• Structural Engineering and Mechanics
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• 제75권4호
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• pp.455-464
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• 2020

Reinforcement corrosion is one of the major problems in the durability of reinforced concrete structures exposed to aggressive environments. Deterioration caused by reinforcement corrosion reduces the durability and the safety margin of concrete structures, causing excessive costs in managing these structures safely. This paper aims to investigate the effects of reinforcement corrosion on the load bearing capacity deterioration of the corroded reinforced concrete structures. A new analytical method is proposed to predict the crack growth of cover concrete and evaluate the residual strength of concrete structures with corroded reinforcement failing in bond. The structural performance indicators, such as concrete crack growth and flexural strength deterioration rate, are assumed to be a stochastic process for lifetime distribution modelling of structural performance deterioration over time during the life cycle. The Weibull life evolution model is employed for analysing lifetime reliability and estimating remaining useful life of the corroded concrete structures. The results for the worked example show that the proposed approach can provide a reliable method for lifetime performance assessment of the corroded reinforced concrete structures.

• 한국세라믹학회지
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• 제28권9호
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• pp.712-720
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• 1991

The effect of cyclic compressive stress on fracture responses of Al2O3 was investigated under uniaxial stress cycling. Experimental data were obtained for Al2O3 tension specimens under uniaxial tension-unloading and tension-compression cyclic loading conditions. To investigate the effect of compressive stress on the crack growth, theoretical results from the crack growth rate were compared with measured stress vs. failure relations. At low stress level in tension-compression cycling, residual tensile strains were also observed about failure time.

• 한국해양공학회지
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• 제7권2호
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• pp.131-140
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• 1993

To study the corrosion fatigue begavior of T.M.C.P. steel, the rotary bending fatigue test with the change of concentration of NaCl solution was carried out. Fatigue life in the corrosion environment is decreased markedly in comparision with that in the air. Fatigue limit in the air was about 225 MPa. In case of 3.5% NaCl solution fatigue life could be expressed as .sigma./sub f/=10,392 * (N/sub f/)/sup -o.2923 . According to the paris's rule, crack growth rates could be expressed as da/dN=2.62.*10/sup -7/ .DELTA. K/sup 1.09/(3.5% NaCl solution), da/dN=1.95 *10/sup -7 .DELTA. K/sup 1.05/(1% NaCl solution), da/dN=2.62 * 10/sup -7/.DELTA./sup 0.72/(0.01% NaCl solution) with da/dN expressed in mm/cycle and .DELTA.K in MPa.GAMMA.m. The crack growth rate in the corrosion environment was highest under 3.5% NaCl solution.

• 한국해양공학회지
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• 제9권1호
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• pp.142-151
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• 1995

A simulation program concerned with multi-surface fatigue cracks which initiated at the semi-circular surface notches has been developed to predict their growth and coalescence behaviors at the elevated temperature. Three kinds of coalescence models such as SPC(surface point connection), ASME and BSI(British Standards Institution) conditions were applied, and the results of the simulation were compared with those of the experiment. This simulation is able to enhance the reliance and integrity of structures especially under the elevated temperature which have lots of difficulties in experiments and applications. This shows that the simulation result has utility for fatigue life prediction. Even though all the specimens were the same shape, the error rate was increased in accordance with the applied stress to the specimen. Among the material constants C and m in the narrow band, the results applied upper values of the band to the simulation has shown quite small error compared with the experiment results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.604-609
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• 2003

Flaw geometries, applied stress, and material properties are major input variables for the fracture mechanics analysis. Probabilistic approach can be applied for the consideration of uncertainties within these input variables. But probabilistic analysis requires many assumptions due to the lack of initial flaw distributions data. In this study correlations are examined between initial flaw distributions and in-service flaw distributions on structures under cyclic load. For the analysis, LEFM theories and Monte Carlo simulation are applied. Result shows that in-service flaw distributions are determined by initial flaw distributions rather than fatigue crack growth rate. So initial flaw distribution can be derived from in-service flaw distributions.

