• Title/Summary/Keyword: toughness limit

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A Study on the Evaluation of Fracture Resistance Characteristics of Large Pipe by using the Curved CT Specimen (대형배관의 Curved CT 시편을 이용한 파괴저항특성평가에 관한 연구)

  • Kim, Ik Hyun;Shin, In Hwan;Park, Kweon Tae;Hong, Suk Woo;Park, Seon Soon;Yoon, Seon Hyun;Koo, Jae Mean;Seok, Chang Sung
    • Journal of the Korean Society for Precision Engineering
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    • v.31 no.7
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    • pp.623-626
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    • 2014
  • The LBB (Leak Before Break) concept is based on evaluating the fracture toughness. NUREG 1061, Vol.3 announced that the specimen for evaluating fracture resistance needs to have same thickness or thicker than pipe. Therefore, it is difficult to collect specimen from pipe which has same thickness as a pipe. So, ASTM standard suggested the use of standard specimen with 1 inch thickness. However, it has been known that an application of LBB by test results of standard specimen is conservative compare with that by real pipe. In this study, to supplement such conservatism, the evaluation of fracture resistance characteristics was performed with curved CT specimen, which has same thickness and curvature as a pipe. In addition, fracture resistance characteristics of curved CT specimen were compared with those of CT specimen. For this, shape factor F, hpl and g were obtained from FEM analysis using the limit load method.

The Effect of the Reinforced Particles on the Mechanical and Fracture Behaviors of the SiC/Al2O3/Vinyl-Ester Composites (SiC/Al2O3/Vinyl-Ester 복합재료의 강화재 입자가 기계적 특성 및 파괴거동에 미치는 영향)

  • Kim, Da Jin Sol;Yun, Yu Seong;Kwon, Oh Heon
    • Journal of the Korean Society of Safety
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    • v.32 no.3
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    • pp.1-7
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    • 2017
  • Particle reinforced composites are materials that have enhanced physical properties by adding particle reinforcements to polymer materials and have been applied to a wide range of fields such as the aerospace, bio-technology and automative industry. In this study, particle reinforced composites were prepared by mixing $SiC/Al_2O_3$ to the vinyl ester as the thermoset resin. The purpose of this study is to evaluate mechanical properties and fracture behavior by the tensile test and single edge notch specimen according to the addition ratio of reinforcement. Addition of 1 and 2 wt% of the particle reinforcement to the vinyl-ester resin was effective for the strength improvement. However, when it was more than 3 wt%, its strength was decreased. Also the highest elastic modulus obtained as 3.19 GPa was found at the 2 wt% addition of reinforcement. Futhermore the fracture toughness was evaluated by the energy release rate and the maximum critical energy release rate was obtained when 1 wt% reinforcement. The results show that the limit of adding of $SiC/Al_2O_3$ for improvement of the mechanical and fracture performance is 2 wt% reinforcement particles.

The Assessment for Coupling Integrity of Pressurizer Support Bolting (가압기 지지대 볼트 연결부의 건전성 평가에 관한 연구)

  • Cho, Nam-Jin;Kim, Woo-Chang;Kim, Hak-Joong
    • Fire Science and Engineering
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    • v.27 no.5
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    • pp.26-31
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    • 2013
  • In nuclear power plant, anchor bolts for pressurizer supports are sufficiently used in terms of safety reason, but field inspections have reported that some bolts exceed the limit of their allowable hardness. Because the high level of hardness may lead to failures due to the stress corrosion or fracture toughness, a regular inspection is required for the bolts in nuclear power plant. Thus, this research measures the hardness of bolts currently used in pressurizer supports and then estimates maximum allowable stresses preventing failures by stress corrosion and fracture toughness. Using the ANSYS program, the stresses of the bolts in the regular condition and accidental condition have been calculated, and the possible maximum stress has been compared with the estimated allowable stresses. From the results, the stresses of bolts in the accidental condition satisfy the allowable safety stress from the stress corrosion failure. However, in the future, it shall be needed to consider the reflection of the structure assembling method on the assembling procedure to ensure the pressurizer integrity during maintenance period time.

