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1.
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
2.
Yongbin Zhang 《Theoretical and Computational Fluid Dynamics》2009,23(4):239-254
Boundary film shear elastic modulus effect is analyzed in a hydrodynamic contact. The contact is one-dimensional composed
of two parallel plane surfaces, which are, respectively, rough rigid with rectangular micro projections in profile periodically
distributed on the surface and ideally smooth rigid. The whole contact is consisted of cavitated area and hydrodynamic area.
The hydrodynamic area consists of many micro Raleigh bearings which are discontinuously and periodically distributed in the
contact. Analysis is thus carried out for a micro Raleigh bearing in this contact. The hydrodynamic contact in this micro
Raleigh bearing consists of boundary film area and fluid film area which, respectively, occur in the outlet and inlet zones.
In boundary film area, the film slips at the upper contact surface due to the limited shear stress capacity of the film–contact
interface, while the film does not slip at the lower contact surface due to the shear stress capacity large enough at the
film–contact interface. In boundary film area, the viscosity, density and shear elastic modulus of the film are varied across
the film thickness due to the film–contact interactions, and their effective values are used in modeling, which depend on
the film thickness. The analytical approach proposed by Zhang (J Mol Liq 128:60–64, 2006) and Zhang et al. (Int J Fluid Mech
Res 30:542–557, 2003) is used for boundary film area. In fluid film area, the film does not slip at either of the contact
surfaces, and the shear elastic modulus of the film is neglected. Conventional hydrodynamic analysis is used for fluid film
area. The present paper presents the theoretical analysis and a typical solution. It is found that for the simulated case
the boundary film shear elastic modulus effects on the mass flow through the contact, the overall film thickness of the contact
and the carried load of the contact are negligible but the boundary film shear elastic modulus effect on the local film thickness
of the contact may be significant when the boundary film thickness is on the 1 nm scale and the contact surfaces are elastic.
In Part II will be presented detailed results showing boundary film shear elastic modulus effects in different operating conditions.
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3.
Current nanoindentation measurement techniques normally assume that one material function (such as the Poisson's function)
is a constant, and measures just one material function, such as the creep compliance in shear. For materials with significant
viscoelastic effects and unknown viscoelastic functions, assuming a constant for one material function is not satisfactory.
Accurate measurements require simultaneously determining two independent material functions. This paper provides a method
to use nanoindentation to measure both bulk and shear relaxation functions. Two different nanoindenter tips, namely Berkovich
and spherical indenters, are used for nanoindentation on polymers. Any two independent viscoelastic functions, such as bulk
relaxation modulus and shear relaxation modulus, have different representations in the load–displacement curves obtained with
these two indenters so that the two independent viscoelastic functions can be separated and determined. Two polymers, poly(vinyl
acetate) (PVAc) and poly(methyl methacrylate) (PMMA) were used in nanoindentation. Nanoindentation measurements were conducted
on PVAc above glass transition temperature (Tg) and on PMMA below Tg. Both shear and bulk relaxation functions determined
from nanoindentation were found in a reasonably good agreement with data obtained from conventional tests, providing validation
of the method presented. The new method can be applied in measurements of two independent viscoelastic functions at sub-micron
scale of very small amounts of materials such as polymeric films on a substrate, heterogeneous materials such as bones, tissues,
and nanocomposites. 相似文献
4.
Yongbin Zhang 《Theoretical and Computational Fluid Dynamics》2009,23(4):255-269
The present paper is the subsequent research of the first part (Theor Comput Fluid Dyn, 2009). It investigates the boundary
film shear elastic modulus effect in a hydrodynamic contact in different operating conditions. The hydrodynamic contact is
one-dimensional, composed of two parallel plane surfaces, which are respectively rough rigid with rectangular micro projections
in profile periodically distributed on the surface and ideally smooth rigid. The whole contact consists of cavitated area
and hydrodynamic area. The hydrodynamic area consists of many micro Raleigh bearings which are discontinuously and periodically
distributed in the contact. The hydrodynamic contact in a micro Raleigh bearing consists of boundary film area and fluid film
area which, respectively, occur in the outlet and inlet zones. In boundary film area, the film slips at the upper contact
surface due to the limited shear stress capacity of the film–contact interface, while the film does not slip at the lower
contact surface due to the shear stress capacity of the film–contact interface large enough. In boundary film area, the viscosity,
density, and shear elastic modulus of the film are varied across the film thickness due to the film–contact interactions,
and their effective values are used in modeling which depends on the film thickness. In fluid film area, the film does not
slip at either of the contact surfaces, and the shear elastic modulus of the film is neglected. It is found from the simulation
results that the boundary film shear elastic modulus influences are normally negligible on the mass flow through the contact,
the carried load of the contact and the overall film thickness of the contact, and the boundary film shear elastic modulus
would normally influence the local film thickness in an elastic contact when the local film thickness is on the film molecule
diameter scale. It is also found that the boundary film shear elastic modulus effect has the tendency of being increased with
the reduction of the width of a micro contact. It is increased with the reduction of the boundary film–contact interfacial
shear strength or with the increase of the critical boundary film thickness, while it is strongest at certain values of the
contact surface roughness, the width ratio of fluid film area to boundary film area, and the lubricant film shear elastic
modulus.
