• Title/Summary/Keyword: Material degradation

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A study on radiation degradation of LDPE by using ESR (ESR을 이용한 저밀도 폴리에틸렌의 방사선 열화에 관한 연구)

  • Kim, Ki-Yup;Kim, Jin-Ah;Lee, Chung;Kim, Pyeong-Jong;Ryu, Boo-Hyung
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2004.07a
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    • pp.473-476
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    • 2004
  • This study has investigated radiation degradation of low density polyethylene(LDPE). Samples were irradiated using a $Co^{60}\;\gamma-ray$ and ray up to 800 kGy at a dose rate of 5 kGy/hr in the presence of air atmosphere at room temperature. After irradiation, free radical measurement of LDPE has established by electron spin resonance(ESR). Then, each sample was stored for 2 weeks. ESR measurement showed that free radical concentration(FRC) was increased with radiation dose and changed from alkyl, allyl radical to peroxy radical with time.

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Study on the analyzing method for examine the thyristor characteristic degradation due to the aging (Thyristor소자의 열화에 따른 특성저하 분석기법에 관한 연구)

  • Kim, Hyoung-Woo;Seo, Kil-Soo;Kim, Ki-Hyun;Lee, Yang-Jae;Choi, Nak-Kwon;Kim, Eun-Dong
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2005.07a
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    • pp.99-100
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    • 2005
  • Reliability of the thyristor has a major effects on the high power systems such as HVDC, SVC and FACTs, etc. Therefore, analyzing method for thyristor aging is important to improve the stability of thyristor and high power systems. In this paper, we explain the analyzing method for examine the thyristor aging effect. And also, the thyristor aging experiments were performed to investigate the characteristic degradation due to the aging.

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Prediction of stiffness degradation in composite laminate with transverse cracking and delamination under hygrothermal conditions-desorption case

  • B. Boukert;M. Khodjet-Kesba;A. Benkhedda;E.A. Adda Bedia
    • Advances in aircraft and spacecraft science
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    • v.11 no.1
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    • pp.1-21
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    • 2024
  • The stiffness reduction of cross-ply composite laminates featuring a transverse cracking and delamination within the mid-layer is predicted through utilization of a modified shear-lag model, incorporating a stress perturbation function. Good agreement is obtained by comparing the prediction models and experimental data. The material characteristics of the composite are affected by fluctuations in temperature and transient moisture concentration distribution in desorption case, based on a micro-mechanical model of laminates. The transient and non-uniform moisture concentration distribution induces a stiffness reduction. The obtained results demonstrate the stiffness degradation dependence on factors such as cracks density, thickness ratio and environmental conditions. The present study underscores the significance of comprehending the degradation of material properties in the failure progression of laminates, particularly in instances of extensive delamination growth.

The flexural strength Changes by the Low Temperature Degradation of Uncolored zirconia Ceramic for All Ceramic Restoration (전부도재 수복을 위한 무색지르코니아 세라믹의 저온열화에 따른 굴곡강도 변화)

  • Kim, Jung-Sook
    • Journal of Technologic Dentistry
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    • v.31 no.2
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    • pp.39-44
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    • 2009
  • In the orthopedic field which firstly used zirconia as artificial joints, researchers had studied the reasons for collapsing zirconia used as restorative material by accumulated inner cracks in several years and they found out Low Temperature Degradation is one of the reasons. In the dentistry field, it has not been too long since they used zirconia as the cores of all-ceramic restoration; however, the study is needed as prophylactic measure against Low Temperature Degradation which can be caused by saliva wetting the mouth all the time and frictional forces such as bite pressure and masticatory pressure. Artificial aging by autoclaving is used because there are difficulties of testing in the patient's mouth. To study the changes in the material properties, the flexural strength of dental zirconia ceramic is measured before and after the test. The following are the result of the test. 1) The zirconia blocks in the autoclaves at $130^{\circ}C$ and $200^{\circ}C$ are phase-shifted tetragonal to monoclinic by Low Temperature Degradation. 2)The non-autoclaved specimens have the average fractural strength of 1346.4MPa, the specimens autoclaved at $130^{\circ}C$ have 1226.4Mpa and the specimens autoclaved at $200^{\circ}C$ have 1024.1MPa. The tests show that as the temperature increases, the flexural strength tend to decrease and the differences are noticeable(p<0.001). 3)Through the Duncan's post-hoc test, the differences in flexural strength of the 3 groups were listed in order of strength like normal temperature>at $130^{\circ}C$ autoclave low temperature degradation> at $200^{\circ}C$ autoclave low temperature degradation.

