• Title/Summary/Keyword: mechanical life

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Creep-Fatigue Life Design with Various Stress and Temperature Conditions on the Basis of Lethargy Coefficient (응력 및 온도 변화시 무기력계수를 이용한 크리프-피로 수명설계)

  • Park, Jung-Eun;Yang, Sung-Mo;Han, Jae-Hee;Yu, Hyo-Sun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.2
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    • pp.157-162
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    • 2011
  • High temperature and stress are encounted in power plants and vehicle engines. Therefore, determination of the creep-fatigue life of a material is necessary prior to fabricating equipments. In this study, life design was determined on the basis of the lethargy coefficient for different temperatures, stress and rupture times. SP-Creep test data was compared with computed data. The SP-Creep test was performed to obtain the rupture time for X20CrMoV121 steel. The integration life equation was considered for three cases with various load, temperature and load-temperature. First, the lethargy coefficient was calculated by using the obtained rupture stress and the rupture time that were determined by carrying out the SP-Creep test. Next, life was predicted on the basis of the temperature condition. Finally, it was observed that life decreases considerably due to the coupling effect that results when fatigue and creep occur simultaneously.

C* Based Life Assessment of 3D Crack at High Temperature (C*에 기초한 3차원 고온균열 수명평가)

  • Han, Tae-Soo;Yoon, Kee-Bong;Lee, Hyung-Il
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.5
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    • pp.823-833
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    • 2001
  • In recent years, the subject of remaining life assessment has drawn considerable attention in chemical plants, where various structural components typically operate at high temperature an pressure. Thus a life prediction methodology accounting for high temperature creep fracture is increasingly needed for the components. Critical defects in such structures are generally found in the form of semi-elliptical surface crack, and the analysis of which is consequently an important problem in engineering fracture mechanics. On this background, we first develop an auto mesh generation program for detailed 3-D finite element analyses of axial and circumferential semi-elliptical surface cracks in a piping system. A high temperature creep fracture parameter C-integral is obtained from the finite element analyses of generated 3-D models. Post crack growth module is further appended here to calculate the amount of crack growth. Finally the remaining lives of surface cracked pipes for various analytical parameters are assessed using the developed life assessment program.

Influence of residual stress due to shot peening on fatigue strength and life (피로강도 및 수명에 미치는 Shot Peening에 의한 잔류응력의 영향)

  • Lee, Jong-Gyu;Kim, Jeong-Gyu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.9
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    • pp.1498-1506
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    • 1997
  • Procedures are presented for influence of shot peening on fatigue strength, fatigue life and effects of shot peening are discussed from experiments were taken between shot peened and unpeened SPS5, SM45C specimens. After the residual stress on shot peened specimens was measured by X-ray diffractometer, rotating bending fatigue tests were carried out. In addition, the compressive residual stress profile was obtained by the superposition method of three stresses which is based on Al-Obaid's equation. Predicted fatigue life considering residual stress profile which was obtained by the Al-Obaid's equation and another predicted fatigue life considering residual stress profile which was measured in test were compared. For the purpose of predicting fatigue life, Morrow's equation considering the residual stress and mean stress was used.

The Contact Fatigue Life Analysis of Transmission Gear considering Running-in (길들이기 과정을 고려한 변속기용 기어의 접촉피로 수명 해석)

  • Moon, Kil-Hwan;Lee, Sang-Don;Cho, Yong-Joo
    • Transactions of the Korean Society of Automotive Engineers
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    • v.15 no.5
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    • pp.133-138
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    • 2007
  • Surface pitting is a major failure mode for gears. The contact fatigue life analysis of transmission gear considering running-in process is presented in this paper. Surface roughness change of rolling test is used in a life analysis. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. The life analysis considering running-in is in good agreement with the experimental results.

Prediction of life of SAPH45 steel with measured fracture time and strength (인장파단시간 및 응력측정에 의한 SAPH45의 수명예측)

  • 박종민
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 1998.03a
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    • pp.269-273
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    • 1998
  • The failure of material structures or mechanical system is considered as a direct or indirect result of fatigue. In the design of mechanical structure for estimating of reliability, the prediction of failure life is the most important failure mode to be considered. However, because of a complicated behavior of fatigue in mechanical structure, the analysis of fatigue is in need of much researches on life prediction. This document presents a prediction of fatigue life of the SAPH45 steel, which is extensively for vehicle frame. The method using lethargy coefficient and stress distribution factor at pediction of fatigue life based on the consideration of the failure characteristics from the tensile test should be provided in this study.

