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  • Title/Summary/Keyword: Thermal-mechanical Fatigue

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Histologic Characteristics and Mechanical Properties of Bovine Pericardium Treated with Decellularization and α-Galactosidase: A Comparative Study

  • Min, Byoung-Ju;Kim, Yong Jin;Choi, Jae-Woong;Choi, Sun Young;Kim, Soo Hwan;Lim, Hong-Gook
    • Journal of Chest Surgery
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    • v.45 no.6
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    • pp.368-379
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    • 2012
  • Background: Bioprostheses for cardiovascular surgery have limitations in their use following as calicification. α-galactosidase epitope is known as a stimulant of immune response and then shows a progressing calcification. The objective of this study was to evaluate histologic characteristics and mechanical properties of decellularization and treated with α-galactosidase. Materials and Methods: Bovine pericardial tissues were allocated into three groups: fixation only with glutaraldehyde, decellularization with sodium dodesyl sulfate and decellularization plus treatment with α-galactosidase. We confirmed immunohistological characteristics and mechanical properties as fatigue test, permeability test, compliance test, tensile strength (strain) test and thermal stability test. Results: Decellularization and elimination of α-gal were confirmed through immunohistologic findings. Decellularization had decreased mechanical properties compared to fixation only group in permeability (before fatigue test p=0.02, after fatigue test p=0.034), compliance (after fatigue test p=0.041), and tensile strength test (p=0.00). The group of decellularization plus treatment with α-galactosidase had less desirable mechanical properties than the group of decellularization in concerns of permeability (before fatigue test p=0.043) and strain test (p=0.001). Conclusion: Favorable decellularization and elimination of α-gal were obtained in this study through immunohistologic findings. However, those treatment including decellularization and elimination of α-gal implied the decreased mechanical properties in specific ways. We need more study to complete appropriate bioprosthesis with decellularization and elimination of α-gal including favorable mechanical properties too.

A Study on the Effects of Package and PCB Materials on Thermal Characteristics of PDIP (패키지 및 PCB 재료가 PDIP 열특성에 미치는 영향에 관한 연구)

  • 정일용;이규봉
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.3
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    • pp.729-737
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    • 1994
  • A three-dimensional finite element model of a 20-pin plastic dual-in-line package(PDIP) plugged into a PCE has been developed by using the finite element code ANSYS. The model has been used for thermal characterization of the package during its normal operation under natural convection cooling. Temperature distributions in the package and PCB are obtained from numerical analysis and compared with experimentally measured data. Various cases are assumed and analyzed to study the effects of package and PCB materials on thermal characteristics of PDIP with and without aluminum heatspreader. Thermal dissipation capability of PDIP is greatly increased due to copper die pad/lead frame and heatspreader. However, thermally induced stresses in the package and fatigue life of chip are improved for PDIP with Alloy 42 die pad/lead frame and no heatspreader. It is also found that the role of PCB on thermal characteristics of PDIP is very imporatant.

A Study on the Mechanical Properties Change by Stress Aging of 2.25Cr-1Mo Steel (2.25Cr-1Mo 강의 응력 시효에 의한 기계적 특성 변화에 대한 연구)

  • Yang, Hyun-Tae;Kim, Sang-Tae
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.517-522
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    • 2001
  • The purpose of this study is to investigate the thermal embrittlement and the mechanical properties of 2.25Cr-1Mo steel aged at high temperature and stress for 250 hours. Original, aged artificially material were tested to obtain the hardness and impact absorbed energy. Hardness and impact absorbed energy decreased with the increasing aging time. The carbide morphology with the thermal embrittlement was found to contribute to the mechanical property change by X-Ray diffraction method.

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Study on Safety Design of Vertical-Type Heat Recovery Steam Generator Based on Large-Scale Analysis (대규모해석을 활용한 수직형 배열회수 증기발생기의 안전설계에 관한 연구)

  • Ryu, Tae-Young;Yang, Sang-Mo;Jang, Hyun-Min;Choi, Jae-Boong;Myung, Ki-Chul;Lee, Dong-Yun;Choi, Shin-Beom
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.12
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    • pp.1535-1542
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    • 2012
  • A Heat Recovery Steam Generator(HRSG) is the main component of a Combined Cycle Power Plant(CCPP). It is a very large structure that is made from relatively thin metal sheets. Therefore, the structural integrity of an HRSG is very important to ensure safe operation during plant lifetime. In particular, thermal deformation and thermal fatigue have been revealed as the main causes of the mechanical degradation of an HRSG. In order to prevent unexpected damage, safety evaluation based on a large-scale analysis is necessary. Therefore, this study aims to improve the safety of HRSG by using Finite Element Analysis(FEA) results derived from large-scale analysis. Furthermore, the modified design is verified by comparing it with the original one. This result will be used as basic data for improving the safety of a vertical-type HRSG.

Thermal Stress Analysis for a Brake Disk considering Pressure Distribution at a Frictional Surface (마찰면의 압력 분포를 고려한 제동디스크의 열응력 해석)

  • Lee Y.M.;Park J.S.;Seok C.S.;Lee C.W.;Kim J.H.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.10a
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    • pp.842-846
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    • 2005
  • A brake disk and a pad are important parts that affect the braking stability of a railway vehicle. Especially, because a brake disk stops the vehicle using conversion of the kinetic energy to frictional energy, thermal fatigue cracks are generated by the cyclic thermal load, as frictional heat, on a frictional surface and these cracks cause the fracture of a brake disk. Therefore, many researches for the thermal stress must be performed to improve the efficiency of brake disk and ensure the braking stability. In this study, we performed the thermal stress analysis for a ventilated brake disk with 3-D analysis model. For that, we simplified the shape of a ventilated hole to minimize problems that could be occurred in analysis process. Thermal stress analysis was performed in case that pressure distributions on a frictional surface is constant and is not. To determine pressure distributions of irregular case, pressure distribution analysis for a frictional surface was carried out. Finally using the results that were obtained through pressure distribution analysis, we carried out thermal stress analysis of each case and investigated the results of thermal stress analysis.

