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181.
V. M. Kulik 《Journal of Applied Mechanics and Technical Physics》2007,48(2):221-228
The longitudinal and transverse components of deformation of the surface of a flat layer of a viscoelastic material glued
onto a solid base under the action of a traveling pressure wave are determined. The coating compliance is described by two
components corresponding to two components of surface displacement. The dimensionless compliance components depend only on
the viscoelastic properties of the material, the ratio of the wave length to the layer thickness λ/H, and the ratio of the
wave velocity to the velocity of propagation of shear oscillations V/C
t
0
. Data on the dynamic compliance are presented for 0.3 < λ/H < 30 and 0.1 < V/C
t
0
< 10. The compliance is demonstrated to be determined by its absolute value and by the phase lag of strain from pressure.
The effect of viscous losses in the material and compressibility of the latter on the dynamic compliance is analyzed. An anomalous
behavior of the compliance with the wave velocity being greater than a certain critical value is explained.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 90–97, March–April, 2007. 相似文献
182.
A method for the detection of small masses with the aid of a longitudinally vibrating band is described and further applications, e.g. for viscosity and humidity measurement are discussed. The complex Young's modulus of the band can also be determined. 相似文献
183.
松弛与蠕变力学特性转换关系的研究 总被引:8,自引:0,他引:8
本文首先论述了拉伸应力松弛模量E(t)与拉伸蠕变柔量D(t)之间的近似与精确转换关系式,提出一种诊断D(t)的数值积分算法,通过应力松弛模量实验给出一种固体推进剂E(t)和D(t)的实测与转换计算结果,计算结果有较小的误差具有重要的实用价值。 相似文献
184.
Chr. Friedrich 《Rheologica Acta》1991,30(1):7-13
A function series g(x; n, m) is presented that converges in the limiting case n and m = constant to the delta-function located at x = = 1. For every finite n, there exists 2n+1(–nmn) approximations of the delta-function (n)(x–x
n,m
). x
n,m
is the argument where the function reaches its maximum. A formula for the calculation is given.The delta-function approximation is the starting point for the approximative determination of the logarithmic density function of the relaxation or retardation time spectrum. The n-th approximation of density functions based on components of the complex modulus (G*) or the complex compliance (J*) is given. It represents an easy differential operator of order n.This approach generalizes the results obtained by Schwarzl and Staverman, and Tschoegl. The symmetry properties of the approximations are explained by the symmetry properties of the function g(x; n, m). Therefore, the separate equations for each approximation given by Tschoegl can be subsumed in a single equation for G and G, and in another for J and J. 相似文献
185.
准确了解二维材料的力学性能对于推动其应用具有重要意义, 无基底压痕技术是目前最广泛采用的二维材料力学性能测试方法之一, 本文综述了二维材料压痕研究的最新进展以及所面临的问题, 并对将来的研究工作进行了展望.无基底压痕技术是将二维材料转移到带有沟槽或柱形孔的基底上, 制备二维材料"梁"和"鼓"模型, 然后利用原子力显微镜测量其在压针作用下的载荷--位移关系, 最后通过基于连续介质薄膜导出的压痕响应分析模型拟合实验结果, 估算出二维材料的弹性模量和本征强度.由于二维材料的厚度远小于连续介质薄膜, 来自于压头以及基底孔侧壁的范德华力对二维材料的压痕响应具有显著影响, 造成二维材料与传统压痕分析模型中的基本假设不符, 导致不能准确预测二维材料的弹性模量; 另外, 由于传统压痕模型无法准确描述二维材料在大变形下的非线性行为, 以及由缺陷等引起的应力集中, 导致由压痕测试表征的二维材料(特别是多晶二维材料)本征强度具有较大的偏差. 因此, 一方面需要正确了解由压痕技术获得的二维材料力学性能, 另一方面还需对目前的研究方法做进一步的改进和完善. 相似文献
186.