• Earthquakes and Structures
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• 제11권5호
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• pp.861-871
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• 2016

The Groningen gas field shows exponential growth in earthquake event counts around a magnitude M1 with a doubling time of 6-9 years since 2001. This behavior is identified with dimensionless curvature in land subsidence, which has been evolving at a constant rate over the last few decades essentially uncorrelated to gas production. We demonstrate our mechanism by a tabletop crack formation experiment. The observed skewed distribution of event magnitudes is matched by that of maxima of event clusters with a normal distribution. It predicts about one event < M5 per day in 2025, pointing to increasing stress to human living conditions.

• 대한기계학회논문집A
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• 제30권12호
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• pp.1573-1580
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• 2006

In this study, fatigue tests were carried out under push-pull loading condition using spheroidal graphite cast iron in order to clarify the internal fatigue fracture mechanism in an extremely low cycle fatigue regime. It is found that a successive observation of internal fatigue damage it is found that the fracture processes go through three stages, that is, the generation, growth and coalescence of microvoids originated from debonding of graphite-matrix interface. It is also found that the crack which is initiated from the void propagates by coalescence of neighboring cracks and the fatigue crack growth rate can be expressed in form of the Manson-Coffin rule type. In this paper, quantitative analyses of fatigue properties for realization of simulation about fatigue life evaluation are also presented.

• 한국세라믹학회지
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• 제36권7호
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• pp.718-724
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• 1999

Densification and grain growth behavior of bimodal size distributed alumina powder mixtures were investigated as a function of amount of coarse alumina powder. The specimens which contained coarse alumina powder for 60to 80wt% showed the highest green density. The amount of shrinkage of sintered specimen lineraly decreased with the increase of coarse alumina powder up to the content that showed the highest green density and then further addition of coarse alumina powder led to drastic decrease of shrinkage of specimen. Especially crack-like void were concurrently revealed in the sintered body with addition of coarse alumina powder above 60wt% When the sintering temperature increased up to 1650$^{\circ}C$ the amount of shrinkage of specimen linearly decreased and the grain growth were also retarded with increase of coarse lauminia powder.

• 한국세라믹학회지
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• 제35권8호
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• pp.850-856
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• 1998

The dynaamic fatigue behavior of alumina ceramics was observed at room temperature using four-point bending method. Dynamic fatigue fracture strength was observed as function of down speed and notch length. The crack growth exponent of the specimens was calculated from the fracture strength and lifetime in dynamic fatigue test. After loading the stresses in the range of 0% to 105% compared with the average in-ert strength the value of residual fracture strength was measured for unnotched and 0.5mm notched speci-mens at the 0.001 and 0.0005 mm/min down speed respectively. After the 95% stress of the average inert strength was applied repeatedly the value of rsidual fracture strength was measured for 0.5mm notched specimens at the 0.001 and 0.0005 mm/min down speed respectively. The material constant A was found to be almost the same and not to depend on the loading mode or the down speed for unnotched and notched specimen. The value of fracture strength with time calculated from the constants n and A was in good agreement with the measured value.

• Journal of Welding and Joining
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• 제13권2호
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• pp.96-105
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• 1995

본 연구에서는 종래의 미소피로균열 성장속도 해석방법에 대한 수정안을 제시하고 수정 후의 방 법에 의해서 계산한 값들과 S4SC 탄소강에 대한 Nisitani와 Goto의 실험결과를 비교하여 계산한 값과 실험데이터 사이에 양호한 일치가 있음을 보였다. 이미 제시된 피로균열성장속도 식에는 하한계수준과 피로한도를 연관시키는 재료상수와 탄소성 거동에 대한 수정 및 균열닫힘효과를 나타내는 방법이 포함되어 있다. 본 연구에서 행한 수정중의 하나는 기하학적인 상수대신에 퍼만(Forman)의 탄성응력 강도계수 범위식을 이용하는 것이고, 다른 하나는 균열이 성장함에 따라 편심형단면으로 되면서 모멘트에 기인해 발생되는 굽힘효과를 고려하는 것이다. 이 방 법을 수명예측에 사용하면 용접구조물은 물론 기계구조물의 보다 정확한 수명예측이 가능할 것 이다.