• Title, Summary, Keyword: Fatigue crack life ratio

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The Influence of the Small Circular Hole Defect on the Fatigue Crack Propagation Behavior in Aluminum Alloys (알루미늄 합금재의 피로크랙 전파거동에 미치는 미소원공결함)

  • Kim, G.H.;Lee, H.Y.
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.6
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    • pp.834-840
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    • 2008
  • We carried out fatigue testing with materials of aluminum alloyC7075-T6, 2024-T4) by rotary bending fatigue tester. We investigated fatigue limit, fatigue crack initiation, fatigue crack propagation behavior and possibility of fatigue life prediction to the different small circular hole defect. The summarized result are as follows; Fatigue limit of the smooth specimens were related tensile strength and yield strength. In case of more large applied stress and small circular hole crack defect, the fatigue crack was grown rapidly. The fatigue crack propagation behavior proceed at according to inclusion. Fatigue crack propagation ratio appeared instability and retardation phenomenon in the first half of fatigue life but appeared stability and replied in the latter half. On other hand, this experimental data of the materials are appeared fatigue life predictability.

A Study on Fatigue Life and Fatigue Crack Propagation Behavior of MMC (MMC의 피로수명과 피로균열전파거동에 관한 연구)

  • 허선철;박원조;최용범
    • Journal of the Korean Society for Precision Engineering
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    • v.19 no.12
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    • pp.127-133
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    • 2002
  • The objective of this study is to investigate fatigue life and fatigue crack propagation behavior The experiment of fatigue life for MMC have been carried out for the stress ratio R=0.1 at 20Hz. Fatigue lift limit of AC4CH alloy is about 70 ㎫ and Fatigue limit of MMC has been increment to 120 ㎫, therefore, fatigue limits of MMC is about 71 % higher than that of AC4CH alloy Crack propagation tests on half-size CT specimen of thickness 12.5mm were conducted by using sinusoidal waveform. The crack length was monitored by compliance method. Test conditions were at 0.1 and 0.05 of load ratio at 10Hz of loading frequency and test load was 2.3kN. The effects of stress ratio on the fatigue crack propagation behavior for MMC was discussed within the Paris law. As the results of this study, Fatigue crack propagation increased with increasing the load ratio.

A Study on the Fatigue Crack Propagation Behavior in the SB41 Welding Material (SB41용접재의 피로크랙 진전거동에 관한 연구)

  • 최병기;장경천
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.11 no.2
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    • pp.43-49
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    • 2002
  • SB41 material is welded automatically and is investigated some effects of the welding residual stress in the growth and propagation of fatigue crack, so as to study the fatigue behaviour in the welding residual stress field. The summarized results are as follows; 1) In case of the load amplitude is constant, as the stress ratio is changing to 0.1, 0.33 and 0.5 the propagation life is constant but the growth life decreases. And than, when maximum load or minimum load is constant as the stress ratio increases the growth life and propagation life. 2) It was shown that fatigue crack propagation ratio da/dN was almost constant regardless of the stress ratio change at constant load amplitude and that the larger stress ratio, the slower was the fatigue crack propagation ratio. 3) The opening ratio U is influenced by $K_max$ but it isn't only the function of $K_max$ because data range is very large. 4) The fatigue life of the specimens on tensile compressive residual stress field was decreased and increased respectably more than that of the base metal.

A Study on the Fatigue Crack Growth Behavior in Residual Stress Field of the SS41 Welding Material (SS41 용접재의 잔류응력장내에서의 피로균열 성장거동에 관한 연구)

  • Choi, Byung-Ki
    • Journal of the Korean Society of Safety
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    • v.17 no.1
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    • pp.33-38
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    • 2002
  • SS41 material is welded automatically and is investigated some effects of the welding residual stress on the growth and propagation of fatigue crack, so as to study the fatigue behaviour in the welding residual stress field. The summarized results are as follows; 1) In case of the load amplitude is constant, as the stress ration is changing to 0.1, 0.33 and 0.5 the propagation life is constant but the initiation life decreases. And than, when maximum load or minimum load is constant, s the stress ration increases the initiation life and propagation life. 2) It was shown that the fatigue crack propagation ratio da/dn was almost constant regardless of the stress ratio change at constant load amplitude and that the larger stress ratio, the slower was the fatigue crack propagation ratio. 3) The opening ratio U is influenced by $K_{max}$ but it isn't only the function of $K_{max}$ because data range is very large. 4) The fatigue life of the specimens on tensile compressive residual stress field was decreased and increased respectably more than that of the base metal.

Fatigue Crack shape Variations by a Residual Stress and Fatigue Life Predition (잔류응력에 의한 피로균열면 형상변화 및 수명예측)

  • 강용구;서창민;박원종
    • Journal of Ocean Engineering and Technology
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    • v.7 no.2
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    • pp.68-78
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    • 1993
  • Fatigue crack shape variation by a residual stress during crack growth and life predition are studied. An analytical method is presented to predict the influence of a residual stress due to heattreatment on crack shape variations. Computer simulation results using this me thod are graphically shown that crack growth rate to surface direction are decreased due to compressive residual stress exisiting in surface area. These results are commpared with experimental results. The fatigue life is also predicted by computer simulation of crack aspect ratio variation which is based on the surface crack length increment per unit cycle calculated from a-N diagram. Predited life is about 12 percent lower than experimental life.

