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1.
A technique was developed for determining the longitudinal shear modulus of uniform diameter single fibers. A length of single
fiber suspended from one end and with a weight attached at the other end was used as a torsional pendulum. Its longitudinal
shear modulus can be experessed as a function of the frequency of oscillation of the torsional pendulum. Tests were conducted
on five different types of fibers: carbon, Kevlar 49, silicon carbide, K-glass fibers and G-glass fibers. 相似文献
2.
X. Nie R. Prabhu W. W. Chen J. M. Caruthers T. Weerasooriya 《Experimental Mechanics》2011,51(9):1527-1534
A novel Kolsky torsion bar technique is developed and successfully utilized to characterize the high strain rate shear response
of a rate-independent end-linked polydimethylsiloxane (PDMS) gel rubber with a shear modulus of about10 KPa. The results show
that the specimen deforms uniformly under constant strain rate and the measured dynamic shear modulus follows reasonably well
the trend determined by dynamic mechanical analysis (DMA) at lower strain rates. For comparison, Kolsky compression bar experiments
are also performed on the same gel material with annular disk specimens. The dynamic moduli obtained from compression experiments,
however, are an order of magnitude higher than those obtained by the torsional technique, due to the pressure caused by the
radial inertia and end constraints. 相似文献
3.
In order to characterize the torsional behavior of microwires, an automated torsion tester is established based on the principle of torsion balance. The main challenges in developing a torsion tester at small scales are addressed. An in-situ torsional vibration method for precisely calibrating the torque meter is developed. The torsion tester permits the measurement of torque to nN m, as a function of surface shear strain to a sensitivity of sub-microstrain. Using this technique, we performed (monotonic and/or cyclic) torsion tests on polycrystalline copper and gold wires. It is found that (i) a size effect appears in both the initial yielding and the plastic flow of torsional response; (ii) a reverse plasticity occurs upon unloading in cyclic torsion response; and (iii) the Hall-Petch effect and the strain gradient effect are synergistic. We also performed cyclic torsion tests on human hairs and spider silk which are natural protein fibers with a different morphological structure to metallic wires. It is shown that the single hair exhibits torsional recovery, and that the spider silk displays torsionally superelastic behavior whereby it is able to withstand great shear strain. 相似文献
4.
A computerized apparatus for the measurement of low shear rate viscosity on polymer solutions at elevated pressure and temperature is described. The pressure is variable from 1 bar to 400 bar with an accuracy of ±5 bar. The temperature is variable from 0° to 100°C with an accuracy of ±0.3 K. The instrument is operated in a free-relaxation mode in which the decay of oscillation of the torsion pendulum after an initial displacement is recorded and used to compute the viscosity of the sample. The measurements are performed according to the contents of a user-specified control file, and the oscillation data are stored digitally and later analyzed for parameter estimation. The instrument operates in the very-low frequency range (0.03 to 0.25 Hz) and the accuracy of the measured viscosity is ±0.03 x 10–3 Ns/m2. 相似文献
5.
The sandwich plate twist test method involves torsion loading of a panel by application of concentrated loads at two diagonally
opposite corners and supporting the panel at the other two corners. Compliance measured in this test can be used to extract
the shear moduli of monolithic, composite and sandwich plates, and it may also be employed for determination of the twist
stiffness, D
66
. Previous studies of the plate twist specimen have shown that classical laminated plate theory does not adequately predict
the compliance of sandwich panels with a low density/modulus core, as a result of transverse shear deformation. This work
proposes a “shear-corrected” model for accurate prediction of the plate twist compliance by incorporation of the transverse
shear stiffnesses of the core. This model was used to extract the transverse shear modulus of a range of low density PVC foam
cores from the measured panel twist compliance. Good agreement with published PVC foam core shear modulus values was obtained. 相似文献
6.
《International Journal of Solids and Structures》2014,51(25-26):4504-4518
In this study, two variations of WBC (Wire-woven Bulk Cross), named semi-WBC and straight-WBC, are introduced. In the variations, helically formed wires in an ordinary WBC are partly or totally replaced with straight wires to obtain higher shear strength and modulus, and the fabrication processes are modified to enhance productivity. Analytic solutions of the relative density, shear strength and modulus for the three variations of WBCs including the ordinary WBC with X-orientation are derived. And CAD modeling, shear tests and FEA were performed to prove the analytic solutions. The effects of the curviness of the struts loaded or floating between face sheets, and the offset at the joints are evaluated. The semi- and straight WBCs had equivalent shear strengths and moduli comparable to those of typical aluminum honeycombs, and all the three variations of WBCs maintained their strengths at low densities down to 1%. 相似文献
7.