Development of Green Cement Type Grouting Materials with High Toughness and Non-Shrinkage Including Powder of Waste Tire and Resin (분말 폐타이어와 분말 수지를 함유한 환경친화적 고인성 시멘트계 무수축 그라우트재의 개발)

  • Park, Seok-Kyun
    • Journal of the Korea Concrete Institute
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    • v.19 no.5
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    • pp.623-630
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    • 2007
  • Grouting materials are used for the unification of superstructural and substructural body like bridge seat (shoe) or machinery pedestal and e.t.c by filling their intercalary voids. Accordingly, grouting materials have been developed and used mainly with products of high strength because those materials are constructed specially in a part receiving large or impact load. In this situation, the structural body constructed by grouting materials with high stiffness-centered (caused by high strength) products is apt to cause brittle failure when receiving over a limit stress and to cause cracks according to cumulative fatigue by continuous and cyclic load. In addition, grouting materials are apt to cause cracks by using too much rapid hardening agents that give rise to high heat of hydration to maintain high strength at early age. In this study, to overcome these problems, cement type grouting materials including powder of waste tire and resin as elastic materials which aim to be more stable construction and to be improvement of mother-body's unification are developed and endowed with properties of high toughness and high durability add to existing properties of high flowability, non-shrinkage and high strength. Besides, this study contribute to of for green construction materials for being possible recycling industrial waste like waste tire and flyash. On the whole, seven type mixing conditions are tested and investigated to choose the best mixing condition.

A Numerical Study on the Behavior of Steel Fiber Reinforced Shotcrete in Consideration of Flexural Toughness (휨인성을 고려한 강섬유보강 숏크리트 거동의 수치해석적 연구)

  • Cho, Byoung-Ouk;You, Kwang-Ho;Kim, Su-Man;Lim, Doo-Chul;Lee, Sang-Don;Park, Yeon-Jun
    • Tunnel and Underground Space
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    • v.17 no.5
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    • pp.411-427
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    • 2007
  • Reliability in tunnel analysis is necessary to accomplish technically sound design and economical construction. For this, a thorough understanding of the construction procedure including the ground-support interaction has to be obtained. This paper describes a proper modelling technique to simulate the behavior of the steel fiber reinforced shotcrete (SFRS) which maintain the supporting capability in post-failure regime. The additional supporting effect of the steel support was also verified by 3-D analyses and a new load distribution factor were proposed. The use of the plastic moment limit (PML) alone can eliminate the occurrence of the awkwardly high tensile stress in the shotcrete and can successfully model the post-peak ductile behavior of the SFRS. But with this method, moment is limited whenever the stress caused by moment reaches tensile strength of the shotcrete irrespective of the stress by axial force. Therefore, it was necessary to find a more comprehensive method which can reflect the influence of the moment and axial force. This can be accomplished by the proper use of "liner element" which is the built-in model in FLAC. In this model, the peak and residual strength as well as the uniaxial compressive strength of the SFRS can be specified. Analyses were conducted with these two models on the 2-lane road tunnels excavated in class IV and V rock mass and results were compared with the conventional elastic beam model. Results showed that both models can reflect the fracture toughness of the SFRS which could not be accomplished by the elastic beam model.

The Crack Analysis and Redesign of Horizontal Fin of F-5E/F's External Fuel Tank (F-5E/F 외부 연료탱크 수평 핀 균열 분석 및 재설계)

  • Kang, Chi-Hang;Yoon, Young-In;Jung, Dae-Han
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.38 no.4
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    • pp.382-388
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    • 2010
  • In this work the replacement material for magnesium alloy was investigated and an optimized design was suggested for the horizontal fin of a fighter's external fuel tank. For the replacement of magnesium alloy, Aluminum alloy, AL 2034-T351, was selected by considering material properties and its procurement. The strength and fracture toughness properties of AL 2034-T351 are stronger than those of magnesium alloy, but the specific weight of AL 2034-T351 is heavier than that of magnesium alloy by 65%. To meet the allowable limit of C.G. shift in the tank, the design of horizontal fin was optimized by reducing the original shape by 20% and resizing the maximum thickness to 7 mm. From the results of the static and dynamic stress analysis for improving the safety factor of the joint section and the joint hole, the radius of curvature in the aft joint section of the new fin was designed as 8.5mm.

Crack Growth Life Prediction of Hollow Shaft with Circumferential Through Type Crack by Torsion (원주방향 관통형 균열을 가지는 중공축의 비틀림에 의한 균열성장수명 예측)

  • Yeonhi Kim;Jungsun Park
    • Journal of Aerospace System Engineering
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    • v.17 no.2
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    • pp.1-8
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    • 2023
  • Power transmission shafts in rotary wing aircraft use a hollow shaft to reduce weight. We can apply linear elastic fracture mechanics to predict crack propagation behavior. This paper predicted crack growth life of a hollow shaft with a circumferential through-type crack by finite element analysis. A 2D finite element model was created by applying a torsion and forming elements considering cracks. We defined the initial crack length and performed the finite element analysis by increasing the crack length to derive stress intensity factor at crack tips. We defined the length just prior to the stress intensity factor exceeding the fracture toughness as the crack limit length. We calculated the crack limit length using a handbook and numerically integrated the crack growth rate equation to derive growth life of each crack. The growth life of each crack was compared to verify the proposed finite element analysis method.

