• 제목/요약/키워드: rate of strain

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Measurement of Inward Turbulent Flows Subject to Plane Rate of Strain in a Rotating 90 Deg. Curved Duct of Variable Cross-Section (단순변형율 조건 하의 회전하는 가변단면 $90^{\circ}$ 곡덕트 내 내향 난류유동 측정)

  • Kim, Dong-Chul;Choi, Young-Don
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.765-770
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    • 2000
  • Hot-wire measurements are reported on the developing turbulent flows subject to plane rate of strain in a rotating $90^{\circ}$ dog bend. The cross-section of the bend varies from $100mm{\times}50mm$ rectangular shape at the bend inlet gradually to the $50mm{\times}100mm$ shape at the bend outlet with remaining a constant area. Data signals from the rotating test section are transmitted through a slip ring to the personal computer which is located at the outside of the rotating disc. 3-dimensional velocity and 6 Reynolds stress components were calculated from the equations which correlate the fluctuating and mean voltage values measured with rotating a slant type hot-wire into 6 orientations. The effects of Coriolis and centrifugal forces on the mean motions and turbulence structures are investigated with respect to rotational speed.

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Effects of α2/β Volume Fraction on the Superplastic Deformation (2 상 Ti3Al-xNb 계 금속간 화합물들의 초소성 특성에 미치는 상분율의 영향)

  • 김지식
    • Transactions of Materials Processing
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    • v.11 no.5
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    • pp.447-456
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    • 2002
  • A study has been made to investigate the boundary sliding and its accommodation mode with respect to the variation of $\alpha$$_2$/$eta$ volume fraction during superplastic deformation of two-phase Ti$_3$Al-xNb intermetallics. Step strain rate and load relaxation tests have been performed at 950, 970 and 99$0^{\circ}C$ to obtain the flow stress curves and to analyze the deformation characteristics by the theory of inelastic deformation. The results show that the grain matrix deformation and boundary sliding of the three intermetallics containing 21, 50 and 77% in $eta$ volume fractions are well described by the plastic deformation and viscous flow equations. Due to the equal accommodation of both $a^2$ and $\beta$ phases, the accommodation modes for fine-grained materials are in good agreement with the iso-strain rate models. The sliding resistance analyzed for the different boundaries is the lowest in the $\alpha$$_2$/$\alpha$$_2$ boundary, and increases in the order of $\alpha$$_2$/$\alpha$$_2$<< $\alpha$$_2$/$\beta$ = $\beta$/$\beta$, which plays an important role in controlling the superplasticity of the alloys with the various $\alpha$$_2$/$\beta$ phase ratio.

Effect of temperature and blank holder force on non-isothermal stamp forming of a self-reinforced composite

  • Kalyanasundaram, Shankar;Venkatesan, Sudharshan
    • Advances in aircraft and spacecraft science
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    • v.3 no.1
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    • pp.29-43
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    • 2016
  • Composite materials are rapidly gaining popularity as an alternative to metals for structural and load bearing applications in the aerospace, automotive, alternate energy and consumer industries. With the advent of thermoplastic composites and advances in recycling technologies, fully recyclable composites are gaining ground over traditional thermoset composites. Stamp forming as an alternative processing technique for sheet products has proven to be effective in allowing the fast manufacturing rates required for mass production of components. This study investigates the feasibility of using the stamp forming technique for the processing of thermoplastic, recyclable composite materials. The material system used in this study is a self-reinforced polypropylene composite material (Curv$^{(R)}$). The investigation includes a detailed experimental study based on strain measurements using a non-contact optical measurement system in conjunction with stamping equipment to record and measure the formability of the thermoplastic composites in real time. A Design of Experiments (DOE) methodology was adopted to elucidate the effect of process parameters that included blank holder force, pre heat temperature and feed rate on stamp forming. DOE analyses indicate that feed rate had negligible influence on the strain evolution during stamp forming and blank holder force and preheat temperature had significant effect on strain evolution during forming.

