• 제목/요약/키워드: Creep Resistance

검색결과 193건 처리시간 0.022초

2.25Cr1Mo강의 크리프 손상에 대한 초음파 시험평가 (Ultrasonic Evaluation for the Creep Damage of 2.25Cr1Mo Steel)

  • 허광범;이인철;정계조;조용상;이상국;김재훈
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2000년도 춘계학술대회논문집A
    • /
    • pp.31-36
    • /
    • 2000
  • High temperature and pressure materials in power plant are degraded by creep damage, if they are exposed to constant loads for long times, which occurs in the load bearing structures of pressurized components operating at elevated temperatures. Many conventional measurement techniques such as replica method, electric resistance method, and hardness test method for measuring creep damage have been used. So far, the replica method is mainly used for the Inspection of High temperature and pressure components. This technique is, however, restricted to applications at the surface of the testpieces and cannot be used to material inside. In this paper, ultrasonic evaluation for the detection of creep damage in the form of cavaties on grain boundaries or integranular microcracks are carried out. And the absolute measuring method of quantitative ultrasonic velocity technique for Cr-Mo material degradation is analyzed. As a result of ultrasonic tests for crept specimens, we find that the sound velocity is decreased as the increase of creep life fraction$({\Phi}_c)$ and also, confirmed that hardness is decreased as the increase of creep life fraction$({\Phi}_c)$ but the coefficient of ultrasonic attenuation is increased as the increase of creep life fraction$({\Phi}_c)$. Finally based on the result in this paper, it can be recognized that the ultrasonic techniques using velocities and attenuation coefficient factor are very useful non-destructive methods to evaluate the degree of material degradation in fossile power plants.

  • PDF

Nb 첨가 Zr 합금의 미세조직과 Creep 특성에 미치는 마지막 열처리 온도의 영향 (Effect of Final Annealing Temperature on Microstructure and Creep Characteristics of Nb-containing Zirconium Alloys)

  • 박용권;윤영권;위명용;김택수;정용환
    • 한국재료학회지
    • /
    • 제11권10호
    • /
    • pp.879-888
    • /
    • 2001
  • The effects of final annealing temperature on the microstructure and creep characteristics were investigated for the Zr-lNb-0.2X (X=0, Mo, Cu) and Zr-lNb- 1Sn-0.3Fe-0.1X (X=0, Mo, Cu) alloys. The microstructures were observed by using TEM/EDS, and grain size and distributions of precipitates were analyzed using a image analyzer. The creep test was performed at $400^{\circ}C$ under applied stress of 150 MPa for 10 days. The $\beta$-Zr was observed at annealing temperature above $600^{\circ}C$. In the temperature above$ 600^{\circ}C$, the grain sizes of both alloy systems appeared to be increased with increasing the final annealing temperature. The creep strengths of Zr-1Nb-1Sn-0.3Fe-0.1X alloys were higher than those of Zr-1Nb-0.2X ones due to the effect of solid solution hardening by Sn in Zr-lNb-lSn-0.3Fe-0.1X alloy system. Also, Mo addition showed the strong effect of precipitate hardening in both alloy systems. The creep strength rapidly decreased with increasing the annealing temperature up to $600^{\circ}C$. However, a superior creep resistance was obtained in the sample that annealed to have a second phase of $\beta$-Zr. It was considered that the appearance of $\beta$-Zr would play an important role in the strengthening mechanism of creep deformation.

  • PDF

용융탄산염 연료전지의 양극 대체재료의 개발에 관한 연구 (A Study on the Development of Anode Material for Molten Carbonate Fuel Cell)

  • 황응림;김선지;강성군
    • 에너지공학
    • /
    • 제2권3호
    • /
    • pp.293-299
    • /
    • 1993
  • 용융탄산염연료전지(MCFC)용 다공성 Ni 양극에 3~10 wt% Al를 첨가하여 tape casting 법으로 제조된 Ni-Al 양극의 전기화학적성능 및 구조적안정성이 조사되었다. 본 연구에서 제조된 양극의 전기화학적 성능이 $650^{\circ}C$, MCFC 양극분위기(80% H$_2$+20% $CO_2$)를 모사한 half-cell 에서 양분극 특성으로 평가되었는데, 전류밀도 150 ㎃/$\textrm{cm}^2$ 에서의 분극전압은 약 100 ㎷로 실용전지의 양극으로서 가능성을 보였다. Ni-Al 양극의 소결과 creep에 대한 저항성은 Ni 양극에 비해 증가되었는데, 이는 Ni 입자 표면에 형성된 $Al_2$O$_3$의 영향으로 판단되었다.