Dr. Lucas Duffrène René Gy Hélène Burlet Roland Piques Annelise Faivre Anas Sekkat Joseph Perez 《Rheologica Acta》1997,36(2):173-186
The linear viscoelastic behavior of a soda-lime-silica glass under low frequency shear loading is investigated in the glass transition range. Using the time-temperature superposition technique, the master curves of the shear dynamic relaxation moduli are obtained at a reference temperature of 566°C. A method to determine the viscoelastic constants from dynamic relaxation moduli is proposed. However, some viscoelastic constants cannot be directly measured from the experimental curves and others cannot be precisely obtained due to non-linearity effects at very low frequencies. The generalized Maxwell model is investigated from the experimental dynamic moduli without fixing the viscoelastic constants. A set of parameters is shown to be in good agreement with the experimental dynamic relaxation moduli, but does not give the correct values of the viscoelastic constants of the investigated glass. The soda-lime-silica glass exhibits a non-linear viscoelastic behavior at very low stress level which is usually observed for organic glasses. This non-linear behavior is questioned. 相似文献
8.
9.
This work is concerned with the Saint-Venant torsion problem of a two-phase circumferentially symmetric compound prismatic
bar. By generalizing a method originally proposed by Packham and Shail [12], we demonstrate that for a particular two-phase
configuration, simply or multiply connected, which is invariant with phase interchange, the solutions can be constructed from
solutions of two analogous problems with constant material properties. An effective shear modulus is derived in analytic form,
which is approximately the harmonic mean of the component shear moduli. We also show that the effective torsional shear modulus
is homogeneous for arbitrary configurations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Identification of Dynamic (Young’s and Shear) Moduli of a Structural Adhesive Using Modal Based Direct Model Updating Method 总被引:1,自引:1,他引:0
In this paper, mechanical characteristics (Young’s modulus and shear modulus) of an adhesive are identified using modal based
direct model updating method and experimental modal data. The results show that both Young’s and shear moduli of adhesive
are frequency dependent. Also, it is demonstrated that the thickness and length of the adhesive-line have influence on these
properties. All experiments and subsequent identifications are conducted both in bending and shear modes, and it has been
shown that the shear modulus of adhesive is more sensitive to length and thickness variations. The repeatability and consistency
of method is proved through repeating the process several times and with different adherends. 相似文献
11.
The purpose of this paper is to compare the value of the shear modulus of an isotropic material (PMMA) obtained from both tensile and losipescu shear tests. A finite-element model is introduced to account for a nonuniform stress distribution in the losipescu coupon. A correction accounting for nonuniform strain values over the strain-gage section is also introduced. Rigorous statistical data processing leads to an estimation of the error between the moduli obtained by the two tests. Some points relevant to the losipescu test are reviewed, particularly concerning the sample preparation. Provided that a careful procedure is followed, excellent agreement is achieved between the shear moduli measured by the two methods. 相似文献
12.
High-frequency viscoelasticity of crosslinked actin filament networks measured by diffusing wave spectroscopy 总被引:2,自引:0,他引:2
We study the short-time relaxation dynamics of crosslinked and uncrosslinked networks of semi-flexible polymers using diffusing
wave spectroscopy (DWS). The networks consist of concentrated solutions of actin filaments, crosslinked with increasing amounts
of α-actinin. Actin filaments (F-actin) are long semi-flexible polymers with a contour length 1–100μm and a persistence length
of 5–15μm; α-actinin is a small 200kDa homodimer with two actin-binding sites. Using the large bandwidth of DWS, we measure
the mean-square-displacement of 0.96μm diameter microspheres imbedded in the polymer network, from which we extract the frequency-dependent
viscoelastic moduli via a generalized Langevin equation. DWS measurements yield, in a single measurement, viscoelastic moduli
at frequencies up to 105Hz, almost three decades higher in frequency than probed by conventional mechanical rheology. Our measurements show that the
magnitude of the small-frequency plateau modulus of F-actin is greatly enhanced in the presence of α-actinin, and that the
frequency dependence of the viscoelastic moduli is much stronger at intermediate frequencies. However, the frequency-dependence
of loss and storage moduli become similar for both crosslinked and uncrosslinked networks at large frequencies, G′(ω)∝G′′(ω)∝ω0.75±0.08. This high-frequency behavior is due to the small-amplitude, large-frequency lateral fluctuations of actin filaments between
entanglements.
