• Title/Summary/Keyword: thermal initiation

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Development of probabilistic primary water stress corrosion cracking initiation model for alloy 182 welds considering thermal aging and cold work effects

  • Park, Jae Phil;Yoo, Seung Chang;Kim, Ji Hyun;Bahn, Chi Bum
    • Nuclear Engineering and Technology
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    • v.53 no.6
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    • pp.1909-1923
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    • 2021
  • We experimentally investigated the effects of thermal aging and cold work on the microstructure, mechanical properties, and primary water stress corrosion cracking (PWSCC) initiation time for Alloy 182 welds. The effects of thermal aging and cold work on the PWSCC initiation time of Alloy 182 were modeled based on the plastic energy concept and the PWSCC initiation data of this study and previous reports by considering censored data. Based on the results, it is estimated that the PWSCC resistance of the Alloy 182 weld firstly increases and then decreases with thermal aging time when the applied stress is kept constant.

Effect of Initiator on Performance of Polyvinylacetate as Emulsion Adhesive

  • Lee, Kangseok;Shim, Sang Eun
    • Elastomers and Composites
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    • v.50 no.4
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    • pp.286-291
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    • 2015
  • Polyvinylacetate (PVAc) was prepared using thermal initiation and redox initiation via emulsion polymerization at $80^{\circ}C$. The polymerization conditions had a significant effect on the properties of the synthesized PVAc. When hydrogen peroxide and tartaric acid as the initiator for redox polymerization were used, the synthesized PVAc had a low molecular weight. In comparison with thermal polymerization, smaller PVAc particles were formed during the redox polymerization due to relatively faster polymerization rate, which in turn resulted in improved adhesion property. It is considered that the rapid generation of smaller particles induces the formation of a large surface area.

The Application of the Pseudo Molecular Complex to Thermal Polymerization (Ⅰ). Proposal of A New Initiation Mechanism (의사분자 착물의 응용 (제1보). 열중합 개시기구 제안)

  • Byung Kack Park
    • Journal of the Korean Chemical Society
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    • v.18 no.6
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    • pp.447-452
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    • 1974
  • A mechanistic possibility for the initiation of the thermal polymerization reactions are envisaged theoretically. As result of the considerations, it is assumed that the thermal polymerization reactions take place via the pseudo molecular complex which has been supposed to be an intermediate in the transition state of Diels-Alder reactions.

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Thermal Shock Resistance of $Al_{2}O_{3}$- and Fe-$Al_{2}TiO_{5}$-based Castable Refractories

  • Liu, T.;Latella, B.A.;Bendeich, P.
    • The Korean Journal of Ceramics
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    • v.4 no.4
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    • pp.345-351
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    • 1998
  • Thermal shock resistance of $Al_2O_3$- and Fe-$Al_2TiO_5$-based Castable Refractories was studied using a central heating technique. Ring type specimens, 10mm thick and 20 and 100mm inner and outer diameters, respectively, were rapidly heated on the internal surface of the centre hole using a high power electrical heating element. The temperature field was measured experimentally and modelled using finite element analysis (FEA). The thermal stress field was also modelled using FEA. A radial notch was introduced to the ring specimens to enable calculation of the thermal stress intensity factors (SIF). A special LVDT device was incorporated in the thermal shock tester to monitor crack mouth opening displacement (COD). The thermal shock fracture initiation and crack propagation behaviour of the castable refractories were ascertained using the COD measurements and the fracture mechanics analysis data.

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Prediction of Liquation Crack Initiation at HAZ of Laser Weldment Based on Strain Analysis at Elevated Temperature

  • Yamamoto, Motomichi;Shinozaki, Kenji;Kitamura, Mitsuru;Shirai, Makoto
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.244-249
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    • 2002
  • The purpose of this study is to develope the prediction method of liquation crack initiation in HAZ of laser weldment. Thermal two dimensional strain analyses were performed by FEM for bead-on-plate welding in order to obtain the plastic strain at elevated temperature in HAZ of the laser weldment. From these results, it became clear that the plastic strain at elevated temperature affected liquation crack initiation in HAZ, and it could be proposed that the critical strain, which controlled liquation crack initiation, existed. Moreover, an attempt was made to develop thermal and dynamic three dimensional strain analysis method for the laser weldment in order to obtain the plastic strain at elevated temperature in HAZ of the laser weldment in more detail and precisely.

