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.

회주철의 미세구조와 인장거동 분석 및 확률론적 피로수명평가

성용현(Yong Hyeon Sung),한승욱(Seung-Wook Han),최낙삼(Nak-Sam Choi) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.8

보통회주철(GC300)에 Cr, Mo, Cu 첨가제를 넣어 고급 회주철(HCI350)을 제작하고, 미세 조직과 기계적 물성치, 피로강도의 변화를 연구하였다. 주철을 환봉형과 평판형 주물로 제작하였으며, 이들을 절단 및 연마하여 나이탈 수용액으로 에칭한 후 미세조직의 면적비율을 측정하였다. 첨가물에 의해 편상 흑연결정(flake graphite)의 크기가 감소하고 고밀 펄라이트 함량이 증가하여 인장강도, 피로강도의 향상이 확인되었다. 피로시험 결과 획득한 피로수명 데이터를 바탕으로 최우추정법이 적용된 2모수 와이블 분포를 이용하여 확률-응력-수명 곡선을 산출하였다. 확률-응력-수명곡선 산출 결과 HCI350은 GC300에 비해 피로강도는 크게 개선되었고 수명데이터의 분산성은 낮아졌으나, 피로응력완화에 따른 피로수명의 증가가 크게 나타났다. 산출된 확률-응력-수명 곡선을 이용하여 요구수명 사이클 수에 대한 허용응력 값을 정량적으로 제시함으로써 신뢰성 수명설계에 위한 기초자료를 제시하였다. High-grade gray cast iron (HCI350) was prepared by adding Cr, Mo and Cu to the gray cast iron (GC300). Their microstructure, mechanical properties and fatigue strength were studied. Cast iron was made from round bar and plate-type castings, and was cut and polished to measure the percentage of each microstructure. The size of flake graphite decreased due to additives, while the structure of high density pearlite increased in volume percentage improving the tensile strength and fatigue strength. Based on the fatigue life data obtained from the fatigue test results, the probability - stress - life (P-S-N) curve was calculated using the 2-parameter Weibull distribution to which the maximum likelihood method was applied. The P-S-N curve showed that the fatigue strength of HCI350 was significantly improved and the dispersion of life data was lower than that of GC300. However, the fatigue life according to fatigue stress alleviation increased further. Data for reliability life design was presented by quantitatively showing the allowable stress value for the required life cycle number using the calculated P-S-N curve.

STS304강의 순수 및 외팔보형 굽힘피로에 대한 파괴확률특성

노성국,정순억 경상대학교 해양산업연구소 2002 해양산업연구소보 Vol.15 No.-

Big accidents of flyings, vessel, subways, gas equipments, buildings and bridge happens frenquently. Therefore many people are suffering harm of property. The destruction cause of macaine components is almost accused by fatigue. This study is test for STS304 specimen by using pure and cantilever bending state. Rounded specimen and notched specimen including fracture surface investigation was comparatively experimented, fatigue life according to degree of surface finishing was examined. Fatigue fracture probability of notched canilever specimens were predicted by P-S-N curve, median rank and Weibull distribution. And at the relation with the rotational speed and stress the fatigue life of the test specimen was higher than low speed at high speed.

확률밀도함수를 이용한 상수도 실 배관의 피로수명 특성 평가

최정훈(Jung-Hun Choi),구재민(Jae-Mean Koo),석창성(Chang-Sung Seok),송원근(Weon-Keyu Song) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.9

The fatigue characteristics of a material or a structure are generally derived from fatigue tests of standard specimens. However, test results of standard specimens are different from those of real structures or components. Therefore, to calculate more accurate fatigue life, the geometrical effect and surface condition must be considered by comparing test results of standard specimens with those of real structures or components. Thus the object of this paper is to evaluate the fatigue characteristics of a real waterwork pipe. Also, to evaluate fatigue characteristic based on life distribution, the statistical fatigue characteristics were analyzed by the normal distribution and related data of P-S-N curve.

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.

