• Title, Summary, Keyword: 피로한도

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Evaluation of Mechanical Properties and Fatigue Behavior of STS 304L due to Plastic Working (소성가공에 따른 STS 304L 재료의 기계적 특성 및 피로평가)

  • Shim, Hyun-Bo;Kim, Young-Kyun;Suh, Chang-Min
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.7
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    • pp.635-643
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    • 2017
  • The purpose of this study is to investigate the influence of the cold reduction rate and an ultrasonic fatigue test (UFT) on the fatigue behaviors of STS 304L. The tensile strength, yield strength, hardness value and fatigue limit in the UFT fatigue test linearly increased as thickness decreased from 1.5 mm to 1.1 mm, as the cold reduction rate of STS 304L increased. As a result of the UFT fatigue test (R = -1) of four specimens, the fatigue limit of the S-N curve formed a knee point in the region of $10^6$, and the 2nd fatigue limit caused by giga cycle fatigue did not appeared. In the case of t = 1.1 mm, the highest fatigue limit was 345 MPa, which was 64.3% higher than the original material (t = 1.5 mm). As a result of the UFT fatigue test of STS 304L, many small surface cracks occurred, grown, coalesced while tearing.

Comparison of the fatigue limit of fiber-reinforced composites and stainless steel wires when attached to the tooth surface for anchorage reinforcement (고정원 강화를 위해 치면에 부착한 fiber-reinforced composite과 스테인리스강 와이어의 피로한도 비교)

  • Kim, Moon-Jung;Park, Soo-Byung
    • The korean journal of orthodontics
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    • v.35 no.4
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    • pp.302-311
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    • 2005
  • This study was performed to compare the fatigue limit of stainless steel wires and Fiber-reinforced composites (FRC) under conditions of permitting physiologic tooth movement. and to evaluate the clinical value of FRCs which was used to reinforce the anchorage unit. The stainless steel wire groups were divided into round and rectangular wire groups. The FRC groups were divided into uni-directional and woven groups, with resin coating and without resin coating in the Proximal area After the number of cycles to failure of each of the 6 groups were measured within the $5{\times}10^5\;cycle$ fatigue limit simulating the orthodontic treatment period. the fatigue limit of each group was compared with each other The findings of this study were as follows. In stainless steel wires, the fatigue limit of rectangular wires were higher than that of round wires. But there was no statistically significant difference (p>0.05). In FRCs with resin coating and without resin coating in the interproximal area, the fatigue limit of uni-directional type was higher than that of the woven type (p<0.05). In uni-directional and woven type FRCs, the fatigue limit of FRC with resin coating in the interproximal area was higher thar that of FRC without resin coating (P<0.05) As the FRCs and stainless steel wires did not fracture until the $5{\times}10^5\;cycle$ fatigue limit which clinically is useful. it is sufficient to use FRC and stainless steel wire for reinforcing anchorage. When esthetics is important and the attachment of additional devices are necessary. it seems sufficient to use FRC as anchorage reinforcement.

Prediction of Reliability of Fatigue Limit of S34MnV Steel for Marine Diesel Engine Crank Throw Components (선박용 디젤 엔진 크랭크 스로 부품용 S34MnV강의 피로한도에 대한 신뢰도 예측)

  • Kim, Seon Jin;Kong, Yu Sik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.8
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    • pp.751-757
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    • 2016
  • The aim of this study is to estimate the reliability of fatigue limit of the material used for crank throw components according to the staircase method. The material used for crank throw components is forged S34MnV grade steel, which is heat treated by normalizing and tempering. In this work, to predict the reliability of the design fatigue strength, axially loaded constant amplitude fatigue testing was conducted. The test specimens were loaded with an axial push/pull load with a mean stress of 0 MPa, which corresponds to a stress ratio of R=-1. The fatigue test results were evaluated by Dixon-Mood formulas. The values of mean fatigue strength and standard deviation predicted by the staircase method were 296.3 MPa and 10.6 MPa, respectively. Finally, the reliability of the fatigue limit in some selected probability of failure is predicted. The proposed method can be applied for the determination of fatigue strength for design optimization of the forged steel.

Evaluation of Fretting Fatigue Behavior for Inconel Alloy at 320℃ (320℃에서의 인코넬 합금의 프레팅 피로 거동 평가에 관한 연구)

  • Kwon, Jae-Do;Jeung, Han-Kyu;Chung, Il-Sup;Park, Dae-Kyu;Yoon, Dong-Hwan
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.8
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    • pp.951-956
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    • 2011
  • Inconel alloys are generally used as steam generator tubes in nuclear power plants. These alloys are highnickel chromium alloys that exhibit excellent resistance to aqueous corrosion. In this paper, the effects of elevated temperatures such as an operating temperature of $320^{\circ}C$ on the fretting fatigue behavior of inconel 600 and 690. We observed that the plain and fretting fatigue limits at $320^{\circ}C$ were slightly lower than those at room temperature. The frictional forces varied depending on the number of load cycles. After each test, we studied the fretting fatigue mechanisms via SEM observations. These results can be used for structural integrity evaluations at elevated temperatures and for studying fretting damage in steam generator systems.

