• 한국분말재료학회지
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• 제13권5호
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• pp.321-326
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• 2006

Electronic packaging involves interconnecting, powering, protecting, and cooling of semiconductor circuits fur the use in a variety of microelectronic applications. For microelectronic circuits, the main type of failure is thermal fatigue, owing to the different thermal expansion coefficients of semiconductor chips and packaging materials. Therefore, the search for matched coefficients of thermal expansion (CTE) of packaging materials in combination with a high thermal conductivity is the main task for developments of heat sink materials electronics, and good mechanical properties are also required. The aim of this work is to develop copper matrix composites reinforced with carbon nanofibers. The advantages of carbon nanofibers, especially the good thermal conductivity, are utlized to obtain a composite material having a thermal conductivity higher than 400 W/mK. The main challenge is to obtain a homogeneous dispersion of carbon nanofibers in copper. In this paper, a technology for obtaining a homogeneous mixture of copper and nanofibers will be presented and the microstructure and properties of consolidated samples will be discussed. In order to improve the bonding strength between copper and nanofibers, different alloying elements were added. The microstructure and the properties will be presented and the influence of interface modification will be discussed.

• Restorative Dentistry and Endodontics
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• 제44권4호
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• pp.44.1-44.11
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• 2019

Objectives: To compare the flexural cyclic fatigue resistance and the length of the fractured segments (FLs) of recently introduced M-Pro rotary files with that of RaCe rotary files in curved canals and to evaluate the fracture surface by scanning electron microscopy (SEM). Materials and Methods: Thirty-six endodontic files with the same tip size and taper (size 25, 0.06 taper) were used. The samples were classified into 2 groups (n = 18): the M-Pro group (M-Pro IMD) and the RaCe group (FKG). A custom-made simulated canal model was fabricated to evaluate the total number of cycles to failure and the FL. SEM was used to examine the fracture surfaces of the fragmented segments. The data were statistically analyzed and comparisons between the 2 groups for normally distributed numerical variables were carried out using the independent Student's t-test. A p value less than 0.05 was considered to indicate statistical significance. Results: The M-Pro group showed significantly higher resistance to flexural cyclic fatigue than the RaCe group (p < 0.05), but there was no significant difference in the FLs between the 2 groups (p ≥ 0.05). Conclusions: Thermal treatment of nickel-titanium instruments can improve the flexural cyclic fatigue resistance of rotary endodontic files, and the M-Pro rotary system seems to be a promising rotary endodontic file.

• The Journal of Advanced Prosthodontics
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• 제9권6호
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• pp.416-422
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• 2017

PURPOSE. To investigate the effect of reducing tooth preparation and ceramic thickness on fracture resistance of lithium disilicate crowns. MATERIALS AND METHODS. Specimen preparation included a standard complete crown preparation of a typodont mandibular left first molar with an occlusal reduction of 2 mm, proximal/axial wall reduction of 1.5 mm, and 1.0 mm deep chamfer (Group A). Another typodont mandibular first molar was prepared with less tooth reduction: 1 mm occlusal and proximal/axial wall reduction and 0.8 mm chamfer (Group B). Twenty crowns were milled from each preparation corresponding to control group (n=5) and conditioned group of simultaneous thermal and mechanical loading in aqueous environment (n=15). All crowns were then loaded until fracture to determine the fracture load. RESULTS. The mean (SD) fracture load values (in Newton) for Group A were 2340 (83) and 2149 (649), and for Group B, 1752 (134) and 1054 (249) without and with fatigue, respectively. Reducing tooth preparation thickness significantly decreased fracture load of the crowns at baseline and after fatigue application. After fatigue, the mean fracture load statistically significantly decreased (P<.001) in Group B; however, it was not affected (P>.05) in Group A. CONCLUSION. Reducing the amount of tooth preparation by 0.5 mm on the occlusal and proximal/axial wall with a 0.8 mm chamfer significantly reduced fracture load of the restoration. Tooth reduction required for lithium disilicate crowns is a crucial factor for a long-term successful application of this all-ceramic system.

• 한국재료학회지
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• 제8권11호
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• pp.993-998
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• 1998

본 연구는 형상기억합금을 이용하여 제조한 신소재 중의 하나인 형상기억복합재료를 소개하고자 한다. 이 복합재료는 TiNi 섬유의 형상기억효과로 금속복합재료의 취약점이라 할 수 있는 기지와 섬유간의 열팽창차이로 인한 인장잔류응력을 제거하고 기지내에 압축잔류응력을 발생시켜 높은 인장강도를 갖는다. 따라서 본 연구에서는 용탕단조법으로 복합재료를 제조한 후 미세조직을 관찰하고 TiNi 섬유의 역변태온도 이상에서 피로실험을 수행하여 복합재료의 피로특성을 검토하였다. 이 결과 363K에서의 피로균열전파제어효과는 섬유체적률과 예변형에 의하여 증가된다.

