• Journal of Ocean Engineering and Technology
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• v.10 no.1
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• pp.65-74
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• 1996

Up to now, the existing crack growth modelling has used a mathematical approximation but an assumed function have a great influence on this method. Especially, crack growth behavior that shows very strong nonlinearity needed complicated function which has difficulty in setting parameter of it. The main characteristics of neural network modelling to engineering field are simple calculations and absence of assumed function. In this paper, after discussing learning and generalization of neural networks, we performed crack growth modelling on the basis of above learning algorithms. J'-da/dt relation predicted by neural networks shows that test condition with unlearned data is simulated well within estimated mean error(5%).

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.710-715
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• 2001

Rubber is used extensively in many industries because of its large reversible elastic deformation, excellent damping and energy absorption characteristics, and wide availability. It becomes very important to predict the fatigue life of rubber components. But a great deal of time and cost are necessary for the fatigue test of rubber components. In this study the fatigue life of rubber components is evaluated by performing the fatigue test of a specimen and FE analysis. The fatigue life of Jang-gu type specimen which is considered as a simple rubber component is predicted and compared with experimental results. Its material is natural rubber of which hardness is 60 and used for the engine mount of commercial vehicles.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.52-57
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• 1997

국제 열 핵융합로 (International Thermonuclear Experimental Reactor) 의 중앙 솔레노이드(solenoid) 초전도 전자석의 피복관 (conduit) 으로서 가장 유력한 후보 재료인 니켈-철 기저 초합금에 대한 개선된 파괴역학적 거동 예측 모형을 개발하기 위하여 피로균열 성장과 파괴 인성 치의 측정이 사용되었다. 유한 요소법을 사용하는 상용 구조해석 코드인 ANSYS 제 5.2판에 의해 초전도 전자석 피복관 재료에 대한 탄소성 파괴역학적 거동을 살펴보았다. 정확한 파괴 기준을 개발하기 위하여 삼차원 J 적분 인자에 의한 결과를 사용하였다. 얇은 피복관재의 경우에 절대온도 4도에서의 적합한 파괴 인성치는 실제 단면효과를 고려한 표면균열 인장시험 결과를 토대로 J 적분으로 도출한 150 MPaㆍm$^{1}$2/ 로 제시되었다.

• Journal of the Korea Institute of Military Science and Technology
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• v.1 no.1
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• pp.154-165
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• 1998

In this paper, the mongrel singular element with 6 node triangle and 8 node quadrilateral element with J-integral are developed and applied to the various plane crack problems for the isotropic material. The convergence nature is excellent for various crack size with even coarse mesh using the direct method. But the results of the mongrel element with J-integral are worse than the former's ones. Fracture tests were conducted on precracked CT specimens. Results show that, for 7075-T6 aluminum wing spar materials, the fracture toughness is 31.06 ksi.inch $\frac{1}{2}$ in the L-T direction.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.112-122
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• 1995

In this work, prediction of fatigue life and fatigue crack growth are studied. 4th order polynominal function is presented to describe the crack growth behaviors from artifical pit of SM45C steel. Crack growth curves obtained from 4th order polyminal growth equations are in good agreement with experimental data The crack growth behaviors at arbitrary stress levels and investigated by the concept of elastic-plastic fracture mechanics using ${\Delta}J$. Fatigue life prediction are carried out by numerical integral method. Prediction lives obtained by proposed method in this study, is in good agreement with the experimental ones. Life prediction results calculated by using of ${\Delta}J$ better than those of ${\Delta}K$.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.333-337
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• 2008

This study investigates crack propagation behavior of Sn-3.0Ag-0.5Cu solder under pull-push loading conditions. Fatigue Crack Growth (FCG) tests were conducted on Center Cracked Plate (CCP) specimens in fast-fast (pp) strain waveform. The fast-slow (pc), slow-fast (cp) and slow-slow (cc) strain waveforms were also used to study the effect of strain rates. The crack propagation rates for the four strain waveforms were correlated with J-integral range and a scatter band of factor 4 was found. The crack growth rates for the pc waveform was highest, followed by cp, cc and then pp waveforms.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.9
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• pp.2843-2853
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• 1996

The multi-point procedure is developed to predict the shape change of a semi-elliptical surface crack during stable fatigue crack growth. 3-D stress intensity factors along a crack front are calculated using the simplified 3-D J-intergral. Crack growth rate coefficient in the Paris law is assumed to be constant along the crack growth. Crack growth rate is set to be the distance between the two parallel tangent lines on the two semi-elliptic crack fronts before and after crack growth.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.2752-2759
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• 1996

This paper presents crack growth analysis approach on the basis of neural networks, a branch of cognitive science to high temperature low cycle fatigue that shows strong nonlinearity in material behavior. As the number of data patterns on crack growth increase, pattern classification occurs well and two point representation scheme with gradient of crack growth curve simulates crack growth rate better than one point representation scheme. Optimal number of learning data exists and excessive number of learning data increases estimated mean error with remarkable learning time J-da/dt relation predicted by neural networks shows that test condition with unlearned data is simulated well within estimated mean error(5%).

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.5
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• pp.539-547
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• 1985

The low-cycle fatigue crack growth behavior of SUS 304 Stainless steel was investigated at 650.deg. C by the nonlinear fracture mechanics. Crack Propagation can be separated in to cycle-dependent and time-dependent, the former is correlated with .DELTA. $J_{f}$ , J-intergral range and the latter is correlated with J', modified J integral. Transition from cycle-dependent to time-dependent crack growth was successfully predicted using the .betha. hypothesis, which was proposed by the authors on the basis of an analysis on the interaction of elastic and creep strain. To investigate the reliability of .betha.-hypothesis, experimenting by the change of stress-level, stress rate and frequency, following conclusions were obtained. (1) High temperature fatigue crack propagation was separated into cycle-dependent and time-dependent. (2) Transition of crack propagation was predicted by .DELTA. $J_{c}$/.DELTA.$_{f}$ or .betha. (3) Lower limit in cycle-dependent crack propagation was obtained..

• Journal of Ocean Engineering and Technology
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• v.6 no.1
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• pp.122-130
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• 1992

The effect of loading waveform on elevated temperature low-cycle fatigue crack growth behavior in a SUS 304 stainless steel have been investigated under symmetrical trangular (fast-fast), trapezoidal and asymmetrical(fast-slow, slow-fast) waveforms at 650.deg. C. It was found that the crack growth rate in fast-slow loading waveform appeared to be higher a little and the crack growth rate in slow-fast loading waveform much higer than that in fast-fast loading waveform, and difference in crack growth rate between fast-show and slow-fast waveforms nearly didn't appear in the region of da/dN>10/sup -2/ The crack growth rate in the trapezoidal loading waveform with t/sub h/=500sec appeared to be faster than that in slow(500sec)-fast(1sec). In addition, parameter modified J-integral could be considered as useful parameter for fatigue crack growth rate in all waveforms. The result obtained are as follow. da/dN=4.91*10/sup -3/ (.DELTA. J/sub c/)/sup 0.565/.