomb core and did the fracture of welded joint part. Experimental results obtained by static and fatigue tests were considered in modifications of design parameters of the hybrid joint.
틸팅차량용 KTX 차체의 하니컴복합재 측벽판 체결부의 피로파괴평가
정달우(Dal-Woo Jung),김정석(Jung-Seok Kim),최낙삼(Nak-Sam Choi) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.1
틸팅형 고속열차의 차체에 적용되는 하니컴 복합재 조인트 구조물의 경우 운행중 외팔보형 굽힘하중을 받게된다. 하이브리드 복합재 조인트 구조물에 대한 굽힘시험평가를 수행하기 위해 실제 틸팅열차 차체 구조물에서 조인트부를 절단 채취하여 시험편으로 제작하였다. 굽힘시험결과 시험편의 파괴거동은 정적하중과 피로하중하에서 확연히 달라짐을 보였다. 정적굽힘하중 하에서는 하니컴 코어 영역에서 전단변형과 파괴가 발생하였으며, 피로굽힘하중 하에서는 복합재 표피층과 하니컴 코어층 사이에서 계면분리가 발생하거나, 또는 금속재 언더프레임과의 용접부에서 파괴가 발생하였다. 이러한 파괴거동은 다른 산업분야에서 사용되는 유사한 구조의 하니컴 복합재 조인트 구조물에서도 발생할 수 있기 때문에, 본 실험 결과를 하니컴 복합재 조인트 구조물의 설계변수를 개선하기 위해 이용될 수 있다. The honeycomb composite joint structure designed for application to a tilting KTX railroad car body is subjected to bending loads of a cantilever type. Honeycomb sandwich composite panel-joint attached in the real tilting car body was fabricated and sectioned as several beam-joint specimens for the bending test. The fracture behaviors of these specimens under static loads were different from those under cyclic loads. Static bending loads caused shear deformation and fracture in the honeycomb core region, while fatigue cyclic bend loading caused delamination along the interface between the composite skin and the honeycomb core, and/or caused a fracture in the welded part jointed with the steel under-frame. These fracture behaviors could occur in other industrial honeycomb composite joints with similar sub-structures, and be used for improving design parameters of a honeycomb composite joint structure.
가속수명시험을 위한 KTX고속열차 구조물의 S-N 선도 추정
정달우(Dal-Woo Jung),최낙삼(Nak-Sam Choi),박수한(Su-Han Park) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.4
An accelerated fatigue test is essentially required to maintain the reliability of the actual structures of KTX under operation conditions. However, actual fatigue life cannot be obtained because the conventional fatigue tests are not adequate to the real load conditions. Moreover foreign component makers have not provided data of the loading stresses (S) versus cycles at the failure (N). In this study, we suggested a deduction method of the S-N curve for establishing an accelerating test under various load levels. Load history was acquired from the field tests. A Rainflow method was used on the cycle counting of the field load data. After that, an S-N curve was obtained through the iteration process under the condition that the damage index satisfies to 1 in the Miner's rule. The deduced S-N curve was applied to the performance evaluation of Korean-made sealed knuckles compared with imports.
저상버스용 하이브리드 복합재 조인트부의 통계적 피로수명평가
정달우(Dal-Woo Jung),최낙삼(Nak-Sam Choi) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.11
피로시험의 결과가 큰 편차를 보이는 하이브리드 복합재 조인트부에 대해서 통계적 피로수명 평가법을 이용하여 신뢰도 높은 피로수명을 추정하고자 한다. 저상버스 차체에 사용되는 하이브리드 복합재 조인트부를 절취하여 시험대상으로 하였으며, 이 조인트 시편으로 외팔보형 피로굽힘시험을 수행하였다. 피로시험 데이터를 정규분포, 대수정규분포, 와이블 분포를 이용하여 근접시킨 피로수명곡선들과 각각 비교함으로써 하이브리드 복합재 조인트부의 내구수명 추정에 가장 적합한 확률분포를 선정하였다. 선정된 와이블 확률분포를 이용해 확률-응력-수명(P-S-N) 곡선을 구함으로써 하이브리드 복합재 조인트부에 대한 통계적 수명예측 평가절차와 신뢰성설계의 기초자료를 제시하였다. The reliable fatigue life for hybrid composite joint structures was estimated by a statistical method for evaluating fatigue life; the results of the fatigue test varied widely. Cyclic bending tests were performed on a cantilever beam with a hybrid composite joint, which was developed for the body of a low-floor bus. In order to estimate the fatigue life of the hybrid composite joint structure by comparing the data obtained during the fatigue tests, the most suitable probabilistic density function among the normal, lognormal, and Weibull distributions was selected. The probabilistic-stress-life (P-S-N) curves calculated by using the selected Weibull distribution was suggested for process of statistical fatigue life estimation and reliability design.
차량용 하이브리드 복합재 조인트부의 통계적 피로수명평가
정달우(Dal-Woo Jung),윤상재(Sang-Jae Yoon),최낙삼(Nak-Sam Choi) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.4
차량용 하이브리드 복합재 조인트부의 피로수명을 통계적으로 평가하기 위해 저상버스 차체에 사용되는 하이브리드 복합재 조인트부를 대상으로 외팔보형 피로굽힘시험을 수행하였다. 정규분포, 대수정규분포, Wei bull 분포를 이용하여 하이브리드 복합재 조인트부의 피로시험 데이터에 가장 적합한 확률분포를 선정하고 이를 이용해 P-S-N 곡선을 구함으로써 하이브리드 복합재 조인트부에 대한 통계적 수명 예측 평가절차와 신뢰성설계의 기초자료를 제시하였다. Fatigue bending test of a cantilever beam type specimen was performed for statistical fatigue life evaluation of the hybrid composite joints which were developed for low-floor bus car body. The suitable probabilistic density function was selected among the normal, lognomal and Weibull distribution for the life estimation of hybrid composite joint structure. A probabilistic-stress-life (P-S-N) curve was suggested for statistical fatigue life estimation and reliability design.
정달우(Dal-Woo Jung),최낙삼(Nak-Sam Choi),박수한(Su-Han Park) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
An accelerated fatigue test is essentially required to maintain the reliability of the actual structures of KTX under operation conditions. However, actual fatigue life cannot be obtained because the conventional fatigue tests are not adequate to the real load conditions. Moreover foreign component makers have not provided data of the loading stresses (S) versus cycles at the failure (N). In this study, we suggested a deduction method of the S-N curve for establishing an accelerating test under various load levels. Load history was acquired from the field tests. A Rainflow method was used on the cycle counting of the field load data. After that, an S-N curve was obtained through the iteration process under the condition that the damage index satisfies to I in the Miner's rule. The deduced S-N curve was applied to the performance evaluation of Korean-made sealed knuckles compared with imports.
정달우(Dal-Woo Jung),최낙삼(Nak-Sam Choi),박수한(Su-Han Park) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
An accelerated fatigue test is essentially required to maintain the reliability of the actual structure of KTX under operation conditions. However, actual fatigue life cannot be obtained if specimens are not adequate to the conventional fatigue test. Moreover component maker did not provide data of loading stress (S) - cycles at the failure (N). In this study, we suggest a prediction method of the S-N curve for establishing an accelerating test under various load levels. Load history was acquired from the field tests. A Rainflow method was used on the cycle counting of the field load data, and then, an S-N curve was obtained through the iteration process under the condition that the damage index satisfies to 1 in the Miner's rule.