• Title/Summary/Keyword: Shear-rate

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BOUNDS ON THE GROWTH RATE FOR THE KUO PROBLEM

  • S. LAVANYA;V. GANESH;G. VENKATA RAMANA REDDY
    • Journal of applied mathematics & informatics
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    • v.41 no.2
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    • pp.363-372
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    • 2023
  • We consider Kuo problem of hydrodynamic stability which deals with incompressible, inviscid, parallel shear flows in the 𝛽-plane. For this problem, we derived instability region without any approximations and which intersects with Howard semi-circle region under certain condition. Also, we derived upper bound for growth rate and amplification factor of an unstable mode and proved Howard's conjecture.

Effect of Cooling Rate on Mechanical Properties of Carbon/Nylon66 Composites (카본/나일론 복합재료의 냉각속도에 따른 기계적 특성변화)

  • 홍순곤;변준형;황병선;강범수
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2001.05a
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    • pp.122-125
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    • 2001
  • The objective of this research is to develop hybridized yarns for thermoplastic composites, and to examine tile effect of cooling rate on mechanical properties of the composites. The co-braided yarn utilizing carbon fibers as reinforcements and Nylon 66 fibers as matrix materials has been fabricated. Thermoplastic composites have been manufactured by the hot-press forming process. For the processing conditions, cooling rates of $-2.5^{\circ}C$/min and $-60^{\circ}C$/min have been considered. Three-point bending test and losipescu shear test were performed to investigate the effect of the cooling rate and the surface treatment of carbon fibers. SEM photographs were used to investigate the fracture surfaces of the tested samples. The cooling rate of $-60^{\circ}C$/min resulted in the higher strength and elastic modulus for bending and shear tests. The composites of the epoxy-sized carbon fibers showed the lowest strength due to the degradation of the sizing material during the thermoforming process.

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Rate-dependent shearing response of Toyoura sand addressing influence of initial density and confinement: A visco-plastic constitutive approach

  • Mousumi Mukherjee;Siddharth Pathaka
    • Geomechanics and Engineering
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    • v.34 no.2
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    • pp.197-208
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    • 2023
  • Rate-dependent mechanical response of sand, subjected to loading of medium to high strain rate range, is of interest for several civilian and military applications. Such rate-dependent response can vary significantly based on the initial density state of the sand, applied confining pressure, considered strain rate range, drainage condition and sand morphology. A numerical study has been carried out employing a recently proposed visco-plastic constitutive model to explore the rate-dependent mechanical behaviour of Toyoura sand under drained triaxial loading condition. The model parameters have been calibrated using the experimental data on Toyoura sand available in published literature. Under strain rates higher than a reference strain rate, the simulation results are found to be in good agreement with the experimentally observed characteristic shearing behaviour of sand, which includes increased shear strength, pronounced post-peak softening and suppressed compression. The rate-dependent response, subjected to intermediate strain rate range, has further been assessed in terms of enhancement of peak shear strength and peak friction angle over varying initial density and confining pressure. The simulation results indicate that the rate-induced strength increase is highest for the dense state and such strength enhancements remain nearly independent of the applied confinement level.

Cyclic behavior of various sands and structural materials interfaces

  • Cabalar, Ali Firat
    • Geomechanics and Engineering
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    • v.10 no.1
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    • pp.1-19
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    • 2016
  • This paper presents the results of an intensive experimental investigation on cyclic behavior of various sands and structural materials interface. Comprehensive measurements of the horizontal displacement and shear stresses developed during testing were performed using an automated constant normal load (CNL) cyclic direct shear test apparatus. Two different particle sizes (0.5 mm-0.25 mm and, 2.0 mm-1.0 mm) of sands having distinct shapes (rounded and angular) were tested in a cyclic direct shear testing apparatus at two vertical stress levels (${\sigma}=50kPa$, and 100 kPa) and two rates of displacement ($R_D=2.0mm/min$, and 0.025 mm/min) against various structural materials (i.e., steel, concrete, and wood). The cyclic direct shear tests performed during this investigation indicate that (i) the shear stresses developed during shearing highly depend on both the shape and size of sand grains; (ii) characteristics of the structural materials are closely related to interface response; and (iii) the rate of displacement is slightly effective on the results.

A Study of Localization of the Adiabatic Shear Band with Numerical Method (단열전단변형에서 국부화에 대한 수치해석적 연구)

  • 이병섭
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1999.03b
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    • pp.225-228
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    • 1999
  • In a plastically deformed body the formation of a shear band is widely observed in the engineering materials during rapidly forming process for a thermally rate-sensitive material. The localized shear bond stems from evolution of a narrow region in which intensive plastic flow occurs. The shear band often plays as a precursor of the ductile fracture during a forming process. The objectives of this study are to investigate the localization behaivor by using numerical method thus predict the failure. In this work the implicit finite difference scheme is preformed due to the ease of covergence and the numerical stability. This study is based on an analysised material with hardening as well as thermally softening behavior which includes isotropy strain hardening. Furthermore this paper suggests that an anticipated and suggested a kinematic hardening constitutive equation be requried to predicte a more accurate strain level wherein a shear band occurs.

