자동차 조향 링크의 피로해석

고승기(Seung-Kee Koh) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Fatigue analysis was performed in order to predict the fatigue lifetime of an automotive steering drag link. Specimens taken from the drag link tube was used for the monotonic tensile test and strain-controlled low-cycle fatigue test, that resulted in the monotonic and cyclic properties of the drag link steel. Finite element method was employed to investigate local stress and strain distributions of the link. From the experimental stress analysis using strain-gages, the accuracy of the FE stresses at the curved region of the link was verified. Based on the fatigue life curves and the stress analysis, the fatigue life of the drag link was predicted and compared with the experimentally determined fatigue life, resulting in a fairly good correlation.

자동차 조향 드래그 링크의 피로수명평가

고승기(Seung-Kee Koh),나의균(Eui-Gyun Na),백태현(Tae-Hyun Baek) 한국자동차공학회 2003 한국자동차공학회 지부 학술대회 논문집 Vol.- No.-

Fatigue life estimation was made in order to predict the fatigue lifetime of an automotive steering drag link. Specimens taken from the drag link tube was used for the monotonic tensile test and strain-controlled low-cycle fatigue test, that resulted in the monotonic and cyclic properties of the drag link steel. Finite element method was employed to investigate local stress and strain distributions of the link. From the experimental stress analysis using strain-gages, the accuracy of the FE stresses at the curved region of the link was verified. Based on the fatigue life curves and the stress analysis, the fatigue life of the drag link was predicted and compared with the experimentally determined fatigue life, resulting in a fairly good correlation.<br/> <br/>

탄소성 이론과 유한요소법에 의한 강판재의 프레스 성형성 해석

백태현(Tae Hyun Baek),고승기(Seung Kee Koh),박태근(Tae-Geun Park),정걸(Girl Jung),황한영(Han Young Han) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.8

This paper presents the results obtained from the analysis for centralized stress distributions on the steel sheet metal sheet of vehicle's front bumper developed in press-forming and bending process. After calculating the stress distribution by finite element analysis, the point where the maximum stress comes into being can be determined. In order to avoid the crack which might be occurred in material when bending process, the product's material, shape and the minimum bending radius are proposed to be calculated by the simple elasto-plastic and empirical equation.

자동차용 박판 점 용접부의 용접성 평가

나의균(Eui-guyen Na),고승기(Seung-Kee Koh),백태현(Tae-Hyun Baek),오석형(Suck-Hyung Oh),오원철(Won-Cherl Oh) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.9

The purpose of this study is to evaluate the strength at spot welded region for the automotive thin plates and to find out the fracture region by a finite element method. spot welding against the thin plate of 0.8㎜, 1.0㎜, 1.2㎜ and 1.6㎜ was conducted under various welding currents. The weldability of spot welded region was dependent upon the thickness and welding current, Nugget diameter of the spot welded region was proportional to the applied current. Generally, Maximum load at spot welded region increased with the welding current. However, too high current was inappropriate in acquiring the better weldability because of the sputtering effect. It was verified through FEM analysis that fracture was initiated at boundary region between nugget and parent.

SUS 316스테인리스 강 TIG용접부의 부식특성평가에 관한 연구

나의균(Eui Gyun Na),고승기(Seung-Kee Koh),김훈(Hoon Kim),이상근(Sang-Keun Lee) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.5-3

본 연구에서는 고온고압용으로 많이 사용되고 있는 스테인리스 강을 대상으로 부식특성을 평가하였다. 시험재는 모재, 용접후 열처리재 및 용접재를 대상으로 하였다. 용접후열처리는 730℃까지 온도를 올린 후 4시간동안 유지한 다음 노냉을 시켰다. 부식특성 평가는 양극분극법을 이용하였으며, 분극실험에서 H₂SO₄+KSCN용액을 이용하였다. 또한 저변형률실험법을 이용하여 인공해수 중에서 용접재와 모재 등의 부식특성을 평가하였다. 아울러 시험편의 미시균열 손상의 정도를 알아보기 위해 음향방출실험도 동시에 실시하였다. 후열처리재의 부식의 정도가 가장 심했으며, 모재가 부식환경에 가장 안정적이었다. 용접재의 음향방출 결과는 전 변형구간에 걸쳐 음향방출신호가 나탔으며, 용접후 열처리재의 경우에는 항복강도 이후에는 거의 음향방출신호가 탐지되지 않았다. The purpose of this study is to evaluate the corrosive characteristics for the TIG weld region for SUS-316 stainless steel. Basemetal, weldment and heat treated specimens were prepared and heat treatment was conducted under the 730℃ of temperature, 4hours of holding and cooling in furnace. Anodic polarization test was applied to evaluate the corrosive characteristics for the specimens in the environment of H₂SO₄+KSCN solution. Besides, corrosive characteristics for the specimens was evaluated using slow strain rate test(SSRT) and acoustic emission(AE) test was carried out to examine the sources of micro-crack initiation simultaneously. In case of post weld heat treated specimen, degree of corrosion was the greatest and basemetal was shown to be most stable among 4 specimens. Lots of acoustic emission signals were emitted for the weldment over the all plastic deformationg range. However, In case of the PWHT specimen, acoustic emission signals were produced within the yield strength almost only unlike the weldment. Besides, number of AE counts for the weldment was the largest and those for the PWHT specimen was decreased considerably.

