Effect of Shear Surface Boundaries on Stress for Shearing Flow of Dry Metal Powders—An Experimental Study

1987 ◽  
Vol 109 (2) ◽  
pp. 232-237 ◽  
Author(s):  
K. Craig ◽  
R. H. Buckholz ◽  
G. Domoto
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Normal Stress ◽  
Particle Diameter ◽  
Surface Boundary ◽  
Metal Powders ◽  
Shear Surface ◽  
Shear Cell ◽  
Shearing Flow ◽  
Solids Content

This paper studies the rapid simple shearing flow of dry cohesionless metal powders contained between parallel rotating plates. In this study, an annular shear cell test apparatus was used; the dry metal powders are rapidly sheared by rotating one of the shear surfaces while the other shear surface remains fixed. Such a flow geometry is of interest to tribologists working in the area of dry or powder lubrication. The shear stress and normal stress on the stationary surface are measured as a function of the following parameters: shear surface boundary material and roughness, the shear-cell gap thickness, the shear-rate and the fractional solids content. Both the fractional solids content and the gap thickness are kept at prescribed values during stress measurements. In this experiment the metal powder tested is different from the shear transmission surface material; the effect on the measured normal and shear stress data are reported. The results show the dependence of the normal stress and the shear stress on the shear-rate, particle density and particle diameter. Likewise, a significant stress dependence on both the fractional solids content and the shear-cell gap thickness was observed.

An Experimental Study of the Rapid Flow of Dry Cohesionless Metal Powders

1986 ◽  
Vol 53 (4) ◽  
pp. 935-942 ◽  
Author(s):  
K. Craig ◽  
R. H. Buckholz ◽  
G. Domoto
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Normal Stress ◽  
Experimental Studies ◽  
Metal Powders ◽  
Shear Surface ◽  
Shear Cell ◽  
Rapid Flow ◽  
Cell Test ◽  
Solids Content

This paper studies the rapid shearing flow of dry metal powders. To perform this study, we built and used an annular shear cell test apparatus. In this apparatus the dry metal powders are rapidly sheared by rotating one of the shear surfaces while the other shear surface remains fixed. The shear stress and normal stress on the stationary surface were measured as a function of three parameters: the shear-cell gap thickness, the shear-rate and the fractional solids content. Stresses are measured while holding both the fractional-solids content and the gap thickness at prescribed values. The results show the dependence of the normal stress and the shear stress on the shear-rate. Likewise, a significant stress dependence on both the fractional solids content and the shear-cell gap thickness was observed. Our experimental results are compared with the results of other reported experimental studies.

Particle Flow Behavior in a Shear Cell Device

2011 ◽  
Author(s):  
Adam Rosenkrantz ◽  
John Tichy
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Film Thickness ◽  
Normal Stress ◽  
Small Scale ◽  
Ongoing Research ◽  
Shear Cell ◽  
Discrete Particle ◽  
Frictional Shear Stress ◽  
Load Carrying

This presentation describes ongoing research performed on a simple shear cell apparatus, previously described [1]. As a complement, discrete particle simulations and continuum models have been used to predict normal and shear forces in the ongoing experiments. The trends and orders-of-magnitude of the models and experiment are in basic agreement. Theoretical models used are constructed with basic principles, rather than curve fitting, to obtain effective properties of the mixture such as viscosity or conductivity. The experiment itself serves to determine the effects of shear rate, packing fraction, particle size and film thickness on the load carrying normal stress. Additionally, the frictional shear stress can be investigated. The working particulate medium within the apparatus consists of glass of aluminum spheres, poly-dispersed over four size increments, all less than 1.00 mm diameter. The upper annular disk is held stationary in a rotational sense by a force transducer, and applies predetermined normal stress values which vary according to a system of interchangeable counterweights. The lower transfer surface and the sidewalls of the annular ring are rotated by applied mechanical torque. Experimental trials consist of shear initiation, after which the trough velocity, film thickness, supporting load, and frictional torque are measured. From these measurements one can calculate the average shear rate, the average load-carrying normal stress, the average frictional shear stress, and the solids volume fraction. Such third body granular flow may apply to some solid lubrication mechanisms, and to applications such as smart clutches and dampers. The continuum theory presented is unique in that it addresses solid-like behavior and its transition to fluidized behavior. The discrete particle dynamics rely on the conceptual models of Iordanoff and colleagues [2]. Our findings are that the two theoretical predictions agree reasonably with the experimental results, suggesting validity of the approach. These results are promising, and may be used to further develop high level predictive models. Furthermore, similar methods of small scale experimental particle simulation can be used to develop simpler more usable continuum approaches.

