• Title/Summary/Keyword: fatigue behaviors

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A Study on the VHCF Fatigue Behaviors of Hydrogen Attacked Inconel 718 Alloy (수소취화된 인코넬 718의 VHCF(Very High Cycle Fatigue) 피로특성에 관한 연구)

  • Suh, Chang-Min;Nahm, Seung-Hoon;Kim, Jun-Hyong;Pyun, Young-Sik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.7
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    • pp.637-646
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    • 2016
  • This study is to investigate the influence of hydrogen attack and UNSM on fatigue behaviors of the Inconel 718 alloy. The decrease of the fatigue life between the untreated and the hydrogen attacked material is 10-20%. The fatigue lives of hydrogen attacked specimen decreased without a fatigue limit, similar to those of nonferrous materials. Due to hydrogen embrittlement, about 80% of the surface cracks were smaller than the average grain size of $13{\mu}m$. Many small surface cracks caused by the embrittling effect of hydrogen attack were initiated at the grain boundaries and surface scratches. Cracks were irregularly distributed, grew, and then coalesced through tearing, leading to a reduction of fatigue life. Results revealed that the fatigue lives of UNSM-treated specimens were longer than those of the untreated specimens.

The Effects of 3.5% NaCl Aqueous Solution Temperature on the Corrosion Fatigue Fracture of Dual phase steel (3.5% NaCl 수용액의 온도변화가 복합조직강의 부식피로파괴에 미치는 영향)

  • 오세욱;도영문;박수영;김재철;김광영
    • Journal of Ocean Engineering and Technology
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    • v.6 no.1
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    • pp.140-147
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    • 1992
  • Corrsion fatigue test was performed under rotated bending in 3.5% NaCl aqueous solution having a temperature from 278.deg.K in order to investigate the effects of aqueous solution remperature on the corrosion fatigue fracture of raw material steel(SS41) and dual phase steel that was produced from SS41 by a series of heat treatment. Corrosion fatigue life decreases remarkably with increase in solution temperature or with decrease in stress level. The corrosion fatigue life and the crack propagation rate at 303.deg.K show the similar behaviors with those at 318.deg.K, which is assumed to be caused by concentration polarization phenamena. The number and the lengths of microcracks increase with increase in solution temperature, so they lead to the decrease in corrosion fatigue life.

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The Effects of Heat Treatment on Cyclic Deformation of Ni-Ti Shape Memory Alloy (Ti-Ni 형상기억합금의 반복 변형 거동에 미치는 열처리의 영향)

  • 박영철;조용배;오세욱
    • Journal of Ocean Engineering and Technology
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    • v.8 no.1
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    • pp.154-164
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    • 1994
  • In this paper, fatigue testing was carried out under the change of aging time(0.5,1.5.10hrs) by electric heating method which is one of the useful method in the application of Robot's actuator. Fatigue degradation behaviors such as cyclic deformation property, amount of deformation, decrease in recovery and variation of transformation temperature for each specimen were examined closely, and the effect of aging time condition was studied on their fatigue degradation behaviors.

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A Study on Fatigue Behaviors of RC Beams Strengthened with Carbon Fiber Sheets (CFS로 보강된 RC보의 피로거동에 관한 연구)

  • Park, Jeong-Yong;Cheung, Jin-Hwan;Kim, Seong-Do;Cho, Baik-Soon;Jang, Jun-Hwan
    • Proceedings of the Korea Concrete Institute Conference
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    • 2005.05a
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    • pp.35-38
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    • 2005
  • Carbon fiber sheets are widely used for strengthening the deteriorated RC structures. However most studies on the strengthening method of RC structures with carbon fiber sheets are concerning static problems. The purpose of this experimental study is to present the basic data on fatigue behaviors of. RC beams strengthened with carbon fiber sheets. The experimental parameters of this study are ; 1) the existence of U-shaped carbon fiber sheets at the ends for anchoring, 2) the number of carbon fiber sheet layers in strengthening the RC beams, 3) the load levels of $60\%\~90\%$ of the static bending moment strength, which is obtained form the static tests. Experimental results are estimated from the relationships of load level, displacement, number of repeated load and released energy. It is concluded that U-shaped carbon fiber sheets for end anchoring is very effective and the beams strengthened with one layer of carbon fiber sheet have longer fatigue life than that with three layers.

