• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2002년도 추계학술발표대회 논문집
• /
• pp.75-78
• /
• 2002

복합재구조물에 대한 피로수명과 잔류강도를 평가하기 위한 단순화된 방법을 소개하였다. 모델의 특성화를 위해 필요한 실험을 줄이기 위하여 강도저하 파라미터수를 피로수명의 함수로 가정하였다. 임의의 순서로 배열된 하중 스펙트럼에서 응력수준에 따른 피로수명을 추출하기위해 S-N 선도를 사용하였다. 그리고 상이한 응력비(stress ratio)에 대한 영향을 고려하기위해 Goodman 형식의 방법(fatigue envelope)을 사용하였다. 잔류강도는 하중 사이클 수와 응력진폭의 함수로 가정하였으며 임의의 하중사이클 후의 잔류강도분포는 2 모수 Weibull 분포로 표현하였다.

• Composites Research
• /
• 제16권1호
• /
• pp.13-18
• /
• 2003

복합재료의 피로수명을 평가하는 것은 여러 가지 파손모드와 파손모드 간의 강호작용 때문에 복잡하다. 본 논문에서는 현상론적인 모델(비선형 강도저하 모델)을 이용하여 피로수명과 잔류강도를 예측할 수 있는 방법을 제시하였다. 잔류강도를 하중 사이클 수와 피로응력의 함수로 가정하였으며, 계산에 필요한 모델변수(강도저하 파라미터, 피로수명형상 파라미터)를 피로수명의 함수로 가정하였다 임의로 배열된 하중 스펙트럼 상에서 응력수준에 따른 모델 매개변수를 구하기 위해 S-N 선도를 이용하였고, 상이한 응력비에 대하여 전술한 매개변수를 Goodman식의 보정을 통하여 계산하였다(피로선도). 임의의 하중이력 후의 잔여강도 분포를 2모수 weibull 함수로 표현하였다.

• 한국자동차공학회논문집
• /
• 제25권2호
• /
• pp.250-256
• /
• 2017

Automatic transmission(A/T) is one of a car's core components. The durability of A/T has an effect on the durability of the car. The input shaft of A/T passes the power directly from the engine, so the durability of the input shaft for A/T is likewise vital. In this study, the test method of the input shaft is considered and the load spectrum of A/T is analyzed to secure durability of the input shaft. The shape parameter, T-N curve of the input shaft torsional fatigue test are obtained for life evaluation and analysis. Results of this study can be used to get the basic background of the durability test for A/T components.

• 한국자동차공학회논문집
• /
• 제12권1호
• /
• pp.106-113
• /
• 2004

Most of mechanical structures are composed of many substructures connected to one another by various types of mechanical joints. In automotive engineering, it is important to study these connected structures under various dynamic forces for the evaluations of fatigue life and stress concentration exactly. In this study, the dynamic response of vehicle structure to external forces is classified an inverse problem involving strains from the experiment and the analysis. The practical dynamic forces are determined by the combination of the analytical and experimental method with analyzed strain by quasi-static finite element analysis under unit force and with measured strain by a strain gage under driving load, respectively. In a stressed body, inter-molecular chemical bonds are failed beyond the certain magnitude. The failure of molecular structure in material is considered as a time process of which rate is determined by mechanical stress. That is, the failure of inter-molecular chemical bonds is the fatigue lift of material. This kinetic concept is expressed as lethargy coefficient. And S-N curve is obtained with the lethargy coefficient from quasi-static tensile test. Equivalent practical dynamic force is obtained from the identification of practical dynamic force for one loading point. Using the practical dynamic force and S-N curve, fatigue life of a window pillar is analyzed with FEM under the identified force by the procedure of above mentioned.

• 한국항공우주학회지
• /
• 제41권7호
• /
• pp.561-568
• /
• 2013

7,000lb 급 헬리콥터를 위한 무베어링 로터 허브 시스템을 설계한 후, 무베어링 로터 허브 시스템의 주요 구성품 중 하나인 유연보에 대해 요구수명 8,000시간을 만족하는지 확인하기 위한 피로해석을 수행하였다. 2차원 탄성 보 모델에 대한 단면 구조해석 방법을 적용하였으며, 정적구조해석을 통해 피로손상에 취약할 것으로 예상되는 두 단면에 대한 피로해석을 수행하였다. 구조해석을 위해 VABS를 사용하여 유연보 단면 형상에 대한 인장, 굽힘 및 뒤틀림 강성을 계산하였고, wohler equation을 적용하여 유연보를 구성하는 두 가지 복합재 소재에 대한 S-N 곡선을 생성하였다. CAMRAD II를 통해 무베어링 로터 시스템의 하중해석을 수행하였으며, 하중해석 결과를 HELIX/FELIX 표준하중 스펙트럼에 적용하여 무베어링 로터 시스템의 하중 스펙트럼을 생성한 후, 이를 통해 피로해석을 수행하였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.1740-1743
• /
• 2007

In this study, two types of fatigue tests were conducted. First, cyclic bending tests were performed using the micro-bending tester. A four-point bending test method was adopted, because it induces uniform stress fields within a loading span. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. The pseudo-power cycling method makes up for the weak points in a power cycling and a chamber cycling method. Two compositions of solder are tested in all test condition, one is lead-free solder (95.5Sn4.0Ag0.5Cu) and the other is eutectic lead-contained solder (63Sn37Pb). In the cyclic bending test, the solder that exhibits a good reliability can be reversed depending on the load conditions. The lead-contained solders have a longer fatigue life in the region where the applied load is high. On the contrary, the lead-free solder sustained more cyclic loads in the small load region. A similar trend was detected at the thermal cycling test. A three-dimensional finite element analysis model was constructed. A finite element analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. A constitutive model which includes both creep and plasticity was employed. Thermal fatigue was occurred due to the creep. And plastic deformation is main damage for bending failure. From the inelastic energy dissipation per cycle versus fatigue life curve, it can be found that the bending fatigue life is longer than the thermal fatigue life.

