• Title, Summary, Keyword: 피로파단수명비

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Evaluation of the Fatigue Behavior before and after Wall Thickness Penetration in Carbon Steel Pipes with Circumferential Part Through-Wall Surface Crack (원주방향 미관통 표면결함을 가지는 탄소강 배관의 두께관 통전.후의 피로거동 평가)

  • Seok-Hwan AHN
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.36 no.2
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    • pp.147-154
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    • 2000
  • 실온 대기 중에서 탄소강배관(STS370)의 피로시험을 행하였다. 배관에는 외부결함을 인공적으로 상정하여, 피로균열진전 및 관통의 거동, 균열형상, 누설 및 파단수명, 균열개구변위를 실험과 이론의 양면으로부터 비교·검토하였다. 특히, 배관의 벽두께 관통후에 있어서의 응력확대계수를 평가하기 위하여 새로운 식을 제안하였다. 피로균열이 관벽을 관통하기 전에 있어서는 판모델에 의한 Newman-Raju의 응력확대계수 평가식을 이용하므로서 aspect비와 누설수명 등 관통전의 피로균열성장거동을 평가할 수 있음을 나타내었다. 또한, 피로균열이 관벽을 관통한 후에 있어서는 본 논문에서 제안한 배관모델에 의한 응력확대계수의 평가식을 이용하여 관통후의 균열형상, 파단수명 및 균열개구변위 등 관통후의 피로균열성장거동을 평가하였다.

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Thermal Fatigue Failure of Solder Joints in Electronic Systems (미세솔더접속부의 열피로파단)

  • 박화순
    • Journal of Welding and Joining
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    • v.13 no.4
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    • pp.7-13
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    • 1995
  • 마이크로솔더링에 의한 전자기기는, 사회기능의 중추가 되는 컴퓨터, 통신 기기, 항공기 인공위성 등의 제어계를 구성하므로, 그 접속부에 대한 높은 신뢰성의 요구는 그 무엇보다 중요하다. 전자기기에 있어서의 솔더 접속부는 집과 기판의 전기 적.기계적 접속의 역할을 하고 있으며, 따라서 개개의 접속부의 파단은 전체의 불량 으로 연결된다. 실제 전자콤포넌트와 그 시스템의 단선 등의 사고에 있어서 자주 발생 하는 사고중의 하나가 솔더접속부의 단선에 의한 것이며, 그 단선중에서도 가장 보편 적이며 또한 대단히 심각한 문제로서 주목을 받고 있는 것이 솔더접속부의 열피로파단 이다. 전자기기를 사용할 때, 스위치의 on-off에 의한 power cycle과 환경의 온도변화 에 기인하는 반복열 사이클은 솔더접속부의 피로를 일으키게 되고, 결국에는 사용중에 파단을 초래하게 된다. 이러한 온도변화의 범위는 약 -55.deg. - 150.deg.C로 예상할 수 있으며, 여기서 최고온도인 150.deg.C는 Pb-Sn 공정합금의 경우 0.9Tm.p.이상의 고온에 해당한다. 이 피로는 등온적으로 또는 열사이클중에 발생하기도 한다. 솔더접 속부의 열피로수명은 대부분의 공업재료에서 나타나는 저사이클피로거동과 유사하게 발생하며, 솔더 접속부에 인가되는 열변형/응력(thermal strain/stress)의 크기에 크게 의존하는 것으로 알려져 있다. 솔더는 서로 다른 열팽창계수를 갖는 칩과 회로 기관의 두종류의 재료를 접속하기 때문에, 상기한 바와 같은 반복열사이클에 의하여 발생하는 열변형/응력이 접속부의 피로.파단을 야기시킨다. 이러한 솔더접속부에 대한 주기적인 응력/변형의 인가는 접속부에 내.외적으로 현저한 변화를 야기시키게 되고, 열피로로 연결되며 결국에는 시스템의 전기적 단선을 초래하게 된다. 또한 열피로파단 현상는 변형/응력의 크기 뿐 만아니라 솔더합금자체의 야금학적인 물성에도 크게 의존 하며, 내적.외적인 열변화에 의한 야금학적인 특성변화도 크게 영향을 미친다. 솔더 접속부의 신뢰성에 대한 연구는, 그 중요성에 비추어 볼 때, 지금까지 수많은 연구가 행하여져 왔다. 그러나 신뢰성과 관련된 열피로파단현상에 대한 야금학적인 면에서의 연구는 비교적 적은 편이다. 따라서 본 해설에서는 전자기기의 마이크로 솔더접속부 에서 발생하는 열피로파단현상에 대한 야금학적인 면에 중점을 두어 서술하고자 한다.