Finite Element Analysis of the Hot Rolled Cladding for the Ni-based Superalloy/steel Corrosion-resistant Alloy (CRA) Plate (니켈 기반 초합금 클래드 판재의 열간 압연 제조 공정 유한요소해석)

  • C. Kim;S.J. Bae;H. Lee;H.J. Bong;K.S. Lee
    • Transactions of Materials Processing
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    • v.33 no.3
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    • pp.208-213
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    • 2024
  • Ni-based superalloys have exceptional performance in high-temperature strength, corrosion resistance, etc, and it has been widely used in various applications that require corrosion resistance at high-temperature operations. However, the relatively expensive cost of the Ni-based superalloys is one of the major hurdles. The corrosion-resisted alloy(CRA) clad materials can be a cost-effective solution. In this study, finite element analysis of the hot rolling process for manufacturing of the Alloy 625/API X65 steel CRA clad plates is conducted. The stress-strain curves of the two materials are measured in compressive tests for various temperature and strain rate conditions, using the Gleeble tester. Then, strain hardening behavior is modeled following the modified Johnson-Cook model. Finite element analysis of the hot rolled cladding process is performed using this strain rate and temperature dependent hardening model. Finally, the thickness ratio of the CRA and base material is predicted and compared with experimental values.

Thermal Stress Analysis of the Support System in Cryogenic Liquid Hydrogen Storage Tank (극저온 액체수소 저장탱크 지지시스템의 열응력 해석)

  • Park, Dong-Huen;Yun, Sang-Kook;Lee, Jung-Hyan;Jo, Won-Il;Baek, Young-Sun
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2005.06a
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    • pp.239-245
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    • 2005
  • The reduction of heat transfer rate to the stored liquid hydrogen from outside condition is extremely important to keep the liquid hydrogen longer. In this paper the highly efficient support system for the liquid hydrogen storage vessel was newly developed and analysed. The support system was composed of a spherical ball in the center of supporter to reduce the heat transfer area, with its above and below supporting blocks which are the SUS and PTFE blocks inserted in the SUS tube. The heat transfer rate and temperature distribution of the support system were evaluated by FLUENT, and the thermal stress and strain were estimated by ANSYS software. The results showed that the heat transfer rate from outer vessel to inner one was extremely decreased compared with the common method which is simply SUS tubes inserted between inner and outer tanks. The thermal stress and strain were obtained well below the limited values. As a result, it was the most efficient support system of storage vessel for liquid hydrogen and most cryogenic fluids.

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Experimental Study on Unconfined Compression Strength and Split Tensile Strength Properties in relation to Freezing Temperature and Loading Rate of Frozen Soil (동결 온도와 재하속도에 따른 동결토의 일축압축 및 쪼갬인장 강도특성)

  • Seo, Young-Kyo;Choi, Heon-Woo
    • Journal of Ocean Engineering and Technology
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    • v.26 no.6
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    • pp.19-26
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    • 2012
  • Recently the world has been suffering from difficulties related to the demand and supply of energy due to the democratic movements sweeping across the Middle East. Consequently, many have turned their attention to never-developed extreme regions such as the polar lands or deep sea, which contain many underground resources. This research investigated the strength and initial elastic modulus values of eternally frozen ground through a uniaxial compression test and indirect tensile test using frozen artificial soil specimens. To ensure accurate test results, a sandymud mixture of standard Jumunjin sand and kaolinite (20% in weight) was used for the specimens in these laboratory tests. Specimen were prepared by varying the water content ratio (7%, 15%, and 20%). Then, the variation in the strength value, depending on the water content, was observed. This research also established three kinds of environments under freezing temperatures of $-5^{\circ}C$, $-10^{\circ}C$, and $-15^{\circ}C$. Then, the variation in the strength value was observed, depending on the freezing environment. In addition, the tests divided the loading rate into 6 phases and observed the variation in the stress-strain ratio, depending on the loading rate. The test data showed that a lower freezing temperature resulted in a larger strength value. An increase in the ice content in the specimen with the increase in the water content ratio influenced the strength value of the specimen. A faster load rate had a greater influence on the uniaxial compression and indirect tensile strengths of a frozen specimen and produced a different strength engineering property through the initial tangential modulus of elasticity. Finally, the long-term strength under a constant water content ratio and freezing temperature was checked by producing stress-strain ratio curves depending on the loading rate.

High Temperature Deformation Behavior of SiCp/2124Al Metal Matrix Composites

  • Tian, Y.Z.;Cha, Seung I.;Hong, Soon H.
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2002.05a
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    • pp.69-72
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    • 2002
  • The high temperature deformation behavior of SiCp/2124Al composite and 2124Al alloy was investigated by hot compression test in a temperature ranged $400~475^{\circ}C$ over a strain rate ranged $10^{-3}~1s^{-1}$. The billets of 2124Al alloy and SiCp/2124Al composite were fabricated by vacuum hot pressing process. The stress-strain curve during high temperature deformation exhibited a peak stress, and then the flow stress decreased gradually into a steady state stress with increasing the strain. It was found that the flow-softening behavior was attributed to the dynamic recovery, local dynamic recrystallization and dynamic precipitation during the deformation. The precipitation phases were identified as S' and S by TEM diffraction pattern. Base on the TEM inspection, the relationship between the Z-H parameter and subgrain size was found based on the experiment data. The dependence of flow stress on temperature and strain rate could be formulated well by a hyperbolic-sinusoidal relationship using the Zener-Hollomon parameter.

