• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.589-597
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• 2010

Steel structures have a higher probability of being damaged by fatigue than by other causes of deterioration. As such, their maintenance to prevent fatigue damage is essential to sustain their safety and performance during their service period. In their maintenance, the current state of their fatigue cracks must be assessed to determine appropriate reinforcement methods and the suitable time intervals of periodic inspections when fatigue cracks are detected. Determining the crack growth rate is a successful method of predicting fractures, but it requires technical knowledge on fracture mechanics and experience in numerical methods and software for finite element analysis. In this study, a fatigue crack growth test on through-thickness cracked steel plates was conducted to assess the crack growth rate without superior technical knowledge and experience. The relationship between the Crack Opening Displacement (COD) and the crack growth rate was found in relatively long fatigue cracks.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.2
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• pp.174-180
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• 2004

If Fiber Reinforced Metal Laminates(FRMLs) were delaminated, the decrease of stiffness and fiber bridging effect would result in the sudden aggravation of fatigue characteristics. It was reported that the delamination of FRMLs resulted from the crack of metal layers and that it depended on the crack growth. While cracks were made in FRMLs containing a saw-cuts under fatigue loading, cracks could be produced or not in FRMLs with circular holes under the same condition. When the FRMLs with the circular holes produce not the crack but the delamination, it is not possible to analyze it by the conventional fracture parameters expressed as the function of the crack. And so, this research suggests a new analytical model of the delamination to make the comparison of the delamination behavior possible whenever the cracks occur or not. Therefore, a new analytical model called Pseudo Crack Model(PCM) was suggested to compare the delaminations whether cracks were made or not. The relationship between the crack energy consumption rate( $E_{crack}$) and the delamination energy consumption rate( $E_{del}$) was discussed and it was also known that the effect of $E_{del}$ was larger than that of $E_{crack}$.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.635-638
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• 1999

The crack of concrete is one of the most important factors to evaluate the safety of the structures. The more important point for the safety-evaluation of the concrete structures is to check the crack development, the conventional window paper (Chang Ho Ji) have been used as a simple method in the past, and nowadays the strain gauge is used for more correct way to check the development of the concrete crack quantitatively. However the window-paper method is too simple and not so scientific, and the strain-gauge method is rather complicated for people in general. This Easy-Check Sensor provides the simple usage for the various concrete structures, but also the more correct results to evaluate the development of the concrete crack.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.321-329
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• 1998

To ensure the structural integrity of the autofrettaged thick-walled cylinder subjected to cyclic internal pressure loading, the fatigue crack propagation life of the cylinder was evaluated. Stress intensity factors of the external cracked cylinder due to internal pressure and autofrettage loadings were calculated using the finite element method. The fatigue crack propagation lives of the cylinder based on the fracture mechanics concepts were predicted and compared to the experimental fatigue lives evaluated from the C-shaped simulation specimens. There were good correlations between the predicted and experimental fatigue lives within a factor of 3 for the single and double grooved C-shaped simulation specimens. Predicted fatigue crack propagation lives of the double grooved cylinders were about 1.5-5 times longer than those of the single grooved cylinders depending on the levels of autofrettage.

• 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.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.11
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• pp.75-82
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• 2002

Welding is used not only for the shipbuilding, but also for the repairing of ships. While repairing of ships, it is inevitable to weld new materials with degraded materials. In this case, it is predicted that the strength of both the sections is not identical each other. In this study, the respective welded joints in terms of mechanical properties such as microstructure, mechanical strength and fatigue crack propagation, with the component obtained from the barge used for a long-term period, were analyzed. It was found that the material degradation had a significant effect on the welded joints. The fatigue crack propagation in welded sections showed a big difference. The rate of fatigue crack growth of degraded material for both heat affected zone and parent metal was faster than that of new material. By contrast, the result from identical materials showed that the rate of fatigue crack growth of the heat-affected zone was slower than that of parent metal.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.954-957
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• 2004

Tire belt durability is characterized by the initiation of a crack at the belt edge region, and the propagation of the crack until the ply is separated. Experimental methods have been used to analysis of the belt durability in the cord-reinforced rubber composite tires, but it takes much cost and time to make experiments. In this paper, a finite element method to analyze the fatigue life of a crack at the belt edge of tires is presented. The fatigue life is analyzed by using a three-dimensional Finite Element Modeling. This method includes a global-local finite element analysis to provide the detail necessary to model explicitly an internal crack and use of the J-integral for energy release rate evaluation.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.617-620
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• 2006

This study is related to comprehending performance for watertightness and crack control of concrete added with crack reducing agent concerning to high strength concrete mixs. It was confirmed that watertightness of concrete added with agent could be improved by evaluation absorption ratio, permeability ratio and pore size distribution of hardened concrete. As well resistance to crack resulted from shrinkage was transferred to better state by the addition of agent.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.334-338
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• 1995

In recent years, the prediction of the deterioration rate of concrete structures has become major research interest. However, there are still many uncertain factors in the deterioration process and the relation between deterioration and durability of structures. This is mainly due to various uncertainties involved in the construction process and the environmental conditions which affect the rate of deterioration of concrete structures. In this study a limit state model in terms of random crack width due to applied dead and live loads is proposed for the assessment of crack damage of reinforced concrete structures. The AFOSM reliability method is used for the reliability evaluation of the crack durability of concrete bridges. The proposed model for crack durability of concrete bridges is applied to the Seoul interior circuit elevated expressway. The sensitivity analyses are performed for the proposed model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.6
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• pp.1448-1454
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• 1994

Data which gathered and used in the field of fatigue and fracture mechanics have a lot of uncertainties. In this case, those uncertainties will make scatter band in evaluation of fatigue life and fracture toughness. Thus, the probabilistic analysis of these data will be needed. For determining the fatigue life in mixed mode, using crack direction law and fatigue crack growth law, the problem is studied as a constrained life minimization. Stress intensity factor(SIF) is computed by approximate solution table(Ewalds/Wanhill 1984) and 0th order PFEM. The variance of fatigue life and SIF are computed by differentiation of tabulated approximate solution and 1st order PFEM. And these are used for criterion of design values, principal parameter determination and modelling. The problem of center cracked plate is solved for checking the PFEM model which is influenced by various parameters like as initial crack length, final crack length, two fatigue parameters in Paris Equation and applied stress.