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1.
Two types of amorphous TiO2 particles with different particle sizes were synthesized by a simple sol–gel method and were characterized by X-ray diffraction
analysis, field emission scanning electron microscopy, and Fourier transform infrared spectrometry. The electrorheological
(ER) results show that the TiO2/silicone oil suspensions exhibited a remarkable ER effect. The static shear stress can be up to 130 kPa (shear rate 0.2 s − 1) under the DC electric field of 4 kV/mm at room temperature. The polar molecules present on the particles’ surface play a
decisive role for the observed giant ER effect, which arises from the alignment of polar molecules in the gap between neighboring
particles. 相似文献
2.
Gerald Henry Meeten 《Rheologica Acta》2007,46(6):803-813
Various soft solid suspensions were squeezed at constant force between polished and roughened circular glass plates and the
time-dependence of the interplate separation was measured. The filterability of suspensions was quantified by their desorptivity
S obtained from measurements of capillary suction time. The squeeze flow (SF) of suspensions for which S < 2 μm s−1/2 was largely consistent with rheological theory, which neglected radial filtration: the relative motion between the liquid
and solid phases of the suspension in the radial pressure gradient. Suspensions having S > 2 μm s−1/2 showed SF behavior that was consistent with the presence of radial filtration. 相似文献
3.
The effects of shear, uniaxial extension and temperature on the flow-induced crystallization of two different types of high-density
polyethylene (a metallocene and a ZN-HDPE) are examined using rheometry. Shear and uniaxial extension experiments were performed
at temperatures below and well above the peak melting point of the polyethylenes in order to characterize their flow-induced
crystallization behavior at rates relevant to processing (elongational rates up to 30 s − 1 and shear rates 1 to 1,000 s − 1 depending on the application). Generally, strain and strain rate found to enhance crystallization in both shear and elongation.
In particular, extensional flow was found to be a much stronger stimulus for polymer crystallization compared to shear. At
temperatures well above the melting peak point (up to 25°C), polymer crystallized under elongational flow, while there was
no sign of crystallization under simple shear. A modified Kolmogorov crystallization model (Kolmogorov, Bull Akad Sci USSR,
Class Sci, Math Nat 1:355–359, 1937) proposed by Tanner and Qi (Chem Eng Sci 64:4576–4579, 2009) was used to describe the crystallization kinetics under both shear and elongational flow at different temperatures. 相似文献
4.
Yi Wu Hangfeng Wang Zhaohui Liu Jing Li Liqi Zhang Chuguang Zheng 《Acta Mechanica Sinica》2006,22(2):99-108
Particle-laden flows in a horizontal channel were investigated by means of a two-phase particle image velocimetry (PIV) technique.
Experiments were performed at a Reynolds number of 6 826 and the flow is seeded with polythene beads of two sizes, 60 μm and 110 μm. One was slightly smaller than and the other was larger than the Kolmogorov length scale. The particle loadings were relatively
low, with mass loading ratio ranging from 5×10−4 to 4×10−2 and volume fractions from 6×10−7 to 4.8×10−5, respectively. The results show that the presence of particles can dramatically modify the turbulence even under the lowest
mass loading ratio of 5×10−4. The mean flow is attenuated and decreased with increasing particle size and mass loading. The turbulence intensities are
enhanced in all the cases concerned. With the increase of the mass loading, the intensities vary in a complicated manner in
the case of small particles, indicating complicated particle-turbulence interactions; whereas they increase monotonously in
the case of large particles. The particle velocities and concentrations are also given. The particles lag behind the fluid
in the center region but lead in the wall region, and this trend is more prominent for the large particles. The streamwise
particle fluctuations are larger than the gas fluctuations for both sizes of particles, however their varying trend with the
mass loadings is not so clear. The wall-normal fluctuations increase with increasing mass loadings. They are smaller in the
60 μm particle case but larger in the 110 μm particle case than those of the gas phase. It seems that the small particles follow the fluid motion to certain extent while
the larger particles are more likely dominated by their own inertia. Finally, remarkable non-uniform distributions of particle
concentration are observed, especially for the large particles. The inertia of particles is proved to be very important for
the turbulence modification and particles behaviors and thus should be considered in horizontal channels.
The project supported by the National Natural Science Foundation of China (50276021), and Program for New Century Excellent
Talents in University, Ministry of Education (NCET-04-0708) The English text was polished by Yunming Chen. 相似文献
5.
