• Title/Summary/Keyword: fatigue life curve

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Fatigue Life Estimation Using the Multi-Axial Multi-Point Load Counting Method under Variable Amplitude Loading (가변진폭하중하에서 다축-다점 하중 Counting method를 이용한 피로수명평가)

  • Lee, W.S.;Lee, H.W.
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.6
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    • pp.22-27
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    • 1997
  • In general, the load which acts on the structure is almost independent of time in many locations. In this case. It is difficult to estimate the life with the service load history, because the structure is on the multi- axial and multi-point loading states. In this study, the service load of the excavator which is widely used in industry field was calculated using measured cylinder pressures and displacements. The fatigue life was estimated using the multi-axial and multi-point load counting method. Service load history of 4 pin joint which act independently each other is yielded by mult-axial and multi-point load counting method. The stress spectrum is yielded by superposition of the results of FEM stress analysis applied unit load. Palm- gren-Miner's cumulative Damage is 0.000804 for Von Mises equivalent stress sequence by one side fillet weld S-N curve. This result agress with Bench test results. As a result of this study, the fatigue life esti- mation using the multi-axial and multi-axial and multi-point load counting method is useful.

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Cyclic Deformation and Fatigue Behavior of Short Fiber Reinforced Metal Matrix Composites (단섬유보강 금속복합재료의 반복적 변형 및 피로특성)

  • 양유창;송정일;한경섭
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.6
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    • pp.1422-1430
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    • 1995
  • Al6061 alloy reinforced with 15 volume% of Saffil fibers was fabricated by squeeze infiltration method. Uniform distribution of reinforcements and good bondings between reinforcements and matrix alloy were found in the microstructure of composites. Comparing with A16061 matrix alloy, tensile strength and elastic modulus of $Al_{2}$O$_{3}$/Al composites were increased up to 26% and 31%, respectively. Cyclic deformation and fatigue behavior of $Al_{2}$O$_{3}$/Al metal matrix composites were studied. The specimens were cycled using tension-tension(R=0.1) loading and under load controlled fatigue test. Cyclic stress-displacement curve through fatigue test was obtained. Fatigue strength of $Al_{2}$O$_{3}$/Al composites was about 200 MPa, i.e.0.55 of applied stress level(q). During fatigue test, $Al_{2}$O$_{3}$/Al composites displayed cyclic hardening at all applied stress levels. The most of resultant displacement due to permanent plastic deformation occurred in less than the first 5% of fatigue life. Displacement-to-failure of the fatigue test was smaller than that of the tensile test because of accumulative damage by cumulative plastic deformation.

Fatigue Properties of Ti-Ni Shape Memory Alloy Wire Welded by Nd: YAG Laser

  • Kim, Y.S.;Kim, J.D.;Kil, B.L.
    • International Journal of Korean Welding Society
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    • v.3 no.1
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    • pp.39-44
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    • 2003
  • The welded specimens were made by butt welding of the 2 wires of 50mm length using the pulsed YAG laser. The laser welded wires were tested for investigating the shape memory effect and the ability of super elasticity. The fatigue properties of the welded wires were investigated using the rotary bending fatigue tester specially designed for wires. Moreover, the effect of defocusing distance during laser welding on the static and fatigue properties was Investigated. The shape memory effect and super elasticity of the laser welded wires were approximately identical with that of base metal at the test temperature below 353K. However, the welded wires were broken within elastic limit at the test temperature above 353k. Under the cyclic bending loading conditions, the welded wires could be useful only below the elastic limit, while the base metal had sufficient fatigue life even the stress induced M-phase region. The fatigue strength of the welded wires was about half of that of the base metal. The deterioration of the static and fatigue properties in the welded wires was proven to be from the large difference of the transformation behavior between the base metal and welded part that is caused by vaporization of Ni-content at the welded part during the welding process. The defocusing distance below 3mm acted more largely on lowering the strength of the welded wires than that of 6mm or 8mm.

