• Title/Summary/Keyword: Fatigue Life(피로수명)

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Comparison and Evaluation of Low-Cycle Fatigue Life Prediction Methods Using Cu-Cr Alloy Developed for Rocket Engines (로켓엔진용 구리크롬 합금의 저주기 피로수명 예측방법 비교 및 평가)

  • Jongchan Park;Jae-Hoon Kim;Keum-Oh Lee
    • Journal of the Korean Society of Propulsion Engineers
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    • v.26 no.5
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    • pp.1-10
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    • 2022
  • For Cu-Cr alloy developed for rocket engines, estimated fatigue lives were calculated using various fatigue life prediction methods and compared with fatigue life acquired from low-cycle fatigue tests. The utilized methods for fatigue life prediction are as follows: Coffin-Manson relation, plastic/total strain energy density relations, Smith-Watson-Topper relation, Tomkins relation, and Jahed-Varvani relation. As results of estimation of fatigue lives, it satisfied within scatter band two compared to the test fatigue lives in all methods. The quantitative calculation of the deviation of predicted fatigue lives gives that the total strain energy density relation presents the best result.

Study on Fatigue Behavior of Carbon Fiber Reinforced Polyimide Composites (탄소섬유강화 복합적층판의 피로특성에 관한 연구)

  • 이창수;황운봉;한경섭;윤병일
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.1
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    • pp.49-60
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    • 1991
  • Fatigue behavior of carbon fiber reinforced polyimide composite materials was studied experimentally and analytically. The physical variables, such as cyclic displacements and hysteresis loop energy were observed during fatigue tests. Fatigue life of the investigated [0/90]$_{2S}$ laminates was predicted by H'||'&'||'H models which was proposed based on the fatigue modulus and resultant strain. The predicted fatigue life by H'||'&'||'H curves was reasonably close to the experimental data. Fractography study shows that fatigue failure mechanism of [0/90]$_{2S}$ laminated composite materials involves failure break, matrix tearing and fiber-matrix debonding as well as delamination of layers.

A Study on Characteristics of Fatigue Life in LOP Cruciform Fillet Welding Zone (미 용입 십자형 필릿 용접부에서의 피로 수명 특성에 관한 연구)

  • Lee, Yong-Bok
    • Journal of the Korean Institute of Gas
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    • v.16 no.3
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    • pp.29-34
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    • 2012
  • Investigating safer ways to design and use to prevent a loss of life and property by failure of the structures are necessary and assessing total fatigue life with initiation and propagation of fatigue crack accurately through fatigue analysis is very important. The object of this study is to examine the initial life and propagation life when the fatigue crack is introduced from the root which is likely to appear in LOP(Lack of Penetration) cruciform fillet welded structure including bridges, ships and gas storage facilities which are impossible to be fully penetrated and to measure the rate of fatigue life until the final cleavage failure. As the result, each rate of fatigue life for fatigue failure is somewhat different in the range of 5% according to the thickness of material, however, the overall rate of initial life is in the range of 34~39% and propagation life showed the range of 61~66%.

Research on Fafigue Life Prediction of Muffler with Weld-zone Shape (용접부 형상을 고려한 머플러의 피로수명 예측에 관한 연구)

  • Kim, Jong-Yun;Kang, Sung-Su;Kim, Gug-Yong;Park, Soon-Cheol;Kim, Chung-Kwan
    • Journal of Advanced Marine Engineering and Technology
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    • v.36 no.1
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    • pp.85-93
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    • 2012
  • In this study, the geometry of the weld is used to develop the process of fatigue life prediction. For the development of fatigue life prediction process, bending fatigue test of muffler is conducted to obtain M(Moment)-N(Fatigue life) diagram. Modeling the geometry of the weld which is failed is performed to conduct static load analysis and analysis results are used to calculate the stress concentration factor. The stress concentration factor is used to get the fatigue notch factor and this was based on the fatigue life prediction. As a result of the comparison of test values and predicted values, predicted values are verified.

Fatigue Life Estimation of Induction-Hardened Drive Shaft Under Twisting Loads (비틀림 하중을 받는 고주파열처리 드라이브 차축의 피로수명 평가)

  • Kim, Tae Young;Kim, Tae An;Han, Seung Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.6
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    • pp.567-573
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    • 2017
  • The drive shaft of passenger vehicle has an important role in transmitting the torque between the power train system and the wheels. Torsional fatigue failures occur generally in the connection parts of the spline edge of the drive shaft, when there is significant fatigue damage under repeated twisting loads. A heat treatment, an induction hardening process, has been adopted to increase the torsional strength as well as the fatigue life of the drive shaft. However, it is still unclear how the extension of the induction hardening process in a used material relates to its shear-strain fatigue life range. In this study, a shear-strain controlled torsional-fatigue test with a specially designed specimen was conducted by an electro-dynamic torsional fatigue test machine. A finite element analysis of the drive shaft was carried out using the results obtained by the fatigue experiment. The estimated fatigue life was verified through a twisting load test of the real drive shaft in a test rig.