Development of Control Technology of Austempered Ductile Iron with High Strength and High Toughness for Gear Parts. (고강도 ADI의 기어부품 개발에 관한 연구)

  • Kim, Won-Yong;Kim, Kwang-Bae;Kang, In-Chan;An, Sang-Uk
    • Journal of Korea Foundry Society
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    • v.13 no.2
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    • pp.187-193
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    • 1993
  • In this study, it was examined the relationship between the microstructure, fatigue properties, mechanical properties and retained austenite volume of Mo-Ni ADI corresponding to various austempering temperatures. When the austempering temperature is increased to $370^{\circ}C$, acicular bainite structure was found to be transformed to feathery bainite structure. But at the austempering temperature of $420^{\circ}C$, the dissolved bainite lath was showned. Up to the austempering temperature of $370^{\circ}C$, the volume of retained austenite was increased. However at the austempering temperature of $420^{\circ}C$ a large amount of retained austenite was decreased. In this study, the retained austenite volume was determined by XRD(X-ray diffraction). It was observed that the optimum fatigue properties can be obtained at the condition of austempering temperature $370^{\circ}C$. Under the such conditions, fatigue limit determined as the value of 290 MPa, tensile strength 877MPa elongation 6%, hardness 285(BHN), impact values(CVN) 9.2J and retained austenite volume 30.3%, respectively.

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Evaluation of Mechanical Properties and Fiber Dispersing Characteristics of Fiber Reinforced Lean Concrete Using Fly Ash and Reject Ash (도로 기층 재료로 활용하기 위한 섬유보강 빈배합 콘크리트에 플라이애시와 리젝트애시를 사용한 경우 역학적 특성 및 섬유 분산성 분석)

  • Jang, Young Jae;Park, Cheol Woo;Park, Young Hwan;Yoo, Pyeong Jun;Jung, Woo Tae;Kim, Yong Jae
    • International Journal of Highway Engineering
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    • v.15 no.1
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    • pp.11-21
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    • 2013
  • PURPOSES: As pavement generally provides service shorter than an expected life cycle, maintenance cost increases gradually. In order to help extending the service life and reduce maintenance cost, a new multi-functional composite pavement system is being developed in Korea. METHODS: This study is a part to develop the multi-functional composite pavement and is to investigate the mechanical performances of fiber-reinforced lean concrete for pavement subbase. The inherent problem of fiber reinforced concrete is dispersion of fibers in concrete mix. This study additionally evaluated fiber dispersion characteristics with respect to different fiber types. RESULTS: From the test results, the compressive strengths of the concretes satisfied the required limit of 5MPa at 7days. The standard deviation of the measured number of fibers were lower in the order of nylon, steel fiber and polypropylene. CONCLUSIONS: Reject ash was shown to be satisfactory as a replacement material to Portland cement in lean concrete base. The fiber volume fraction is suggested to be 0.4% even though the fracture toughness did not vary significantly with respect to fiber types. However, fracture energy absorbed up to complete failure increased with the increased fiber volume fraction increment.

Probabilistic Fracture Mechanics Analysis of Boling Water Reactor Vessel for Cool-Down and Low Temperature Over-Pressurization Transients

  • Park, Jeong Soon;Choi, Young Hwan;Jhung, Myung Jo
    • Nuclear Engineering and Technology
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    • v.48 no.2
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    • pp.545-553
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    • 2016
  • The failure probabilities of the reactor pressure vessel (RPV) for low temperature over-pressurization (LTOP) and cool-down transients are calculated in this study. For the cool-down transient, a pressure-temperature limit curve is generated in accordance with Section XI, Appendix G of the American Society of Mechanical Engineers (ASME) code, from which safety margin factors are deliberately removed for the probabilistic fracture mechanics analysis. Then, sensitivity analyses are conducted to understand the effects of some input parameters. For the LTOP transient, the failure of the RPV mostly occurs during the period of the abrupt pressure rise. For the cool-down transient, the decrease of the fracture toughness with temperature and time plays a main role in RPV failure at the end of the cool-down process. As expected, the failure probability increases with increasing fluence, Cu and Ni contents, and initial reference temperature-nil ductility transition ($RT_{NDT}$). The effect of warm prestressing on the vessel failure probability for LTOP is not significant because most of the failures happen before the stress intensity factor reaches the peak value while its effect reduces the failure probability by more than one order of magnitude for the cool-down transient.