Received: 20 January 1998 Accepted: 12 February 1998 相似文献
13.
A mixing rule as suggested by the Doi-Edwards theory is checked experimentally. For this purpose, the dynamic shear moduli as functions of circular frequency are measured first for the melts of a series of polystyrenes of narrow molecular mass distributions. After the careful preparation of mixtures the same moduli are also determined for these mixtures. A discussion is given of the remarkable but limited validity of the additivity of contributions by the single macromolecules to the mentioned moduli. 相似文献
14.
G. Harrison 《Rheologica Acta》1974,13(1):28-32
Summary An instrument has been developed for measuring the viscoelastic behaviour of polymer melts at low frequencies, in the range 10–3 to 50 Hz. The sample is contained between a cone and a fixed plate, or between parallel plates. The moving member is driven in torsional oscillation through a torsion wire. The amplitude of the resulting oscillation is compared in amplitude and phase with the driven end of the torsion wire. The amplitudes are measured digitally using optical diffraction gratings, and either an oscilloscope or a high-speed ultra-violet recorder is used to determine the phase angle between the two signals. The moving member is supported on an air bearing, which provides a very low friction support with a high degree of positional control thus giving a well defined sample geometry. The torsion wire is driven using a vibrator with a d.c. drive amplifier fed from a very low frequency oscillator. The sample temperature is controlled to better than 0.01 °C, with temperature gradients across the sample of a similar order of magnitude. The temperature range of the instrument is from –50 °C to +200 °C.The angular resolution of the measuring system is 3 × 10–5 radius, so that an accuracy of better than ±1% in the amplitude measurements can be obtained with the amplitude of shear in the sample kept sufficiently low that a linear stress-strain relation is maintained.With 3 figures 相似文献
15.
P. Kuzhir A. Gómez-Ramírez M.T. López-López G. Bossis A.Yu. Zubarev 《ournal of non Newtonian Fluid Mechanics》2011,166(7-8):373-385
This paper reports the first study on the large amplitude oscillatory shear flow for magnetic fiber suspensions subject to a magnetic field perpendicular to the flow. The suspensions used in our experiments consisted of cobalt microfibers of the average length of 37 μm and diameter of 4.9 μm, dispersed in a silicon oil. Rheological measurements have been carried out at imposed stress using a controlled stress magnetorheometer. The stress dependence of the shear moduli presented a staircase-like decrease with, at least, two viscoelastic quasi-plateaus corresponding to the onset of microscopic and macroscopic scale rearrangement of the suspension structure, respectively. The frequency behavior of the shear moduli followed a power-law trend at low frequencies and the storage modulus showed a high-frequency plateau, typical for Maxwell behavior. Our simple single relaxation time model fitted reasonably well the rheological data. To explain a relatively high viscous response of the fiber suspension, we supposed a coexistence of percolating and pivoting aggregates. Our simulations revealed that the former became unstable beyond some critical stress and broke in their middle part. At high stresses, the free aggregates were progressively destroyed by shear forces that contributed to a drastic decrease of the moduli. We have also measured and predicted the output strain waveforms and stress–strain hysteresis loops. With the growing stress, the shape of the stress–strain loops changed progressively from near-ellipsoidal one to the rounded-end rectangular one due to a progressive transition from a linear viscoelastic to a viscoplastic Bingham-like behavior. 相似文献
16.
剪切流作用下层合梁非线性振动特性研究 总被引:1,自引:1,他引:0
针对剪切流中层合梁的大变形非线性振动问题, 采用高阶剪切变形锯齿理论和冯·卡门应变描述层合梁的变形模式和几何非线性效应, 构建了大变形层合梁非线性振动有限元数值模型; 采用基于任意拉格朗日?欧拉方法的有限体积法求解不可压缩黏性流体纳维-斯托克斯方程, 结合层合梁和流体的耦合界面条件建立了剪切流作用下层合梁流固耦合非线性动力学数值模型, 采用分区并行强耦合方法对层合梁的流致非线性振动响应进行了迭代计算. 研究了不同速度分布的剪切流作用下单层梁和多层复合材料梁的振动响应特性, 并验证了本文数值建模方法的有效性. 结果表明: 剪切流作用下单层梁的振动特性与均匀流作用下的情况不同, 梁的运动轨迹受剪切流影响向下偏斜, 随着速度分布系数增加, 尾部流场中的涡结构发生改变; 刚度比对剪切流作用下层合梁的振动特性有显著影响, 随着刚度比的增加, 层合梁振动的振幅增大, 主导频率下降, 运动轨迹由‘8’字形逐渐变得不对称; 发现了不同厚度比和铺层角度情况下, 层合梁存在定点稳定模式、周期极限环振动模式和非周期振动模式三种不同的振动模式, 改变层合梁铺层角度可实现层合梁周期极限环振动模式向非周期振动模式转变. 相似文献
17.