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Thermal Fatigue Degradation Behavior of Ni-Ti Shape Memory Alloy (Ti-Ni 형상기억합금의 열피로열화 거동)

  • 박영철;조용배;오세욱
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.11
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    • pp.2913-2921
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    • 1994
  • In SMA(shape memory alloy), the degradation by fatigue is one of the most important problems to be overcome, when SMA is used for robot-actuator material. The actuator is operated repeatitively for long time and its repeating operation develops the fatigue degradation of SMA. The fatigue degradation changes the transformation temperature and deformation behavior and results in inaccurate operation control of robot. Accordingly, the changing behavior of transformation temperature and deformation which results from repeating operation is to be investigated in advance and the scheme to resolve those problems have to be made for the design of actuator. In this study, the fatigue tests were carried out on SMA specimens prepared to have different condition of aging time and pre-strain with the direct-current heating-cooling method, which was a general method of operation in robot actuators. The behavior of transformation temperature and deformation were examined and analyzed in each specimen and the study was performed to establish the optimistic manufacturing condition of SMA against the fatigue degradation.

Assessment of Creep-Fatigue Crack Growth for a High Temperature Component (고온 기기의 크리프-피로 균열성장 평가)

  • Lee, Hyeong-Yeon;Kim, Jong-Bum;Lee, Jae-Han
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.264-268
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    • 2008
  • An assessment of creep-fatigue crack behavior is required to ensure the structural integrity for high temperature components such as fast breeder reactor structures or thermal power plant components operating at an elevated temperature. In this study, an evaluation of creep-fatigue crack growth has been carried out according to the French assessment guide of the RCC-MR A16 for austenitic stainless steel structures. The assessment procedures for creep-fatigue crack growth in the recent version of the A16 (2007 edition) have been changed considerably from the previous version (2002 edition) and the material properties (RCC-MR Appendix A3) have been changed as well. The impacts of those changes on creep-fatigue crack growth behavior are quantified from the assessments with a structural model. Finally the assessment results were compared with the observed images obtained from the structural tests of the same structural specimen.

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Comparison of Experimental and Numerical Analysis for Durability Design Criteria in Ceramic Catalyst Substrate (세라믹 촉매 담체의 내구 설계 기준에 대한 실험 및 수치해석의 비교)

  • Beak, Seok-Heum;Cho, Seok-Swoo
    • Journal of the Korean Society for Precision Engineering
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    • v.27 no.9
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    • pp.58-66
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    • 2010
  • This study examines thermal safety on three-way catalyst that dominates 70 % among whole exhaust gas purification device in 2003. Three-way catalyst durability in the Korea requires 5 years/80,000 km in 1988 but require 10 years/120,000 km after 2002. Three-way catalyst durability in the USA requires 7 years/120,000 km but require 10 years/160,000 km after 2004. Three-way catalyst maintains high temperature in interior domain but maintains low temperature on outside surface. Therefore this device shows tensile stress on outside surface. Temperature distribution of three-way catalyst was acquired by thermal flow analysis for predicted thermal flow parameter. Thermal stress analysis for three-way catalysis was performed based on this temperature distribution. Thermal safety of three-way catalyst was estimated by power law dynamic fatigue life estimation and strength reduction methods for thermal stress.

Thermo-Mechanical Fatigue Analysis of Ribbon Wire/Ag Electrode Interfaces for PV Module

  • Park, No-Chang;Hong, Won-Sik;Han, Chang-Un;Kim, Dong-Hwan
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2011.05a
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    • pp.48.1-48.1
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    • 2011
  • In this presentation, We monitored weather data, such as global irradiance, ambient temperature, temperature of PV module, relative humidity and windspeed for 2 years, for determining accelerated test condition. then, we determined the temperature limit of accelerated test through weather data and FEM analysis. Detailed procedures will be summarized in this work. After analysing outdoor stress such as thermal stress, we decided main failure modes and mechanisms of PV module, especially solder joint of ribbon wire. we carried out the measurement of material properties such as thermal expansion coefficient for planning of accelerated test. we designed accelerated test based on FEM analysis results. we carried out thermal cycling test with 1 cell mini module for 3 months. We monitored the change of electrical performance every 1 week such as Voc, Isc, Pmax, etc. and then, we analized the ribbon wire/electrode intefaces. Detailed results will be summarized in this work.

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Assessment of fatigue damage in 5% chrome cold rolling work roll (5% 크롬 냉간 압연용 작업롤의 피로손상 평가에 대한 연구)

  • Kwak, G.J.;Kim, K.S.;Lee, S.W.;Yeo, W.K.;Park, Y.C.
    • Proceedings of the KSME Conference
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    • 2000.11a
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    • pp.316-321
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    • 2000
  • The role of fatigue on the surface damage of 5% chrome cold milling work roll is evaluated. Uniaxial and torsional fatigue tests are carried out, and the baseline data for fatigue life evaluation are established. An appropriate multiaxial fatigue parameter is developed from the fatigue data. Fatigue tests are also performed under compressive mean stresses, and a mean stress model is formulated. A computer program is developed to assess the interaction of fatigue and grinding of the roll. The fatigue damage is computed for selected servicing conditions. It is found that the fatigue damage can be an important issue when the effect of mean stress is ignored, however the fatigue damage is negligibly small when the effect of mean stress including the residual stresses currently used is fully accounted. The result indicates that spalling due to the growth of thermal shock cracks is more important than fatigue damage in roll surface failure.

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