The flow-induced microstructure of a mesophase pitch was studied within custom-made dies for changing wall shear rates from
20 to 1,100 s − 1, a flow scenario that is typically encountered during fiber spinning. The apparent viscosity values, measured at the nominal
wall shear rates ranging from 500 to 2,500 s − 1 using these dies, remain fairly constant. The microstructure was studied in two orthogonal sections: r–θ (cross section) and r–z (longitudinal mid plane). In these dies, the size of the microstructure gradually decreases toward the wall (to as low as
a few micrometers), where shear rate is highest. Furthermore, as observed in the r–θ plane of the capillary, for a significant fraction of the cross section, discotic mesophase has a radial orientation. Thus,
the directors of disc-like molecules were aligned in the vorticity (θ) direction. As confirmed from the microstructure in the r–z plane, most of the discotic molecules remain nominally in the flow plane. Orientation of the pitch molecules in the shear
flow conditions is consistent with that observed in controlled low-shear rheometric experiments reported earlier. Microstructral
investigation suggests that the radial orientation of carbon fibers obtained from a mesophase pitch originates during flow
of pitch through the die. 相似文献
6.
An Australian hard wheat flour–water dough has been characterised using parallel plate and capillary rheometers over an extensive
range of apparent shear rates (10 − 3–103 s − 1) relevant to process conditions. Torsional measurements showed that the shear viscosity of the dough increased with strain
to a maximum value and then decreased, suggesting a breakdown of the dough structure. Both torsional and capillary experiments
revealed the shear-thinning behaviour of the dough. The wall slip phenomenon in capillary rheometry was investigated and found
to be diameter dependent and occurred at a critical shear stress of approximately 5–10 kPa. A two-regime power law behaviour
was observed, with the power law index approximately 0.3 in the low shear rate range increasing to 0.67 in the high shear
rate range. Pressure fluctuation was observed in the capillary data and increased with shear rate, in particular, at shear
rates approaching 104 s − 1. The results demonstrate that capillary rheometry is a viable means of rheologically testing dough at high shear rates provided
pressure fluctuation is carefully monitored and capillary rheometry corrections, including wall slip, are accounted for. 相似文献
7.
Understanding the radiation embrittlement of reactor pressure vessel (RPV) steels is required to be able to operate safely
a nuclear power plant or to extend its lifetime. The mechanical properties degradation is partly due to the clustering of
solute under irradiation. To gain knowledge about the clustering process, a Fe−1.1 Mn−0.7 Ni (at.%) alloy was irradiated in
a test reactor at two fluxes of 0.15 and 9 ×1017 n
E > 1MeV
.m − 2.s − 1 and at increasing doses from 0.18 to 1.3 ×1024 n
E > 1MeV
.m − 2 at 300°C. Atom probe tomography (APT) experiments revealed that the irradiation promotes the formation in the α iron matrix of Mn/Mn and/or Ni/Ni pair correlations at low dose and Mn–Ni enriched clusters at high dose. These clusters
dissolve partially after a thermal treatment at 400°C. Based on a comparison with thermodynamic calculations, we show that
the solute clustering under irradiation can just result from an induced mechanism. 相似文献
8.
A modified miniaturized version of the Direct Impact Compression Test (DICT) technique is described in this paper. The method
permits determination of the rate-sensitive plastic properties of materials up to strain rate ∼105 s−1. Miniaturization of the experimental setup with specimen dimensions: diameter d
S = 2.0 mm and thickness l
S = 1.0 mm, Hopkinson bar diameter 5.2 mm, with application of a novel optical arrangement in measurement of specimen strain,
makes possible compression tests at strain rates from ∼103 s−1 to ∼105 s−1. In order to estimate the rate sensitivity of a low-alloy construction steel, quasi-static, Split Hopkinson Pressure Bar
(SHPB) and DICT tests have been performed at room temperature within the rate spectrum ranging from 5*10−4 s−1 to 5*104 s−1. Adiabatic heating and friction effects are analyzed and the final true stress versus true strain curves at different strain
rates are corrected to a constant temperature and zero friction. The results have been analyzed in the form of true stress
versus the logarithm of strain rate and they show two regions of a constant rate sensitivity : relatively low up to the strain rate threshold ∼50 s−1, and relatively high above the threshold, up to strain rate ∼4.5*104 s−1. 相似文献
9.
Kinetics of deformation and fracture of nickel–iron alloy Inconel 718 under dynamic shear loading was measured using a split
torsional Hopkinson bar facility and high-speed photography. Tubular specimens with a reduced gage length and a starter notch
were sheared at strain rates up to 6 × 103 s−1. High-speed photographs of fiducial lines scribed on the specimen surface showed the development of local strains and cracking.