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Research on Turbulent Premixed Flame with Simultaneous PIV/OH PLIF measurements (PIV/OH PLIF 동시측정을 이용한 난류 예혼합 화염 연구)

  • Cho Yong-jin;Kim Ji-ho;Cho Tae-young;Yoon Young-bin
    • 한국가시화정보학회:학술대회논문집
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    • 2002.11a
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    • pp.97-99
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    • 2002
  • Turbulent premixed flames were a subject of many researches for a number of decades. Especially, Borghi suggested a manificent diagram classifying turbulent combustion reasions and Lipatnikov and Chomiak modified this diagram. But this diagram has difficulties tn defining a flame thickness and velocity and measuring integral length scales In addition, recently experimental techniques are being developed, so we can accurately use PIV diagnostics measuring 2D velocity field instead of LDV and make good use of PLIF techniques for obtaining the flame information. In this study, according to developing techniques, suggest a new diagram replacing the existing Borghi diagram. Simultaneous PIV/OH PLIF measurements are used, which measure a shear strain rate and a location of flames, respectively. The shear strain rate represents turbulence and the OH signal indicates the flame information, but there is no geometric Information which is very important to flame quenching. Hence, to consider the geometric information, calculate fractal dimensions of the OH images. So the diagram suggested in this research has three axes which consist of strain rate, OH signal, and fractal dimension and can classify turbulent premixed flames.

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Influence of dynamic strain aging on material strength behavior of virgin and service-exposed Gr.91 Steel (신재 및 가동이력 Gr.91강의 재료강도 거동에 미치는 동적변형시효의 영향)

  • Ki-Ean Nam;Hyeong-Yeon Lee;Jae-Hyuk Eoh;Hyungmo Kim;Hyun-Uk Hong
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.20 no.1
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    • pp.66-74
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    • 2024
  • This study investigates the effects of temperatures and strain rates on the strength and ductility of Gr.91 (ASME Grade 91) steel which is widely being used as a heat-resistant material in Generation IV nuclear and super critical thermal power plants. The tensile behavior of modified 9Cr-1Mo (Gr.91) steel was studied for the three strain rates of 6.67×10-5/s, 6.67×10-4/s and 6.67×10-3/s over the temperature range from room temperature (RT) to 650℃. Experimental results showed that at specific combinations of temperatures (300~400℃) and strain rates, serrations appeared in the stress-strain curves. Concurrently, abnormal behaviors such as a plateau in yield strength and tensile strength, a minimum in ductility and negative strain rate sensitivity were observed. These phenomena were analyzed as significant characteristics of dynamic strain aging (DSA). Since this abnormal behavior in Gr.91 steel affects the material strength, it is judged that a correlation analysis between DSA and material strength should be crucial in the design and integrity evaluation of Gr. 91 steel pressure vessel and piping subjected to high-temperature loading.

Forging of 1.9wt%C Ultrahigh Carbon Workroll : Part I - Analysis on Void Formation and Microstructure (1.9wt%C 초고탄소 워크롤 단조 공정 : Part I - 기공생성 및 미세조직 분석)

  • Lim, H.C.;Lee, H.;Kim, B.M.;Kang, S.H.
    • Transactions of Materials Processing
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    • v.22 no.8
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    • pp.456-462
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    • 2013
  • Compression tests were conducted at the various temperatures and strain rates to investigate void formation and microstructures behavior of a 1.9wt%C ultrahigh carbon steel used in forged workrolls. The microstructure, grain size and volume fraction of cementite were determined using specimens deformed in the temperature range from 800 to $1150^{\circ}C$ and strain rates from 0.01 to 10/s. It was found from the microstructural analysis that the grain size is larger at higher temperatures and lower strain rate deformation conditions. In addition, a higher volume fraction of cementite was measured at lower temperatures. The brittle blocky cementite was fractured at $800^{\circ}C$ and $900^{\circ}C$ regardless of strain rate. As a result, numerous new micro voids were formed in the fragmented blocky cementite. It was also found that local melting can occur at temperatures of more than $1130^{\circ}C$. Therefore, the forging temperature should be controlled between $900^{\circ}C$ and $1120^{\circ}C$. The temperature rise, which depends on the anvil stroke and velocity, was estimated through cogging simulation to find the appropriate forging temperature and to prevent local melting due to plastic work.