• Title/Summary/Keyword: Fatigue Life Test

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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.

A study on Accelerated Life Prediction of Gas Welded joint of STS301L (1. Plug and Ring type) (STS301L 가스용접이음재의 가속수명에측에 관한 연구 (1. Plug and Ring type))

  • Baek, Seung-Yeb;Bae, Dong-Ho
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.1355-1360
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    • 2008
  • Stainless steel sheets are widely used as the structure material for the railroad cars and the commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding. Gas welding is very important and useful technology in fabrication of an railroad car and vehicles structure. However fatigue strength of the gas welded joints is considerably lower than parent metal due to stress concentration at the weldment, fatigue strength evaluation of gas welded joints are very important to evaluate the reliability and durability of railroad cars and to establish a criterion of long life fatigue design. In this paper, ${\Delta}P-N_f$ curve were obtained by fatigue tests. Using these results, the accelerated life test (ALT) is conducted. From the experimental results, an acceleration model is derived and acceleration factors are estimated. So it is intended to obtain the useful information for the fatigue lifetime of plug and ring gas welded joints and data analysis by statistic reliability method, to save time and cost, and to develop optimum accelerated life prediction plans.

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A Study on Accelerated Life Prediction Automation of Gas Welded Joint of STS301L (Plug and Ring Type) (STS301L 가스용접이음재의 가속수명예측 자동화에 관한 연구 (Plug and Ring Type))

  • Baek, Seung-Yeb;Sohn, Il-Seon
    • Transactions of the Korean Society of Automotive Engineers
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    • v.19 no.3
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    • pp.1-8
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    • 2011
  • Stainless steel sheets are widely used as the structure material for the railroad cars and the commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding. Gas welding is very important and useful technology in fabrication of an railroad car and vehicles structure. However fatigue strength of the gas welded joints is considerably lower than parent metal due to stress concentration at the weldment, fatigue strength evaluation of gas welded joints are very important to evaluate the reliability and durability of railroad cars and to establish a criterion of long life fatigue design. In this paper, ${\Delta}-N_f$ curve were obtained by fatigue tests. Using these results, the accelerated life test (ALT) is conducted. From the experimental results, an acceleration model is derived and acceleration factors are estimated. So it is intended to obtain the useful information for the fatigue lifetime of plug and ring gas welded joints and data analysis by statistical reliability method, to save time and cost, and to develop optimum accelerated life prediction plans.

Assessment of Fatigue Life on Curved Self-Piercing Rivet Joint Specimen (곡률을 갖는 셀프-피어싱 리벳 접합시편의 피로수명 평가)

  • Kim, Min-Gun;Cho, Seok-Swoo;Kim, Dong-Youl
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.19 no.1
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    • pp.71-79
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    • 2010
  • One of methods that accomplish fuel-efficient vehicle is to reduce the overall vehicle weight by using aluminum structure typically for cross members, rails and panels in body and chassis. For aluminum structures, the use of Self Piercing Rivet(SPR) is a relatively new joining technique in automotive manufacture. To predict SPR fatigue life, fatigue behavior of SPR connections needs to be investigated experimentally and numerically. Tests and simulations on lap-shear specimen with various material combinations are performed to obtain the joining strength and the fatigue life of SPR connections. A Finite element model of the SPR specimen is developed by using a FEMFAT SPR pre-processor. The fatigue lives of SPR specimens with the curvature are predicted using a FEMFAT 4.4e based on the liner finite element analysis.

A Study for the Improvement on a Fatigue Life for Cr-Si Alloyed Valve Springs (Si-Cr강 밸브스프링의 피로수명 향상에 관한 연구)

  • 임철록;김태호;박상언;김기전;정태훈
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2000.11a
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    • pp.421-424
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    • 2000
  • Valve springs with high fatigue strength corresponding to the incresement of working stresses, are required for the higher generating power and the better fuel economy of automobile engines. For this purpose, high strength oil tempered wires are being used. By a method of the high strength for the valve spring, modification of manufacturing processes is being applied. In this case, the cause and effect for the improvement of the fatigue strength has not yet been explained obviously. Therefore, in this report, comparison of fatigue life between valve springs of conventional processes with oil tempered wires and new manufacturing processes was made. As a result of the fatigue test, the fatigue life of the latter was attained maximum 7 times than that of the former. It was cleared that the improvement of the fatigue life was caused by difference of compressive residual stresses at depth of 0.2mm below the inner side surface of both valve springs.

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A Study on the Effect of Inclusions on the Fatigue Life of Titanium Investment Castings (티타늄 정밀주조품의 피로수명에 미치는 개재물의 영향에 관한 연구)

  • Park, Yong-Kuk;Ret, P.L.;Kim, Jin-Gon
    • Journal of Korea Foundry Society
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    • v.26 no.2
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    • pp.85-91
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    • 2006
  • Inclusions in Ti investment castings are generally known to have detrimental effects on the performance of the castings. However, actual inclusions are infrequent and hard to be located. As a result, it is extremely difficult to obtain sufficient amount of fatigue test specimens of titanium investment castings having inclusions in the gage section. Thus, in-depth research of the adverse influence of inclusions is also hindered. To address this problem, a new casting methodology of specimens containing hard alpha inclusions was developed in this study. To guarantee successful introduction of an inclusion and casting, a carefully designed mold with 8 legs and a special tool were employed. After solidification, castings were cut, and X-ray radiography determined that the inclusions were successfully incorporated into the castings. The castings were further prepared to obtain multiple test specimens and they were fatigue-tested consecutively. Fractography analysis confirmed that fatigue cracks initiated at the hard alpha inclusion. In a nonlinear regression model, the fatigue life can be modeled as an exponential function with a negative exponent of the cross-sectional area of an inclusion. The fatigue life of Ti specimens containing inclusions is inversely proportional to the cross-sectional area of an inclusion.

