• 제목/요약/키워드: growth life prediction

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Surface Crack Behavior and the Fatigue Life Prediction of Notched Specimens (표면균열의 거동과 피로수명예측에 관한 연구)

  • 서창민;이정주;정은화;박희범
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.5
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    • pp.1097-1103
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    • 1988
  • This paper deals with surface crack behavior and the fatigue life prediction of notched specimens using the relation between surface crack length, a, and the cycle ratio, $N/N_{f}$. From the $a-N\;/\;N_{f}$ curves, UC(the upper limit curve), LC(the lower limit curve) and MC(the middle limit curve) were assumed and utilized to predict the fatigue life and crack growth rate. The data computed from the three assumed curves were compared with the experimental data. It has been found that in the stable crack growth region ($N/N_{f}=0.3-0.8$) fatigue life can be predicted within 20% errors. Using the characteristics of $a-N\;/\;N_{f}$ curve, it is possible to predict the $da/dN-K_{max}$ curve, the $da/dN-{\Delta}K_{{\varepsilon}_t}$ curve, and the $S-N_{f}$ curve.

Life Prediction and Fatigue Strength Evaluation for Surface Corrosion Materials (인공부식재의 피로강도평가와 통계학적 수명예측에 관한 연구)

  • 권재도;진영준;장순식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.8
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    • pp.1503-1512
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    • 1992
  • The strength evaluation and life prediction on the corrosion part of structure is one of the most important subjects, as a viewpoint of reducing economic loss by regular inspection, maintenance, repair and replace. For this purpose, it has been difficult to obtain the available data on growth of pit depth or growth rate of each pit which depends on time. In this paper, the life prediction and strength evaluation method was suggested for the structure with irregular stress concentration part by surface corrosion. The statistical distribution pattern of corrosion depth and the degree of fatigue strength decline were confirmed according to corrosion period by artificial corrosion of SS41 steel. The life prediction and the fatigue strength evaluation of materials with consideration of the corrosion period on the extreme value statistic analysis by the data of maximum depth of corrosion and on random variable was studied.

Growth Characteristics and Life Prediction of Single Surface Fatigue Crack with the Variation of crack Configuration Ratios (균열 형상비 변화에 따른 단일표면파로균열의 성장특성과 수명예측)

  • 서창민;서덕영;정정수
    • Journal of Ocean Engineering and Technology
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    • v.7 no.2
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    • pp.173-181
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    • 1993
  • This work has been investigated the ralationship between single surface crack length and crack depth have influence on the fatigue life. The simulation based on experimental results of 2.25 Cr-1Mo steel at various crack configuration ratios has enabled successful prediction of fatigue life at room temperature. The effect of crack depth should be considered for predicting fatigue crack growth rates as well as that of surface crack length. It is also shwn that the crack growth mechanisms are in good agreement with expreimental data according to the interaction of crack length and crack depth.

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Prediction of Thermal Fatigue Life of Alumina ceramics (알루미나 세라믹스의 열피로 수명 예측)

  • 정우찬;한봉석;이홍림
    • Journal of the Korean Ceramic Society
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    • v.36 no.8
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    • pp.871-875
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    • 1999
  • Theoretical equation to calculate thermal fatigue life was derived in which slow crack growth theory was adopted. The equation is function of crack growth exponent n. Cyclic thermal fatigue tests were performed at temperature difference of 175, 187 and 200$^{\circ}C$ respectively. At each temperature difference critical thermal fatigue life cycles of the alumina ceramics were 180,37 and 7 cycles. And theoretical thermal fatigue life cycles were calculated as 172, 35 and 7 cycles at the same temperature difference conditions. Therefore thermal fatigue behavior of alumina ceramics can be represented by derived equation. Also theoretical single cycle critical thermal shock temperature difference can be calculated by this equation and the result was consistent with the experimental result well.

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Strength Evaluation and Life Prediction of the Multistage Degraded Materials (다단계 모의 열화재의 재료강도 평가와 수명예측)

  • 권재도;진영준;장순식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.9
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    • pp.2271-2279
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    • 1993
  • In the case of life prediction on the structures and machines after long service, it is natural to consider a degradation problems. Most of degradation data form practical structures are isolated data obtained at the time of periodical inspection or repair. From such data, it may be difficult to obtain the degradation curve available and necessary for life prediction. In this paper, for the purpose of obtaining a degradation curves, developed the simulate degradation method and fatigue test and Charpy impact test were conducted on the degraded, simulate degraded and recovered materials. Fatigue life prediction were conducted by using the relationship between fracture transition temperature (DBTT : vTrs) obtained from the Charpy impact test through the degradation process and fatigue crack growth constants of m and C obtained from the fatigue test.