Viscoelastic Behavior of Disperse Systems with Silicone Oil and Different Fillers

2002 ◽  
Vol 12 (6) ◽  
pp. 297-302 ◽  
Author(s):  
Dimiter Hadjistamov
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Normal Stress ◽  
Silicone Oil ◽  
Flow Behavior ◽  
Normal Stress Difference ◽  
Filler Concentration ◽  
Stress Difference ◽  
Disperse Systems ◽  
First Normal Stress Difference

Abstract The rheological behavior of model suspensions with the silicone oil M20000 and different concentrations of Cab-o-sil TS 720 resp. Durcal 5 are compared. The increase of the Cab-o-sil concentration changes the flow behavior of the suspension from shear-thinning, to pseudoplastic, and to plastic flow behavior. The first normal stress difference rises at the same time at certain shear rate. The disperse systems with Durcal 5 keep the structural viscous behavior of the silicone oil even with a filler concentration of 40.5 wt%. The dependence of the first normal stress difference on shear rate represents for suspensions with Durcal 5 only one straight line with a slope of n = 2. The normal stress has double the amount of the silicone oil M20000 at given shear rate and is independent of the used Durcal 5 concentration. It was established that suspensions with the silicone oil M20000 have a first normal stress difference that can, depending on the filler type, either increase (with Cab-o-sil TS 720) or decrease (with Durcal 5) at certain shear stress with increasing filler concentration. It is to be supposed that the decrease of the normal stress at a given shear stress, with increasing Durcal concentration, is a softening effect, caused by the filler.

Stresses developed by dry cohesionless granular materials sheared in an annular shear cell

1984 ◽  
Vol 142 ◽  
pp. 391-430 ◽  
Author(s):  
S. B. Savage ◽  
M. Sayed
Keyword(s):  
Shear Rate ◽  
Granular Materials ◽  
Volume Fraction ◽  
Particle Diameter ◽  
Shear Stresses ◽  
Normal Stresses ◽  
Shear Cell ◽  
Shear Rates ◽  
Polystyrene Beads ◽  
Annular Shear Cell

Experimental results obtained during rapid shearing of several dry, coarse, granular materials in an annular shear cell are described. The main purpose of the tests was to obtain information that could be used to guide the theoretical development of constitutive equations suitable for the rapid flow of cohesionless bulk solids at low stress levels. The shear-cell apparatus consists of two concentric disk assemblies mounted on a fixed shaft. Granular material was contained in an annular trough in the bottom disk and capped by a lipped annular ring on the top disk. The bottom disk can be rotated at specified rates, while the top disk is loaded vertically and is restrained from rotating by a torque arm connected to a force transducer. The apparatus was thus designed to determine the shear and normal stresses as functions of solids volume fraction and shear rate.Tests were performed with spherical glass and polystyrene beads of nearly uniform diameters, spherical polystyrene beads having a bimodal size distribution and with angular particles of crushed walnut shells. The particles ranged from about ½ to 2 mm in size. At the lower concentrations and high shear rates the stresses are generated primarily by collisional transfer of momentum and energy. Under these conditions, both normal and shear stresses were found to be proportional to the particle density, and the squares of the shear rate and particle diameter. At higher concentrations and lower shear rates, dry friction between particles becomes increasingly important, and the stresses are proportional to the shear rate raised to a power less than two. All tests showed strong increases in stresses with increases in solids concentrations. The ratio of shear to normal stresses showed only a weak dependence upon shear rate, but it increased with decreasing concentration. At the very highest concentrations with narrow shear gaps, finite-particle-size effects became dominant and differences in stresses of as much as an order of magnitude were observed for the same shear rate and solids concentration.