날카로운 균열을 갖는 다층용접부의 음향방출거동 평가에 관한 연구

나의균(Eui Gyun Na),오석형(Seok-Hyung Oh),고승기(Seung-Kee Koh),이상근(Sang-Keun Lee) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5

본 연구에서는 압력용기 날카로운 균열을 갖는 강 다층용접부를 대상으로 음향방출거동을 평가하였다. 용집된 판으로부터 표준 샤르피 시험편을 가공하여 날카로운 균열을 내고 난 다음 굽힘과 음향방출실험을 동시에 실시하였다. 이어 음향방출인자와 굽힘하중과 굽힘량 곡선과의 관계에서 음향방출거동을 평가하였으며, 균열선단에서 소성역역의 진전거동을 음향방출법에 의해 평가하였다. 시험편에 관계없이 탄성영역애서는 음향방출신호가 거의 발생하지 않았으며, 소성영역에서 발생하였다. 음향방출신호강도는 용접재의 경우가 모재와 후 열처리재에 비해 가장 큰 값을 보였다. 주사전자현미경 관찰결과 용접재의 경우 용접시 발생하는 산화물 등이 모재와 후 열처리재에 비해 훨씬 많이 분포되었음을 확인할 수 있었다. The purpose of this study is to evaluate the behaviors of acoustic emissions(AE) at multi-pass weld region with sharp crack for the pressure vessle steel. Charpy standard specimens were extracted from the welded plate. Machined notch was made and then sharp crack was made using repetitive load. Four point bend and AE tests were conducted simultaneously. After tests, relationships between AE parameters such as AE strength etc. and load-deflection curves were obtained. Besides, relations of plastic deformed zone size at sharp crack tip and AE parameter were discussed. AE signals were absent within an elastic region, regardless of the specimens. Most of AE signals are produced in the process of plastic deformation. The deformation modes of basemetal and weldment are quiet different. Value of AE strength for the weldment was larger than those for PWHT specimen and basemetal. SEM observations were made. In case of the weldment. Much more particles such as oxides which are formed in the process of weld in air were distributed on the fractured surfaces compared with the PWHT specimen and basemetal.

하중방식에 따른 강 용접부의 음향방출 특성에 관한 연구

유용재(Yong-Jae Yu),나의균(Eui-Gyun Na),고승기(Seung-kee Koh),백태현(Tae-Hyun Baek) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3

The purpose of this study is to find out the suitable test method to detect the AE signals at notch tip of the Charpy test specimens under bending tests and to evaluate the AE characteristics of the basemetal and weldment for SA-516 steel. Besides, micro-crack initiation region was chosen non-destructively and deformation behaviours were discussed from the viewpoint of the accumulated AE energy. In case of the Charpy sized specimens with small volume fraction, four point bend test is found to be the suitable test method to detect the AE signals at notch tip compared with the three point bending test. Regardless of the specimens like the basemetal and weldment, AE signals were absent within the elastic region at all and AE signals were produced from the region corresponding to the plastic deformation initiation point and micro-cracks were initiated at the mid-point between yield and maximum load. Deformation behaviours of the basemetal and weldment were different because of the differences of the micro-structure and mechanical properties at weld region.