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A Study on Growth Behavior of Small Fatigue Crack in 304 Stainless Steel at Elevated Temperatures (고온하 304 스테인레스강의 작은 표면구열의 성장거동에 관한 연구)

  • 서창민;김영호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.1
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    • pp.87-95
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    • 1990
  • Rotating bending fatigue tests of an authentic steel 304 were performed at various temperatures such as room temperature, $538^{\circ}$ and $593^{\circ}C$. The plastic replica method was also applied in order to estimate the fatigue life on the basis of serial observation of small fatigue crack initiation and growth on the pit specimen surface. The fatigue crack growth behavior of 304 stainless steel was investigated within the frame work of elastic-plastic fracture mechanics within a narrow scatterband in spite of different stress levels at elevated temperature as at room temperature. The growth law of small surface crack is determined uniquely by the term. $\DELTA\sigma^{n}a$ where $\DELTA\sigma$ is the stress amplitude, a is the crack length, and n is a constant. It is found that the small crack growth behavior is basically equivalent to the S-$N_{f}$ relationship, where S and $N_{f}$ are stress and number of cycles to failure, and the fatigue life prediction is in good agreement with the experimental results.

Fatigue Analysis of Reduction Gears Unit in Rolling Stock Considering Operating Characteristics (운행특성을 고려한 철도차량 감속기의 피로해석)

  • Kim, Chul-Su;Kang, Gil-Hyun
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.12 no.3
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    • pp.1085-1090
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    • 2011
  • To assure the safety of rolling stock, it is important to perform the fatigue analysis of reduction gear unit in rolling stock considering a variation of velocity and traction motor capability. This paper presents fatigue analysis of the damage of reduction gear unit of railway vehicle under variable amplitude loading(VAL) based on quasi-static fatigue analysis using finite element model and linear Miner's rule. The VAL for the simulation was constructed from the tractive effort curve and train run curves of railway vehicle under commercial operation condition using MSC.ADAMS dynamic analysis. The finite element model for evaluating the carburizing effect on the gear surface was used for predicting the fatigue life of the middle gear based on strain-life based approach. The results showed that the frequent high starting torque due to a quick start as well as increasing numbers of stops at station would decrease the fatigue life of reduction gear unit.

A Study on the 43$0^{\circ}C$ Degradation Behavior of Cast Stainless Steel(CF8M)(II)-Evaluation of Low Cycle Fatigue Characteristics- (주조 스테인리스강 CF8M의 43$0^{\circ}C$ 열화거동에 관한 연구 (II) -저사이클 피로특성 평가-)

  • Gwon, Jae-Do;U, Seung-Wan;Park, Jung-Cheol;Lee, Yong-Seon;Park, Yun-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.9 s.180
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    • pp.2183-2190
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    • 2000
  • A thermal aging is observed in a primary reactor cooling system(RCS) made of a casting stainless steel when the RCS is exposed for long period at the reactor operating temperature, 290~3300C An investigation of effects of thermal aging on a low cycle fatigue characteristics included a stress variations caused by a reactor operation and trip, is required. The purpose of the present investigation is to find an effect of a thermal aging of the CF8M on a low cycle fatigue life. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 300 and 1800hr at 4300C respectively. The low cycle fatigue tests for the virgin and two aged specimens are performed at the room temperature for various strain amplitudes($\varepsilon$ta), 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5% strain. Through the experiment, it is found that the fatigue life is rapidly reduced with an creasing of the aging time. The experimental fatigue life estimation formulas between the virgin and two aged specimen are obtained and are proposed to a analysis purpose.

