• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.4
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• pp.352-361
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• 2004

One important element of the Leak-Before-Break analysis of nuclear piping is how to determine relevant fracture toughness (or the J-resistance curve) for nonlinear fracture mechanics analysis. The practice to use fracture toughness from a standard C(T) specimen is known to often give conservative estimates of toughness. To improve the accuracy, this paper proposes a new method to determine fracture toughness using a nonstandard testing specimen, curved wide-plate in tension. To show validity of the proposed curved wide-plate test, the J-resistance curve from the full-scale pipe test is compared with that from the curved wide-plate test and that from the C(T) specimen. It is shown that the J-resistance curve form the curved wide-plate tension test is similar to, but that from the C(T) specimen is lower than, the J-resistance curve from the full-scale pipe test. Further validation is performed by investigating crack-tip constraint conditions via detailed 3-D FE analyses, which shows that the crack-tip constraint condition in the curved wide-plate tension specimen is indeed similar to that in the full-scale pipe under bending.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2390-2398
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• 2002

For integrity analysis of nuclear reactor pressure vessel, including the Pressurized thermal shock analysis, the fast and accurate calculation of the stress intensity factor at the crack tip is needed. For this, a simple approximation scheme is developed and the resulting stress intensity factors for axial semi-elliptical cracks in cylindrical vessel under various loading conditions are compared with those of the finite element method and other approximation methods, such as Raju-Newman's equation and ASME Sec. Xl approach. For these, three-dimensional finite-element analyses are performed to obtain the stress intensity factors for various surface cracks with t/R = 0.1. The approximation methods, incorporated in VINTIN (Vessel INTegrity analysis-INner flaws), utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite clement analysis for internal pressure, cooldown, and pressurized thermal shock loading conditions. The approximation solutions are within $\pm$2.5% of the those of FEA using symmetric model of one-forth of a vessel under pressure loading, and 1-3% higher under pressurized thermal shock condition. The analysis results confirm that the VINTIN method provides sufficiently accurate stress intensity factor values for axial semi-elliptical flaws on the surface of the reactor pressure vessel.

• Journal of the Korea Concrete Institute
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• v.26 no.1
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• pp.57-62
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• 2014

In this study, the vertical pipe cooling method was developed to propose the pipe cooling method suited for the vertically long mass concrete structures. FEM (finite element method) analysis was carried out to investigate the validity of the vertical pipe cooling method, and the temperature, the behavior of tensile stress of concrete and the crack index were investigated. In result, it was confirmed that the vertical pipe cooling method was effective in the thermal cracking control of mass concrete member.

• Journal of the Korea Institute of Building Construction
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• v.23 no.2
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• pp.123-131
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• 2023

In this study, the analysis of concrete cracks was conducted with a total of three variables: coating thickness, oxygen diffusion rate, and reinforced diameter of reinforced concrete structures. Cracks occurred after about 3, 4, and 6 years at the coating thickness of 30, 40, and 50mm when the coating thickness was used as a variable, and cracks occurred after about 4, 5, and 10 years at oxygen diffusivity of 2e-9, 2e-11, and 2e-12(m²/s) when the oxygen diffusion rate was used as a variable. In the case of reinforcing bar diameters, cracks occurred after about 4, 3, and 2 years on the reinforcing bar diameters of D10, D19, and D25.

• Transactions of Materials Processing
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• v.10 no.7
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• pp.525-533
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• 2001

PET bottles are main]y manufactured by the stretch blow-molding process. In order to improve the thickness distribution to avoid crack generation at bottom region of one-piece PET bottle, process analysis of stretch blow-molding using a finite element method has been carried out. Finite element analysis has been carried out using ABAQUS/Standard. CREEP user subroutine provided in ABAQUS has been used to model PET behavior that is rate sensitive. Among the process parameters, the effect of plunger movement to thickness distribution of bottle has been considered by axisymmetric analysis. A modified process of plunger movement, which yields more uniform thickness distribution, has been proposed. 3D FE analysis has been done to confirm the validity of the proposed process.