Factors Influencing Compassion Fatigue among Hospice and Palliative Care Unit Nurses

  • Cho, Eun-Ju;Cho, Hun Ha
    • Journal of Hospice and Palliative Care
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    • v.24 no.1
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    • pp.13-25
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    • 2021
  • Purpose: This descriptive study aimed to explore nursing workplace spirituality, end-of-life care stress, and resilience as factors influencing compassion fatigue among nurses working in hospice and palliative care units. Methods: Data were collected using a self-report questionnaire completed by 146 nurses at 14 hospice and palliative care institutions across South Korea who had worked in a hospice and palliative care institution for at least 6 months and had experience providing end-of-life care. Data were collected from February 25, 2019 to April 12, 2019, and analyzed using SPSS for Windows version 18.0. As appropriate, descriptive statistics, the t-test, analysis of variance, the Scheffé test, Pearson correlation coefficients, and stepwise multiple regression were used. Results: The survey results showed that factors influencing compassion fatigue were resilience, subjective health status, current satisfaction with the hospice ward, and end-of-life care stress. Higher levels of resilience, a subjective health status of "healthy", high levels of current satisfaction with the hospice ward, and lower levels of end-of-life care stress were associated with lower levels of compassion fatigue, explaining 42.9% of the total variance. Conclusion: The results of this study suggest that resilience is an important factor mitigating compassion fatigue among nurses at hospice and palliative care institutions. Therefore, intervention programs should be developed to reduce compassion fatigue.

A Probabilistic Analysis for Fatigue Cumulative Damage and Fatigue Life in CFRP Composites Containing a Circular Hole (원공을 가진 CFRP 복합재료의 피로누적손상 및 피로수명에 대한 확률적 해석)

  • 김정규;김도식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.8
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    • pp.1915-1926
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    • 1995
  • The Fatigue characteristics of 8-harness satin woven CFRP composites with a circular hole are experimentally investigated under constant amplitude tension-tension loading. It is found in this study that the fatigue damage accumulation behavior is very random and history-independent, and the fatigue cumulative damage is linearly related with the mean number of cycles to a specified damage state. From these results, it is known that the fatigue characteristics of CFRP composites satisfy the basic assumptions of Markov chain theory and the parameter of Markov chain model can be determined only by mean and variance of fatigue lives. The predicted distribution of the fatigue cumulative damage using Markov chain model shows a good agreement with the test results. For the fatigue life distribution, Markov chain model makes similar accuracy to 2-parameter Weibull distribution function.

Estimation of Probability Distribution of Fatigue Lives in Crank Throw Forged Steel (크랭크스로 단조강의 피로수명의 확률분포 추정)

  • Kim, Seon-Jin;Ahn, Seok-Hwan
    • Journal of Power System Engineering
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    • v.20 no.3
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    • pp.29-35
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    • 2016
  • Because of the severe service environment of the large marine vessel, the fatigue strength and its evaluation play an important role in design and maintenance of marine crankshaft. The aim of this work is to investigate the probability distribution of fatigue lives in crank throw forged steel and to develop the methodology for estimation of the probabilistic design fatigue strength. Detailed studies were performed on the constant amplitude axial loading fatigue test. The experiments were controlled by stress ratio of -1 and 15Hz frequency for each stress level. The considerable variability of fatigue life was observed in each stress level under rigidly controlled constant fatigue testing conditions. The fatigue life of crank throw forged steel was well followed the log-normal and Weibull distribution. In addition, it can be used for the estimation of probabilistic design fatigue strength by using the proposed methodology.

Fatigue Crack Growth Characteristics by the Cover Plate Shapes in the Steel Plate Girder (강판항(鋼板桁) 덮개판 형상에 따른 피로균열성장특성)

  • Jung, Young-Hwa;Kim, Ik-Gyeom;Jung, Jin-Suck;Lee, Hyung-Koon
    • Journal of Industrial Technology
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    • v.19
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    • pp.269-278
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    • 1999
  • When a variety of repeated loads are given, most steel structures failed in much lower level of loads than static failure loads. In addition, bridge always includes the internal defects or discontinuities. from these, fatigue cracks initiates and can lead to sudden failure. Thus, in this study, tensile specimens by the cover plate shapes were used as the test specimens. The fatigue test was performed by constant amplitude fatigue loading and beach mark. From the results of this study, each specimen's fatigue section was observed. in addition, stress intensity factor at crack tip was calculated by using the Green's function which applied to discontinuous section where causing stress concentration. Therefore, the fatigue life of structural detail was investigated by adopting the theories of fracture mechanics. each specimen's crack shape is a semi-elliptical surface crack or center crack sheet, stress gradient correction factor, Fg is the most subjective of all stress intensity correction factors and fatigue life should be predicted by previous proposed function and finite element analysis.

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