• 제목/요약/키워드: thermal initiation

검색결과 148건 처리시간 0.023초

EVALUATION AND TEST OF A CRACK INITIATION FOR A 316 SS CYLINDRICAL Y-JUNCTION STRUCTURE IN A LIQUID METAL REACTOR

  • Park, Chang-Gyu;Kim, Jong-Bum;Lee, Jae-Han
    • Nuclear Engineering and Technology
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    • 제38권3호
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    • pp.293-300
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    • 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.

Thermal Fatigue Test of an Annular Structure

  • Hwang Jeong-Ki;Suh Chang-Min;Kim Chae-Ho
    • Journal of Mechanical Science and Technology
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    • 제20권1호
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    • pp.59-65
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    • 2006
  • A half-scaled large test model for the main components of the real annular structure was built and the thermal behaviors were experimented and obtained by thermal cyclic loads. The model design and the test conditions for the thermal loads were determined to take into consideration the thermal and mechanical loads acting on the real annular structure by finite element analyses. Temperature profiles and strains of the main components of the model were measured at an early stage of the test and periodically throughout the test in the given test conditions. After completion of the thermal cyclic tests, no evidence of crack initiation and propagation were identified by a dye penetration test. The measured strains at the critical parts were slightly increased proportionally with the increase in the number of the thermal cycles.

Fe-Ni 합금 클래드 리드 프레임을 이용한 전자 재료 접합부의 품질향상과 그 신뢰성 (Quality improvement on joints of electronic materials and its reliability by Fe-Ni alloy clad lead frame)

  • 신영의;최인수;안승호
    • Journal of Welding and Joining
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    • 제13권2호
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    • pp.82-95
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    • 1995
  • This paper discusses distribution of thermal stress, strain at near the joint and investigates the reliability of solder joints of electronic devices on a printed circuit board. As Electronic devices are composed of different materials, thermal stresses generate at near the interface, such as solder joints and interface between lC device and lead frame pad due to the differences of thermal expansion coefficients, As results of thermal stress, strain, micro crack often occurs thermal fatigue fracture at the interface of different materials, The initiation and propagation of micro crack depend on the environmental conditions, such as storage temperature and thermal cycling. Finally, this paper experimentally shows a way to suppress micro cracks by using Fe-Ni alloy clad lead frame, and investigates crack and thermal fatigue fracture of TSOP(Thin small outline package) type on printed circuit board.

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A STUDY ON THE THERMAL FATIGUE TEST AND ANALYSIS METHOD FOR THE DEVELOPMENT OF BRAKE DISK MATERIALS

  • 임충환;구병춘
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2008년도 추계학술대회A
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    • pp.127-131
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    • 2008
  • In the disk braking of the railway trains, kinetic energy of the vehicles is converted into thermal energy by friction between a brake disk and the pad materials. This can be cause of the iterative thermal shock and generates thermal cracks on the brake disk surface. In this study, we show the comparative thermal fatigue test procedures and thermal crack analysis process to evaluate the thermal fatigue characteristics of candidate materials designed for development of heat-resistant brake disk material. We carried out tests on the conventional brake disk materials used for Saemaul and Mugunghwa trains, then we comparatively analyzed the thermal crack initiation and propagation on the surface of a specimen. A thermal fatigue test procedure and a crack analysis process were suggested to evaluate the heat resistance of the developed materials at later studies.

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가압열충격을 받는 원자로용기의 확률론적 건전성 평가 (Probabilistic Evaluation of RV Integrity Under Pressurized Thermal Shock)

  • 김종민;배재현;손갑헌;윤기석;최택상
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 추계학술대회
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    • pp.90-95
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    • 2004
  • The probabilistic fracture analysis is used to determine the effects of uncertainties involved in material properties, location and size of flaws, etc, which can not be addressed using a deterministic approach. In this paper the probabilistic fracture analysis is applied for evaluating the RV(Reactor Vessel) under PTS(Pressurised Thermal Shock). A semi-elliptical axial crack is assumed in the inside surface of RV. The selected random parameters are initial crack depth, neutron fluence, chemical composition of material (copper, nickel and phosphorous) and $RT_{NDT}$. The deterministically calculated $K_I$ and crack tip temperature are used for the probabilistic calculation. Using Monte Carlo simulation, the crack initiation probability for fixed flaw and PNNL(Pacific Northwest National Laboratory) flaw distribution is calculated. As the results show initiation probability of fixed flaw is much higher than that of PNNL distribution, the postulated crack sizes of 1/10t in this paper and 1/4t of ASME are evaluated to be very conservative.

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탄소나노튜브를 첨가한 나노 반도전층 재료의 기계적/열적 특성 변화 연구 (Mechanical and Thermal Properties Changes of Nano Semiconducting Materials due to Addition of Carbon Nanotubes)

  • 양종석;이경용;신동훈;최유진;박노준;박대희
    • 대한전기학회:학술대회논문집
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    • 대한전기학회 2006년도 추계학술대회 논문집 전기물성,응용부문
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    • pp.28-29
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    • 2006
  • To improve Mechanical and Thermal Properties of semiconducting materials in power cable, we have investigated those of semiconducting materials showed by changing the content of carbon black and Carbon Nanotube. Density were measured by EW-200SG. High temperature, heat degradation initiation temperature, and heat weight loss were measured by TGA (Thermogravimetric Analysis). The dimension of measurement temperature was $0[^{\circ}C]$ J to $700[^{\circ}C]$, and rising temperature was $10[^{\circ}C/min]$. Heat degradation initiation temperature from the TGA results was decreased according to increasing the content of Carbon Nanotube. That is, heat stabilities of EVA containing the weak VA (vinyl acetate) against heat was measured the lowest. From the results of the experiment applied in this study, it is evident that a small amount of Carbon nanotube additives significantly improved the Mechanical and Thermal Properties of semiconducting materials.

