• Title, Summary, Keyword: 피로균열진전시험

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Experimental Study on Evaluation of Fatigue Crack Growth Rate of Steel Plates using Crack Opening Displacement (COD(Crack Opening Displacement) 측정을 통한 강재의 피로균열진전속도 추정에 관한 실험적 연구)

  • Kim, Kwang-Jin;Kim, In-Tae;Ryu, Yong-Yeol
    • Journal of Korean Society of Steel Construction
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    • v.22 no.6
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    • pp.589-597
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    • 2010
  • Steel structures have a higher probability of being damaged by fatigue than by other causes of deterioration. As such, their maintenance to prevent fatigue damage is essential to sustain their safety and performance during their service period. In their maintenance, the current state of their fatigue cracks must be assessed to determine appropriate reinforcement methods and the suitable time intervals of periodic inspections when fatigue cracks are detected. Determining the crack growth rate is a successful method of predicting fractures, but it requires technical knowledge on fracture mechanics and experience in numerical methods and software for finite element analysis. In this study, a fatigue crack growth test on through-thickness cracked steel plates was conducted to assess the crack growth rate without superior technical knowledge and experience. The relationship between the Crack Opening Displacement (COD) and the crack growth rate was found in relatively long fatigue cracks.

Evaluation of Fatigue Crack Growth Rate on the Surface of Steel Members Using COD(Crack Opening Displacement) Measurement (COD(Crack Opening Displacement) 측정에 의한 강재표면의 피로균열진전속도 평가)

  • Kim, Kwang Jin;Kim, In Tae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.15 no.2
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    • pp.179-188
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    • 2011
  • Steel structures have been allowed to have fatigue damage tolerance in fact. If it would be assessed whether fatigue crack is growing or not and How fast fatigue crack is propagating, we should make a rational decision on methods and a period of reinforcement in the maintenance. In this study, fatigue crack growth tests on two kinds of through-thickness cracked steel plates and a out-of-plane gusset welded joint were conducted to evaluate fatigue crack growth rate using the COD(Crack Opening Displacement), and COD measurement using strain gauges was examined to offer a practical method. As a result, we proposed a reasonable assessing method for fatigue crack growth rate using the COD and it was experimentally proved practical to estimate the COD through measuring strains.

Assessment of Fatigue Life of Out-Of-Plane Gusset Welded Joints using 3D Crack Propagation Analysis (3차원 피로균열 진전해석을 통한 면외거셋 용접이음의 피로수명 평가)

  • Jeong, Young-Soo;Kainuma, Shigenobu;Ahn, Jin-Hee;Lee, Wong-Hong
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.22 no.1
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    • pp.129-136
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    • 2018
  • The estimation of the fatigue design life for large welded structures is usually performed using the liner cumulative damage method such as Palmgren-Miner rule or the equivalent damage method. When a fatigue crack is detected in a welded steel structure, the residual service life has to be estimated base on S-N curve method and liner elastic fracture mechanics. In this study, to examine the 3D fatigue crack behavior and estimate the fatigue life of out-of-plane gusset fillet welded joint, the fatigue tests were carried out on the model specimens. Investigations of three-dimensional fatigue crack propagation on gusset welded joint was used the finite element analysis of FEMAP with NX NASTRAN and FRANC3D. Fatigue crack growth analysis was carried out to demonstrate the effects of aspect ratio, initial crack length and stress ratio on out-of-plane gusset welded joints. In addition, the crack behaviors of fatigue tests were compared with those of the 3D crack propagation analysis in terms of changes in crack length and aspect ratio. From this analysis result, SIFs behaviors and crack propagation rate of gusset welded joint were shown to be similar fatigue test results and the fatigue life can also be predicted.

Damage Tolerance Assessment for Fatigue-Critical Locations of Wing Structure of Aged Aircraft (장기운영 항공기 주익 구조물 피로임계부위의 손상허용평가)

  • Chun, Young-Cheol;Kim, Won-Cheol;Jin, Ji-Won;Chung, Tae-Jin;Kang, Ki-Weon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.2
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    • pp.129-136
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    • 2017
  • This study aims to assess the damage tolerance of the wing structure of aged aircraft with long-term service through the fatigue crack growth analysis and tests. For the fatigue-critical locations (FCL) W2 and W4 in the wing structure, the fatigue stress spectrum was derived based on a previous study. Thereafter, a crack propagation analysis for the FCLs was conducted using the commercial software $NASGRO^{TM}$. The algorithm for the fatigue stress spectrum was verified. Fatigue crack growth tests were then performed for two types of specimens: Type #1 was extracted from the wing structure of aged aircraft, and Type #2 was made of the same material as the wing structure. By comparing the experimental results of these specimens, we assessed the damage tolerance of the wing structure of aged aircraft with service time.

A Study on Fatigue Life Prediction of Welded Joints Through Fatigue Test and Crack Propagation Analysis (피로실험 및 균열진전 해석을 통한 용접부의 피로수명 예측에 관한 연구)

  • Y.C. Jeon;Y.I. Kim;J.K. Kang;J.M. Han
    • Journal of the Society of Naval Architects of Korea
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    • v.38 no.3
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    • pp.93-106
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    • 2001
  • T-joint and hopper knuckle joint models are typical welded joints in ship structure, which are very susceptible to fatigue damage under service condition. Fatigue test and fracture mechanical analysis were performed on these joints to find out characteristics of fatigue behavior. Unified S-N curve was developed from the test results of these two types of joint using hot spot stress concept, and also propagation life was also estimated using Paris' crack propagation law. Residual stress effect on propagation life was considered in calculating propagation life, as was done with thermo-elasto-plastic FE analysis and residual stress intensity factor calculation. Fatigue life of similar kinds of welded joint could be predicted with this unified S-N curve and fracture mechanical analysis technique.

