• Title, Summary, Keyword: 크리프

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Creep Characteristics Verification of FE Model for SnPb Solder (SnPb 솔더에 대한 유한요소모델의 크리프 특성 검증)

  • Han, Chang-Woon;Park, No-Chang;Oh, Chul-Min;Hong, Won-Sik;Song, Byeong-Seok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.1
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    • pp.43-48
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    • 2010
  • The heat sink system for a main board in a network server computer is built on printed circuit board by an anchor structure, mounted by eutectic SnPb solder. The solder creeping is caused by a constant high temperature condition in the computer and it eventually makes fatal failures. The FE model is used to calculate the stress and predict the life of soldered anchor in the computer. In the model, Anand constitutive equation is employed to simulate creep characteristics of solder. The creep test is conducted to verify and calibrate the solder model. A special jig is designed to mitigate the flexure of printed circuit board and to get the creep deformation of solder only in the test. Test results are compared with analysis and calibration is conducted on Anand model's constants. Precise life prediction of soldered anchor in creep condition can be performed by this model.

Transient Creep Analysis in Indentation Tests (압입시험의 천이 크리프 해석)

  • Lee, Jin-Haeng;Lee, Hyung-Yil
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.1
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    • pp.81-90
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    • 2012
  • The indentation test, which is one of the testing methods for evaluating the mechanical properties of materials, can be applied to the evaluation of creep properties. Many studies related to the indentation creep test, however, have just focused on the characteristics of the steady-state creep, so there are wide discrepancies between the uniaxial test and the indentation test. To obtain accurate creep properties, it is therefore important to consider the effects of transient creep. In the present work, the Ogbonna et al.'s work on the spherical indentation test including the transient creep was expanded and applied to the conical indentation creep test. The characteristics of the transient creep were analyzed via finite element simulations and compared with those obtained through spherical indentation. Other effects, such as elastic strain, indenter shape, contact area, and representative strain, which have not been considered properly in prior studies on the creep test, are also discussed.

Effect of crystalline lamellar orientation on the creep and wear of ultra-high molecular weight polyethylene (초고분자량 폴리에닐렌 미세구조가 변형과 마모에 미치는 영향)

  • 이권용
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • pp.100-105
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    • 1998
  • 초고분자량 폴리에틸렌(Ultra-High Molecular Weight Polyethylene)은 인공관절 라이너에 쓰이는 대표적 생체재료이다. 초고분자량 폴리에틸렌의 변형과 마모에 영향을 주는 인자에 대한 기본적 연구를 위하여 본 연구에서는 미세구조 결정상의 정도와 결정구조 방향성에 따른 초고분자량 폴리에틸렌의 크리프 변형 및 마모 특성의 연구를 행하였다. 압출 제작된 초고분자량 폴리에틸렌 봉(extruded UHMWPE rod)단면의 중앙(center) 부분과 원주(periphery)부분으로부터 각각 직사각형 및 원통형의 시편을 제작하여 크리프 실험과 마모 실험을 실시하였다. 원주 시편의 크리프 변형율은 중앙 시편의 크리프 변형율보다 11% 크며 (p<0.05), 마모양도 원주 시편이 중앙 시편보다 두 배나 큰 것으로(p<0.05)관측되었다. 이 결과들로부터 초고분자량 폴리에틸렌의 크리프 변형과 마모가 미세 결정구조 방향성에 영향을 받는 것으로 나타났다.

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Improvement of long-time creep life prediction of steam turbine rotor steel (증기 터빈축 강재의 장시간 크리프 수명 예측법 개선)

  • 오세규;정순억;전태언
    • Journal of Ocean Engineering and Technology
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    • v.10 no.1
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    • pp.47-52
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    • 1996
  • This paper deals with a study on improvement of long-time creep life prediction of steam turbine rotor steels by using initial strain method as a new approach at high temperatures of 500 to 70$0^{\circ}C$ . The main result shows that the inital strain method could be reliably utilized to predict and evaluate the long-time creep life as creep rupture strength and that the predicting equation for long-time creep life under a certain creep stress at a certain high temperature could be empirically derived out from each initial instantaneous strain measured.

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Effect of Crystalline Lameliar Orientation on the Creep and Wear of Ultra-high Molecular Weight Polyethylene (초고분자량 폴리에틸렌 미세구조가 변형과 마모에 미치는 영향)

  • 이권용
    • Tribology and Lubricants
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    • v.14 no.3
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    • pp.46-50
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    • 1998
  • 초고분자량 폴리에틸렌(Ultra-High Molecular Weight Polyethylene)은 인공관절 라이너에 쓰이는 대표적 생체재료이다. 초고분자량 폴리에틸렌의 변형과 마모에 영향을 주는 인자에 대한 기본적 연구를 위하여 본 연구에서는 미세구조 결정상의 정도와 결정구조 방향성에 따른 초고분자량 폴리에틸렌의 크리프 변형 및 마모 특성의 연구를 행하였다. 압출 제작된 초고분자량 폴리에틸렌 봉(extruded UHMWPE rod)단면의 중앙(center)부분과 원주(periphery)부분으로부터 각각 직사각형 및 원통형의 시편을 제작하여 크리프 실험과 마모 실험을 실시하였다. 원주 시편의 크리프 변형율은 중앙 시편의 크리프 변형율보다 11%크며(p<0.05), 마모량도 원주 시편이 중앙 시편보다 두 배나 큰 것으로 (p<0.05)관측되었다. 이 결고달로부터 초고분자량 폴리에틸렌의 크리프 변형과 마모가 미세 결정구조 방향성에 영향을 받는 것으로 나타났다.