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Finite Element Analysis of Mechanical Properties of a Balloon-Expandable Stent (풍선확장식 스텐트의 기계적 특성에 대한 유한요소해석)

  • Oh, Byung-Ki;Cho, Hae-Yong;Kim, Yong-Yun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.7
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    • pp.915-922
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    • 2004
  • A stent is small tube-like structure expanded into stenotic arteries to restore blood flow. The stent expansion behaviors define the effectiveness of the surgical operation. In this paper, finite-element method was employed to analyze expansion behaviors and fatigue life of a typical diamond-shaped balloon-expandable stent. Beyond safety considerations, this type of analysis provides mechanical properties that are often difficult to obtain by experiments. Mechanical properties of the stent expansion pressure, radial recoil, longitudinal recoil and foreshortening were simulated using commercial FEM code, ANSYS and fatigue life were estimated using NISAII ENDURE. The FEM results showed that the pressures necessary to expand the stent up to a diameter of 3mm, 4mm and 5mm were 0.75MPa, 0.82MPa and 0.97MPa. The fatigue lifes according to expansion diameter were 114${\times}$10$^{7}$cycles, 714${\times}$$^{6}$cycles and 163${\times}$10$^{6}$cycles. As a result, a finite element model used in this study can simulate expansion behaviors of stents and should be useful to design new stents or analyze actual stents.

Low Cycle Fatigue of PPS Polymer Injection Welds (I) -Fatigue Crack Behavior-

  • Song, Jun-Hee;Lim, Jae-Kyoo;Kim, Yon-Jig;Kim, Hong-Gun
    • Journal of Mechanical Science and Technology
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    • v.17 no.5
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    • pp.647-653
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    • 2003
  • An important class of short-fiber reinforced composites is the sheet molding compound, which is recently developed and currently used in many engineering applications. Fatigue failure of the composites is a subject of major concern in design and cyclic crack propagation is of particular significance in the fatigue life prediction of short fiber composites. However, research on the fatigue behavior of polymer injection weld, especially short glass fiber-filled polymer injection weld, has not been carried out. In this study the analyses of the fatigue crack growth behaviors at weld line and in the bulk are performed based on low cycle fatigue test.

Fracture Mechanic's Approach on Retardation Behaviors under Overloading (과대 하중작용 시 균열성장 지연 거동에 대한 파괴역학적 정리)

  • Kang, Yong-Goo;Park, Jun-Young
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.11 no.5
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    • pp.13-20
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    • 2012
  • In order to clarify the effect of overload on crack growth behaviors, fatigue tests for overload were carried out for round plain specimens of SM45C steel. In the experiment, typical semi-elliptical crack shape was found and further crack growth behaviors were tested. Using three types of single overload fatigue tests, Crack growth retardation phenomenon were examined. The growth rate of surface crack(da/dN) during retardation period was analyzed in terms of ${\Delta}K$ and ${\Delta}K_{eff}$. On the growth rate of surface crack analyzed by ${\Delta}K$, the dependence of overload stress levels appears. However, on the growth rate by ${\Delta}K_{eff}$ obtained by Willenborg analysis, there is a non-liner relationship between da/dN and ${\Delta}K_{eff}$ with narrow scatter band.

Characteristic of Fatigue Properties with Tension and Bending Loading Using High Strength Steel Wire (고강도 강선의 인장 및 회전굽힘 피로특성)

  • U, Byeong-Cheol;Kim, Sang-Su;Kim, Byeong-Geol;Seo, Chang-Min
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.1
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    • pp.161-167
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    • 2001
  • The overhead transmission wires operating both at warm temperature and tighten state for a long period of time in a power transmission plant are degraded by air pollution, wind, creep and slip between steel wire and aluminium conductor. The objective of this study is to investigate to investigate the characteristics of fatigue properties with tension and bending loading of a high carbon steel wire. The fatigue behaviors have been carried out by tension-tension, 4 points bending and 3 points bending loading. In the present study, a conventional fatigue strengths between 4 points bending and tension-tension fatigue were determined by Gerber, Sorderberg and Goodmans theory and we investigated S-N diagram for bending and tensile loading.

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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