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5.
Slimane Merdaci Abdelouahed Tounsi Mohammed Sid Ahmed Houari Ismail Mechab Habib Hebali Samir Benyoucef 《Archive of Applied Mechanics (Ingenieur Archiv)》2011,81(11):1507-1522
Two refined displacement models, RSDT1 and RSDT2, are developed for a bending analysis of functionally graded sandwich plates.
Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation
theories. The developed models are variationally consistent, have strong similarity with classical plate theory in many aspects,
do not require shear correction factor, and give rise to transverse shear stress variation such that the transverse shear
stresses vary parabolically across the thickness satisfying shear stress-free surface conditions. The accuracy of the analysis
presented is demonstrated by comparing the results with solutions derived from other higher-order models. The functionally
graded layers are assumed to have isotropic, two-constituent material distribution through the thickness, and the modulus
of elasticity, Poisson’s ratio of the faces, and thermal expansion coefficients are assumed to vary according to a power-law
distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic
ceramic material. Numerical results for deflections and stresses of functionally graded metal–ceramic plates are investigated.
It can be concluded that the proposed models are accurate and simple in solving the bending behavior of functionally graded
plates. 相似文献
6.
Xian-Fang Li Bao-Lin Wang Jie-Cai Han 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(10):1197-1212
The higher-order theory is extended to functionally graded beams (FGBs) with continuously varying material properties. For
FGBs with shear deformation taken into account, a single governing equation for an auxiliary function F is derived from the basic equations of elasticity. It can be used to deal with forced and free vibrations as well as static
behaviors of FGBs. A general solution is constructed, and all physical quantities including transverse deflection, longitudinal
warping, bending moment, shear force, and internal stresses can be represented in terms of the derivatives of F. The static
solution can be determined for different end conditions. Explicit expressions for cantilever, simply supported, and clamped-clamped
FGBs for typical loading cases are given. A comparison of the present static solution with existing elasticity solutions indicates
that the method is simple and efficient. Moreover, the gradient variation of Young’s modulus and Poisson’s ratio may be arbitrary
functions of the thickness direction. Functionally graded Rayleigh and Euler–Bernoulli beams are two special cases when the
shear modulus is sufficiently high. Moreover, the classical Levinson beam theory is recovered from the present theory when
the material constants are unchanged. Numerical computations are performed for a functionally graded cantilever beam with
a gradient index obeying power law and the results are displayed graphically to show the effects of the gradient index on
the deflection and stress distribution, indicating that both stresses and deflection are sensitive to the gradient variation
of material properties. 相似文献
7.
Habib Ammari Hyeonbae Kang Hyundae Lee 《Archive for Rational Mechanics and Analysis》2009,193(3):679-714
We investigate the band-gap structure of the frequency spectrum for elastic waves in a high-contrast, two-component periodic
elastic medium. We consider two-dimensional phononic crystals consisting of a background medium which is perforated by an
array of holes periodic along each of the two orthogonal coordinate axes. In this paper we establish a full asymptotic formula
for dispersion relations of phononic band structures as the contrast of the shear modulus and that of the density become large.
The main ingredients are integral equation formulations of the solutions to the harmonic oscillatory linear elastic equation
and several theorems concerning the characteristic values of meromorphic operator-valued functions in the complex plane, such
as the generalized Rouché’s theorem. We establish a connection between the band structures and the Dirichlet eigenvalue problem
on the elementary hole. We also provide a criterion for exhibiting gaps in the band structure which shows that smaller the
density of the matrix is, the wider the band-gap is, provided that the criterion is fulfilled. This phenomenon was reported
by Economou and Sigalas (J Acoust Soc Am 95:1734–1740, 1994) who observed that periodic elastic composites whose matrix has lower density and higher
shear modulus compared to those of inclusions yield better open gaps. Our analysis in this paper agrees with this experimental
finding. 相似文献
8.