研究了直流电场下钛酸钙系电流变液在动态振荡剪切模式下损耗模量的变化。用流变仪测试了不同颗粒体积分数材料在不同的温度和电场下损耗模量随应变的关系曲线。讨论了颗粒体积分数、温度、电场强度以及频率对材料损耗模量的影响。以理论推导和试验数据拟合的方法给出了损耗模量与颗粒体积分数、振荡频率、温度以及电场强度等参数的半经验数学关系式。理论值对比试验结果表明,本文损耗模量表达式与试验结果符合较好,可以用于预测直流电场下钛酸钙系电流变液在动态振荡剪切模式下颗粒体积分数、温度、电场强度、频率和剪切应变对损耗模量的影响。 相似文献
18.
Nonlinear viscoelastic properties of MR fluids under large-amplitude-oscillatory-shear 总被引:3,自引:0,他引:3
Nonlinear viscoelastic properties of the MR fluid, MRF-132LD, under large-amplitude oscillatory shear were investigated. This was accomplished by carrying out the experiments under the amplitude sweep mode and the frequency sweep mode, using a rheometer with parallel-plate geometry. Investigations under the influence of various magnetic field strength and temperatures were also conducted. MR fluids behave as nonlinear viscoelastic or viscoplastic materials when they are subjected to large-amplitude shear, where the storage modulus decreases rapidly with increasing strain amplitude. Hence, MR fluid behaviour ranges from predominantly elastic at small strain amplitudes to viscous at high strain amplitudes. Large-amplitude oscillatory shear measurements with frequency sweep mode reveal that the storage modulus is independent of oscillation frequency and approaches plateau values at low frequencies. With increasing frequency, the storage modulus shows a decreasing trend before increasing again. This trend may be explained by micro-structural variation. In addition, the storage modulus increases gradually with increasing field strength but it shows a slightly decreasing trend with temperature. 相似文献
19.
Grain-scale local fluid flow is an important loss mechanism for attenuating waves in cracked fluid-saturated poroelastic rocks. In this study, a dynamic elastic modulus model is developed to quantify local flow effect on wave attenuation and velocity dispersion in porous isotropic rocks. The Eshelby transform technique, inclusion-based effective medium model (the Mori–Tanaka scheme), fluid dynamics and mass conservation principle are combined to analyze pore-fluid pressure relaxation and its influences on overall elastic properties. The derivation gives fully analytic, frequency-dependent effective bulk and shear moduli of a fluid-saturated porous rock. It is shown that the derived bulk and shear moduli rigorously satisfy the Biot-Gassmann relationship of poroelasticity in the low-frequency limit, while they are consistent with isolated-pore effective medium theory in the high-frequency limit. In particular, a simplified model is proposed to quantify the squirt-flow dispersion for frequencies lower than stiff-pore relaxation frequency. The main advantage of the proposed model over previous models is its ability to predict the dispersion due to squirt flow between pores and cracks with distributed aspect ratio instead of flow in a simply conceptual double-porosity structure. Independent input parameters include pore aspect ratio distribution, fluid bulk modulus and viscosity, and bulk and shear moduli of the solid grain. Physical assumptions made in this model include (1) pores are inter-connected and (2) crack thickness is smaller than the viscous skin depth. This study is restricted to linear elastic, well-consolidated granular rocks. 相似文献
20.
A method to measure very small torques that subject micro-diameter copper wires to plasticity is developed for quasi-static
torsion experiment. Following the concept in the work by Fleck et al. (Acta Metall. Mater. 42:2, 1994), we employed a glass fiber filament as the torque cell. To calculate the small torques applied on the micro-diameter copper
wires, an additional rotation sensor is required to measure the rotation of the glass fiber torque cell. The rotation sensor
system is attached between the glass fiber and the copper wire specimen. It uses a laser extensometer to gauge the distance
between a helical and a horizontal reflection tapes on a foam cylinder, which is calibrated with the angle of rotation. A
new set of torsional experimental data for the copper wires with four different diameters, from 16–180 μm, are presented.
All copper wires exhibit a typical elastic-plastic response. The torsional properties of these copper wires were not found
to be significantly different. The uncertainties of the measurement and analysis are discussed. 相似文献