This paper describes the experimental and analytical procedures, illustrates average and local plastic strain evolution, and
presents shear crack initiation times and propagation speeds. 相似文献
10.
Surjani Uthayakumaran Marcus Newberry Nhan Phan-Thien Roger Tanner 《Rheologica Acta》2002,41(1-2):162-172
The rheological properties of wheat gluten were studied under both small and large deformation and compared with those of
the parent flours. The limiting strain of linear viscoelastic behaviour of gluten doughs, 3 × 10−2, was an order of magnitude larger than that of the flour doughs, 10−3. The role of starch in the lower limiting strain of flour doughs was indicated by the exponential decrease in the limiting
strain of gluten-starch mixtures with greater quantities of starch. Large strain measurements showed gluten doughs possessed
greater shear and elongational viscosities than flour doughs and these differences were greatest at lower shear and elongation
rates (0.01 and 0.1 s−1). The larger viscosities of flour and gluten doughs at the low strain rates help to stabilise and prevent the collapse of
gas bubbles during bread fermentation and baking. Increasing starch levels in gluten-starch mixtures, at either constant or
optimal water levels, lowered the elongational viscosity. Dynamic measurements were, however, more sensitive to the level
of water added to the gluten-starch mixtures. The storage modulus decreased with increasing starch levels when constant water
levels were used to prepare the mixtures, but when optimal water levels were used the storage modulus increased. Gluten and
starch are major contributors to the large and small strain rheological properties of flour doughs; however, gluten-starch
mixtures were unable to duplicate exactly the rheological properties of flour doughs, indicating that other flour components
such as pentosans, lipids and water soluble proteins also influence dough rheology.
Received: 20 March 2001 Accepted: 11 July 2001 相似文献
11.
Tungsten/copper (W/Cu) particle reinforced composites were used to investigate the scaling effects on the deformation and fracture behaviour. The effects of the volume fraction and the particle size of the reinforcement (tungsten particles) were studied. W/Cu-80/20, 70/30 and 60/40 wt.% each with tungsten particle size of 10 μm and 30 μm were tested under compression and shear loading. Cylindrical compression specimens with different volumes (DS = H) were investigated with strain rates between 0.001 s−1 and about 5750 s−1 at temperatures from 20 °C to 800 °C. Axis-symmetric hat-shaped shear specimens with different shear zone widths were examined at different strain rates as well. A clear dependence of the flow stress on the deformed volume and the particle size was found under compression and shear loading. Metallographic investigation was carried out to show a relation between the deformation of the tungsten particles and the global deformation of the specimens. The size of the deformed zone under either compression or shear loading has shown a clear size effect on the fracture of the hat-shaped specimens.The quasi-static flow curves were described with the material law from Swift. The parameters of the material law were presented as a function of the temperature and the specimen size. The mechanical behaviour of the composite materials were numerically computed for an idealized axis-symmetric hat-shaped specimen to verify the determined material law. 相似文献
12.
Mahmoud Rajabian Ghassem Naderi Charles Dubois Pierre G. Lafleur 《Rheologica Acta》2010,49(1):105-118
Transient elongational rheology of two commercial-grade polypropylene (PP) and the organoclay thermoplastic nanocomposites
is investigated. A specifically designed fixture consisting of two drums (SER Universal Testing Platform) mounted on a TA
Instruments ARES rotational rheometer was used to measure the transient uniaxial extensional viscosity of both polypropylene
and nanoclay/PP melts. The Hencky strain rate was varied from 0.001 to 2 s − 1, and the temperature was fixed at 180°C. The measurements show that the steady-state elongational viscosity was reached at
the measured Hencky strains for the polymer and for the nanocomposites. The addition of nanoclay particles to the polymer
melt was found to increase the elongation viscosity principally at low strain rates. For example, at a deformation rate of
0.3 s − 1, the steady-state elongation viscosity for polypropylene was 1.4 × 104 Pa s which was raised to 2.8 × 104 and 4.5 × 104 Pa s after addition of 0.5 and 1.5 vol.% nanoclay, respectively. A mesoscopic rheological model originally developed to predict
the motion of ellipsoid particles in viscoelastic media was modified based on the recent developments by Eslami and Grmela
(Rheol Acta 47:399–415, 2008) to take into account the polymer chain reptation. We show that the orientation states of the particles and the rheological
behavior of the layered particles/thermoplastic hybrids can be quantitatively explained by the proposed model. 相似文献
13.