Damped inertial water flow in a cylindrical vessel is investigated. A return effect or "recoil" as the shear strain rate falks
to a value of the order of 10−3s−1 is observed. Over the range of low strain rates the water behaves like a medium with very low shear strength and a shear
modulus of the order of 10−6 Pa.
Ekaterinburg. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 3–7, January–February,
1997. 相似文献
9.
Using the fact that for simple fluids the most general constitutive equation in constant stretch history flows for the extra
stress tensor τ is known in an explicit form, the Giesekus fluid model is cast into this (ω–D) form for two-dimensional flows. The three material functions needed to characterize τ are listed. The explicit results for
simple shear and planar elongation reveal that the parameter α should be restricted to values less than 0.5. It is demonstrated
that in this explicit form the constitutive equation is free from thermodynamic objections and can thus be used as a starting
point for numerical calculations of general, but steady, two-dimensional flows.
Received: 9 November 1998 Accepted: 20 May 1999 相似文献
10.
I. Yu. Tsvelodub 《Journal of Applied Mechanics and Technical Physics》2008,49(1):129-135
A variant of the multimodulus elasticity theory for isotropic materials is proposed under the assumption that the shear modulus
in Hooke’s law is a constant and the volume modulus depends on the sign of the first invariant of the stress tensor. Plane
problems (plane strain and generalized plane stressed state) and problems of plate bending are considered. Some examples are
given.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 1, pp. 157–164, January–February, 2008. 相似文献
11.
Analytical expressions are derived for the stresses near a rigid circular inclusion in a transversely isotropic shallow spherical
shell under uniform pressure. The form of solution depends on the range of the transverse shear compliance parameter. The
influence of the relative radius of a rigid inclusion and transverse shear compliance on stress concentration is analyzed
__________
Translated from Prikladnaya Mekhanika, Vol. 41, No. 12, pp. 67–73, December 2005. 相似文献
12.
In wall-bounded turbulent flows, determination of wall shear stress is an important task. The main objective of the present
work is to develop a sensor which is capable of measuring surface shear stress over an extended region applicable to wall-bounded
turbulent flows. This sensor, as a direct method for measuring wall shear stress, consists of mounting a thin flexible film
on the solid surface. The sensor is made of a homogeneous, isotropic, and incompressible material. The geometry and mechanical
properties of the film are measured, and particles with the nominal size of 11 μm in diameter are embedded on the film’s surface
to act as markers. An optical technique is used to measure the film deformation caused by the flow. The film has typically
deflection of less than 2% of the material thickness under maximum loading. The sensor sensitivity can be adjusted by changing
the thickness of the layer or the shear modulus of the film’s material. The paper reports the sensor fabrication, static and
dynamic calibration procedure, and its application to a fully developed turbulent channel flow at Reynolds numbers in the
range of 90,000–130,000 based on the bulk velocity and channel full height. The results are compared to alternative wall shear
stress measurement methods. 相似文献
13.
David C. Venerus 《Rheologica Acta》2000,39(1):71-79
The behavior of a low-density polyethylene melt in exponential shear strain histories is examined and compared to its behavior
in constant rate planar elongation. A new set of shear stress and first normal stress difference data in exponential shear
are presented and used in several different material functions that have been previously proposed. Viscosities composed of
principal stress differences for the two flows showed no correspondence suggesting that, contrary to previous assertions,
exponential shear and constant rate planar elongation flows are fundamentally different. It is further suggested that the
presence of vorticity makes exponential shear a weak, rather than strong, flow.
Received: 5 March 1999/Accepted: 1 September 1999 相似文献
14.
H. Henning Winter 《Rheologica Acta》2009,48(3):241-243
A slight rearrangement of the classical Cox and Merz rule suggests that the shear stress value of steady shear flow, , and complex modulus value of small amplitude oscillatory shear, G ∗ (ω) = (G′2 + G″2)1/2, are equivalent in many respects. Small changes of material structure, which express themselves most sensitively in the steady
shear stress, τ, show equally pronounced in linear viscoelastic data when plotting these with G ∗ as one of the variables. An example is given to demonstrate this phenomenon: viscosity data that cover about three decades
in frequency get stretched out over about nine decades in G ∗ while maintaining steep gradients in a transition region. This suggests a more effective way of exploiting the Cox–Merz rule
when it is valid and exploring reasons for lack of validity when it is not. The τ −G ∗ equivalence could also further the understanding of the steady shear normal stress function as proposed by Laun. 相似文献
15.
