• Title/Summary/Keyword: Elastic strain

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Formulation of Special Constitutive Equations for Inelastic Responses of Porous Metals(II) - Elastic, Plastic Strain Hardening Material - (다공질 금속의 비탄성거동을 위한 특수 구성방정식의 형성 II)

  • Kim, K.T.;Suh, J.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.1
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    • pp.64-71
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    • 1988
  • A special set of constitutive equations is formulated to predict elastic-plastic strain hardening responses of porous metals. Including the effect of the material's strain hardening in the yield function, the constitutive equations are capable of showing no dip phenomena in uniaxial strain compression and prediction work-hardening response for plastically precyled porous metal. The proposed constitutive equations are compared with experimental data for porous tungsten.

Size dependent torsional vibration of a rotationally restrained circular FG nanorod via strain gradient nonlocal elasticity

  • Busra Uzun;Omer Civalek;M. Ozgur Yayli
    • Advances in nano research
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    • v.16 no.2
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    • pp.175-186
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    • 2024
  • Dynamical behaviors of one-dimensional (1D) nano-sized structures are of great importance in nanotechnology applications. Therefore, the torsional dynamic response of functionally graded nanorods which could be used to model the nano electromechanical systems or micro electromechanical systems with torsional motion about the center of twist is examined based on the theory of strain gradient nonlocal elasticity in this work. The mathematical background is constructed based on both strain gradient theory and Eringen's nonlocal elasticity theory. The equation of motions and boundary conditions of radially functionally graded nanorods are derived using Hamilton's principle and then transformed into the eigenvalue analysis by using Fourier sine series. A general coefficient matrix is obtained to assemble the Stokes' transformation. The case of a restrained functionally graded nanorod embedded in two elastic springs against torsional rotation is then deeply investigated. The effect of changing the functionally graded index, the stiffness of elastic boundary conditions, the length scale parameter and nonlocal parameter are investigated in detail.

Determination of Elastic Constants of Transversely Isotropic Rocks (이방성 암석에 대한 탄성계수의 실험적 결정)

  • 김호영
    • Tunnel and Underground Space
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    • v.5 no.4
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    • pp.318-322
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    • 1995
  • For transversely isotropic rocks such as schist, shale, etc, a method to determine the anisotropic elastic constants was proposed. Theoretically, equations of elastic constants E1, E2, and G2 can be derived from the measured strains in arbitrary three directions. If we attach three strain gages in accordance with the directons of anisotropy on the rock specimen under uni-axial compression, anisotropic elastic constants can be determined by these equations. With this method, the degree of anisotropy of transversely isotropic rocks will be easily evaluated by simple laboratory test.

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An Experimental Study on the Fracture Strength of Steel Fiber Reinforced Concrete

  • Chai, Won-Kyu
    • International Journal of Safety
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    • v.11 no.1
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    • pp.19-21
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    • 2012
  • In this thesis, fracture test was performed in order to investigate the fracture strength of SFRC(steel fiber reinforced concrete) structures. The relationship between the compressive force and strain value of SFRC specimens were observed under the compressive strength test. From the fracture test results, the relationship between percentage of fiber by volume, compressive strength, elastic modulus, and tensile strength of SFRC beams were studied, and the measured elastic modulus of SFRC were compared with the calculated elastic modulus by ACI committee 544.

Measurements of Elastic Moduli of Rock Cores Using Free-Free Resonance Tests (자유단 공진시험을 이용한 암석의 탄성계수 측정)

  • 목영진
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 1998.10a
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    • pp.353-360
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    • 1998
  • Dynamic measurements are used rather sparingly to determine the elastic moduli of rock cores and modulus values are not much utilized in design practice. The reason seems to result from the general perception that values obtained by dynamic measurement are much higher (about 10 times) than those determined statically. This paper presents results from dynamic and static tests on rock cores. The findings are : 1) elastic moduli can be consistently determined by laboratory seismic testing. 2) nonlear deformation characteristic of rock cores was tentatively proposed with variation in elastic modulus with strain.

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Variation of Elastic Stiffness of Polydimethylsiloxane (PDMS) Stretchable Substrates for Wearable Packaging Applications (웨어러블 패키징용 Polydimethylsiloxane (PDMS) 신축성 기판의 강성도 변화거동)

  • Choi, Jung-Yeol;Park, Dae-Woong;Oh, Tae Sung
    • Journal of the Microelectronics and Packaging Society
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    • v.21 no.4
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    • pp.125-131
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    • 2014
  • In order to develop stretchable substrates for wearable packaging applications, the variation behavior of elastic modulus was evaluated for transparent PDMS Sylgard 184 and black PDMS Sylgard 170 as a function of the base/curing agent mixing ratio. Both for Sylgard 184 and Sylgard 170, the true elastic modulus evaluated on a true stress-true strain curve was higher more than two times compared to the engineering elastic modulus obtained from an engineering stres-sengineering strain curve, and their difference became larger with increasing the stiffness of the PDMS. Sylgard 184 exhibited a maximum engineering elastic modulus of 1.74 MPa and a maximum true elastic modulus of 3.57 MPa at the base/curing agent mixing ratio of 10. A maximum engineering elastic modulus of 1.51 MPa and a maximum true elastic modulus of 3.64 MPa were obtained for Sylgard 170 at the base/curing agent mixing ratio of 2.