쇼트피닝 처리를 한 베어링강의 고사이클 피로수명 및 파괴거동

윤상재(Sang Jae Yoon),최낙삼(Nak Sam Choi) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.9

쇼트피닝(shot-peening) 처리를 한 베어링강의 고사이클 피로거동을 연구하였다. 열처리한 베어링강(JISSUJ2) 시험편과 열처리 후 쇼트피닝 표면가공을 추가한 시험편을 사용해 회전굽힘피로시험을 수행하고 파단된 시험편의 파면을 분석하였다. 시험편의 피로파괴는 표면 결함에서 비롯된 표면 파괴와, 내부의 비금속개 재물에서 비롯된 내부형 파괴의 두 종류로 발생하였다. 내부 파괴의 경우 비금속 개재물 주변에 어안(fisheye) 모양의 파괴양식이 관찰되었다. 개재물은 표면으로부터의 깊이와 형상에 따라 피로 수명에 큰 영향을 주었다. 쇼트피닝 가공을 한 베어링강은 저사이클 하중영역 및 고사이클 하중영역에서 모두 피로수명이 향상 되었으며, 하중이 작아질수록 피로수명의 개선은 더욱 커졌다. 또한 2 모수 와이블(Weibull) 분포를 이용하여 베어링강의 확률-응력-수명 (P-S-N) 곡선을 구하여 신뢰도 높은 피로수명 예측을 하였다. Shot-peening effects on the fatigue behavior of bearing steel were investigated under the high cyclic loading. Hourglass shape specimens were made of bearing steel(JIS-SUJ2) for rotary bending fatigue tests. Two kinds of treatments were performed : a heat treatment and a shot-peened surface treatment after the heat treatment. The fracture surfaces of specimens were classified into two types of fracture mode : the surface fracture mode induced by a surface defect and the internal fracture mode induced by a nonmetallic inclusion. Inclusion depth and shape affected considerably the fatigue life. Shot-peening treatment improved much the fatigue life of the bearing steel under low and high levels of cyclic loads. Probabilistic-stress-life (P-S-N) curves were suggested for the reliable fatigue life estimation of the improved bearing steel.

TiNi/Al6061-T6과 TiNi/Al2024-T4 형상기억복합재료에 대한 피로강도기준의 비교

조영직(Young-Jik Jo),박영철(Young-Chul Park) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.2

This study produced a design curve and fatigue limit for a variation in volume ratio and reduction ratio of TiNi/Al composites. In many cases, stress-life curve does not indicate fatigue limit, so it was presented by probabilistic-stress-life curve. Goodman diagram was used to analyze the fatigue strength of materials with a finite life determined by repeated load and the fatigue strength of endurance limit with an infinite life. The fatigue experiment was conducted using the scenk-type plane bending specimen in same shape. The result of the fatigue test, which had been conducted under consistent stress amplitude, was examined. (ⅰ) The optimal condition for TiNi/Al in accordance with hot pressing (ⅱ) Impacts of fatigue limit caused by a variation in reduction ratio and volume ratio of TiNi/Al composites (ⅲ) Probability distribution for fatigue limit of TiNi/Al2024 and TiNi/Al6061.

기계구조용강의 피로수명특성에 관한 신뢰성 평가

장성수 한국기계기술학회 1999 한국기계기술학회지 Vol.1 No.1

피로강도 변동성을 고려한 Pulley의 내구성 평가

심희진(Hee-Jin SHIM),김철수(Chul-Su KIM),오원철(Won-Chul OH),김정규(Jung-Kyu KIM) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4

In order to secure the safety of power steering system, it is necessary to perform the strength and the fatigue analysis of pulley in this paper. The applied stress distribution of the pulley subject to combined loads condition was obtained using finite element analysis. Based on these results, the fatigue life of the pulley with the variation of the fatigue strength was evaluated using durability analysis simulator. The optimal hole size to improved the safety of the pulley was investigated using parametric study. Moreover, the predicted fatigue life cycle with the simulator was verified by experimental tests.

파워스티어링 오일펌프용 풀리의 내구성 해석 및 최적화

심희진(Hee Jin Shim),김정규(Jung Kyu Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

The pulley is one of core mechanical elements in the power steering system for vehicles. The pulley operates under both the fatigue compressive loading and the torque. Therefore, to assure the safety of the power steering system, it is very important to investigate the durability and the optimization of the pulley. In this study, the applied stress distribution of the pulley under high tension and torsion loads was obtained by using finite element analysis. Based on these results, the fatigue life of the pulley with the variation of the fatigue strength was evaluated by a durability analysis simulator. The results at 50% and 1%for the failure probability were compared with respect to the fatigue life. In addition the to optimum design for the fatigue life is obtained by the response surface method. Moreover, optimum design by considering its durability and validity is verified by the durability test.