弹塑性有限变形的拟流动理论 总被引:13,自引:0,他引:13
本文提出一种弹塑性有限变形的拟流动理论。该理论从正交性法则出发,通过引入“拟弹性模量”和模量衰减函数并改进应变率的弹塑性分解,实现了由有限变形Prandtl-Reuss流动理论(J2F)向基于非正交法则的率形式形变理论(J2D)的合理的光滑过渡;并适用于初始及后继各向异性变形分析。在特殊条件下,可退化为J2F、J2D理论以及由任意各向异性屈服函数描述的流动理论。将该理论用于韧性金属平面应力/应变拉伸失稳与变形局部化的有限元模拟,并与理论分析及实验结果相比较,表明了本文理论的正确性。 相似文献
187.
In order to develop criteria for the physical evaluation of wood for soundboards of musical instruments, measurements were made of dynamic Young's modulusE, static Young's modulusE, internal frictionQ
–1 in longitudinal direction, and specific gravity for numerous species of broad-leaved wood. From the results obtained, including those of our previous paper on coniferous wood [1], it was found that the suitability of wood for soundboards could be evaluated by the quantity ofQ
–1/(E/), and that there were very high correlations betweenQ
–1/(E/) andE/, and betweenE andE, regardless of wood species. Consequently, it becomes possible to select practically any wood suitable for soundboards by using the value ofE/, which can be measured easily, and it was derived that the relation betweenE/ andQ
–1 of wood could be expressed by an exponential equation regardless of wood species. 相似文献
188.
To date, there is no method to measure non-destructively the modulus of trabeculae within cancellous bone, whilst retaining
its structural integrity. In this study ultrasonic scanning, coupled with microCT imaging, is employed to determine trabeculae
modulus along the three major anatomical axes non-destructively. The proposed method allows cancellous bone specimens to remain
intact, for possible use in subsequent studies. Volume rendering of the microCT images allows three-dimensional visualization
of cancellous bone specimens to be tested. This facilitates trabeculae selection and accurate measurement of distance traveled
by the ultrasonic wave, thus yielding a good degree of confidence in the acoustic velocity measured. For all the three principal
anatomical directions, the measured acoustic speeds ranged from 2,115 to 3,077 m/s, giving an average of 2,505 m/s. Average
wave velocities in the superior–inferior, medial–lateral and anterior–posterior anatomical directions were found to be 2,295,
2,469 and 2,754 m/s, respectively; the differences corresponding to the three directions do not appear to be significant.
Subsequently, the modulus was then determined using elastic wave propagation theory. 相似文献
189.
Dimitre Hadjistamov 《Rheologica Acta》1996,35(4):364-368
The work describes a way to obtain loss modulus and storage modulus master curves from oscillatory measurements of silicone oils.The loss modulus master curve represents the dependence of the viscous flow behavior on ·
0
*
and the storage modulus master curve — the dependence of the elastic flow behavior on ·
0
*
.The relation between the values of the loss modulus and storage modulus master curves (at a certain frequency) is a measurement of the viscoelastic behavior of a system. The G/G-ratio depends on ·
0
*
which leads to a viscoelastic master curve. The viscoelastic master curve represents the relation between the elastic and viscous oscillatory flow behavior. 相似文献
190.
A numerical approach to spherical indentation techniques for material property evaluation 总被引:1,自引:0,他引:1
In this work, some inaccuracies and limitations of prior indentation theories, which are based on experimental observations and the deformation theory of plasticity, are investigated. Effects of major material properties on the indentation load-deflection curve are examined via finite element (FE) analyses based on incremental plasticity theory. It is confirmed that subindenter deformation and stress-strain distribution from deformation plasticity theory are quite dissimilar to those obtained from incremental plasticity theory. We suggest an optimal data acquisition location, where the strain gradient is the least and the effect of friction is negligible. A new numerical approach to indentation techniques is then proposed by examining the FE solutions at the optimal point. Numerical regressions of obtained data exhibit that the strain-hardening exponent and yield strain are the two key parameters which govern the subindenter deformation characteristics. The new indentation theory successfully provides a stress-strain curve and material properties with an average error of less than 3%. 相似文献