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Effect of Geometrical Discontinuity on Ductile Fracture Initiation Behavior under Static Leading

  • An, G.B.;Ohata, M.;Toyoda, M.
    • International Journal of Korean Welding Society
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    • v.3 no.1
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    • pp.51-56
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    • 2003
  • It is important to evaluate the fracture initiation behaviors of steel structure. It has been well known that the ductile cracking of steel would be accelerated by triaxial stress state. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameters, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of notch radius, which can elevate plastic constraint due to heterogeneous plastic straining on critical condition to initiate ductile crack using two-parameters. Hense, the crack initiation testing were conducted under static loading using round bar specimens with circumferential notch. To evaluate the stress/strain state in the specimens was used thermal elastic-plastic FE-analysis. The result showed that equivalent plastic strain to initiate ductile crack expressed as a function of stress triaxiality obtained from the homogeneous specimens with circumferential notched under static loading. And it was evaluated that by using this two-parameters criterion, the critical crack initiation of homogeneous specimens under static loading.

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Criterion for ductile crack initiation with strength mismatch under dynamic loading (강도적 불균질을 갖는 구조물의 동적하중하에서의 연성크랙 발생조건)

  • 안규백;일본명;일본명;방한서;일본명
    • Proceedings of the KWS Conference
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    • 2003.11a
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    • pp.179-181
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    • 2003
  • The present study focuses on the effect of geometrical discontinuity, strength mismatch, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on the ductile crack initiation using two-parameter criterion. Fracture initiation testing has been conducted under static and dynamic loading using circumferentially notched round-bar specimens. 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.

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Nondestructive Evaluation of Thermal Shock Damage for Alumina Ceramics (알루미나 세라믹에 대한 열충격 손상의 비파괴적 평가)

  • Lee, Jun-Hyeon;Lee, Jin-Gyeong;Song, Sang-Heon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.8
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    • pp.1189-1196
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    • 2001
  • The objective of this paper is to investigate the applicability of acoustic emission(AE) technique to monitor the progress of the thermal shock damage on alumina ceramic. For this purpose, alumina ceramic specimen was heated in the furnace and then was quenched in the water tank. When the specimen was quenched in the water tank, complex AE signals due to the initiation of micro-cracks and boiling effect were generated by the progress of thermal shock damage. These mixed AE signals have to be classified for monitoring the degree of the thermal shock damage of alumina ceramics. In this paper, the mixed AE signals generated from both the boiling effect and the crack initiation under thermal shock test was analyzed. The characteristics of AE signals were also discussed by considering the variation of bending strength and Yongs modulus of specimens.

Investigation of the Contributions of Creep and Thermal Fatigue to Failure of a High-Intermediate Pressure Steam Turbine Casing

  • Lee, Jaehong;Jung, Nam-gun
    • KEPCO Journal on Electric Power and Energy
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    • v.6 no.1
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    • pp.41-47
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    • 2020
  • The contribution of damage mechanisms to failure of steam turbine casing made of Cr-Mo-V steel was investigated. Creep-fatigue interaction on the HP side corner of turbine casing was revealed as the root cause of the catastrophic failure performed by metallurgical analysis. The steady-state pressure and transient thermal stress were analyzed based on the actual operating condition of the thermal plant. Damage of creep-fatigue interaction to crack initiation was evaluated with multiaxial effects. The contribution ratio of creep and fatigue to the crack initiation was estimated to 3:1. Temporary geometrical correct action with repair weld was executed. For long-term operation, design improvement of casing equipment for creep resistance should be needed.

Thermal Impact Characteristics by Forest Fire on Porcelain Insulators for Transmission Lines

  • Lee, Won-Kyo;Choi, In-Hyuk;Choi, Jong-Kee;Hwang, Kab-Cheol;Han, Se-Won
    • Transactions on Electrical and Electronic Materials
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    • v.9 no.4
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    • pp.143-146
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    • 2008
  • In this study the thermal impact characteristics by forest fire are extensively investigated using temperature controlled ovens. The test conditions for thermal impact damage are simulated according to the characteristics of natural forest fire. The test pieces are suspension porcelain insulators made by KRI in 2005 for transmission lines. In the thermal impact cycle tests with $300\;^{\circ}C$ thermal impact gradient (-70 to $230\;^{\circ}C$), cycling in 10 minute periods, no critical failures occurred in the test samples even with long cycle times. But in tests with thermal impact gradient from room temperature to $200-600\;^{\circ}C$, cycling in 10 to 30 minute periods, there were critical failures of the porcelain insulators according to the thermal impact gradient and quenching method. In the case of thermal impact by forest fire, it was found of that duration time is more important than the cycling time, and the initiation temperature of porcelain insulator failures is about $300\;^{\circ}C$, in the case of water quenching, many cracks and fracture of the porcelain occurred. It was found that the thermal impact failure is closely related to the displacement in the cement by thermal stress as confirmed by simulation. It was estimated that the initiation displacement by the thermal impact of $300\;^{\circ}C$ is about 0.1 %. Above 1% displacement, it is expected that the most porcelain insulators would fail.