• Journal of Ocean Engineering and Technology
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• v.14 no.1
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• pp.88-94
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• 2000

Recently various pressure vessels like an atomic reactor and plant facilities become more larger and are needed to bear in both very high temperature and pressure condition. And in making such a high pressure vessels the amount of annual usage of 2 $\frac {1}{4}$ Cr-1Mo steels which are predominant to resist high temperature high pressure and corrosive circumstances are increasing. But despite of this advantage of 2 $\frac {1}{4}$Cr-1Mo steel. when PWHT(post welding heat treatment) is carried out lots of reheating cracks are occur. In this reason it is strongly needed to study and examine the mechanical behavior of welded joints through welding to PWHT process. So in this study welded nozzle of pressure vessel where reheat cracks are frequently occur are selected for analysis the crack-occurrence mechanism.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.227-227
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• 2000

Pressure vessels usually consist of main body and pipes which are connected with the main body. And as joining method of such main body and pipes, welding is carried out. After welding, welding residual stresses inevitably occur around welded joints. As residual stresses act harmfully on fatigue strength, corrosion and buckling strength of structure, PWHT is carried out for the purpose of removing the residual stress. But, during PWHT process, 2 ¼Cr-1Mo steels are frequently apt to generate reheat crack. For this reason, it is strongly needed to analyze and examine the mechanical behavior of welded joints before and after PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks frequently occur are selected for examining the mechanism of crack-occurrence. (Received December 2, 1999)

• Journal of Welding and Joining
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• v.18 no.2
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• pp.100-104
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• 2000

Pressure vessels usually consist of main body and pipes which are connected with the main body. And as joining method of such main body and pipes, welding is carried out. After welding, welding residual stresses inevitably occur around welded joints. As residual stresses act harmfully on fatigue strength, corrosion and buckling strength of structure, PWHT is carried out for the purpose of removing the residual stress. But, during PWHT process, $2\frac{1}{4}Cr-1Mo$ steels are frequently apt to generate reheat crack. For this reason, it is strongly needed to analyze and examine the mechanical behavior of welded joints before and after PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks frequently occur are selected for examining the mechanism of crack-occurrence.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.171-178
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• 2004

Techniques and procedures are presented for measuring mechanical properties on thin-film Polysilicon. Narrow platinum lines are deposited 250 ${\mu}{\textrm}{m}$ apart on tensile specimens that are 3.5 ${\mu}{\textrm}{m}$ thick and 600 ${\mu}{\textrm}{m}$ wide. Load is applied by a piezo-actuator and by hanging weights. Strain is measured by an ISDC at temperatures up to 500 $^{\circ}C$. Measurements of the elastic modulus with jig modifications, loading speed and temperature change are presented first. And then, the preliminary data for the coefficient of thermal expansion and creep behavior are presented as a reference.

• Nuclear Engineering and Technology
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• v.55 no.7
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• pp.2454-2465
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• 2023

Film boiling may lead to burnout of the heating element. Even though burnout does not occur, the heating element is subject to deformation because it is not sufficiently strong to withstand external loads. In particular, the ballooning and rupture of a tube under film boiling are important phenomena in the field of nuclear reactor safety. If the tube-type cladding of nuclear fuel ruptures owing to high internal pressure and thermal load, radioactive materials inside the cladding are released to the coolant. Therefore, predicting the ballooning and rupture is important. This study presents numerical simulations to predict the ballooning behavior and rupture time of a horizontal tube at high internal pressure under saturated film boiling. To do so, a multi-step coupled simulation of conjugated film boiling heat transfer and ballooning using creep model is adopted. The numerical methods and models are validated against experimental values. Two different nonuniform heat flux distributions and four different internal pressures are considered. The three-step simulation is enough to obtain a convergent result. However, the single-step simulation also successfully predicts the rupture time. This is because the film boiling heat transfer characteristics are slightly affected by the tube geometry related to creep ballooning.