FATIGUE LIFE PREDICTION OF RUBBER MATERIALS USING TEARING ENERGY

  • Kim, H.;Kim, H.Y.
    • International Journal of Automotive Technology
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    • v.7 no.6
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    • pp.741-747
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    • 2006
  • It has been almost impossible to predict the fatigue life in the field of rubber materials by numerical methods. One of the reasons is that there are no obvious fracture criteria and excessively various ways of mixing processes. Tearing energy is considered as a fracture criterion which can be applied to rubber compounds regardless of different types of fillers, relative to other fracture factors. Fatigue life of rubber materials can be approximately predicted based on the assumption that the latent defect caused by contaminants or voids in the matrix, imperfectly dispersed compounding ingredients, mold lubricants and surface flaws always exists. Numerical expression for the prediction of fatigue life was derived from the rate of rough cut growth region and the formulated tearing energy equation. Endurance test data for dumbbell specimens were compared with the predicted fatigue life for verification. Also, fatigue life of industrial rubber components was predicted.

Method using XFEM and SVR to predict the fatigue life of plate-like structures

  • Jiang, Zhansi;Xiang, Jiawei
    • Structural Engineering and Mechanics
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    • v.73 no.4
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    • pp.455-462
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    • 2020
  • The hybrid method using the extended finite element method (XFEM) and the forward Euler approach is widely employed to predict the fatigue life of plate structures. Due to the accuracy of the forward Euler approach is determined by a small step size, the performance of fatigue life prediction of the hybrid method is not agreeable. Instead the forward Euler approach, a prediction method using midpoint method and support vector regression (SVR) is presented to evaluate the stress intensity factors (SIFs) and the fatigue life. Firstly, the XFEM is employed to calculate the SIFs with given crack sizes. Then use the history of SIFs as a function of either number of fatigue life cycles or crack sizes within the current cycle to build a prediction model. Finally, according to the prediction model predict the SIFs at different crack sizes or different cycles. Three numerical cases composed by a homogeneous plate with edge crack, a composite plate with edge crack and center crack are introduced to verify the performance of the proposed method. The results show that the proposed method enables large step sizes without sacrificing accuracy. The method is expected to predict the fatigue life of complex structures.

Fatigue Crack Growth, Coalescence Behavior and Its Simulation on Multi-Surface Cracks (복수 표면피로균열의 성장합체거동과 시뮬레이션에 관한 연구)

  • 서창민;황남성;박명규
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.3
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    • pp.716-728
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    • 1994
  • In this paper, fatigue tests were carried out to study the behavior of growth and coalescence of multi-surface cracks which were initiated at the semi-circular surface notches, and a simulation program was developed to predict their growth and coalescence behavior. By comparing the experimental result with those of the simulation based on SPC(surface point connection), ASME and BSI(British Standards Institution) conditions, we tried to enhance the reliance and integrity of structures. This shows that the simulation result has utility for fatigue life prediction.

A Fracture Mechanic Study on Life Prediction of Surface Cracks at Elevated Temperature (고온화 표면균열의 수명예측에 관한 파괴역학적 연구)

  • Chang-Min,Suh;Young-Ho,Kim;Bung-Ho,Son;Sang-Yeub,Oh
    • Bulletin of the Society of Naval Architects of Korea
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    • v.27 no.3
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    • pp.100-106
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    • 1990
  • Microcracking of type 304 stainless steel at $593^{\circ}C(1,100^{\circ}F)$ has been studied, in particular, initiation, growth, and coalescence of fatigue and creep microcracks on smooth specimens and small notch specimens via surface replicas and photomicrographs. Quantitative information, such as, initiation period, growth, and coalescence behavior, statistical distributions of crack length, density of cracks, distribution patterns and crack growth properties, were obtained. From this study, the fracture process, fatigue life, and creep life prediction characterized by the growth of surface microcracks have been analysed by a new approach unifying the conventional approaches based on the final fracture of materials with the fracture mechanics approach. Knowledge of these parameters is critical for the application of fracture mechanics to fatigue and creep life assessment, and the damage evaluation of structures at elevated temperature.

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Prediction and Application of Fatigue Life on Characteristics of Fatigue Crack Propagation of Thin Sheet Alloy (박판합금재료의 피로균열 전파특성에 대한 피로수명예측과 활용)

  • Lee, Ouk-Sub;Kim, Seung-Gwon
    • Journal of the Korean Society for Precision Engineering
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    • v.24 no.2 s.191
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    • pp.103-109
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    • 2007
  • In fatigue life prediction, it is important that fatigue life is affected by crack closure phenomenon in thin sheet Al alloy. In this research, we attempt to (1)analyze the characteristics of fatigue crack propagation in constant loading condition for thin sheet Al 2024-T3 alloy which is generally used in transportation structures, (2)identify the crack closure phenomenon in thin sheet comparing experimental results of thin and thick sheet specimen under same fatigue loading condition. In using the fatigue related material constants from these fatigue crack propagation analysis, we attempt to (3)operate the fatigue life estimating process with considering crack closure phenomenon and (4)analyze the experimental and prediction results of fatigue life in thin sheet Al alloy.