Creep Property Assessment and Creep Life Estimation for High-Temperature Tube Material(2.25Cr1Mo Steel) in Power Plants by LMP (발전용 고온 배관재료 2.25Cr1Mo 강의 크리프 특성과 LMP에 의한 크리프 수명의 예측)

  • Lee, Sang-Guk;Jeong, Min-Hwa;O, Se-Gyu;Song, Jeong-Geun
    • Journal of Ocean Engineering and Technology
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    • v.12 no.2
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    • pp.65-70
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    • 1998
  • In this report, the creep properties and creep life estimation by Larson-Miller Parameter(LMP) Method for 2.25Cr1Mo steel to be used as power plant tubes or other components were presented at the high temperatures of 500, 550, and $600^{\circ}C$. It was confirmed experimentally and quantitatively that a creep life estimation equation at such various high temperatures was well derived by LMP and could be used very effectively within the creep life of 10$^3$ hours, but very unreliable and even dangerous for design in a long term of creep life such as 10$^4$ or $10^5$ hours.

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Creep Behavior of Plastics Used in Automobile Instrument Panels (자동차 인스트루먼트 패널에 사용되는 플라스틱의 크리프 거동)

  • Kim, Young-Sam;Jeon, Chi-Hoon;Tumur-Ochir, Erdenebat;Yum, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.12
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    • pp.1549-1556
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    • 2011
  • Tensile and creep tests were performed at various temperatures to investigate the mechanical properties of plastics used in automotive instrument panels. Mechanical properties such as Young's modulus and Poisson's ratios changed markedly with the test temperature. Three-point bending creep tests were performed for three kinds of plastics under four loading conditions. Coefficients in the time-hardening power law creep equation were obtained from the experiment, and the creep behavior was represented by a simple expression. The results of finite element creep analysis showed good agreement with the experimental results, while the difference between the numerical and experimental results increased with the load.

Experimental Studies on Creep of Concrete under Multiaxial Stresses (다축응력 상태에 놓인 콘크리트외 크리프 특성에 관한 실험 연구)

  • Kwon Seung-Hee;Kim Sun-Young;Kim Jin-Keun;Lee Soo-Gon
    • Journal of the Korea Concrete Institute
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    • v.16 no.2
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    • pp.185-194
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    • 2004
  • It is difficult to analyze and predict the long-term behavior of concrete structures and members under multiaxial stresses because most of existing researches on creep of concrete were mainly concerned about uniaxial stress state. Therefore, the main objective of this paper is the investigation of creep properties of concrete under multiaxial stresses. This paper presents experimental study on creep of concrete under multiaxial compression. Twenty seven cubic specimens($20{\times}20{\times}20 cm$) for three concrete mixes were tested under uniaxial, biaxial, and triaxial stress states. Creep strains were measured in three directions of principal stresses. Poisson's ratio at the initial loading was obtained, as was Poisson's ratio due to creep stain and Poisson's ratio due to the combined creep strain and elastic strain. These Poisson's ratios were approximately equal for each concrete mix. The Poisson's ratio at the initial loading and the Poisson's ratio for the combined strain Increased slightly as the strength of the concrete increased. In addition, the volumetric creep strain and deviatoric creep strain were linearly proportional to volumetric stress and deviatoric stress, respectively.

A Study on Creep Behavior of Geosynthetics Considering Effect of Temperature and Confining Stress (온도 및 구속응력을 고려한 토목섬유의 크리프거동에 관한 연구)

  • 방윤경;김홍택
    • Journal of the Korean Geotechnical Society
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    • v.19 no.5
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    • pp.291-299
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    • 2003
  • The effect of temperature and soil confining stress on geosyntheic creep behaviour was studied by performing the temperature dependent confined creep tests for HDPE geogrid and geomembrane specimen. The visco-elastic creep coefficients of the geosynthetics were evaluated by the test results and it was proposed that the simple expressions for the instantaneous and limit creep strain of geosynthetics was considered as a function of temperature and confining stress on geosynthetics. Based on the time-temperature superposition principle, a master curve has been drawn for extrapolating tensile creep strains to longer time intervals(1$\times$10 $^7$min.∼1$\times$10$^{10}$min.). By using this master curves, the shift factors which can be used in establishing master curve considering confining stress on geosynthetics were carried out. Each tests was performed during 8,000∼12,000 min., with temperature ranging between 5$^{\circ}C$ and 4$0^{\circ}C$ and with confining stress ranging between 0 t/$m^2$ and 9 t/$m^2$.

A Study on Evaluation of High Temperature Creep Properties of 9Cr1MoVNb Steel by Small Punch-Creep test (소형펀치-크리프 시험에 의한 9Cr1MoVNb강의 고온 크리프 특성 평가 연구)

  • Yu, Hyo-Sun;Na, Sung-Hoon;Baek, Seung-Se;Kwon, Il-Hyun;Ahn, Byung-Guk;Na, Eui-Gyun
    • Proceedings of the KSME Conference
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    • pp.99-104
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    • 2000
  • This paper describes the high temperature creep characteristics for virgin material of 9Cr1MoVNb steel using small punch creep(SP-Creep) test technique which is developing recently. In addition, the several results of SP-Creep test are compared with that of 2.25Cr- 1Mo steel which is widely used as boiler materials and that of conventional uniaxial creep test. The obtained SP-Creep curves show the creep behaviors of three regimes like that obtained from conventional uniaxial creep test, and SP-Creep properties are definitely depended on applied load and test temperature. The correlation of SP-Creep rate and creep rupture life with applied load has been determined like the correlation between creep rate/rupture life and stress in uniaxial creep test, and also is satisfied with Power law. The creep rupture times of newly 9Cr1MoVNb steel are higher than those of 2.25Cr1Mo steel at the same creep temperature and applied loading condition, and the decrease extent of creep rupture life with loads is very lower compared with 2.25Cr1Mo steel.

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