• Title/Summary/Keyword: stress intensity factor

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Thermal, Mechanical, and Electrical Properties of Fluorine-Containing Epoxy Resins (불소함유 에폭시 수지의 열적, 기계적 및 전기적 특성)

  • 박수진;김범용;이재락;신재섭
    • Polymer(Korea)
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    • v.27 no.3
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    • pp.183-188
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    • 2003
  • The dielectric constants of fluorine-containing epoxy resins, 2-diglycidylether of benzotrifluoride(FER)/4,4'-diamino-diphenyl methane (DDM) and diglycidylether of bisphenol-A (DGEBA)/DDM systems were evaluated by dielectric spectrometer. Glass transition temperature and thermal stability factors, including initial decomposed temperature, temperatures of maximum rate of degradation, and decomposition activation energy of the cured specimens were investigated by dynamic mechanical analysis and thermogravimetric analysis. For the mechanical properties of the casting specimens, the fracture toughness, flexural, and impact tests were performed, and their fractured surfaces were examined by scanning electron microscope. The dielectric constant of FER/DDM system was lower than that of commercial DGEBA/DDM system, and the mechanical properties of the cured specimens showed higher values than those of DGEBA/DDM system. This was probably due to the introduction of trifluoromethyl (CF$_3$) group into the side chain of the epoxy resins, resulting in improving the electric and mechanical properties of the epoxy cure system studied.

Analysis of Fatigue Crack Growth in a Viscoelastic Material using ${\Delta}J$-integral (${\Delta}J$-적분을 이용한 점탄성 재료의 피로균열 성장분석)

  • Yu, Seong-Mun;Zi, Goang-Seup;Thanh, Chau Dinh;Lee, Hyun-Jong;Mun, Sung-Ho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.23 no.5
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    • pp.483-491
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    • 2010
  • In this paper, ${\Delta}J$-integral is used to analyze fatigue crack growth of viscoelastic material. Using analytical integral value, the J-integral is calculated. So, reduction of calculation time and increase of accuracy are made possible. The stress intensity factor is calculated using the finite element method code. In difference with existed fatigue crack analysis using ${\Delta}K$, we were successfully able to analyze various load amplitude and the fatigue crack of load cycle only with two fatigue crack growth parameters and creep compliance. The analysis gives N-${\alpha}$ curve for simulation of crack growth, and the curve almost corresponds with test results.

On the Fracture Behaviour of the Concrete Gravity Dam Subjected to Water Pressure at the Crack Faces (균열면에 수압을 받는 중력식 콘크리트 댐의 파괴거동에 관한 연구)

  • 장희석
    • Computational Structural Engineering
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    • v.9 no.4
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    • pp.189-198
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    • 1996
  • The fracture behaviour of concrete gravity dam mainly due to uplift pressure acting at the crack face was studied. Triangular type and parabolic type distribution of the uplift pressure including uniform type were first considered in case of calculating stress intensity factor(SIF) by the surface integral method. Second, the directions of crack propagation according to the uplift pressure distribution were pursued by FRANC(FRacture ANalysis Code). Third, critical crack lengths according to the uplift pressure distribution under the overflow depth were calculated. The SIF values obtained from the surface integral method were compared with those by FRANC and relatively good agrements could be obtained between both of them. And it could be seen that the direction of crack propagation in case of triangular pressure distribution was a little benter to the dam base than the one by the uniform type. Maximum critical crack lengths under the overflow depth were obtained at about 2/5-1/2 of the dam height.

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A Study on the Fatigue Crack Evaluation Method of Railway Bogie Frame (철도차량 대차를 피로균열 평가법 연구)

  • Jun, Hyun-Kyu;Seo, Jung-Won;Lee, Dong-Hyong;Kim, Hyeong-Jin
    • Journal of the Korean Society for Railway
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    • v.12 no.1
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    • pp.16-24
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    • 2009
  • In this study, fatigue crack growth rate of a cracked railway bogie frame under variable amplitude loading is predicted by applying linear elastic fracture mechanics. For this purpose, we find the critical points by reference surveying on cracked railway bogie frames. And we make an effective load history by synthesizing the dynamic load measured from the critical points of railway bogie frame during commercial line operation and the static load calculated from structural analysis. Crack growth analyses are performed at the 3 critical points under the commercial operation loading condition by assuming an initial crack size as 40 mm. and the results are compared with the experimental results from Japanese railway bogie frame crack growth case. From the analysis results, we find that around 500,000 km operating distance is necessary to bring crack growth from the initial crack to unstable crack. And it takes around 3.8 normal operating years. We conclude that it is enough time to detect the crack between normal maintenance period.