• 대한약침학회지
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• 제4권3호
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• pp.7-14
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• 2001

Objective: This study was done to observe the effects on the thermal changes and side effects of Bee Venom acupuncture. The objectives are as follows; If there are remarkable local thermal changes between pre and post Bee Venom acupuncture therapy on D.I.T.I. or not. If there are those, we examine how long it' s changes are maintained, what is the adequate interval on Bee Venom acupuncture therapy, and what the reactions in a local or whole body are on that therapy. Methods: To study the local thermal changes in Bee Venom acupuncture therapy, D.I.T.I. was used. Determination of this analysis periods are pre and post-therapy(5 minutes, 1 hour, 1day,2days, 3days, 5days and 7days later). The study group was divided into two groups. One was BV group(N=19), another was NS(Normal Saline) group. The Bee Venom acupuncture was injected by 0.2ml divided into 0.05ml at the Fengmen(風門:12), Feishu(肺兪:B13), Fufen(附分:B41), Pohu(魄戶: B42) 4 points. Then, in order to analyze the clinical form, we have observed responses of 23 students whenever we checked the thermal changes of their after performing. Results: The following results were obtained. 1. In BV group, there was a significant dermatothermal difference between pre and post therapy. That difference was most remarkable in post-therapy 1 hour to lday, and was not remarkable in post-therapy 5-7days later. 2. There was no significant dermatothermal changes at NS group, but BV group had remarkable changes between operated and non operated area in post-therapy 1hour, 1day, 2days. But there was none 7 days later. 3. Among the physical reactions after Bee Venom acupuncture therapy, operated-area pain, itching, pain on moving and fatigue sign most appeared until post-therapy 3days. Itching and fatigue sign appeared until post-therapy 7days. 4. In comparison the dermatothermal changes with the physical reactions, the decrease of { CT = (Rt Temperature -Lt. Temperature) / Rt. $Temperature{\times}100$} and the disappearance of physical reactions were about the same.

• 공업화학
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• 제26권4호
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• pp.452-457
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• 2015

네온변압기용 에폭시계 수지는 변압기로 완성되었을 경우 내열성 및 온도차 피로극복 등 열내구성이 우수하여야 한다. 따라서 본 연구에서는 에폭시계 수지에 보강제로 이산화규소를 첨가하고 증량제로 silica를 선정하여 입자크기별 혼합비에 따른 열전도도와 열안정성을 측정하였다. 혼합 silica의 최적 첨가량은 50 wt%이었으며, 혼합 silica 중 입자크기가 큰 규사의 첨가량이 증가함에 따라 열안정성이 우수하였다. 혼합 silica의 입자크기별 최적 혼합비는 (28/35 : 14/18 : 8/10 mesh = 1 : 1 : 1)이었으며, 이로부터 열내구성이 향상된 네온변압기를 제작할 수 있었다.

• 한국안전학회지
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• 제24권2호
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• pp.17-22
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• 2009

Thermal stress and elastic creeping stress analysis was conducted by finite element method to simulate start-up process of a boiler header of 500MW standard fossil power plant. Start-up temperature and operating pressure history were simplified from the real field data and they were used for the thermal stress analysis. Two kinds of thermal stress analysis were considered. In the first case only temperature increase was considered and in the second case both of temperature and operating pressure histories were considered. In the first analysis peak stress was occurred during the temperature increase from the room temperature. Hence cracking or fracture may occur at the temperature far below the operating maximum temperature. In the results of the second analysis von Mises stress appeared to be higher after the second temperature increase. This is due to internal pressure increase not due to the thermal stress. When the stress components of radial(r), hoop($\theta$) and longitudinal(z) stress were investigated, compression hoop stress was occurred at inner surface of the stub tube when the temperature increased from room temperature to elevated temperature. Then it was changed to tension hoop stress and increased because of the operating pressure. It was expected that frequent start-up and shut-down operations could cause thermal fatigue damage and cracking at the stub tube hole in the header. Elastic-creeping analysis was also carried out to investigate the stress relaxation due to creep and stabilized stress after considerable elapsed time. The results could be used for assessing the creep damage and the residual life of the boiler header during the long-tenn service.

• 대한금속재료학회지
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• 제46권8호
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• pp.538-544
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• 2008

MMCs were manufactured in two different forms. One was two-layered non FGM composite and the other was four-layered FGM composite. The matrix used in this study was AZ31 magnesium alloy and the reinforcement was $Al_{18}B_4O_{33}$. The composite materials contained reinforcement fibers with a volume fraction of 0, 15, 25 and 40%. Squeeze infiltration method was used for the fabrication of each block. The thermal properties of the FGM alloy and composite joints were studied by conducting thermal cycling tests. The numerical calculation (the finite elements method-FEM) results exhibited a good agreement with the experimental results. Thermal stresses induced by thermal cycling test were clearly reduced in the functionally graded materials.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2004년도 ISMP Pb-free solders and the PCB technologies related to Pb-free solders
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• pp.1-26
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• 2004

The implementation of Pb-free solder technology is making good progress in electronic industry. Further understanding on fundamental issues on Pb-free solders/processes is required to reduce reliability risk factors of Pb-free solder joints. Several reliability issues including thermal fatigue, impact reliability, IMC growth, spalling, void formation are reviewed for Pb-free solder joints. Several applications of Pb-free technology are discussed, such as Pb-free, CBGA, CuCGA, flip chips, and wafer bumping by IMS.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 춘계학술대회 논문집
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• pp.371-372
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• 2012