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DCPD법에의한 316LN 스테인레스강의 고온 피로균열진전특성

  • Maeng, Wan-Young;Nam, Ho-Yun;Kang, Young-Hwan;Cho, Man;Kim, Mun-Hwan;Kwon, Hyuk-Mu;Nam, Tae-Woon
    • Proceedings of the Korean Nuclear Society Conference
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    • pp.36-41
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    • 1997
  • 액체금속로는 고온 하중 효과(피로, 크립, 크립-피로)를 고려한 내열응력설계가 중요하다. 최근에는 액금로 후보재료로서 종래의 스테인레스강에 질소를 첨가하여 고온강도를 계량한 316LN 스테인레스강이 개발되었다. 본 연구에서는 액체금속로 재료의 가장 지배적인 손상 기구로 인식되고 있는 피로-크립 파손에 대한 설계자료를 확보하기 위해 DCPD(Direct Current Potential Drop)법에 의한 고온피로균열 측정 시스템을 개발하고 316L 및 스테인레스강인 316LN 스테인레스강에 대한 고온 피로균열진전시험을 수행하였다. 본 연구에 의해 개발된 피로균열진전속도 측정 시스템에 의하면 25$\mu\textrm{m}$ 이하의 분해능으로 균열길이를 측정할 수 있다. 한편 316L 스테인레스강에 질소를 적당량 첨가하면 상온에서 $600^{\circ}C$사이의 온도에서 피로균열진전에 대한저항성이 증가하는 것을 확인하였다.

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Effect of Temper-Embrittlement on Surface Crack Growth and Fatigue Life Prediction (재질열화가 표면 균열 진전에 미치는 영향과 수명 예측에 관한 연구)

  • 권재도
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.5
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    • pp.921-927
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    • 1989
  • One of the most important problems in recent life prediction is to introduce the degradation effects into life prediction procedure. In the present paper, the effect of the material degradation on the fatigue surface crack growth and fatigue life prediction in a 2 1/4 Cr-1Mo steel were investigated. The 2 1/4 Cr-1Mo steel has been used in a plant having operated for over 60000hours and subjected to material degradation due to temper-embitterment. A Monte-Carlo simulation was made on the basis of the data obtained in the experiment in order to determine the P-S-N diagrams of surface crack growth for the degraded and recovered steels.

Initiation and Growth Behavior of Small Surface Fatigue Crack on SiC Particle Reinforced Aluminum Composite (SiC 입자 강화 알루미늄기 복합재료의 표면미소 피로균열 발생 및 초기진전거동)

  • Lee, Sang-Hyoup;Choi, Young-Geun;Kim, Sang-Tae;Lee, Moon-Hwan
    • Composites Research
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    • v.21 no.6
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    • pp.15-22
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    • 2008
  • Reversed plane bending fatigue tests were conducted on SiC particle aluminum composite. The initiation and growth behaviors of small surface fatigue cracks were continuously monitored by the replica technique and investigated in detail. The fatigue life of MMC is shorter than that of matrix because there exists interface debonding of SiC particles and matrix on the whole face of the notch part in the casting metal matrix composite(MMC). The coalescence of micro-cracks was observed in the tests conducted at high stress levels. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn-$K_{max}$ relationship.

Evaluation of Fatigue Crack Propagation Behavior of Nickel-based Powder Metallurgy Superalloy for Aircraft at Elevated Temperature (항공기 터빈 디스크용 니켈기 초내열 분말야금 합금의 고온 피로균열진전 거동 비교 평가)

  • Yoon, Dong Hyun;Na, Seong Hyeon;Kim, Jae Hoon;Kim, Hongkyu;Kim, Donghoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.8
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    • pp.751-758
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    • 2017
  • The behavior of fatigue crack growth of nickel-based powder metallurgy superalloy that could be used in aircraft turbine disc is investigated at room temperature, and $650^{\circ}C$ considering real operating conditions. The direct current potential drop(DCPD) method was used to measure the crack length of material in real time according to ASTM E647. Tests were performed with various stress ratios (0.1 and 0.5). Experimental results show that stress ratio, and temperature all affect the behavior of fatigue crack growth. As the stress ratio and temperature increase, the fatigue crack growth rate of nickel-based powder metallurgy superalloy also increases. Results were compared and reviewed with fatigue crack growth rates of other nickel-based superalloy materials (Inconel-100) that were studied in previous papers. Fractography analysis of the fractured specimens was performed using as SEM.

Estimation of Fatigue Crack Growth using Gamma Process Model (감마과정 모델을 적용한 피로균열 진전거동의 예측)

  • Park, Sung Ho;Kim, Jae Hoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.11
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    • pp.1245-1256
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    • 2014
  • The physical nature of fatigue shows the considerable amount of scatter from intrinsic and extrinsic factors. In this study, some degradation models, such as the gamma process model, were reviewed in terms of uncertainties associated with the continuous, gradual, and monotonic nature of fatigue crack growth. Statistically varying fatigue crack growth data obtained from Lu and Meeker were used as an example to demonstrate the use of the gamma process model. This model can describe the condition and lifetime as statistical distribution curves whose shapes vary with cycles. From the skewness of the statistical distribution curves, it was confirmed that the median is suitable for being considered as the expected life. The use of the gamma process model enables the optimum replacement period and percentile life to be employed as criteria for preventive maintenance policy.