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A Study on the Prediction of Fatigue Damage in 2024-T3 Aluminium Alloy Using Neural Networks (신경회로망을 이용한 AI 2024-T3합금의 피로손상예측에 관한 연구)

  • Cho, Seok-Swoo;Jang, Deuk-Yul;Joo, Won-Sik
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.7
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    • pp.168-177
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    • 1999
  • Fatigue damage is the phenomena which is accumulated gradually with loading cycle in material. It is represented by fatigue crack growth rate da/dN and fatigue life ratio $N/N_{f}$. Fracture mechanical parameters estimating large crack growth behavior can calculate quantitative amount of fatigue crack growth resistance in engineering material. But fatigue damage has influence on various load, material and environment. Therefore, In this study, we propose that artificial intelligent fatigue damage model can predicts fatigue crack growth rate da/dN and fatigue life ratio $N/N_{f}$ simultaneously using fracture mechanical and nondestructive parameters.

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A Study on the effect of Compressive residual stress on fatigue crack propagation behavior of the spring steel (스프링강의 피로파괴에 미치는 압축잔류응력의 영향)

  • Jin, Young-Beom;Park, Keyung-Dong
    • Proceedings of the KSME Conference
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    • pp.348-352
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    • 2004
  • Recently the steel parts used for automiles and trains are required to be used under higher stress than ever before in need of the weight down. However, threr are a lot of problems with developing such of fatigue strength and fatigue life are mainly focused on by adopting residual stress. And got the following characteristics from crack growth test carried out stress ratio. Fatigue life shows more improvement in the Un-peening material. And Compressive residual stress of surface on the Shot-peening processed operate resistance force of fatigue. So we cam obtain fallowings. (1) The fatigue crack growth rate on stage II is conspicuous with the size of compressive residual stress and is dependent of Paris equation. (2) Although the maximum compressive residual stress is deeply and widely formed from surface, fatigue life does not improve than when maximum compressive residual stress is formed in surface. (3) The threshold stress intensity factor range is increased with increasing compressive residual stress.

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Fatigue Crack Propagation Behavior for Electron Beam Welded Joint of SUS 321 (SUS 321 전자비임 용접부의 피로균열진전거동)

  • 김재훈
    • Journal of the Korean Society of Safety
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    • v.12 no.2
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    • pp.57-64
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    • 1997
  • Fatigue crack propagation behaviors and life prediction for SUS 321 plate and its electron beam weld metal were investigated using compact tension specimens. The larger the stress ratio is, the faster the crack propagates, but the variation of crack propagation rate decreases. The effect of stress ratio is greater in the slow crack propagation area than in the faster one. The crack propagation rate of electron beam weld metal is faster than that of base metal because of hardening, weld defect and residual stress in welding area. The crack propagation rate of transverse weld metal has a lower than that of base metal due to the effect of residual stress, but in the time of passing through welding area, has a higher rate. The crack propagation rate using $\Delta$K$_{eff}$ can be well plotted regardless of stress ratio. The fatigue life prediction method of considering crack closure more exactly predicts fatigue life than conventional one. conventional one.e.

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A Fatigue Life Prediction by Growth Characteristics of a Small Surface Crack (작은 표면균열의 성장특성에 의한 수명예측)

  • Suh, Chang-Min;Lim, Chang-Soon;Gang, Yong-Gu
    • Journal of Ocean Engineering and Technology
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    • v.3 no.2
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    • pp.108-117
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    • 1989
  • This paper deals with a fatigue life prediction of a surface crack based on the experimentally obtained relationship between surface crack length ratio $a/a_{f}$ and cycle ratio $N/N_{f}$ using micro computer. Firstly $a/a_{f}$-$N/N_{f}$ curves obtained from experimental tests, were assumed as three curves UC(the upper limit curve), LC(the lower limit curve) and MC(the middle curve), and these were utilized to predict the fatigue life. Comparing the calculated values which represent the characteristics of crack growth behaviors from the three assumed curves with the experimental ones, it has been found that in the stable crack growth region, they coincide reasonably well each other. And the differences between the fatigue lives obtained from the assumed curves and the experimental fatigue life did not exceed 20%. Using the characteristics of $a/a_{f}$-$N/N_{f}$ curves, it is possible to predict the da/dN-Kmax curves and the S-$N_{f}$ curves.

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A Study on Fatigue Damage Modeling Using Neural Networks

  • Lee Dong-Woo;Hong Soon-Hyeok;Cho Seok-Swoo;Joo Won-Sik
    • Journal of Mechanical Science and Technology
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    • v.19 no.7
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    • pp.1393-1404
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    • 2005
  • Fatigue crack growth and life have been estimated based on established empirical equations. In this paper, an alternative method using artificial neural network (ANN) -based model developed to predict fatigue damages simultaneously. To learn and generalize the ANN, fatigue crack growth rate and life data were built up using in-plane bending fatigue test results. Single fracture mechanical parameter or nondestructive parameter can't predict fatigue damage accurately but multiple fracture mechanical parameters or nondestructive parameters can. Existing fatigue damage modeling used this merit but limited real-time damage monitoring. Therefore, this study shows fatigue damage model using backpropagation neural networks on the basis of X -ray half breadth ratio B / $B_o$, fractal dimension $D_f$ and fracture mechanical parameters can estimate fatigue crack growth rate da/ dN and cycle ratio N / $N_f$ at the same time within engineering limit error ($5\%$).