Reliability based optimization of spring fatigue design problems accounting for scatter of fatigue test data (피로시험 데이터의 산포를 고려한 스프링의 신뢰성 최적설계)

  • An, Da-Wn;Won, Jun-Ho;Choi, Joo-Ho
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.1314-1319
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    • 2008
  • Fatigue reliability problems are nowadays actively considered in the design of mechanical components. Recently, Dimension Reduction Method using Kriging approximation (KDRM) was proposed by the authors to efficiently calculate statistical moments of the response function. This method, which is more tractable for its sensitivity-free nature and providing the response PDF in a few number of analyses, is adopted in this study for the reliability analysis. Before applying this method to the practical fatigue problems, accuracies are studied in terms of parameters of the KDRM through a number of numerical examples, from which best set of parameters are suggested. In the fatigue reliability problems, good number of experimental data are necessary to get the statistical distribution of the S-N parameters. The information, however, are not always available due to the limited expense and time. In this case, a family of curves with prediction interval, called P-S-N curve, is constructed from regression analysis. Using the KDRM, once a set of responses are available at the sample points at the mean, all the reliability analyses for each P-S-N curve can be efficiently studied without additional response evaluations. The method is applied to a spring design problem as an illustration of practical applications, in which reliability-based design optimization (RBDO) is conducted by employing stochastic response surface method which includes probabilistic constraints in itself. Resulting information is of great practical value and will be very helpful for making trade-off decision during the fatigue design.

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Fatigue Damage Analysis of the Caliper Housing under ABS Mode (ABS 작동에 의한 캘리퍼하우징에 미치는 피로손상평가)

  • 김정엽;모종운
    • Transactions of the Korean Society of Automotive Engineers
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    • v.4 no.4
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    • pp.156-163
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    • 1996
  • The brakes are the most important safety-critical accident avoidance components of a motor vehicle. They must perform safely under a variety of operating conditions and must have enough strength not to fail during the life of a vehicle. Recently, anti-lock brake systems are used on more and more passenger cars. The ABS brakes modulate brake line pressure to prevent brakes from locking during braking. In this study, finite element analysis, material test for FCD45, measurement of stress and cumulative fatigue damage analysis were performed to evaluate fatigue damage of the caliper housing under ABS mode.

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An Experimental Study on the Flexural Fatigue Behavior of Steel Fiber Reinforced High Strength Concretes Beams with Single Edged Notch (노치를 가진 강섬유 보강 고강도 콘크리트 보의 휨 피로거동에 관한 실험적 연구)

  • 구봉근;김태봉;김흥룡
    • Proceedings of the Korea Concrete Institute Conference
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    • 1992.04a
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    • pp.120-125
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    • 1992
  • The fatigue tests were performed on the high strength concrete beams with single edged notch which was reinforced steel fiber. The steel fibers were used 1.0 percent by volume fraction. These were tested consists of constant amplitude tests for different levels of loading. The test program included endurance limit with repect to flexural fatigue and relation of load-CMOD(crack mouth opening displacement). The results of test, it is found from S-N curve that the fatigue strength for a life of 2 million cycles of load was approximately 70percent with respect to the static ultimate strength .

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A Study on the Weldability and the Fatigue Characteristics in Resistance pot Welding of 5182-O/6061-T6 Dissimilar Aluminum Alloy Sheets (이종 AI합금의 저항점용접부 용접성과 피로특성에 관한 연구)

  • 박진철;정원욱;강성수
    • Journal of Welding and Joining
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    • v.17 no.2
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    • pp.44-52
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    • 1999
  • This study deals with spot weld ability of dissimilar aluminum alloy sheets in order to take advantage of its lightweight and strength. The paper also shows the relationship between weld elements(i.e. current, welding time and tip force) and weld quality on the resistance spot weld part of the same and dissimilar Al alloy. The conclusions are: (1) Because of excessive tip force, deep indentation remained at the Al 5182 side which is lower stiffness at the dissimilar Al alloy. (2) Weld quality (i.e. tensile shear strength) of dissimilar Al alloy is superior to that of the same Al 6061 alloy. (3) As long cycles, fatigue life of spot weld specimen on dissimilar Al alloy sheets was better than that of the same Al alloy.

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