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CNT 함량에 따른 전력케이블용 반도전층 재료의 열적 특성 (Thermal Properties of Semiconducting Materials for Power Cable by Carbon Nanotube Content)

  • 양종석;이경용;신동훈;박대희
    • 대한전기학회논문지:전기물성ㆍ응용부문C
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    • 제55권12호
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    • pp.570-575
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    • 2006
  • In this paper, we have investigated thermal properties by changing the content of carbon nanotube, which is component part of semiconductive shield in underground power transmission cable. Heat capacity (${\Delta}H$), glass transition temperature (Tg) and melting temperature (Tm) were measured with the samples of eight, through DSC (Differential Scanning Calorimetry), and the measurement ranges of temperature selected from $-100[^{\circ}C]\;to\;100[^{\circ}C]$ with heating temperature selected per $4[^{\circ}C/min]$ Also, high temperature, heat degradation initiation temperature, and heat weight loss were measured by TGA (Thermogravimetric Analysis) in the temperature from $0[^{\circ}C]\;to\;700[^{\circ}C]$ with rising temperature of $10[^{\circ}C/min]$. As a result, the Glass transition temperatures of the sample were showed near $-20[^{\circ}C]{\sim}25[^{\circ}C]$, and the heat capacity and melting temperature from the DSC was increased according to increasing the content of carbon nanotube, while, thermal diffusivity was increased according to increasing the content of carbon nanotube. Also, heat degradation initiation temperature from the TGA results was increasing according to increasing the content of carbon nanotube with CNT/EEA. Therefore, heat stabilities of EVA, which contained the we VA (vinyl acetate), showed the lowest.

로켓 노즐 재료의 열충격특성에 관한 연구 (A Study on the Thermal Shock Characteristics of the Rocket Nozzle Material)

  • 이장원;이영신;김재훈;김승중
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 추계학술대회
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    • pp.562-566
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    • 2004
  • Thermal shock is a physical phenomenon that occurs in the condition of the exposure of a rapidly large temperature and pressure change of in the quenching condition of material. The rocket nozzle is exposed to high temperature combustion gas, it may have failure and erosion deformation. So, it is important to select a suitable material having excellent thermal shock properties and evaluate these materials in rocket design. In this study, the temperature gradient and crack initiation of rocket nozzle material is investigated using by FEM under thermal shock condition. This is very important information in the design process of thermal structure.

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이종 전자재료 JO1NT 부위의 신뢰성에 관한 연구 (A Study on Reliability of Solder Joint in Different Electronic Materials)

  • 신영의;김경섭;김형호
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 1993년도 추계학술대회 논문집
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    • pp.49-54
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    • 1993
  • This paper discusses the reliability of solder joints of electronic devices on printed circuit board. Solder application is usually done by screen printing method for the bonding between outer leads of devices and thick film(Ag/Pd) pattern on Hybrid IC as wel1 as Cu lands on PCB. As result of thermal stresses generated at the solder joints due to the differences of thermal expansion coefficients between packge body and PCB, Micro cracking often occurs due to thermal fatigue failure at solder joints. The initiation and the propagate of solder joint crack depends on the environmental conditions, such as storage temperature and thermal cycling. The principal mechanisms of the cracking pheno- mana are the formation of kirkendal void caused by the differences in diffusion rate of materials, ant the thermal fatigue effect due to the differences of thermal expansion coefficient between package body and PCB. Finally, This paper experimentally shows a way to supress solder joints cracks by using low-${\alpha}$ PCB and the packages with thin lead frame, and investigates the phenomena of diffusion near the bonding interfaces.

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동적하중하에서의 강도적 불균질재의 연성크랙 발생한계의 해석적 검토 - 강도적 불균질 및 동적부하의 영향에 의한 연성크랙 발생조건 (제 2 보) - (Analytical Examination of Ductile Crack Initiation with Strength Mismatch under Dynamic Loading - Criterion for Ductile Crack Initiation Effect of Strength Mismatch and Dynamic Loading (Report 2) -)

  • 안규백;;;방한서
    • Journal of Welding and Joining
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    • 제21권7호
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    • pp.49-58
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    • 2003
  • It has been well known that ductile fracture of steel is accelerated by triaxiality stresses. The characteristics of ductile crack initiation in steels are evaluate quantitatively using two-parameter criterion based on equivalent plastic strain and stress triaxiality. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameter, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of geometrical heterogeneity and strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on critical condition to initiate ductile crack using two-parameter. Then, the crack initiation testing were conducted under static and dynamic loading. To evaluate the stress/strain state in the specimens especially under dynamic loading, thermal elastic-plastic dynamic FE-analysis considering the temperature rise was used. The result showed that the critical global strain to initiate ductile fracture in specimens with strength mismatch under various loading rate cu be estimated based on the local criterion, that is two-parameter criterion obtained on homogeneous specimens under static tension, by mean of FE-analysis taken into account accurately both strength mismatch and dynamic loading effects on stress/strain behavior.