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Control Performance Investigation of MR Fluid Damper using Herschel-Bulkley Shear Model (Herschel-Bulkley 모델을 이용한 MR 댐퍼 승용차의 제어 성능 고찰)

  • 이덕영;황우석
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.05a
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    • pp.323-328
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    • 2002
  • The control performance of a vehicle installed with an MR(magnetorheological) fluid-based damper is investigated on the basis of Herschel-Bulkley shear model. Generally, most of MR fluid damper has been analyzed based on a simple Bingham-plastic shear model. However, the Bingham-plastic shear model can not well describe the behavior of the damper on the condition of high velocity and high current field input. Therefore, in this study, the Herschel-Bulkley shear model in which the constant post-yield plastic viscosity in Bingham model is replaced with a power law model dependent on shear rate is used to assess control performance of a vehicle with MR fluid damper suspension system. This study deals with a two-degree-of-freedom suspension using the MR fluid damper for a quarter car model. The response for the bump input to identify the fastness of MR fluid damper embedded skyhook controller and requested magnetic field are investigated.

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Rheological behavior and wall slip of dilute and semidilute CPyCl/NaSal surfactant solutions

  • Kibum Sung;Han, Min-Soo;Kim, Chongyoup
    • Korea-Australia Rheology Journal
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    • v.15 no.3
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    • pp.151-156
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    • 2003
  • In this research, experimental studies were performed to examine the rheological behavior of equimolar solutions of cetylpyridinium chloride (CPyCl) and sodium salicylate (NaSal) solutions with concentration. The surfactant solutions were prepared by dissolving 2 mM/2 mM - 80 mM/80 mM of surfactant/counterion in double-distilled water. It has been observed that the zero shear viscosity shows abrupt changes at two critical values of C^*$ and C^{**}$. These changes are caused by the switching of relaxation mechanism with concentration of CPyCl/NaSal solutions at those concentrations. The wall slip velocities of dilute and semidilute CPyCl/NaSal solutions show a dramatic increase with shear rate where the shear viscosity exhibits shear thickening behavior for dilute solutions and shear thinning behavior for semi-dilute solutions, respectively. Considering that the dramatic increase in wall slip velocity should be related to the formation of shear-induced structure (SIS) in the surfactant solution, the shear thickening behavior of semi-dilute solutions is caused by elastic instability unlike the case of dilute solutions.

A Laboratory Study on Erosional Properties of the Deposit Bed of Kaolinite Sediments (고령토 퇴적저면의 침식특성에 대한 실험적 연구)

  • Kim, Yong-Muk;Kim, Hyun-Min;Hwang, Kyu-Nam;Yang, Su-Hyun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.34 no.4
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    • pp.1181-1190
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    • 2014
  • In this study, the erosional parameters for deposit beds were quantitatively estimated domestically for the first time through the erosion tests using an annular flume. Four erosion tests were carried out for the deposit beds with different consolidation structures, which were obtained by consolidating the kaolinite slurries for a given time durations. Results of erosion tests showed that the bed shear strength ${\tau}_s$ increased with the consolidation time and bed depth. The erosion rate ${\epsilon}$ was also shown to be related well with the excess shear stress ${\tau}_b-{\tau}_s$ which was given by the difference between flow shear stress ${\tau}_b$ and bed shear strength ${\tau}_s$. While the logarithm of the erosion rate was linearly related with the excess shear stress as ${\tau}_b-{\tau}_s{\geq}0.1N/m^2$, however, the erosion rate decreased rapidly with it when ${\tau}_b-{\tau}_s{\leq}0.1N/m^2$. These erosion test results were also shown to be good enough to verify by comparing with the test results from previous studies and a new equation was suggested to describe the erosion rate more well in the region of ${\tau}_b-{\tau}_s{\leq}0.1N/m^2$.

An Experimental Study for the Hydraulic Behavior of Artificial Rock Joint under Compression and Shear Loading (압축과 전단 하중을 받는 인공 암석 절리의 수리적 거동에 관한 실험적 연구)

  • 이희석;박연주;유광호;이희근
    • Tunnel and Underground Space
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    • v.10 no.1
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    • pp.45-58
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    • 2000
  • Cyclic shear test system, which is capable of measuring flow rate inside rock joint, was established to investigate the hydraulic behavior of rough rock joints under various loading conditions. Laboratory hydraulic tests during compression and shear were conducted for artificial rough rock joints. Prior to tests, aperture characteristics of specimens were examined by measuring surface topography. Permeability changes under compression were well approximated with several hydraulic model. Hydraulic behavior conformed to dilation characteristics in the first stage, and permeability increased with increase of dilation. As the shear displacement progressed, flow rate became somewhat constant due to gouge production and offset of apertures. Hydraulic behavior under cyclic shear loading was also influenced by the degradation of asperities and gouge production. In addition. the relation between hydraulic aperture and mechanical aperture under compression and shear loading was investigated and compared.

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Analyses of Fracture Tube Tearing using Gurson Model and Shear Failure Model (Gurson Model과 Shear Failure Model을 이용한 파쇄튜브의 찢어짐 해석)

  • Yang, Seung-Yong;Kwon, Tae-Su;Choi, Won-Mok
    • Journal of the Korean Society for Railway
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    • v.11 no.3
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    • pp.280-285
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    • 2008
  • Two kinds of failure model, that is, the Gurson model and a shear failure model were used for the finite element analyses of simple and notch tensile specimens and axial compression of a fracture tube with initial saw-cuts. The parameter values for the shear failure model were determined by a combined experimental and numerical analysis of the notch tensile specimens. After fitting the numerical parameters such as the yielding stress and the fracture shear strains, the Gurson model and the shear failure model were applied to the analysis of the fracture tube. Although the Gurson model and the shear failure model showed similar fracture behavior for the case of the tensile specimens, the respective results were different in the axial force and the crack growth rate of the fracture tube. That is, the shear failure model required more axial force to make the cracks propagate along the tube than the Gurson model. These are believed to show the lack of damage evolution process of the shear failure model. To decide which model is better in the tube analysis, experimental verification will be necessary.