• Title/Summary/Keyword: thermal initiation

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가속 시험을 통한 솔더조인트의 건전성 평가

  • 명노훈;이억섭;김동혁
    • 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.

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Numerical analysis of plasma-sprayed ceramic coatings for high-temperature applications

  • St. Doltsinis, Ioannis;Haller, Kai-Uwe;Handel, Rainer
    • 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.

Polymerization of Methyl Methacrylate with Phenylsilane

  • 유희권;박선희;박진영;양수연;함희숙;김환기
    • Bulletin of the Korean Chemical Society
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    • v.17 no.4
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    • pp.373-376
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    • 1996
  • The bulk thermal and photopolymerization of methyl methacrylate(MMA) with phenylsilane were performed to produce poly(MMA)s containing phenylsilyl moiety presumably as an end group. It was found for both thermal and photopolymerization that while the polymerization yields and polymer molecular weights decreased as the relative phenylsilane concentration increases, the TGA residue yields and the relative intensities of SiH IR stretching bands increased with increasing molar ratio of phenylsilane over MMA. The polymerization yield, molecular weight, and TGA residue yield for the thermal polymerization were higher than those for the photopolymerization. Thus, the phenylsilane seemed to significantly influence on the polymerization as both chain initiation and chain transfer agents. However, an appreciable silane effect was not observed on the thermal and photopolymerization of 4-vinylpyridine, acrylonitrile, styrene, and vinyltrimethoxysilane.

Evaluation of Thermal Dmage for Railway Weel (차륜에 대한 열손상 평가)

  • Kwon, Seok-Jin;Seo, Jung-Won;Lee, Dong-Hyong;Kim, Young-Kyu;Kim, Jae-Chul
    • Proceedings of the KSR Conference
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    • 2011.10a
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    • pp.966-970
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    • 2011
  • The thermo-mechanical interaction between brake block and wheel tread during braking has been found to cause thermal crack on the wheel tread. Due to thermal expansion of the rim material, the thermal cracks will protrude from the wheel tread and be more exposed to wear during the wheel/block contact than the rest of the tread surface. The wheel rim is in residual compression stress when is new. After service running, the region in the tread has reversed to tension. This condition can lead to the formation and growth of thermal cracks in the rim which can ultimately lead to premature failure of wheel. In the present paper, the thermal cracks of railway wheel, one of severe damages on the wheel tread, were evaluated to understand the safety of railway wheel in running condition. The residual stresses for damaged wheel which are applied to tread brake are investigated. Mainly X-ray diffusion method is used. Under the condition of concurrent loading of continuous rolling contact with rails and cyclic frictional heat from brake blocks, the reduction of residual stress is found to correlate well with the thermal crack initiation.

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Studies on the effect of thermal shock on crack resistance of 20MnMoNi55 steel using compact tension specimens

  • Thamaraiselvi, K.;Vishnuvardhan, S.
    • Nuclear Engineering and Technology
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    • v.53 no.9
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    • pp.3112-3121
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    • 2021
  • One of the major factors affecting the life span of a Reactor Pressure Vessel (RPV) is the Pressurised Thermal Shock (PTS). PTS is a thermo-mechanical load on the RPV wall due to steep temperature gradients and structural load created by internal pressure of the fluid within the RPV. Safe operating life of a nuclear power plant is ensured by carrying out fracture analysis of the RPV against thermal shock. Carrying out fracture tests on RPV/large scale components is not always feasible. Hence, studies on laboratory level specimens are necessary to validate and supplement the prototype results. This paper aims to study the fracture behaviour of standard Compact Tension [C(T)] specimens, made of RPV steel 20MnMoNi55, subjected to thermal shock through experimental and numerical investigations. Fracture tests have been carried out on the C(T) specimens subjected to thermal transient load and tensile load to quantify the effect of thermal shock. Crack resistance curves are obtained from the fracture tests as per ASTM E1820 and compared with those obtained numerically using XFEM and a good agreement was found. A quantitative study on the crack tip plastic zone, computed using cohesive segment approach, from the numerical analyses justified the experimental crack initiation toughness.

EFFECT OF STRENGTH MISMATCH AND DYNAMIC LOADING ON THE DUCTILE CRACK INITIATION FROM NOTCH ROOT

  • An, Gyn-Baek;Yoshida, Satoshi;Ohata, Mitsuru;Toyoda, Masao
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.145-150
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    • 2002
  • It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameters criterion based on equivalent plastic strain and stress triaxiality. It has been demonstrated by authors using round-bar specimens with circumferential notch in single tension that the critical strain to initiate ductile crack from specimen center depends considerably on stress triaxiality, but surface cracking of notch root is in accordance with constant strain condition. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal, elastic-plastic, dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out. This study provides the fundamental clarification of the effect of strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, loading mode and loading rate on critical condition to initiate ductile crack from notch root using equivalent plastic strain and stress triaxiality based on the two-parameter criterion obtained on homogeneous specimens under static tension. The critical condition to initiate ductile crack from notch root for strength mismatched bend specimens under both static and dynamic loading would be almost the same as that for homogeneous tensile specimens with circumferential sharp notch under static loading.