Round robin analysis of vessel failure probabilities for PTS events in Korea

  • Jhung, Myung Jo;Oh, Chang-Sik;Choi, Youngin;Kang, Sung-Sik;Kim, Maan-Won;Kim, Tae-Hyeon;Kim, Jong-Min;Kim, Min Chul;Lee, Bong Sang;Kim, Jong-Min;Kim, Kyuwan
    • Nuclear Engineering and Technology
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    • v.52 no.8
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    • pp.1871-1880
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    • 2020
  • Round robin analyses for vessel failure probabilities due to PTS events are proposed for plant-specific analyses of all types of reactors developed in Korea. Four organizations, that are responsible for regulation, operation, research and design of the nuclear power plant in Korea, participated in the round robin analysis. The vessel failure probabilities from the probabilistic fracture mechanics analyses are calculated to assure the structural integrity of the reactor pressure vessel during transients that are expected to initiate PTS events. The failure probabilities due to various parameters are compared with each other. All results are obtained based on several assumptions about material properties, flaw distribution data, and transient data such as pressure, temperature, and heat transfer coefficient. The realistic input data can be used to obtain more realistic failure probabilities. The various results presented in this study will be helpful not only for benchmark calculations, result comparisons, and verification of PFM codes developed but also as a contribution to knowledge management for the future generation.

Studies on Rheological Properties and Cure Behaviors of Difunctional Epoxy/Biodegradable Poly(butylene succinate) Blends (2관능성 에폭시/생분해성 폴리부틸렌 숙시네이트 블렌드의 유변학적 특성 및 경화거동에 관한 연구)

  • 박수진;김승학;이재락;민병각
    • Composites Research
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    • v.15 no.6
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    • pp.8-15
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    • 2002
  • In this work, the effect of biodegradable poly(butylene succinate)(PBS) in difunctional epoxy(21:P) resin was investigated in terms of rheological properties, cure kinetics, thermal stabilities, and mechanical interfacial properties. Rheological properties of the blend system were measured under isothermal condition using a rheometer. Cross-linking activation energies($\textrm{E}_c$) were determined from the Arrhenius equation based on gel time and curing temperature. The $\textrm{E}_c$ was increased in the presence of 10 wt% PBS as compared with neat 2EP. From the DSC results of the blends, the cure activation energies($\textrm{E}_a$) showed a similar behavior with $\textrm{E}_c$ due to the increased intermolecular interaction between 2EP and PBS. The decomposed activation energies($\textrm{E}_t$) for the thermal stability derived from the integral method of Horowitz-Metzger equation, were also increased in 10 wt% PBS. In addition, 20 wt% PBS showed the highest critical stress intensity factor($\textrm{E}_{IC}$). which was explained by increasing the fracture toughness of the 2EP/PBS blend systems.

Effect of Anodized Carbon Fiber Surfaces on Mechanical Interfacial Properties of Carbon Fibers-reinforced Composites (탄소섬유의 양극산화가 탄소섬유 강화 복합재료의 기계적 계면 특성에 미치는 영향)

  • 박수진;오진석;이재락
    • Composites Research
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    • v.15 no.6
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    • pp.16-23
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    • 2002
  • In this work, the effect of anodic oxidation on surface characteristics of high strength PAN-based carbon fibers was investigated in mechanical interfacial properties of composites. The surface properties of the carbon fibers were determined by acid-base values, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angles. And their mechanical interfacial properties of the composites were studied in interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$). As a result, the acidity or the $O_{ls}/C_{ls}$ ratio of carbon fiber surfaces was increased, due to the development of the oxygen functional groups. Consequently, the anodic oxidation led to an increase in surface free energy of the carbon fibers, mainly due to the increase of its specific (or polar) component. The mechanical interfacial properties of the composites, including ILSS and $K_{IC}$, had been improved in the anodic oxidation on fibers. These results were explained that good wetting played an important role in improving the degree of adhesion at interfaces between fibers and epoxy resin matrix.