  • PDF

Performance Assessment of PVA Geotextile/HDPE Geomembrane Composites

  • 전한용;홍상진;류원석
    • 한국지반신소재학회논문집
    • /
    • 제4권1호
    • /
    • pp.37-46
    • /
    • 2005
  • 폐기물 매립지 관련 특성을 조사하기 위하여 PVA 지오텍스타일/HDPE 지오멤브레인 복합재료를 제조하였다. PVA 지오텍스타일의 인장특성, 인열 및 파열강도, 유효구멍크기와 투수성 등을 각각 측정하였다. 또한 침출수에 대한 화학저항성과 자외선 안정성도 측정하였으며, 하중조건에 따른 크리프 변형거동과 마찰특성도 측정하였다. 이들 결과로부터 PVA 지오텍스타일/HDPE 지오멤브레인 복합재료는 일반적으로 폐기물 매립지에 적용되는 폴리프로필렌이나 폴리에스테르 지오텍스타일에 비해 우수한 특성을 나타내었다. 끝으로, 감소인자 분석으로부터 PVA 지오텍스타일/HDPE 지오멤브레인 복합재료의 크리프 변형거동도 폴리프로필렌이나 폴리에스테르 지오텍스타일에 비해 안정함을 알 수 있었다.

  • PDF

Mechanical Properties of Ultra-High Molecular Weight Polyethylene Irradiated with Gamma Rays

  • Lee, Choon-Soo;Yoo, Seung-Hoo;Jho, Jae-Young;Park, Kuiwon;Hwang, Tae-Won
    • Macromolecular Research
    • /
    • 제12권1호
    • /
    • pp.112-118
    • /
    • 2004
  • With the goal of enhancing the creep resistance of ultra-high molecular weight polyethylene (UHMWPE), we performed gamma irradiation and post-irradiation annealing at a low temperature, and investigated the crystalline structures and mechanical properties of the samples. Electron spin resonance spectra reveal that most of the residual radicals are stabilized by annealing at 100$^{\circ}C$ for 72 h under vacuum. Both the melting temperature and crystallinity increase after increasing the dose and by post-irradiation annealing. When irradiated with the same dose, the quenched sample having a higher amorphous fraction exhibits a lower swell ratio than does the slow-cooled sample. The measured tensile properties correlate well to the crystalline structure of the irradiated and annealed samples. For enhancing creep resistance, high crystallinity appears to be more critical than a high degree of crosslinking.

플라즈마 침탄 및 CrN 코팅된 Ti-6Al-4V 합금의 구조 및 Creep특성 (Creep Properties of Plasma Carburized and CrN Coated Ti-6Al-4V Alloy)

  • 위명용;박용권
    • 한국재료학회지
    • /
    • 제14권8호
    • /
    • pp.558-564
    • /
    • 2004
  • In order to improve the low hardness and low wear resistance of Ti-6Al-4V alloy, plasma carburization treatment and CrN film coating were carried out. Effects of the plasma carburization and CrN coating were analyzed and compared with the non-treated alloy by mechanical and creep tests. After plasma carburization and CrN coating treatments, the carburized layer was about 150 ${\mu}m$ in depth and CrN coated layer was about 7.5 ${\mu}m$ in thickness. Hardness value of about $H_{v}$ 402 of the non-treated alloy was improved to $H_{v}$ 1600 and 1390 by plasma carburization and CrN thin film coating, respectively. Stress exponent(n) was decreased from 9.10 in CrN coating specimen to 8.95 in carburized specimen. However, the activation energy(Q) was increased from 242 to 250 kJ/mol. It can be concluded that the static creep deformation for Ti-6Al-4V alloy is controlled by the dislocation climb over the ranges of the experimental conditions.

확률적 방법에 의한 크리프 균열성장 계수의 분포 추정 (Estimation for the Distribution of Creep Crack Growth Coefficients by Probabilistic Assessment)

  • 이상호;윤기봉;최병학;민두식;안종석;이길재;김선화
    • 대한금속재료학회지
    • /
    • 제48권9호
    • /
    • pp.791-797
    • /
    • 2010
  • The creep crack growth rate (da/dt) of the Cr-Mo steels tested by pre-crack and the voltage (or resistance) variables were related into fracture parameter (Ct), crack growth coefficient (H), and an exponent (q) in the parts of Base, weld and HAZ. The fracture parameter (Ct) has various variables relating to the specimen and crack shape, applied stress, and creep strain curve. The H and q was inferred by OLS regression (ordinary least square method), and the H values were solved in statistics and probability assessment, which were attained fromPDF's distributions (probability density function). The HAZ part has the highest value of q by OLS regression and the widest distribution of H by PDF of WEIBULL, which means that the crack sensitivity of HAZ should be cautioned against the creep crack growth and failure.