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A Study on the Behavior of Fatigue Crack Propagation in Marine Propeller Shaft Materials with Small Circular Defect (미소원공을 갖는 선박 추진축재의 피로크랙 전파 거동에 관한 연구)

  • 정재강;김건호
    • Journal of Advanced Marine Engineering and Technology
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    • v.19 no.2
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    • pp.36-46
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    • 1995
  • In this paper, fatigue crack propagation behaviors were investigated experimentally for the materials, carbon steel forgings (SF45A, SF50A, SF60A) which are used in the marine propeller shaft. The results obtained are as follows: The number of cycles required to grow crack length 1.30mm from microcrack initiation was about 60% of the total fatigue life. Fatigue crack propagation rate was expressed by the equation d(2a)/dN_B 2a/$N_f$ and the result was agreed well with the experimented data. And the equation d(2a)/dN=$C{\sigma}_a^m(2a)^n$ was evaluated also. Obtained material property m and n are 3~5 and 1-1.5 respectably, and the result was reasonably agreed to the data obtained from experiments.

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Prediction of Biaxial Strength and Fatigue Life using the Concept of Equivalent Strength (등가강도 개념에 의한 탄소섬유 복합재료의 이축강도 및 피로수명 예측)

  • 이창수;황운봉
    • Composites Research
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    • v.12 no.2
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    • pp.53-61
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    • 1999
  • A failure criterion must be considered in each failure mode and loading condition to provide easy determining strength parameters, flexibility and rational simplicity. In this study, new failure criterion was developed by introducing equivalent strength under biaxial loading of tension and torsion. The experimental results showed that the equivalent biaxial strength has a power law relation with respect to a parameter, cos($tan^{-1}R_b$). Failure strength under biaxial loadings could be predicted as a function of tensile strength, torsional strength and biaxial ratio. The scattering of experimental data could be predicted using a Weibull distribution function and the concept of equivalent biaxial strength. Also, in this study, a fatigue theory was developed based on a plane stress model which enabled the S-N curve for combined stress states to be predicted from the S-N data for uniaxial loading. The prediction models can be predicted a biaxial strength and fatigue life of general laminated composite naterials under multi-axial loadings.

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The Influence of the Small Circular Hole Defect on the Fatigue Crack Propagation Behavior in Aluminum Alloys (알루미늄 합금재의 피로크랙 전파거동에 미치는 미소원공결함)

  • Kim, G.H.;Lee, H.Y.
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.6
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    • pp.834-840
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    • 2008
  • We carried out fatigue testing with materials of aluminum alloyC7075-T6, 2024-T4) by rotary bending fatigue tester. We investigated fatigue limit, fatigue crack initiation, fatigue crack propagation behavior and possibility of fatigue life prediction to the different small circular hole defect. The summarized result are as follows; Fatigue limit of the smooth specimens were related tensile strength and yield strength. In case of more large applied stress and small circular hole crack defect, the fatigue crack was grown rapidly. The fatigue crack propagation behavior proceed at according to inclusion. Fatigue crack propagation ratio appeared instability and retardation phenomenon in the first half of fatigue life but appeared stability and replied in the latter half. On other hand, this experimental data of the materials are appeared fatigue life predictability.

High Cyclic Fatigue Life and Fracture Behaviors of Shot-Peened Bearing Steel (쇼트피닝 처리를 한 베어링강의 고사이클 피로수명 및 파괴거동)

  • Yoon, Sang-Jae;Choi, Nak-Sam
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.9
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    • pp.1119-1129
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    • 2011
  • 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.