자긴가공된 압력용기의 잔류응력 평가 및 피로수명 예측

송경진(Kyung Jin Song),김은겸(Eun Kyum Kim),고승기(Seung Kee Koh) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.9

외경에 홈이 존재하는 자긴가공된 압력용기의 피로 파손은 외경 홈에서의 피로균열 발생과 전파에 의해 발생한다. 자긴가공된 압력용기의 피로수명을 예측하기 위하여 유한요소법을 이용하여 자긴가공에 의한 잔류응력해석을 수행하였으며, 피로시험을 통하여 재료의 피로특성을 구하였다. 압력용기의 수명은 압력용기 외경 홈 모서리에서 응력 및 변형률 집중에 의한 피로균열의 생성수명과 전파수명의 합으로 총 수명이 계산되었다. 본 연구에서 80 % 자긴도의 압력용기가 424 MPa의 반복적인 내압을 받을 때 압력용기의 수명은 2,598 사이클로 예측되었다. Fatigue failure of an autofrettaged pressure vessel with a groove at the outside surface occurs owing to the fatigue crack initiation and propagation at the groove root. In order to predict the fatigue life of the autofrettaged pressure vessel, residual stresses in the autofrettaged pressure vessel were evaluated using the finite element method, and the fatigue properties of the pressure vessel steel were obtained from the fatigue tests. Fatigue life of a pressure vessel obtained through summation of the crack initiation and propagation lives was calculated to be 2,598 cycles for an 80% autofrettaged pressure vessel subjected to a pulsating internal pressure of 424 MPa.

일정진폭의 반복적인 고압을 받는 챔버의 피로수명평가

김영일(Young Il Kim),김병운(Byung Woon Kim),고승기(Seung Kee Koh),정의초(Ui Cho Jeong) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.4

고압을 받는 챔버의 피로수명을 예측하기 위하여 저주기피로시험, 응력해석, 피로손상해석을 수행하였으며, 예측한 수명의 검증을 위하여 모사시험을 수행하였다. ASTM E606에 따라 저주기피로시험을 수행하여 저주기 피로특성치를 얻었다. 챔버의 응력을 구하기 위하여 평면변형률조건에서 502 MPa의 내압을 작용하여 해석을 수행하였다. 평균응력을 고려한 Morrow식과 SWT식을 이용하여 예측한 피로수명은 각각 1.37 × 10<SUP>6</SUP> 사이클과 2.91 × 10<SUP>5</SUP> 사이클이다. 예측한 수명을 검증하기 위하여 C형 모사시편을 사용한 모사시험을 수행하였으며, 1.37 × 10<SUP>5</SUP> 사이클을 얻었다. SWT식을 이용하여 예측한 피로수명은 모사시험으로 얻은 피로수명과 2배 차이를 나타내어 Morrow식으로 예측한 수명보다 상대적으로 높은 정확도를 나타내었다. Stress analysis and fatigue damage analysis of a chamber subjected to high pressure were performed to predict the fatigue life. Low-cycle fatigue characteristics were obtained by performing the test according to ASTM E606. The stress analysis of a chamber was done using the plane strain condition subjected to an internal pressure of 502 MPa. Two damage parameters of Morrow and SWT were employed to estimate the fatigue life of the chamber, resulting in 1.37 × 10<SUP>6</SUP> cycles and 2.91 × 10<SUP>5</SUP> cycles for crack initiation. The predicted fatigue life was verified by the simulation fatigue test using a C-shaped specimen, and a fatigue life of 1.37 × 10<SUP>5</SUP> cycles was obtained. The predicted fatigue life using the Smith-Watson-Topper(SWT) parameter agreed well with the simulation fatigue life within a factor of 2. The SWT parameter resulted in more accurate fatigue prediction than that by the Morrow parameter.

자동차 조향 드래그 링크의 피로수명예측

고승기 국립7개대학공동논문집간행위원회 2005 공업기술연구 Vol.5 No.-

Fatigue analysis was performed in order to predict the fatigue lifetime of an automotive steering drag link. Specimens taken from the drag link tube were used for the monotonic tensile test and strain-controlled low-cycle fatigue test, that resulted in the monotonic and cyclic properties of the drag link steel. Finite element method was employed to investigate local stress and strain distributions of the link. From the experimental stress analysis using strain-gages, the accuracy of the FE stresses at the curved region of the link was verified. Based on the fatigue life curves and the stress analysis, the fatigue life of the drag link was predicted and compared with the experimentally determined fatigue life, resulting in a fairly good correlation.