• Title/Summary/Keyword: Propagation Life

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Fatigue Crack Propagation Behavior of 316L Stainless Steel and Frequency Characteristics of its Acoustic Emission (316L 스테인리스강의 피로균열 진전 거동과 음향방출신호의 주파수 특성)

  • Lee, S.K.;Do, J.Y.;Nam, K.W.;Kang, C.Y.;Ahn, S.H.
    • Journal of Power System Engineering
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    • v.4 no.2
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    • pp.52-57
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    • 2000
  • We investigated the fatigue crack propagation of base metal, weld metal and heat attected zone in 316L stainless steel. And we analysed acoustic emission signals during the fatigue test by time-frequency analysis method. The specimens of weld metal and HAZ had longer fatigue life and slower rate of crack propagation better than base metal. And as a result of time-frequency was 200-300 kHz was obtained by fatigue crack propagation and 500 kHz was obtained by dimple and separate of inclusion.

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Crack Propagation at Boundary Face of Composite Compact Tension Specimen

  • Cho, Jae-Ung;Han, Moon-Sik
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.22 no.2
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    • pp.337-341
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    • 2013
  • In this study, fatigue crack propagation in composite material under fatigue is investigated by simulation result. When another material on the specimen exists vertically to the crack line, the phenomena that crack may go straight or propagate along the boundary face according to the elastic modulus ratio of another material to matrix are investigated with compact tension specimen by compliance method. Crack propagation direction is evaluated by compliance method. By arranging this study result systematically about the crack propagation behavior due to the stiffness of inhomogeneous material, high-tech material (automobile, aircraft and steel industry) can be improved. The estimation of safety design and life (construction & nuclear power station, etc.) will be of great value industrially.

A fracture mechanics evaluation on the fatigue crack propagation at spot welded aluminum joint in passenger car body (스폿용접된 자동차 차체용 알루미늄 박판의 피로균열진전의 파괴역학적 평가)

  • 박인덕;남기우;강석봉
    • Journal of Ocean Engineering and Technology
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    • v.11 no.3
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    • pp.20-28
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    • 1997
  • The fatigue crack propagation properties and fatigue life of two kinds of Al body panel for automobile were examined experimentally by using the plate specimen and the single spot welding specimen. The fatigue limit of spot welding specimens was lower than that of a plate specimen. The fatigue limit was similar in two kinds of spot welding specimen. The shape and size of crack propagation were observed and measured on beach mark of fracture surface. The crack propagation of surface crack specimen showed almost same tendency to that of a thick plate as almost semi-elliptical. In spot welding specimen, the fatigue crack occurred in inside surface of nugget area was almost semi-elliptical. The crack growth rate can be explained using equation of stress intensity factors.

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A non-destructive method for elliptical cracks identification in shafts based on wave propagation signals and genetic algorithms

  • Munoz-Abella, Belen;Rubio, Lourdes;Rubio, Patricia
    • Smart Structures and Systems
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    • v.10 no.1
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    • pp.47-65
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    • 2012
  • The presence of crack-like defects in mechanical and structural elements produces failures during their service life that in some cases can be catastrophic. So, the early detection of the fatigue cracks is particularly important because they grow rapidly, with a propagation velocity that increases exponentially, and may lead to long out-of-service periods, heavy damages of machines and severe economic consequences. In this work, a non-destructive method for the detection and identification of elliptical cracks in shafts based on stress wave propagation is proposed. The propagation of a stress wave in a cracked shaft has been numerically analyzed and numerical results have been used to detect and identify the crack through the genetic algorithm optimization method. The results obtained in this work allow the development of an on-line method for damage detection and identification for cracked shaft-like components using an easy and portable dynamic testing device.

The Characteristics of Mechanical Properties and Fatigue Crack Propagation of Fire Resistance Steel for Frame Structure (구조용 내화강의 기계적 성질과 피로균열전파 특성에 관한 연구)

  • Kim, Hyeon-Su;Nam, Gi-U;Gang, Chang-Ryong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.1
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    • pp.54-60
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    • 2001
  • This study is to investigate the mechanical properties and the fatigue crack propagation of fire resistance steel for frame structure as the chemical composition was changed by addition of N, B and rolled end temperature was varied. We used two kinds of specimen, the one is parallel and the other is perpendicular to the rolling directions. As rolled end temperature increased, volume fraction of ferrite and pearlite decreased, but volume fraction of baintie and grain size increased. Micro-hardness decreased as rolled end temperature increased, but tensile and yield strength increased. Volume fraction of ferrite and pearlite decreased by addition of N. But volume fraction of bainite, tensile and yield strength increased. Microstructure was changed to martensite by addition of B, and tensile and yield strength increased. Fatigue life of TL direction specimen was shorter than that of LT direction specimen. There was no significant effect to fatigue crack propagation rate by addition of N and changing rolling condition, but fatigue life was increased by addition of B.