• Structural Engineering and Mechanics
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• v.81 no.5
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• pp.565-574
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• 2022

The infrastructures such as offshore, bridges, power plant, oil and gas piping and aircraft operate in a harsh environment during their service life. Structural integrity of engineering components used in these industries is paramount for the reliability and economics of operation. Two regression models based on the concept of Gaussian process regression (GPR) and Minimax probability machine regression (MPMR) were developed to predict stress intensity factor range (𝚫K). Both GPR and MPMR are in the frame work of probability distribution. Models were developed by using the fatigue crack growth data in MATLAB by appropriately modifying the tools. Fatigue crack growth experiments were carried out on Eccentrically-loaded Single Edge notch Tension (ESE(T)) specimens made of API 5L X65 Grade steel in inert and corrosive environments (2.0% and 3.5% NaCl). The experiments were carried out under constant amplitude cyclic loading with a stress ratio of 0.1 and 5.0 Hz frequency (inert environment), 0.5 Hz frequency (corrosive environment). Crack growth rate (da/dN) and stress intensity factor range (𝚫K) values were evaluated at incremental values of loading cycle and crack length. About 70 to 75% of the data has been used for training and the remaining for validation of the models. It is observed that the predicted SIF range is in good agreement with the corresponding experimental observations. Further, the performance of the models was assessed with several statistical parameters, namely, Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Efficiency (E), Root Mean Square Error to Observation's Standard Deviation Ratio (RSR), Normalized Mean Bias Error (NMBE), Performance Index (ρ) and Variance Account Factor (VAF).

• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.287-297
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• 2014

Heat of hydration of mass concrete is one of the most important factors that significantly affect structural quality and construction period. Therefore, appropriate methods to control heat of hydration are essential technologies for mass concrete construction. In this study, probability of thermal cracking was checked by thermal analysis prior to the construction of a turbine foundation in a domestic power plant. Subsequently, changes of concrete mix proportion and an effective curing method were proposed to control heat of hydration of mass concrete structures. Concrete manufactured by slag cement was proposed instead of concrete produced by ordinary Portland cement, and an automated curing method was proposed to improve the curing method using typical moist curing with blanket. The automated curing method maintains the temperature difference between center and surface of concrete below a setting value by temperature monitoring. Concrete with slag cement was used for actual construction. One of two identical turbine foundations was cured by an insulated curing method, and the other was cured by the automated curing method to compare the curing methods. And then, the effects of control of heat of hydration were evaluated based on temperature/strain monitoring and crack investigations.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.280-285
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• 2001

As an integral part of the probabilistic fracture mechanics analysis, stress intensity factor calculation scheme for semi-elliptical surface flaws in thin-walled cylinder has been introduced. The approximation solution utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite element analysis for cooldown boundary condition. The analysis results confirmed that the simplified methods provided sufficiently accurate stress intensity factor values for axial semi-elliptcal flaws on the surface of the reactor pressure vessel.

• Computers and Concrete
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• v.18 no.3
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• pp.421-439
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• 2016

Corrosion of embedded reinforcing bars is recognized as being the major cause of deterioration of reinforced concrete structures. With regard to maintenance strategies of concrete nuclear structures, the monitoring of cracking remains of primary importance. Recently, authors have developed a post-treatment technique to extract crack features from continuous computations. In this paper, such technique is applied to carry out a numerical analysis of an accelerated corrosion test. Obtained results allow highlighting specific propagation and failure mechanisms that characterize corrosion-induced cracking.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.955-960
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• 2004

In this study, three dimensional FE analysis of concrete slab track has been performed in order to develop the realistic design of precast concrete slab track. The precast slab track system including the precast concrete slab panel and the grout layer is modeled using the three dimensional solid element with crack softening effect. The input load is computed from the one dimensional beam element model constituting the rail and several discrete springs. To investigate the effect of the longitudinal connection of slab panels, two different systems-continuous and discrete systems - are modeled. The analytical results show that the stresses of both the slab panel and the grout layer are in the range of linear elastic, and, at the interface between two adjacent panels, the primary stresses of the grout layer of the discrete system are higher than those of the continuous system. However, The overall stress levels of the grout layer are very low relative to the strength of th grout.