• Proceedings of the KSME Conference
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• 2001.06a
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• pp.322-327
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• 2001

The internal leaks of RCS pressure boundary valves may cause thermal fatigue crack because of the TASCS in RCS branch line. After experienced unisolable piping failures in several PWR plants, many studies have peformed to understand these phenomena and various methods were applied to ensure the structural integrity of piping. In this paper, the cause of unisolable piping failures and the alternatives to prevent recurrence of failure were reviewed. Also, the severity of piping failure including susceptibility of valve leaks was evaluated for the Westinghouse 2-loop plant. The length of turbulent penetration on RHR inlet piping was measured and, thermal fluid analysis and fatigue analysis was performed for this piping. As a means of ensuring the structural integrity, temperature monitoring and specialized UT and other alternatives were compared for the further application.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.2
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• pp.66-75
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• 2003

This paper describes about the estimation method of die lift by wear and plastic deformation in hot forging process. The thermal load and the thermal softening are happened by the high temperature in hot forging process. Tool lift decreases considerably due to the softening of the surface layer of a tool caused by high thermal load and long contact time between tool and billet. Also, tool life is to a large extent limited by wear, heat crack and plastic deformation in hot forging process. Above all, the main factors which affects die accuracy and tool lift are wear and the plastic deformation of a die. The new developed technique for predicting tool life applied to estimate the production quantity for a spindle component and these techniques assist to improve the tool life in hot forging process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.163-168
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• 2002

Hot forging is widely used in the manufacturing of industry machine component. The mechanical, thermal load and thermal softening which are happened by the high temperature in hot forging process. Tool life decreases considerably due to the softening of the surface layer of a tool caused by a high thermal load and long contact time between the tool and billet. Also, tool life is to a large extent limited by wear, heat crack and plastic deformation in hot forging process. These are one of the main factors affecting die accuracy and tool life. That is because hot forging process has many factors influencing tool life, and there was not accurate in-process data. In this research, life prediction of hot forging tool by wear and plastic deformation analysis considering tempering parameter has been carried out for automobile component. The new developed technique in this study for predicting tool life can give more feasible means to improve the tool life in hot forging process.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.254-256
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• 2007

In this paper, the effects of the reflow number in the mechanical reliability of flip chip solder joint was investigated by flip chip shear test and thermal shock test. For evaluation mechanical reliability of flip chip, We experiment that specimens were operated 3-times, 6-times, 9-times, 12-times under reflow Process. After shear test and thermal shock test, We measured max shear strength and coming first crack number of thermal cycle. And We observe fracture surface and cross section by using SEM(Scanning Electron Microscope) and optical scope. In the results, the more specimens were operated reflow process, the more decreased maximum shear strength and number of thermal cycle.

• Proceedings of the Korean Reliability Society Conference
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• 2004.07a
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• pp.221-226
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• 2004

The thermal stresses induced by difference in Coefficient of Thermal Expansion between FR-4 board and 63Sn-37Pb solder joint directly affect the reliability of 63Sn-37Pb solder joint. This research, thus, focuses to investigate the crack initiation and propagation behavior around solder joint by imposing a designed Acceleration Life Test Procedure on solder joint by using a newly manufactured Thermal Impact Experimental Apparatus. The fracture mechanism of the solder joint was found to be highly influenced by thermal stresses. The reliability of solder joint was evaluated by using a failure probability model in terms of varying parameters such as frequency and temperature. The relationship between failure probability and safety factor was also studied.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.922-927
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• 1998

Pipe cooling has been popularly used in the mass concreting work to reduce temperature of the structure since it is known to be the easiest way to apply and has been the customary usage. But wrong application of the system results in the harmful effect on the structure by crack formation due to thermal shocks and improper cooling schemes. Thus, this study aims at the suppling of effective cooling methods through parametric study. For this, circulating method, velocity of water supply and circulating duration were selected as critical factors affecting the effectiveness of cooling system. As a results of thermal analysis, it was found that too much thermal gradient in the vicinity of the pipe creates localized radial or circumferential cracks. The duration of circulating cooling may be recommended to be as short as several days which may safely reduce the concrete temperature to below a final stable value. It was also found that pipe cooling is more effective to decrease the degree external restraints than internal one.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.153-159
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• 2001

Recently, the underground reinforced concrete(RC) box structures have been increasingly built in Korea. In such structures, the heat of hydration may cause serious cracking problems. The RC box structures are classified in this category that needs much attention to control the hydration heat during construction, which causes the restraining effects on the boundaries. The purpose of the present study is to develop the rational construction method to control the thermal cracking problem of the box structures. In this study, the causes and mechanism of thermal cracking according to construction stages in the RC box structures are thoroughly analyzed. The major influencing variables are studied through the finite element analysis which affect the thermal cracking of RC box structures. The research results of the present study can be efficiently used for the control of cracking of box structures during construction stages.

• Structural Engineering and Mechanics
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• v.4 no.6
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• pp.679-702
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• 1996

The finite element method is employed in conjunction with micromechanical modelling in order to assess the performance of ceramic thermal barrier coatings applied to structural components. The study comprises the conditions of the deposition of the coating by plasma spraying as well as the thermal cycling of the coated component, and it addresses particularly turbine blades. They are exposed to high temperature changes strongly influencing the behaviour of the core material and inducing damage in the ceramic material by intense straining. A concept of failure analysis is discussed starting from distributed microcracking in the ceramic material, progressing to the formation of macroscopic crack patterns and examining their potential for propagation across the coating. The theory is in good agreement with experimental observations, and may therefore be utilized in proposing improvements for a delayed initiation of failure, thus increasing the lifetime of components with ceramic thermal barrier coatings.

• Journal of the Korean Society of Safety
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• v.23 no.5
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• pp.84-90
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• 2008

The occurrence of longitudinal cracking in concrete deck of box girder bridge is affected by many factors, but the most important factors are the shrinkage and thermal gradient of deck slabs. In this study, therefore, the tensile stresses at the bottom of deck were calculated from the experimental data(autogeneous shrinkage, drying shrinkage, and thermal gradient of deck slab). Also, the possibility of longitudinal cracks at bottom of deck was estimated. For this purpose, full-scale box girder segments have been fabricated and tested. The thermal gradients and shrinkage strains of deck slabs were measured after placement of concrete. Also, analytic program was conducted for the evaluation of longitudinal cracking in bridge deck considering differential shrinkage induced from non-uniform moisture distributions in concrete.

• Journal of the Korean Society for Railway
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• v.12 no.6
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• pp.1024-1029
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• 2009

According to increase of massive concrete structures, Thermal crack done by heat of hydration have been increased in a process of the execution. In case of a subway concrete box structure, thickness of structures are almost over 1 meter, and penetrating crack by external restraint takes a bad effect on the durability with a water leakage and deterioration in especially concrete wall. A try of shortening a constructing period often occurs as subway is generally constructed according to a road to decrease a traffic jam. The research proposes executing method by skipping one block as a plan of shortening a constructing period and investigate an influence on thermal cracking control. Additionally, sensitivity analysis is accomplished by changing a height of a concrete wall, and concrete placing and air temperature met with a field condition.