Magnetorheology in viscoplastic media 总被引:2,自引:0,他引:2
Suspensions of iron particles in media with yield stresses were investigated to determine the effect of the continuous phase
yield stress on the magnetorheological (MR) response. The steady-shear MR response was independent of the continuous phase
yield stress for yield stresses in the range 0.9–37 Pa. The field-induced suspension yield stress increased sub-quadratically
with the flux density. The small amplitude oscillatory shear response exhibited history dependence. The storage modulus depended
not only on the magnitude of the applied magnetic field, but also on its history. This history dependence can be explained
in terms of the field-dependent evolution of the suspension microstructure.
Received: 24 February 1999 Accepted: 12 July 1999 相似文献
16.
Francesco Genna Lorella Annovazzi Cristina Bonesi Paola Fogazzi Corrado Paganelli 《Meccanica》2008,43(1):55-73
This work analyzes some aspects of the experimental determination of the mechanical properties of the periodontal ligament
(PDL). The necessity of extracting small samples, with a geometry as regular as possible, from a complex biological structure,
makes it quite difficult both to establish a correct testing protocol and to obtain reliable results, for instance usable
by bioengineers to develop constitutive models. Here, by means of more than 250 experiments performed on small samples of
porcine PDL, we try both to provide some statistically significant information, and to clarify some issues related to the
testing protocols. Some basic mechanical parameters for the PDL (Young’s modulus, shear modulus, failure stress and strain
for tension, compression, and shear tests) are measured, and a relevant statistical analysis is provided. The influence of
some experimental parameters (sample conservation procedure, testing modalities), is also studied; on the basis of our results,
we can conclude that (i) if conservation is needed, a cooling at −80° is sufficient to guarantee statistically significant
results, (ii) it is important to perform at least the compression tests keeping the samples immersed in pressurized fluid,
and (iii) preconditioning cycles are necessary only for studying the initial (toe) region of the stress–strain curves. It
is also observed that, with these types of samples, some special care is required when computing stresses and strains from
force and displacement measurements. In order to illustrate this aspect, some non-linear Finite Element analyses are performed,
aimed at evaluating the influence of the sample geometry on the stress and strain calculation. Finally, the issue of fiber
damage due to the cutting procedures is briefly discussed. 相似文献
17.
V. A. Ogorodnikov A. L. Mikhailov A. V. Romanov A. A. Sadovoi S. S. Sokolov O. A. Gorbenko 《Journal of Applied Mechanics and Technical Physics》2007,48(1):11-16
The problem of the incidence of a shock wave with a front-pressure amplitude of about 30 GPa at the profiled free surface
of an aluminum sample is studied. It is shown that in the case of large perturbations (amplitude 1 mm and wavelength 10 mm), jet flows occur on the free surface. The data obtained are described using a kinetic fracture model that takes into account
the damage initiation and growth in the material due to tensile stress and shear strain.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 16–23, January–February, 2007. 相似文献
18.
It is known that a transform of Liouville type allows one to pass from an equation of the Korteweg–de Vries (K–dV) hierarchy
to a corresponding equation of the Camassa–Holm (CH) hierarchy (Beals et al., Adv Math 154:229–257, 2000; McKean, Commun Pure
Appl Math 56(7):998–1015, 2003). We give a systematic development of the correspondence between these hierarchies by using
the coefficients of asymptotic expansions of certain Green’s functions. We illustrate our procedure with some examples. 相似文献
19.
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.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 90–97, March–April, 2007. 相似文献
20.
Many instruments used to measure viscoelastic properties are only capable of subjecting a sample to a limited range of loading
frequencies. For thermorheologically simple materials, it is assumed that a change in temperature is equivalent to a shift
of the viscoelastic behavior on the log frequency or time axis. For many materials, time–temperature superposition appears
to work well for modulus or compliance curves over three decades of time or frequency, but some deviations are known if the
window is expanded to five or six decades. To apply a more stringent test of the validity of time–temperature superposition,
broadband viscoelastic spectroscopy is used to isothermally study polymethylmethacrylate and low-density polyethylene at several
temperatures in the glassy region. Shear modulus and damping (tan δ) are measured isothermally over a wide range (up to 11 decades) of time and frequency. Results indicate that, while modulus
curves can be approximately superimposed, the damping (tan δ) curves change in height and shape with temperature. 相似文献