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Contact Fatigue Life Prediction of Automotive Wheel Bearing (차량용 휠베어링의 접촉 피로수명 예측에 관한 연구)

  • Lee, Sang-Don;Moon, Kil-Hwan;Cho, Yong-Joo
    • Transactions of the Korean Society of Automotive Engineers
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    • v.16 no.3
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    • pp.137-143
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    • 2008
  • For most bearings, it is a common requirement to have long durability. Especially wheel bearing fatigue life is the most important in automotive quality. The contact fatigue life analysis of automotive wheel bearing considering real raceway rough surface is presented in this paper. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. The life analysis considering real rough surface of wheel bearing raceway is in good agreement with the experimental results.

Development of energy saving type life testing device for large machinery parts (에너지절감형 대형기계류부품용 수명시험장치의 개발)

  • Lee, Yong Bum;Shin, Suk Shin;Park, Jong Ho
    • Journal of Applied Reliability
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    • v.13 no.1
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    • pp.55-63
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    • 2013
  • For a reliability assessment of large machinery parts, reliable data should be obtained from testing many samples for a long time. However, in case of testing these samples, testing cost is excessive; in case of life test for long time, power consumption is high; and in case of accelerated test by over load, very high cost is required to build the life testing device. Especially it is very frequent that the expensive device's life has ended during a accelerated test by over load. In this study, the design mechanism of the life testing device which excels in energy saving during the reliability test of large machinery parts has been introduced.

Investigation of Thermo-mechanical Behavior of Work Roll and Roll Life in Hot Strip Rolling

  • C.G.Sun;Yun, C.S.;Chung, J.S.;Hwang, S.M.
    • Transactions of Materials Processing
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    • v.6 no.2
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    • pp.161-175
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    • 1997
  • The effects of various process paramenters on the detailed aspects of the thermo-mechanical behavior of work roll and on the roll life are investigated via a series of process simulation, using a mathematical model presented previously. The process conditions are discussed that are favorable or optimal in terms of reducing roll wear in the front finishing stands.

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Comparison of Rolling Element Loads and Stress-based Fatigue Life Predictions for Ball Bearings (볼 베어링의 전동체 기반 및 응력 기반 접촉 피로수명의 비교)

  • Kwak, Jae Seob;Park, Yong Whan;Kim, Chan Jung;Kim, Tae Wan
    • Tribology and Lubricants
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    • v.36 no.6
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    • pp.371-377
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    • 2020
  • In In this study, we compared the results of a ball bearing life prediction model based on rolling element loads with the results of fatigue life prediction of ball bearings when a stress-based contact fatigue life prediction technique is applied to the ball bearing. We calculate the load acting on each rolling element by the external load of the bearing and apply the result to the Lundberg-Palmgren (LP) theory to calculate ball bearing life based on the rolling element. We also calculate stress-based ball bearing life through contact and fatigue analyses based on contact modeling of the ball and raceway while considering the fatigue test results of AISI 52100 steel. In stress-based life prediction, we use three high-cycle fatigue-determination equations that can predict the fatigue life when multi-axis proportional loads such as rolling-slide contact conditions are applied. These equations are derived from the stress invariant and critical plane methods and the mesoscopic approach. Life expectancy results are compared with those of the LP model. Results of the analysis indicated that the fatigue life was predicted to be lower in the order of the Crossland, Dang Van, and Matake models. Of the three, the Dang Van fatigue model was found to be the closest to the LP life.

Study on the Fatigue Crack Initiation Life Under Spherical Contact (구 접촉하에서의 피로균열 시작수명에 관한 연구)

  • Jo, Yong-Ju;Kim, Tae-Wan;Lee, Mun-Ju
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.8
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    • pp.1269-1276
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    • 2001
  • In case of contact fatigue, the accurate calculation of surface tractions and subsurface stress is essential to the predication of crack initiation life. Surface tractions influencing shear stress amplitude have been obtained by contact analysis based on influence function. Subsurface stress has been obtained by using rectangular patch solutions. In this study, to simulate asperity contact under sliding condition, the tip of asperity was simulated by sphere and to calculate crack initiation life in the substrate, dislocation pileup theory was used.