지오그리드의 공학적 특성 및 설계인자 적용성 평가에 관한 연구 (A Study on Engineering Characteristics of Geogrids and the Applicability in fields)

  • 신은철;김두환;신동훈
    • 한국지반공학회:학술대회논문집
    • /
    • 한국지반공학회 1999년도 봄 학술발표회 논문집
    • /
    • pp.105-112
    • /
    • 1999
  • In recent the superior economic benefits and the convenience of installation increased the use of geosynthetics, especially geogrids with the effects of high tensile strength. In this study, various tests were conducted to determine the physical and chemical properties of geogrids which contains durability under various critical conditions, creep behavior and the stability for installation damage in fields. With analysis of test results, the partial and total safety factors were determined and presented the long term design strength of flexible geogrids.

  • PDF

Cracking of Fiber-Reinforced Self-Compacting Concrete due to Restrained Shrinkage

  • Kwon, Seung-Hee;Ferron, Raissa P.;Akkaya, Yilmaz;Shah, Surendra P.
    • International Journal of Concrete Structures and Materials
    • /
    • 제1권1호
    • /
    • pp.3-9
    • /
    • 2007
  • Fiber-reinforced self-compacting concrete (FRSCC) is a new type of concrete mix that can mitigate two opposing weaknesses: poor workability in fiber-reinforced concrete and cracking resistance in plain SCC concrete. This study focused on early-age cracking of FRSCC due to restrained drying shrinkage, one of the most common causes of cracking. In order to investigate the effect of fiber on shrinkage cracking of FRSCC, ring shrinkage tests were performed for polypropylene and steel fiber-reinforced SCC. In addition, finite element analyses for those specimens were carried out considering drying shrinkage based on moisture diffusion, creep, cracking resistance of concrete, and the effect of fiber. The analysis results were verified via a comparison between the measured and calculated crack width. From the test and analysis results, the effectiveness of fiber with respect to reducing cracking was confirmed and some salient features on the shrinkage cracking of FRSCC were obtained.

분무성형공정에 의한 세라믹미립자 강화형 금속간화합물 복합재료의 고온파괴거동 (High Temperature Fracture Mechanisms in Monolithic and Particulate Reinforced Intermetallic Matrix Composite Processed by Spray Atomization and Co-Deposition)

  • 정강;김두환;김호경
    • 대한기계학회논문집
    • /
    • 제18권7호
    • /
    • pp.1713-1721
    • /
    • 1994
  • Intermetallic-matrix composites(IMCs) have the potential of combing matrix properties of oxidation resistance and high temperature stability with reinforcement properties of high specific strength and modulus. One of the major limiting factors for successful applications of these composite at high temperatures is the formation of interfacial reactions between matrix and ceramic reinforcement during composite process and during service. The purpose of the present investigation is to develop a better understanding of the nature of creep fracture mechanisms in a $Ni_{3}Al$ composite reinforced with both $TiB_{2}$ and SiC particulates. Emphasis is placed in the roles of the products of the reactions in determining the creep lifetime of the composite. In the present study, creep rupture specimens were tested under constant ranging from 180 to 350 MPa in vacuum at $760^{\cric}C$. The experimental data reveal that the stress exponent for power law creep for the composite is 3.5, a value close to that for unreinforced $Ni_{3}Al$. The microstructural observations reveal that most of the cavities lie on the grain boundaries of the $Ni_{3}Al$ matrix as opposed to the large $TiB_{2}/Ni_{3}Al$ interfaces, suggesting that cavities nucleate at fine carbides that lie in the $Ni_{3}Al$ grain boundaries as a result of the decomposition of the $SiC_{p}$. This observation accounts for the longer rupture times for the monolicthic $Ni_{3}Al$ as compared to those for the $Ni_{3}Al/SiC_{p}/TiB_{2} IMC$. Finally, it is suggested that creep deformation in matrix appears to dominate the rupture process for monolithic $Ni_{3}Al$, whereas growth and coalescence of cavities appears to dominate the rupture process for the composite.