Elastic-Plastic Implicit Finite Element Method Considering Planar Anisotropy for Complicated Sheet Metal Forming Processes (탄소성 내연적 유한요소법을 이용한 평면 이방성 박판의 성형공정해석)

  • Yun, Jeong-Hwan;Kim, Jong-Bong;Yang, Dong-Yeol;Jeong, Gwan-Su
    • Transactions of Materials Processing
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    • v.7 no.3
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    • pp.233-245
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    • 1998
  • A new approach has been proposed for the incremental analysis of the nonsteady state large deformation of planar anisotropic elastic-plastic sheet forming. A mathematical brief review of a constitutive law for the incremental deformation theory has been presented from flow theory using the minimum plastic work path for elastic-plastic material. Since the material embedded coordinate system(Lagrangian quantity) is used in the proposed theory the stress integration procedure is completely objective. A new return mapping algorithm has been also developed from the general midpoint rule so as to achieve numerically large strain increment by successive control of yield function residuals. Some numerical tests for the return mapping algorithm were performed using Barlat's six component anisotropic stress potential. Performance of the proposed algorithm was shown to be good and stable for a large strain increment, For planar anisotropic sheet forming updating algorithm of planar anisotropic axes has been newly proposed. In order to show the effectiveness and validity of the present formulation earing simulation for a cylindrical cup drawing and front fender stamping analysis are performed. From the results it has been shown that the present formulation can provide a good basis for analysis for analysis of elastic-plastic sheet metal forming processes.

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Elastic Wave Propagation in Jointed Rock Mass (절리암반에서의 탄성파 전파 특성)

  • Cha, Min-Su;Cho, Gye-Chun;Baak, Seung-Hyoung
    • Proceedings of the Korean Geotechical Society Conference
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    • 2005.03a
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    • pp.515-520
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    • 2005
  • The behavior of jointed rock mass is much different from that of intact rock due to the presence of joints. Similarly, the characteristics of elastic wave propagation in jointed rock are considerably different from those of intact rock. The propagation of elastic waves in jointed rock is greatly dependent on the state of stress. The roughness, filling materials, and spacing of joints also affect wave propagation in jointed rock. If the wavelength of elastic waves is much larger than the spacing between joints, wave propagation in jointed rock mass can be considered as wave propagation in equivalent continuum. A rock resonant column testing apparatus is made to measure elastic waves propagating through jointed rock in the state of equivalent continuum. Three types of wave, i.e, torsional, longitudinal and flexural waves are monitored during rock resonant column tests. Various roughness and filling materials are applied to joints, and rock columns with various spacings are used to understand how these factors affect wave propagation under a small strain condition. The experimental results suggest that the characteristics of wave propagation in jointed rock mass are governed by the state of stress and influenced by roughness, filling materials and joint spacings.

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Thermal load analysis in an incompressible linear visco-elastic cylinder bonded to an elastic shell (非壓縮 粘彈性 圓筒體의 熱荷重 解析)

  • 이영신;최용규
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.205-213
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    • 1987
  • A linear thermoviscoelastic material model, whose basis is on incremental constitutive equation that takes complete strain and temperature histories into account, is derived and computerized in the finite element code. The thermoviscoelastic F.E.M. code which is intended primarily to analyze the cylinder model during the cool-down period, embodies the assumption of linearly elastic bulk and visco-elastic shear responses, thermo-rheologically simple response to temperature change and isotropic thermal expansion. The verification of computer program is accomplished by first testing it against a closed form solution of A.M. Freudenthal & M. Shinozuka's. The stress and strain analyses of five cylindrical models are presented and compared with experimental results. Analytical results are good agreement with experimental results. Margins of safety are evaluated and its allowable ranges are presented.

Creep behaviour of mudstone in the tertiary Duho Formation at Pohang basin (포항분지 제3기 두호층 이암의 크리프 거동)

  • 김광식;김교원
    • The Journal of Engineering Geology
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    • v.13 no.2
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    • pp.227-238
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    • 2003
  • Understanding of a creep behavior in rocks under a constant load, due to visco-elastic properties of rock, is an essential element to predict a long term ground deformation. In order to clarify the creep characteristics of the mudstone in Duho formation at Pohang basin, deposited during Tertiary, a series of laboratory tests including physical properties, unconfined compressive strength and uniaxial creep tests, was performed. The mudstone showed a higher creep potential due to 26% of clay minerals such as illite and chlorite. The unconfined compressive strength of the rock was $462{\;}kg/\textrm{cm}^2$ in average, and four creep tests were performed under constant stress of 40 to 70 % of the strength. The creep constants in the empirical and theoretical equations were deduced from the time-strain curves obtained from the tests. Among the several equations, the empirical equation proposed by Griggs and theoretical equation of Burger’s model are appreciated as the best one to express the creep behavior of the mudstone. Instantaneous elastic strain was linearly increased with stress level but strain velocity during the first creep is decreased with a similar pattern by time lapse regardless the stress level.