Effect of Mode II in The Fatigue Crack Propagation Behavior by Variation of Multilevel Loading Direction (다단계 하중방향 변화에 의한 피로균열 전파거동에서의 모드II 영향)

  • 홍석표;송삼홍
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2004.10a
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    • pp.725-728
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    • 2004
  • In this study, the effect of mode II by variation of multilevel loading direction was experimentally investigated in the fatigue crack propagation behavior. To generate mixed-mode I+II loading state, the compact tension shear(CTS) specimen and loading device were used in this tests. The experimental method divided into three steps and three cases that were step I(0$^{\circ}$), step II(30$^{\circ}$, 60$^{\circ}$, 90$^{\circ}$),step III(0$^{\circ}$) and case I(0$^{\circ}$ ⇒ 30$^{\circ}$ ⇒ 0$^{\circ}$), case II(0$^{\circ}$ ⇒ 60$^{\circ}$ ⇒ 0$^{\circ}$), case III(0$^{\circ}$ ⇒ 90$^{\circ}$ ⇒ 0$^{\circ}$). The result of test, the step II affected to the step III in the all case. Specially, The fatigue crack propagation rate was faster and the fatigue life was smaller than of mixed mode I+II(30$^{\circ}$,60$^{\circ}$) due to the effect of mode II in the step III of the case III

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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.

Fatigue Crack Propagation and Fatigue Life Evaluation of High-Performance Steel using Modified Forman Model (수정 Forman 모델을 이용한 고성능 강재의 피로균열전파와 피로수명평가)

  • Choi, Sung-Won;Kang, Dong-Hwan;Lee, Jong-Kwan;Kim, Tae-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.11
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    • pp.1361-1368
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    • 2011
  • Fatigue crack propagation behavior and the fatigue life in-high performance steel were investigated by means of fatigue crack propagation tests under constant loading conditions of 'R=0.1 and f=0.1 Hz', 'R=0.3 and f=0.3 Hz', and 'R=0.5 and f=0.5 Hz' for the load ratio and frequency, respectively. A modified Forman model was developed to describe the fatigue crack propagation behavior for the conditions. The modified Forman model is applicable to all fatigue crack propagation regions I, II, and III by implementing the threshold stress intensity factor range and the effective stress intensity factor range caused by crack closure. The results show that predicted fatigue lives of Forman and modified Forman models were 8,814 and 12,292 cycles, respectively when the crack propagated approximately 5.0 mm and the load ratio and frequency were both 0.1. Comparison of the test results indicates that the modified Forman model showed much more effective fatigue crack propagation behavior in high-performance steel.

Prediction of Remaining Life Time and Determination of Inspection Cycle Considering Critical Crack in Tension Bar of Continuous Ship Unloader (연속식 하역기 텐션바의 임계 균열을 고려한 잔존수명 예측 및 검사 주기 선정)

  • Park, S.;Chung, J.Y.;Song, J.I.;Kim, D.J.;Seok, Chang Sung
    • Journal of the Korean Society of Safety
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    • v.33 no.6
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    • pp.1-7
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    • 2018
  • The Continuous Ship Unloader (CSU) is an equipment that unloads freight from the ship docked in the port to the land. And the design target life time is designed to be 30 to 50 years, and it is classified as a semi-permanent large facility. However, cracks may occur due to structural defects, abnormal loads, and corrosion, and fatigue failure may occur before the design life is reached. In this study, we predicted the remaining life time of the main component of the CSU considering crack. And also proposed inspection cycle for maintenance of CSU based on the results of the remaining life time prediction. For this purpose, the structure, operational stresses of the CSU were analyzed and main members were selected. And tensile tests and fatigue crack propagation tests were performed with SM490YA and SM570TMC, which are used as main materials for CSU.

A Study on the Fatigue Behaviors of Cr-Mo-V Alloy for Steam Turbine at High Temperature Difference (터빈용 Cr-Mo-V강의 고온 환경변화에 따른 피로거동에 관한 연구)

  • Song, Sam-Hong;Kang, Myung-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.1
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    • pp.173-179
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    • 1997
  • The high temperature fatigue tests were performed using the specimens taken from Cr-Mo-V steel, widely used as thermal power plant turbine materials for examination fatigue behavior of materials in power plants which have been operated for long periods. The fatigue tests at high temperature were performed at the various temperature and applied stress. The results obtained are summarized as follows : The fatigue crack length increases and the fatigue life decreases with temperature and applied stress according to the same number of stress cycle. The fatigue crack propagation and the fatigue life were much influenced by temperature and applied stress.