• Structural Engineering and Mechanics
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• v.46 no.1
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• pp.53-73
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• 2013

Prediction of prestressed concrete girder integral abutment bridge (IAB) load effect requires understanding of the inherent uncertainties as it relates to thermal loading, time-dependent effects, bridge material properties and soil properties. In addition, complex inelastic and hysteretic behavior must be considered over an extended, 75-year bridge life. The present study establishes IAB displacement and internal force statistics based on available material property and soil property statistical models and Monte Carlo simulations. Numerical models within the simulation were developed to evaluate the 75-year bridge displacements and internal forces based on 2D numerical models that were calibrated against four field monitored IABs. The considered input uncertainties include both resistance and load variables. Material variables are: (1) concrete elastic modulus; (2) backfill stiffness; and (3) lateral pile soil stiffness. Thermal, time dependent, and soil loading variables are: (1) superstructure temperature fluctuation; (2) superstructure concrete thermal expansion coefficient; (3) superstructure temperature gradient; (4) concrete creep and shrinkage; (5) bridge construction timeline; and (6) backfill pressure on backwall and abutment. IAB displacement and internal force statistics were established for: (1) bridge axial force; (2) bridge bending moment; (3) pile lateral force; (4) pile moment; (5) pile head/abutment displacement; (6) compressive stress at the top fiber at the mid-span of the exterior span; and (7) tensile stress at the bottom fiber at the mid-span of the exterior span. These established IAB displacement and internal force statistics provide a basis for future reliability-based design criteria development.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.18-19
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• 2006

The purpose of this study is to evaluate the behavior of residual stress at the weldment of pressure vessel by local Post Weld Heat Treatment(PWHT). In order to do it, residual stress were measured before and after local PWHT by XRD on the test piece first. And then, the results of finite element(FE) analysis based on thermal-elasto-plastic-creep theories were verified by comparing with the measured results.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.723-730
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• 2011

It is very important to experimentally evaluate concrete behavior at elevated temperature because aggregates make up approximately 80 percent of volume in concrete. In this study, an experiment to evaluate mechanical properties of normal weight and light weight concrete of 60 MPa was conducted. Based on loading level of 0, 20 and 40 percent, the tests of 28 days compressive strength, elastic modulus, thermal strain, total strain, and transient creep using ${\phi}100{\times}200mm$ cylindrical specimens at elevated temperature were performed. Then, the results were compared with CEB (Committes Euro-international du Beton) model code. The results showed that thermal strain of light weight concrete was smaller than normal weight concrete. Also, the results showed that compressive strength of light concrete at $700^{\circ}C$ was higher than normal weight concrete and CEB code, similar to that obtained at ambient temperature. Transient creep developed from loading at a critical temperature of $500^{\circ}C$ caused the concrete strains to change from expansion to compression. The transient creep test result showed that internal force was high when the ratio of shrinkage between concrete and aggregate was more influential than thermal expansion.

• Journal of the Korean Ceramic Society
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• v.32 no.9
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• pp.977-988
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• 1995

Several oxide (ZrO2, Al2TiO5, reactive Al2O3) and nonoxide (SiC, Si3N4, "ALON" (5AlN.9Al2O3)) additives were used as a microfiller for alumina based LCC (Low-Cement-Castable). High temperature prooperties (HMOR, softening under load) and the phase changes of developed LCC on various sintering temperatures were examined. In addition, thermal shock test and corrosion test were accomplished. Based on these data the effects of each microfiller on the properties of LCC were established comparing to those of the commercial LCC with amorphous silica as a microfiller. The castables, containing reactive alumina, ZrO2 and "ALON" (5AlN.9Al2O3) as a first portion, exhibited considerably higher HMOR-values over 100$0^{\circ}C$, better creep behavior, and thermal shock resistance than those of castables with amorphous silica. The LCC with 5% Al2TiO5 showed no corrosion against molten aluminum.nst molten aluminum.

• Nuclear Engineering and Technology
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• v.54 no.12
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• pp.4522-4533
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• 2022

For severe accident assessment of reactor pressure vessel (RPV), it is important to develop an accurate model that can predict transient thermo-mechanical behavior of the RPV lower head under the given condition. The present study revisits the lower head failure with two- and three-dimensional finite element models. In particular, we aim to give clear insight regarding the effect of the three-dimensionality present in the distribution of the thickness and thermal load of the lower head. For a rigorous validation of the result, both the OLHF-1 and the OLHF-2 tests are considered in this study. The result suggests that the three-dimensional effect is not negligible as far as the failure location is concerned. The non-uniformity of the thickness distribution is found to affect the failure location and time. The thermal load, which may not be axisymmetric in general, has the most significant effect on the failure assessment. We also observe that the creep property can affect the global deformation of the lower head, depending on the applied mechanical load.