Effect of melt viscosity of polypropylene on fibrillation of thermotropic liquid crystalline polymer in in situ composite film 总被引:1,自引:0,他引:1
Various grades of polypropylene were melt blended with a thermotropic liquid crystalline polymer, a block copolymer of p-hydroxy benzoic acid and ethylene terephthalate (60/40 mole ratio). The blends were extruded as cast films at different values
of draw ratio (slit width/film thickness). Fibrillation of TLCP dispersed phase with high fiber aspect ratio (length/width)
was obtained with the matrix of low melt flow rate, i.e., high viscosity and with increasing film drawing. Melt viscosities
of pure components and blends measured using capillary rheometer were found to decrease with increasing shear rate and temperature.
Viscosity ratios (dispersed phase to matrix phase) of the systems being investigated at 255 °C at the shear rate ranged from
102 to 104 s−1, were found to lie between 0.04 and 0.15. The addition of a few percent of elastomeric compatibilizers; a tri-block copolymer
SEBS, EPDM rubber and maleated-EPDM, was found to affect the melt viscosity of the blend and hence the morphology. Among these
three compatibilizers, SEBS was found to provide the best fibrillation.
Received: 10 January 2000/Accepted: 24 January 2000 相似文献
14.
Based on the mass transfer theory, a new mass transfer model of ion-exchange process on zeolite under liquid film diffusion
control is established, and the kinetic curves and the mass transfer coefficients of –K+ ion-exchange under different conditions were systemically determined using the shallow-bed experimental method. The results
showed that the –K+ ion-exchange rates and transfer coefficients are directly proportional to solution flow rate and temperature, and inversely
proportional to solution viscosity and the size of zeolite granules. It also showed that the transfer coefficient is not influenced
by the ion concentrations. For a large ranges of operational conditions including temperatures (10 − 75°C), flow rates (0.031 m s−1 −0.26 m s−1), liquid viscosities (1.002 × 10−3 N s m−2 − 4.44 × 10−3 N s m−2), and zeolite granular sizes (0.2 − 1.45 mm), the average mass transfer coefficients calculated by the model agree with the
experimental results very well. 相似文献
15.
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
16.
Shear and extensional viscosities and wall slip are determined simultaneously under extrusion processing conditions using
an on-line rheometer. Because it is not possible to independently control flow rate and temperature, classical methods for
interpretation of capillary data cannot be used with on-line rheometry. This limitation is overcome using computational optimization
to fit parameters in a flow model. This consists of three parts, representing shear viscosity, extensional viscosity, and
wall slip. Three-parameter, power law forms, based on local instantaneous deformation rates and including temperature dependence,
are used for each, and analytic solutions applied for entry flow and flow in the capillary. For entry flow, the Cogswell–Binding
approach is used, and for developed flow in the capillary a solution incorporating wall slip is derived. The rheometer, with
interchangeable capillaries, is mounted in place of the die on a rubber profile extrusion line. Pressure drops and temperatures
for extrusion of an EPDM rubber through 2 mm diameter capillaries of length 0, 2, 3, 4, and 5 mm are logged and flow rates
determined for a range of extruder speeds (5 to 20 rpm). Pressures ranged from 60 to 75 bar and temperatures from 86 to 116 °C.
Mean flow velocity in the capillaries was between 5 × 10−3 and 5 × 10−1 m s−1. The nine material parameters are optimized for best fit of the analytic pressure drops to experimental data, using about
100 data points, with the Levenberg–Marquardt method. It is concluded that flow is dominated by extension and wall slip. Shear
flow appears to play little part. The slip model indicates that slip velocity increases much more rapidly than the wall shear
stress (in the range 0.5–1 MPa) and decreases with temperature for a given stress level. Results for the (uniaxial) extensional
viscosity represent an engineering approximation to this complex phenomenon at the high strains (approximately 200) and high
extension rates (up to 800 s−1) applying in the extrusion. Results indicate a slight extension hardening and a decrease with temperature. Results are put
into the context of the available studies in the literature, which, particularly with regard to wall-slip and extensional
flow, consider conditions far removed from those applying in industrial extrusion. The present methods provide a powerful
means for flow characterization under processing conditions, providing data suitable for use in computer simulations of extrusion
and optimization of die design. 相似文献
17.
