• Nuclear Engineering and Technology
• /
• v.38 no.3
• /
• pp.293-300
• /
• 2006

A liquid metal reactor (LMR) operated at high temperatures is subjected to both cyclic mechanical loading and thermal loading; thus, creep-fatigue is a major concern to be addressed with regard to maintaining structural integrity. The Korea Advanced Liquid Metal Reactor (KALIMER), which has a normal operating temperature of $545^{\circ}C$ and a total service life time of 60 years, is composed of various cylindrical structures, such as the reactor vessel and the reactor baffle. This study focuses on the creepfatigue crack initiation for a cylindrical Y-junction structure made of 316 stainless steel (SS), which is subjected to cyclic axial tensile loading and thermal loading at a high-temperature hold time of $545^{\circ}C$. The evaluation of the considered creep-fatigue crack initiation was carried out utilizing the ${\sigma}_d$ approach of the RCC-MR A16 guide, which is the high-temperature defect assessment procedure. This procedure is based on the total accumulated strain during the service time. To confirm the evaluated result, a high-temperature creep-fatigue structural test was performed. The test model had a circumferential through wall defect at the center of the model. The defect front of the test model was investigated after the $100^{th}$ cycle of the testing by utilizing a metallurgical inspection technique with an optical microscope, after which the test result was compared with the evaluation result. This study shows how creep-fatigue crack initiation for a high-temperature structure can be predicted with conservatism per the RCC-MR A16 guide.

• Tribology and Lubricants
• /
• v.12 no.3
• /
• pp.79-84
• /
• 1996

One of the greatest dangers in mechanical face seals is the formation of heat checking and thermal stress cracks on the sliding surfaces. These thermal distortions due to non-uniform heating lead to increase the leakage of the sealed fluids and wear, and with balance of the seal can cause the seal faces to part. In this study heat checking and thermal stress cracks are investigated experimentally. These thermal distortions are explained using the thermal models of the conatct geometries between the seal ring and the seal seat. To overcome these thermal problems, the thermohydrodynamic seal is presented. The newly developed mechanical seal may substantially reduce the friction torque, frictional heating which causes heat checking and thermal stress cracks, and wear.

• Journal of the korean Society of Automotive Engineers
• /
• v.14 no.6
• /
• pp.91-98
• /
• 1992

In the research on the fracture time of soda lime silicate glass under thermal shock, it is shown that the theoretical and experimental fracture times are in good agreement, the suggested method to measure critical stress intensity factor for small three-point bending specimen is useful and the edge temperature before thermal shock on cracked side vs. crack length and fracture time are inversely proportional.

• Journal of Energy Engineering
• /
• v.21 no.3
• /
• pp.249-253
• /
• 2012

In this study, The report analysed the characteristics of power drop in solar cell through thermal shock test. The solar cells were tested 500 cycles in $-40^{\circ}C$ lowest temperature and $120^{\circ}C$ highest temperature by thermal shock test on ironbound conditions, that excerpted standard of PV Module(KS C IEC-61215). The result of the efficiency analysis through measure of I-V, efficiency of Cell decreased from 13.9% to 11.0% and decreasing rate was 20.9% after test. The result of the surface analysis through EL, solar cell has damage of gridfinger and ribbon joint. Cell cracks were founded in damage of cells through cross section of solar cells. Also, Fill factors were decreased from 72.3% to 62.0% after thermal shock test and decreasing rate is 11.8%. therefore, Yearly power drop is aggravated with facts that cell crack, damage of surface and power loss of cell by change of I-V characteristic curve with decreasing of parallel resistance.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.27 no.6
• /
• pp.30-38
• /
• 2023

As the number of old buildings subject to safety inspection increases, the burden on designated institutions and management entities that are responsible for safety management is increasing. Accordingly, when selecting buildings subject to safety inspection, appropriate safety inspection standards and appropriate technology are essential. The current safety inspection standards for old buildings give low scores when it is difficult to confirm damage such as cracks in structural members due to finishing materials. This causes the evaluation results to be underestimated regardless of the actual safety status of the structure, resulting in an increase in the number of aging buildings subject to safety inspection. Accordingly, this study proposed a thermal imaging technique, a non-destructive and non-contact inspection, to detect cracks inside finishing materials. A concrete specimen was produced to observe cracks inside the finishing material using a thermal imaging camera, and thermal image data was measured by exciting a heat source on the concrete surface and cracked area. As a result of the measurement, it was confirmed that it was possible to observe cracks inside the finishing material with a width of 0.3mm, 0.5mm, and 0.7mm, but it was difficult to determine the cracks due to uneven temperature distribution due to surface peeling and peeling of the wallpaper. Accordingly, as a result of performing data analysis by deriving the amplitude and phase difference of the thermal image data, clear crack measurement was possible for 0.5mm and 0.7mm cracks. Based on this study, we hope to increase the efficiency of field application and analysis through the development of technology using big data-based deep learning in the diagnosis of internal crack damage in finishing materials.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.1
• /
• pp.173-179
• /
• 1997

The high temperature fatigue tests were performed using the specimens taken from Cr-Mo-V steel, widely used as thermal power plant turbine materials for examination fatigue behavior of materials in power plants which have been operated for long periods. The fatigue tests at high temperature were performed at the various temperature and applied stress. The results obtained are summarized as follows : The fatigue crack length increases and the fatigue life decreases with temperature and applied stress according to the same number of stress cycle. The fatigue crack propagation and the fatigue life were much influenced by temperature and applied stress.

• Journal of Power System Engineering
• /
• v.7 no.2
• /
• pp.73-79
• /
• 2003

The present study was aimed at analysing the damage of a used gas turbine bucket after 39,500h of total service. Microstructures and cracks of service-induced bucket were observed. The crack might have initiated from the coating in the bucket surface by thermal fatigue and propagated into the GTD111 base metal. Maximum depth of penetration was 2.7 mm(full penetration) at the leading edge. Crack contains a lot of Cr-,Ti-,Al-oxide which will prohibit filling and wetting of insert metal. Depth and propagation direction of crack were accorded with centrifugal force and temperature distribution in turbine bucket. Present result will provide basic data for repair bonding process.

• Structural Engineering and Mechanics
• /
• v.50 no.4
• /
• pp.441-457
• /
• 2014

This paper presents a finite element based numerical model to solve two dimensional bi-material problems. A bi-material beam consisting of two phase materials ceramic and metal is modelled by finite element method. The beam is subjected simultaneously to mechanical and thermal loadings. The main objective of this study is the analysis of crack deviation located in the brittle material near the interface. The effect of temperature gradient, the residual stresses and applied loads on crack initiation, propagation and deviation are examined and highlighted.

• Journal of Welding and Joining
• /
• v.18 no.2
• /
• pp.227-227
• /
• 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
• /
• v.18 no.2
• /
• pp.100-104
• /
• 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.