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Degradation Quantification Method and Degradation and Creep Life Prediction Method for Nickel-Based Superalloys Based on Bayesian Inference (베이지안 추론 기반 니켈기 초합금의 열화도 정량화 방법과 열화도 및 크리프 수명 예측의 방법)

  • Junsang, Yu;Hayoung, Oh
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.27 no.1
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    • pp.15-26
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    • 2023
  • The purpose of this study is to determine the artificial intelligence-based degradation index from the image of the cross-section of the microstructure taken with a scanning electron microscope of the specimen obtained by the creep test of DA-5161 SX, a nickel-based superalloy used as a material for high-temperature parts. It proposes a new method of quantification and proposes a model that predicts degradation based on Bayesian inference without destroying components of high-temperature parts of operating equipment and a creep life prediction model that predicts Larson-Miller Parameter (LMP). It is proposed that the new degradation indexing method that infers a consistent representative value from a small amount of images based on the geometrical characteristics of the gamma prime phase, a nickel-base superalloy microstructure, and the prediction method of degradation index and LMP with information on the environmental conditions of the material without destroying high-temperature parts.

An Evaluation on Electrochemical Polarization Characteristics and Material Degradation for Cr-Mo-V Steel (Cr-Mo-V강의 전기화학적 분극 특성과 재질열화 평가)

  • Kwon, Il-Hyun;Lee, Song-In;Ha, Jeong-Soo;Yu, Hyo-Sun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.22 no.3
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    • pp.267-274
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    • 2002
  • This research is described on the applicability of a electrochemical techniques for evaluating nondestructive material degradation with various polarization characteristics for Cr-Mo-V steel. The applied electrochemical technique is anodic polarization test which are widely used to evaluate the corrosion rate and/or sensitization at depleted zone of strengthening elements mainly caused by thermal experience for stainless steels. The evaluation of material degradation is performed by small punch test which has been well known as micromechanics test method using specimen size of $10{\times}10{\times}0.5mm$. The 1,000hrs aged material at $630^{\circ}C$ shows the highest material degradation$({\Delta}[DBTT]_{SP})$, but the 2,000hrs and 3,000hrs aged materials show the decrease of ${\Delta}[DBTT]_{SP}$ as aging time increases. It is observed that the difference of current density $({\Delta}I_{FP}\;and\;{\Delta}I_{SP})$.

A study on the degradation by the hot carrier trapping of the submicron MOSFET with long stress condition (장시간 스트레스 조건에서 submicron MOSFET의 열전자 트래핑에 의한 노화현상에 대한 연구)

  • 홍순석
    • Electrical & Electronic Materials
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    • v.8 no.3
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    • pp.357-361
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    • 1995
  • An experiment on characteristics of nMOSFET's in the long stress condition with the maximum of the substrate current has been carried out in order to study on the degradation due to the hot-carrier effect. Based on the measured result of the threshold voltage, the damage is mostly due to the hole injection into the oxide. After long stress, it was shown that the drain current increased at low gate voltages and hence decreased at high gate voltages.

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Degradation of PLEDs and a Way to Improve Device Performances

  • Kim, Sung-Han;Hsu, Che;Zhang, Chi;Skulason, Hjalti;Uckert, Frank;Lecloux, Dan;Cao, Yong;Parker, Ian
    • Journal of Information Display
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    • v.5 no.2
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    • pp.14-18
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    • 2004
  • The most significant degradation problem of PLED has been described and new buffer layer material aimed for use as HTL in PLED to solve this issue has been studied. This approach has enabled the increase of the green device efficiency (${\sim}$2x) and lifetime (${\sim}$5-6x).

State of the Art in Life Assessment for High Temperature Components Using Replication Method (표면복제기법을 이용한 고온 설비의 수명평가 현황과 적용사례)

  • Kim, Duck-Hee;Choi, Hyun-Sun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.30 no.5
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    • pp.489-496
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    • 2010
  • The power generation and chemical industry have been subjected to further material degradation with long term operations and need to predict the remaining service life of components, such as reformer tube and steam turbine rotor, that have operated at elevated temperatures. As a non-destructive technique, replication method with reliable metallurgical life and microstructural soundness assessment has been recognized with strongly useful method until now. Developments of this method have variously accomplished by new quantitative approach, such as carbide analysis, with A-parameter and grain deformation method. An overview of replication, some new techniques for material degradation and life assessment were introduced in this paper. Also, on-site applications and its reasonableness were described. As a result of having analyzed microstructure by replication method, carbide approach was quantitatively useful to life assessment.