The prediction of fatigue life of muffler by artificial neural network (인공신경망을 이용한 머플러의 피로 수명 예측)

  • Park, Soon-Cheol;Kang, Sung-Su;Yoon, Jin-Ho;Kim, Gug-Yong
    • Journal of Advanced Marine Engineering and Technology
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    • v.37 no.8
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    • pp.869-876
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    • 2013
  • In order to estimate the fatigue life of mufflers at the early stage of researches and designs, the new prediction process was developed by the artificial neural network, which has the algorism of weldment properties. Bending fatigue test was carried out for defining the characteristics of muffler weldment fatigue life and damage. For considering and predicting mechanical and fatigue properties of the muffler, the maximum stress of weldment was adapted as the variable of artificial neural network training. Also, it was compared with the fatigue life predicting results using fatigue notch factors, for proving the newly developed process of the artificial neural network.

Fatigue Strength of Dental Implant in Simulated Body Environments and Suggestion for Enhancing Fatigue Life (생체유사환경 하의 치과용 임플란트의 피로강도 평가 및 수명 향상법)

  • Kim, Min Gun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.3
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    • pp.259-267
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    • 2014
  • Fatigue tests were performed in various simulated body environments reflecting various factors (such as body fluids, artificial saliva) relevant within a living body. First, the fatigue limit under a simulated body environment (artificial saliva) was evaluated and the governing factors of implant fatigue strength were looked into by observing the fracture mode. The fatigue life of an implant decreased in the artificial saliva environment compared with that in the ringer environment. Furthermore, in the artificial saliva environment, the implant fracture mode was fatigue failure of fixture as opposed to the abutment screw mode in the ringer environment. In the fatigue test, corrosion products were observed on the implant in the simulated body environment. A larger amount of corrosion products were generated on the artificial saliva specimen than on the ringer specimen. It is thought that the stronger corrosion activity on the artificial saliva specimen as compared with that on the ringer specimen led to an overall decrease of fatigue life of the former specimen. In the case of the implant with a nitrided abutment screw eliminated hardened layer (TixN), a several times increase in fatigue life is achieved in comparison with tungsten carbide-coated implants.

Fatigue Assessment of High Strength Steel Welded Joints Under Bending Loading (굽힘 하중하의 고장력강 용접 연결부의 피로 평가)

  • Lee, Myeong-Woo;Kim, Yun-Jae;Park, Jun-Hyub
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.10
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    • pp.1163-1169
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    • 2014
  • In this study, a fatigue assessment method for vehicle suspension systems having welded geometries was established under a bending loading condition. For the fatigue life estimation of the actual product's welded joints made of different steels, bending fatigue tests were performed on welded specimens with a simplified shape for obtaining the moment-fatigue-life plot. Further, geometry modeling of the simplified welded specimens was conducted. Results of finite element analysis were used to obtain the stress-fatigue-life plot. The analysis results were also used to calculate the stress concentration factors for notch-factor-based fatigue life estimation. The test results were compared with results of the general notch-factor-based fatigue life estimation for improving fatigue assessment. As a result, it was concluded that both the welded fatigue tests and the notch-factor-based fatigue life estimation are necessary for accurate fatigue assessment.

Effect of Boundary Conditions on Reliability and Cumulative Distribution Characteristics of Fatigue Failure Life in Magnesium Alloy (마그네슘합금의 피로파손수명의 누적확률분포특성과 신뢰성에 미치는 경계조건의 영향)

  • Choi, Seon-Soon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.12 no.2
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    • pp.594-599
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    • 2011
  • In this paper, the effect of the boundary conditions on the reliability and the cumulative distribution characteristics of the fatigue failure life is analyzed in a magnesium alloy AZ31. The boundary conditions are specimen thickness, stress ratio, and maximum fatigue load. The statistical data of the fatigue failure life are obtained by fatigue crack propagation tests under the detail conditions for each boundary condition. The 3-parameter Weibull distribution is used to analyze a statistical characteristics of the fatigue failure life in magnesium alloy AZ31. It is found that the statistical fatigue failure life is long in the case of a thicker specimen, a larger stress ratio, and a smaller maximum fatigue load. Under the opposite cases, the reliability on the fatigue failure life is rapidly dropped.

Applicability of Hammer-Peening Treatment for Fatigue Life Improvement of Fatigue Damaged Weld Joints (피로손상된 용접이음의 피로수명 향상을 위한 햄머피닝 처리법의 적용)

  • Kim, In Tae;Park, Min Ho;Cheung, Jin Hwan
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.17 no.3
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    • pp.48-55
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    • 2013
  • In this study, fatigue tests were performed on longitudinal out-of-plane gusset fillet welded joints and transverse non-load-carrying cruciform rib fillet welded joints, and then applicability of hammer-peening treatment on improvement of fatigue life for fatigue damaged weld joints were investigated. Fatigue tests were carried out on three types of gusset and rib welded specimens: as-welded specimens, post-weld hammer peened specimens and hammer peened specimens at 50% of as-welded specimen's fatigue life. Before and after hammer peening treatment, the geometry of weld toes and surface stresses near weld toes were measured. As a result of hammer peening treatment, compressive residual stresses of 30-83MPa were introduced near weld toes of the gusset and rib welded joints, and 130% increase in fatigue life and fatigue limit of the welded joints could be realized by hammer peening treatment at 50% fatigue life of as-welded conditions.