The rheological and structural properties of perfluoropolyether (PFPE) lubricant films including viscosity, shear stress,
and birefringence were measured at relatively low to extremely high shear rates using a rotational optical rheometer. The
viscosity of various films with different thicknesses exhibit Newtonian behavior up to a shear rate 1 × 104 s−1, with a transition to shear-thinning behavior obvious at higher shear rates. Birefringence of these films was also measured
for the first time, and these results indicate chain alignment with shear in the shear-thinning regime. The shear rate at
which alignment occurs is similar to that of the onset of shear thinning. This correlation between chain alignment and shear
thinning provides direct evidence that the ability of PFPEs to lubricate hard drives at high shear rates is a direct consequence
of the ability of the applied shear field to align the molecules on a molecular level. 相似文献
18.
K. N. Jonnalagadda I. Chasiotis S. Yagnamurthy J. Lambros J. Pulskamp R. Polcawich M. Dubey 《Experimental Mechanics》2010,50(1):25-35
A new microscale uniaxial tension experimental method was developed to investigate the strain rate dependent mechanical behavior
of freestanding metallic thin films for MEMS. The method allows for highly repeatable mechanical testing of thin films for
over eight orders of magnitude of strain rate. Its repeatability stems from the direct and full-field displacement measurements
obtained from optical images with at least 25 nm displacement resolution. The method is demonstrated with micron-scale, 400-nm
thick, freestanding nanocrystalline Pt specimens, with 25 nm grain size. The experiments were conducted in situ under an optical
microscope, equipped with a digital high-speed camera, in the nominal strain rate range 10−6–101 s−1. Full field displacements were computed by digital image correlation using a random speckle pattern generated onto the freestanding
specimens. The elastic modulus of Pt, E = 182 ± 8 GPa, derived from uniaxial stress vs. strain curves, was independent of
strain rate, while its Poisson’s ratio was v = 0.41 ± 0.01. Although the nanocrystalline Pt films had the elastic properties
of bulk Pt, their inelastic property values were much higher than bulk and were rate-sensitive over the range of loading rates.
For example, the elastic limit increased by more than 110% with increasing strain rate, and was 2–5 times higher than bulk
Pt reaching 1.37 GPa at 101 s−1. 相似文献
19.
V. M. Kulik 《Experiments in fluids》2001,31(5):558-566
Change of drag reduction (DR) along a tube (D=2 mm, L=4 m) was experimentally investigated. To attain turbulent flow with Re=8 × 104, a tank operated under high pressure up to 16 MPa. Solutions of different brands of polyethyleneoxide (PEO) with concentrations
from 1 ppm to 100 ppm were tested. The results indicate that DR is not a constant value but depends on the time and intensity
of interaction between the polymer and the turbulent flow. There are three regions with different behaviors of DR: growth,
maximum, and slope down. Maximum DR coincides with the Virk ultimate DR and can be described by the suggested simple formula
. A decrease in the DR maximum has not been found even for high shear stresses τ
p < 800 Pa. DR dynamics for four brands of PEO with different molecular weight was studied. Direct experimentally determined
DR may be greater than the Virk ultimate value if the change in velocity profile is not taken into account. The corrected
DR never exceeds the ultimate DR.
Received: 10 April 2000/Accepted: 24 May 2001 相似文献
20.
Werner-Michael Kulicke Ulf Reinhardt Gerald G. Fuller Oliver Arendt 《Rheologica Acta》1999,38(1):26-33
Sodium carboxymethylcellulose (NaCMC) in solution represents a complex rheological system, since it forms aggregates and
associations and hence higher-level structures and, depending on the synthesis, is only found in a molecularly dispersed form
in exceptional cases. Rheo-mechanical investigations of the viscoelasticity showed that the Cox-Merz rule is not fulfilled.
The aim was therefore to examine whether rheo-optics could be employed to provide more detailed conclusions about the parameters that influence the flow behavior of NaCMC than
has hitherto been available with mechanical methods. The flow birefringence, Δn
′, rises as the degree of polymerization increases, and exhibits the same dependence on molar mass as does the viscosity: Δn
′∝M
w
3.4. As the degree of polymerization increases while the shear rate remains constant, the polymer segments become more distinctly
aligned in the direction of shear. Hence increasing the degree of polymerization also affects the solution structure, i.e.
the interaction of the molecules with one another. The stress-optical rule only applies to a limited extent for this system.
The stress-optical coefficient, C, is almost independent of the shear rate, but is strongly influenced by the concentration and attains a limiting value of
3 × 10−8 Pa−1. C was determined for a polymer in dilute solution and the curve obtained also enabled transitions in the solution structure to be recognized.
Received: 1 May 1998 Accepted: 5 October 1998 相似文献