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Effects of Clearance on the Formation of Adiabatic Shear Band in Stepped Specimen (계단시편의 간극이 단열전단밴드의 형성에 미치는 영향)

  • Yoo, Y.H.;Jeon, G.Y.;Chung, D.T.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.7 s.94
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    • pp.1700-1709
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    • 1993
  • The stepped specimen which is subjected to step loading is modeled to study the initiation and growth of adiabatic shear band using explicit time integration finite element method. Three different clearance sizes are tested. The material model for the stepped specimen includes effects of strain hardening, strain rate hardening and thermal softening. It is found that the material inside the fully grown adiabatic shear band experiences three phase of deformation, (1) homogeneous deformation phase, (2) initiation/incubation phase, and (3) fast growth phase. The second phase of deformation is initiated after sudden shear stress drop which occurs at the same time regardless of the clearance size. The incubation time prior to fast growth phase increases, as the clearance size of the stepped specimen increases. Whereas, after incubation period, the growth rate of the adiabatic shear band decreases, as the clearance size decreases. It is also found that two adiabatic shear band may develop instead of one for the smaller clearance size.

Study on Combustion and Explosion Hazard of Rice Bran Dusts (쌀겨 분진의 연소 및 폭발 위험성에 관한 연구)

  • 이창우;현성호;이한철;허윤행
    • Journal of environmental and Sanitary engineering
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    • v.14 no.4
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    • pp.93-98
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    • 1999
  • We had investigated combustion properties of rice bran dusts. Decomposition of rice bran dusts with temperature were investigated using DSC and the weight loss according to temperature using TGA in order to find the thermal hazard of rice bran dusts, and the properties of dust explosion in variation of their dust with the same particle size. Using Hartman's dust explosion apparatus which estimate dust explosion by electric ignition after making dust disperse by compressed air, dust explosion experiments have been conducted by varying concentration and size of rice bran dust.According to the results for thermodynamic stability of rice bran dust, there are little change of initiation temperature of heat generation and heating value for used particle size. But initiation temperature of heat generation decreased with high heating rate whereas decomposition heat increased with particle size. Average maximum explosion pressure was $10kgf/cm^2$ for 60/70 mesh and $1.5mg/cm^2$ dust concentration.

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characteristics of Magnesia Dam Block for Tundish Vessel in Steel Making Process (턴디쉬용 마그네시아질 댐블록의 제조와 그특성)

  • 정두화;김상모;이석근
    • Journal of the Korean Ceramic Society
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    • v.36 no.8
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    • pp.876-885
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    • 1999
  • In order to develop high performance basic dam block for tundish vessel in steel-making binders and additives on hydration and thermal characteristics of magnesiz castable refractories were studied. Crack initiation and propagation in cement bonded magnesia castables due to slaking of magnesia clinker at drying process were suppressed by using spinel clinker instead of magnesia powder. In case of Na2O$.$2CaO$.$P2O5(NC2P) bonded castable crack initiation due to slaking of magnesia clinker did not occur but bending strength at high temperature was low. Mechanical properties of NC2P bonded castable refractories at high temperature were improved by using magnesia clinker that contains low SiO2 contents.

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ELECTRICAL BREAKDOWN INITIATION OF ANODIC FILMS DURING ANODIZING IN MOLTEN BISULPHATE MELT

  • Han, S.H.;Thompson, G.E.
    • Journal of the Korean institute of surface engineering
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    • v.32 no.3
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    • pp.341-343
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    • 1999
  • The morphology and composition of anodic films, formed on aluminium at various current densities, in the range $1-100{\;}Am^{-2}$, in the molten bisulphate melt at different temperatures (418-498K), have been studied using transmission electron microscopy of ultramicrotomed film sections, and ion beam thinned films. The first sign of incipient breakdown revealed by transmission electron microscopy of stripped films, is always the appearance of dark regions about 1,000 nm in diameter, representing local overgrowth of the film. The breakdown mechanism is closely related to thermal effects, because temperature rises at regions representing local overgrowth in the stripped films were observed at voltages close to the breakdown voltage, likely arising through impact ionization.

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