The Development of a Non-Linear Finite Element Model for Ductile Fracture Analysis - For Mini-Computer - (연성파괴 해석을 위한 비선형 유한요소 모델의 개발 -소형 컴퓨터를 위한 -)

  • 정세희;조규종
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.10 no.1
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    • pp.25-33
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    • 1986
  • In this paper, the frontal method based elastic-plastic F.E.M. program for mini-computer was developed. Since, the executable source program size was restricted by the system core memory size on the mini-computer, the active variables were memorized by the element base and the nonactive varables were memorized to the external disc file. The active variables of the finally developed program were reduced enough to execute about 1,000 freedom finite element on the mini-computer on which available variables were restricted as 32,767 integers. A modified CT fracture test specimen was examined to test the developed program. The calculated results were compared with experimental results concerning on the crack tip plastic deformation zone. Recrystallization technique was adopted to visualize the intensive plastic deformation regions. The Von-Mises criterion based calculation results were well agreed with the experimental results in the intensive plastic region which was over than 2% offset strain. The F.E.M. results using the developed program were well agreed with the theoritical plastic boundary which was calculated by the stress intensity factor as r$_{p}$=(K$_{1}$$^{2}$/2.pi..sigma.$_{y}$$^{2}$).f(.theta.).).).

The Mixture Ratio Effect of Epoxy Resin, Curing Agent and Accelerator on the Fatigue Behavior of FRMLs (프리프레그 제작용 에폭시 수지.경화제.경화촉진제 혼합비 변화에 따른 FRMLs의 피로거동 특성)

  • Song, Sam-Hong;Kim, Cheol-Ung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.4
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    • pp.592-601
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    • 2001
  • Fiber reinforced metal laminates(FRMLs) are new types of hybrid materials. FRMLs consists of high strength metal(Al 5052-H34) and laminated fiber with structural adhesive bond. The mixture ratio effect of epoxy resin$.$curing agent$.$accelerator on the fatigue behavior of FRMLs was investigated in this study. The epoxy, diglycidylether of bisphenol A(DGEBA), was cured by methylene dianiline(MDA) with or without an accelerator(K-54). Eight different kinds of resin mixture ratios were selected for the test ; five kinds of FRMLs(1) and three others of FRMLs(2). The relationship between da/dN and ΔK with variation of resin mixture ratio was studied. FRMLs(1) and FRMLs(2) indicated approximately 2 times and 2.2 times more improved maximum bending strengths in comparison with those of Al 5052-H34. The resin mixture ratio <1:1> in case of FRMLs(1) indicated the maximum fatigue life, while the resin mixture ratio <1:1:0.2> in case of FRMLs(2) indicated the maximum fatigue life. As results, FRMLs(2) turned out to have more effective characteristics on the fatigue properties and the bending strength than those of FRMLs(1).

A Study on the Corrosion Susceptibility and Corrosion Fatigue Characteristics on the Material of Turbine Blade (Turbine Blade재료의 부식민감성과 부식피로특성에 관한 연구)

  • Jo, Seon-Yeong;Kim, Cheol-Han;Ryu, Seung-U;Kim, Hyo-Jin;Bae, Dong-Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.3 s.174
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    • pp.603-612
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    • 2000
  • Corrosion characteristics on the 12Cr alloy steel of turbine blade was electro-chemically investigated in 3.5wt% NaCI and 12.7wt% Na2S04 solution, respectively. Electro-chemical polarization test, Huey test and Oxalic acid etching test were previously conducted to estimate corrosion susceptibility of the material. And, using the horizontal corrosion fatigue tester, corrosion fatigue characteristics of 12Cr alloy steel in distilled water, 3.5wt% NaCI solution, and 12.7wt%(1M) Na2S04 solution were also fracture-mechanically estimated and compared their results. Parameter considered was room temperature, 60'C and 90'C. Corrosion fatigue crack length was measured by DC potential difference method.Obtained results are as follows,1) 12Cr alloy steel showed high corrosion rate in 3.5wt% NaCI solution and Na2S04 solution at high tempratue.2) Intergranular corrosion sensitivity of 12 Cr alloy was smaller than austenitic stainless steel.3) Corrosion fatigue crack growth rate in 3.5wt% NaCI and 12.7wt%(IM) Na2S04 solution is entirely higher than in the distilled water, and also increased with the temperature increase.