Detection and non-propagating cracks of small fatigue crack (미소피로균열의 검출과 정류균열)

  • 이종형
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.3
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    • pp.603-609
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    • 1990
  • Detection and non-propagating cracks of small fatigue crack for smooth and pre-cracked specimens were examined in a carbon steel. The fretting oxide induced crack closure triggered by the roughness induced crack closure has an important role in determing the length. The fatigue limit for the with no cracks or with a short pre-crack is lower at R=-1 than that at R=0. A non-propagating crack are quite different between points near the specimen's surface and those of deepest penetration.

Quantitative Evaluation for Fatigue Limit and its Application to Spheroidal Graphite Cast Iron (피로한도의 정량평가법과 구상흑연주철에 대한 적용)

  • Kim, Jin-Hak;Kim, Min-Gun
    • Journal of Industrial Technology
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    • v.18
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    • pp.203-208
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    • 1998
  • Fatigue tests were performed to examine the 4 parameter method for specimens prepared by various heat treatment which resulted in different mechanical properties. Obtained main results are as follows. (1) Samples treated by austempering did not show the expected improvement of fatigue limit although hardness and strength increased. This is attributed to the fact that defect sensitivities of materials increase as increasing of hardness and tensile strength, it is also shown that the graphites acting as stress concentration place become larger by austempering heat treatment than by normal annealing. (2) It is very reasonable to predict the fatigue limit of ductile irons with 4 parameter method based on ${\sigma}_{TS}$, $H_v$, ${\Delta}K_{th}$ and ${\sqrt{area}}_{max}$. (3) The half-austempering treatment appeared to be more useful than the full-austempering method to improve the fatigue limit in the spheroidal graphite cast iron with multi defective material.

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The Study on Estimation Fatigue Limit in Induction Surface Hardened S45C Steel (S45C강의 고주파 열처리 표면경화재 피로한도 예측에 관한 연구)

  • 이수진;전형용;성낙원
    • Transactions of the Korean Society of Automotive Engineers
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    • v.6 no.1
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    • pp.134-142
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    • 1998
  • The effects of small hole defect size and effective case depth(ECD) on the four point bending fatigue limit of induction surface hardened S45C steel were investigated the fatigue limit evaluation of hardened materials is very difficult because of relations of the hardness gradient and residual stress. In this study, it was possible to characterize fatigue limit and fatigue life of induction surface hardened S45C steel in terms of the hole defect size and effective case depth(ECD) and quantitative evaluation of the fatigue limit with hole defects use Murakami's evaluation method and the range of evaluated values is a good accuracy compared with results.

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A Study on the Mechanical Properties and Fatigue Limit of the Austenitizing Treatment Conditions in Austempered Ductile Iron (오스템퍼링처리한 구상흑연주철의 오스테나이트화 조건에 따른 기계적 성질 및 피로한도에 관한 연구)

  • Kim, Min-Gun;Lim, Bok-Kyu
    • Journal of Industrial Technology
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    • v.24 no.A
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    • pp.3-8
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    • 2004
  • This study was performed to investigate the effect of two step austenitized treatment on the mechanical properties and fracture characteristic of the ductile cast iron and austempered ductile cast iron(ADI). The obtained results of this study were as follows. The matrix structures of specimens were changed differently by austenitizing heat treatment. Microstructure of austempered ductile cast iron obtained by two step austenitized treatment was bainitic ferrite and retained austenite. With two step austenitized treatment, vield strength, tensile strength and hardness decreased, while the elongation increased.

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Threshold Condition for the Propagation of Short Fatigue Crack (炭素鋼 微小疲勞크랙 전파의 不限界條件)

  • 김민건
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.3
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    • pp.505-512
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    • 1988
  • Since the propagation of a short fatigue crack is directly related to the large crack which causes the fracture of bulk specimen, the detailed study on the propagation of the short crack is essential to prevent the fatigue fracture. However, a number of recent studies have demonstrated that the short crack can grow at a low applied stress level which are predicted from the threshold condition of large crack. In present study, the threshold condition for the propagation of short fatigue crack is examined with respect to the microstructure and cyclic loading history. Specimens employed in this study were decarburized eutectoid steels which have various decarburized ferrite volume fraction. Rotating bending fatigue test was carried out on these specimens with the special emphasis on the '||'&'||'quot;critical non-propagating crack length.'||'&'||'quot; It is found that the reduction of the endurance limit of their particular microstructures can be due to the increase of the length of critical non-propagating crack, and the quantitative relationship between the threshold stress .DELTA. .sigma. $_{th}$ and the critical non-propagating crack length Lc can be written as .DELTA. .sigma. $_{th}$, Lc=C where m, C is constant. Further experiments were carried out on the effect of pearlitic structure and cyclic loading history on the length of critical non-propagating crack. It is shown that the length of critical non-propagating crack is closely related to both pearlite interlamellar spacing and cyclic loading history.ory. cyclic loading history.