Experimental Investigation on Torsional Analysis and Fracture of Tripod Shaft for High-speed Train (고속열차용 트리포드 축의 비틀림 해석 및 파단에 대한 실험적 연구)

  • Lee, Joo Hong;Kim, Do Sik;Nam, Tae Yeon;Lee, Tae Young;Cho, Hae Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.11
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    • pp.979-986
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    • 2016
  • The tripod shafts of constant-velocity joint are used in both the trains KTX and KTX-sanchon. It is an important component that connects the motor reduction unit and the axle reduction unit in a power bogie. The tripod shaft not only transmits drive and brake torque in the rotational direction, but also slides in the axial direction. If the drive system is loaded with an excessive torque, the fuse part of the shaft will be fractured firstly to protect the other important components. In this study, a rig was developed for conducting torsion tests on the tripod shaft, which is a type of mechanical fuse. The tripod shafts were subjected to torsional fracture test and torsional fatigue test on the rig. The weak zone of the tripod shaft was identified, and its fatigue life was predicted using finite element analysis (FEA). After analyzing the FEA results, design solutions were proposed to improve the strength and fatigue life of the tripod shaft. Furthermore, the deterioration trend and time for failure of the tripod shaft were verified using the hysteresis loops which had been changed with the advancement of the torsional fatigue test.

The Influence of Grain Size on the Fatigue Crack Propagation Behavior in the Low Carbon Steel (SM26C) (저탄소강재(SM25C)의 피로크랙 전파거동에 미치는 결정립 크기의 영향)

  • 김건호
    • Journal of Advanced Marine Engineering and Technology
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    • v.26 no.1
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    • pp.76-82
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    • 2002
  • In this study, the rotary bending fatigue test was carried out with low carbon steel(SM25C). The specimens were heat-treated in order to change the grain size, and investigated items are fatigue limit, small crack initiation, fatigue crack propagation behavior and possibility of fatigue life prediction according to the different grain size. The summarized result are as follows ; Fatigue limit of the smooth specimen was dependent upon the grain size. The fatigue crack initiation of the small grain size specimen was delayed more than that of the large grain size specimen. And the small cracks of small grain size specimen were distributed in the narrow region of the main crack circumference contrary to the large grain size specimen. The main crack was grown along the grain boundary having co-alliance with small cracks. The experiment material has quantitatively disclosed the possibility of fatigue life prediction because the fatigue crack propagation behavior is dependent upon the grain size.

An Evaluation of Fatigue Properties on Dissimilar Friction Weld of Heat-Resisting Steels Used in Vehicle Valves (차량 밸브용 내열강재 이종 마찰용접부의 피로특성 평가)

  • 이동길;이상열;정재강
    • Transactions of the Korean Society of Automotive Engineers
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    • v.10 no.2
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    • pp.186-192
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    • 2002
  • The fatigue crack propagation characteristics were investigated on dissimilar friction weld of two kind of heat-resisting steels (STR3 and STR35) commonly used in valve materials for vehicles. A small circular artificial defect was machined to induce fatigue crack at bonded line, heat affected zone and base metal of the weld on the surface of the specimens. From the results of the experiment, the fatigue limits of the materials STR3 and STR35 were obtained to be 429.0MPa and 409.4MPa respectably. The STR35 base metal and 1.0mm HAZ specimens showed 190% and 82% higher fatigue life than STR3 base metal. And the fatigue life of 1.0mm HAZ specimen was shown 99% on STR3 and 29% on STR35 higher than that of their base metal. But the fatigue life of weld interface specimen was shown 18% on STR3 and 72% on STR35 lower than that of their base metal because of the weld interface separation.

Fatigue Damage Evaluation of Cr-Mo Steel with In-Situ Ultrasonic Surface Wave Assessment (초음파 시험에 의한 배관용 Cr-Mo강의 피로손상의 비파괴평가)

  • Kim, Sang-Tae;Lee, Hei-Dong;Yang, Hyun-Tae;Choi, Young-Geun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.21 no.1
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    • pp.32-38
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    • 2001
  • Although the ultrasonic method has been developed and used widely in the fields, it has been used only for measuring the defect size and thickness loss. In this study, the relationship between surface wave attenuation through micro-crack growth and variation of velocity under repeated cyclic loading has been investigated. The specimens are adopted from 2.25Cr-1Mo steel, which is used for power plant and pipeline system, and have dimensions of $200{\times}40{\times}4mm$. The results of ultrasonic test with a 5MHz transducer show that surface wave velocity gradually decreases from the point of 60% of fatigue life and the crack length of 2mm with the increasing fatigue cycles. From the results of this study, it is found that the technique using the ultrasonic velocity change is one of very useful methods to evaluate the fatigue life nondestructively.

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