• 한국자동차공학회논문집
• /
• 제8권3호
• /
• pp.110-118
• /
• 2000

For reasonable fatigue design and estimation of fatigue durability considered fatigue strength and stiffness of the automotive body structure, many fatigue data must be insured according to the shapes, materials, and welding conditions of the spot welded lap joints. However, because it is actually difficult problem, there is need to establish a new method to be able to predict its fatigue life without any additional fatigue tests. Therefore, In order to improve such problems, in this study, the maximum stress function presenting the $\delta\sigma_{1max}―\delta P$ relation was defined form the relation between $\delta\sigma_{1max}-N_f$ and ${\delta}P-N_f$. By using the fatigue data on the IB type spot-welded lap joints previously obtained from the fatigue test results, fatigue life of the spot-welded lap joint previously obtained from the fatigue test results, fatigue life of the spot-welded lap joint having a certain dimension was tried to predict without any additional fatigue tests. And, its result was verified by ${\delta}P-$N_f$ curves. Obtained conclusion are as follows, 1) a maximum stress function considered the relation of the maximum principal stress, fatigue load, and the effects of geometrical factors of the IB type spot-welded lap joint was suggested. 2) the fatigue life predicted by the maximum principal stress function and the relation of $\delta\sigma_{1max}-N_f$ was well agreed with the fatigue life obtained through the actual fatigue test result. 3) the fatigue life of the IB type spot-welded lap joint having a certain dimension is able to be predicted without any additional fatigue tests from the fatigue life prediction method by the maximum principal stress function.

• 한국물환경학회지
• /
• 제34권3호
• /
• pp.270-284
• /
• 2018

Paldang is a river reservoir located in the Midwest of Korea, with a water volume of $244{\cdot}10^6m^3$ and a water surface area of $36.5km^2$. It has eutrophied since the construction of a dam at the end of 1973, and the phosphorus concentration has decreased since 2001. Average hydraulic residence time of the Paldang reservoir is about 10 days during the spring season and 5.6 days as an annual level. The hydraulics and water quality of the reservoir can differ greatly, both temporally and spatially. For the spring period (March to May) in 2001 ~ 2017, the reservoir mean total phosphorus concentration calculated from the budget model based on a plug-flow system (PF) and a continuous stirred-tank reaction system (CSTR) was 13 % higher and 10 % lower than the observed concentration, respectively. A composite flow system (CF) was devised by assuming that the transition zone was plug flow, and that the lacustrine zone was completely mixed. The mean concentration calculated from the model based on CF was not skewed from the observed concentration, and showed just 6 % error. The retention coefficient of the phosphorus derived from the CF was 0.30, which was less than those of the natural lakes abroad or river reservoirs in Korea. The apparent settling velocity of total phosphorus was estimated to be $93m\;yr^{-1}$, which was 6 ~ 9 times higher than those of foreign natural lakes. Assuming CF, the critical load line for the total phosphorus concentration showed a hyperbolic relation to the hydraulic load in the Paldang reservoir. This is different from the previously known straight critical load line. The trophic state of the Paldang reservoir has recently been estimated to be mesotrophic based on the critical-load curve of the phosphorus budget model developed in this study. Although there is no theoretical error in the newly developed budget model, it is necessary to verify the validity of the portion below the inflection point of the critical-load curve afterwards.

• 한국공작기계학회논문집
• /
• 제10권4호
• /
• pp.7-13
• /
• 2001

This Study is to investigate the influence of weld residual stresses on the fatigue crack growth behaviors in pressure ves-sel reinforcement. In order to perform this study, the automatically welded specimens are prepared. The material is ASTM A516 grade 60 steel used in pressure vessel mainly. For pad-on-plate of skip welding continuous welding and PWHT specimen, fatigue crack initiation is generally initiat-ed at weld starting and end toe zone, and ruptured at weld starting toe zone, Fatigue life if pad-on-plate continuous speci-men is increased more than that of pad-on-plate skip fillet welding specimene about 85% under low load, about 20% under high load, and decreased than that of two-pad continuous welding specimen about 85%. In da/dN-$\Delta$ Κ curve under low load, pad-on-plate skip fillet welding specimen showed retardation on the initial crack, and the fatigue crack growth rate at the low region of $\Delta$Κ greater specimene E(3.8{\times}10^{-6}$mm/cycle). And the fatigue life of welding specimen was smaller than that of PWHT specimen.

• 한국안전학회지
• /
• 제16권3호
• /
• pp.1-6
• /
• 2001

The study is to investigate the influence on the fatigue crack growth behaviors for the welded configuration in pressure vessel stiffener. In order to perform this goal, the automatic welded specimens were prepared. The material is ASTM A516 grade 60 steel used in pressure vessel mainly. In skip welding of pad-on-plate, continuous fillet welding and PWHT specimen, fatigue crack is generally initiated at the starting and end old toe zone, and ruptured at the starting old toe zone. The fatigue life of pad-on-plate of the continuous fillet welding specimen is larger than that of pad-on-plate skip fillet welding specimen about 85% under low load, about 20% under high load and less than that of two-pad continuous fillet welding specimen about 85%. In da/dN-$\Delta$K curve under low load, skip fillet welding specimen of pad-on-plate showed retardation on the initial crack, and the fatigue crack growth rate at the low region of $\Delta$K greater specimen E($3.8 {\times} 10^{-6}mm/cycle$). And the fatigue life of welding specimen was smaller than that of PWHT specimen.