Effect of ink and paperboard characteristics on flexographic print quality based on print density

TAPPI Journal ◽  
2011 ◽  
Vol 10 (9) ◽  
pp. 7-13
Author(s):  
KHODADAD MALMIRCHEGINI ◽  
FARSHAD SARKHOSH RAHMANI
Keyword(s):  
Water Absorption ◽  
Significant Influence ◽  
Particle Diameter ◽  
Print Quality ◽  
Printing Technology ◽  
Plastic Films ◽  
Printing Inks ◽  
Packaging Industry ◽  
Solids Content ◽  
Density Results

Flexography is an evolving printing technology that is suitable for printing on coated and uncoated paperboard and board, nonporous substrates including metalized and paperboard foils, and plastic films used especially in the packaging industry. This study evaluated the effect of paperboard and ink characteristics on flexographic print density in paperboard. Three commercial paperboards from different companies were prepared: brown kraft from Thailand, white kraft from Spain, and test liner from Iran. Four samples of process print inks from Iran were used in this investigation. Paperboard properties, such as roughness and water absorption, and ink characteristics, including solids content, PH and particle diameter, were measured. The inks were printed on paperboards using a roll no.15 applicator with a blade metering device, and the print densities were measured. Results showed that solids content, pH, and particle diameter of printing inks influenced print density, while the roughness and water absorption of the three types of paperboard had no significant influence on print density. Results also illustrated that two levels of ink viscosity (25–30 and 50–55 mPa·s) were insignificant to print density.

scholarly journals Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Reinhard Kohlus
Keyword(s):  
Shear Stress ◽  
Liquid Phase ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Wall Slip ◽  
Flow Index ◽  
Concentrated Suspensions

AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.

Investigation on the Rheological Behavior of Polyamide6/Montmorillonite Nanocomposites by Reactive Extrusion

2011 ◽  
Vol 233-235 ◽  
pp. 1998-2001 ◽  
Author(s):  
Ming Zhao ◽  
Xiao Zhong Lu ◽  
Kai Gu ◽  
Xiao Min Sun ◽  
Chang Qing Ji
Keyword(s):  
Activation Energy ◽  
Shear Stress ◽  
Shear Rate ◽  
Rheological Behavior ◽  
Reactive Extrusion ◽  
Shear Thinning ◽  
Experimental Results ◽  
Montmorillonite Nanocomposites

The rheological behavior of PA6/montmorillonite(MMT) by reactive extrusion was investigated using cone-and-plate rheometer. The experimental results indicated that PA6/MMT exhibited shear-thinning behavior. The shear stress of both neat PA6 and PA6/MMT increased with the increase in the shear rate. The reduction of the viscous activation energy with the increase of shear stress reflected PA6/MMT can be processed over a wider temperature.

Are the dynamic response characteristics of brachial artery flow-mediated dilation sensitive to the magnitude of increase in shear stimulus?

2008 ◽  
Vol 105 (1) ◽  
pp. 282-292 ◽  
Author(s):  
K. E. Pyke ◽  
J. A. Hartnett ◽  
M. E. Tschakovsky
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Dynamic Response ◽  
Phase I ◽  
Brachial Artery ◽  
Flow Mediated Dilation ◽  
Final Phase ◽  
Stimulus Magnitude ◽  
Brachial Artery Diameter ◽  
Response Characteristics

The purpose of this study was to determine the dynamic characteristics of brachial artery dilation in response to step increases in shear stress [flow-mediated dilation (FMD)]. Brachial artery diameter (BAD) and mean blood velocity (MBV) (Doppler ultrasound) were obtained in 15 healthy subjects. Step increases in MBV at two shear stimulus magnitudes were investigated: large (L; maximal MBV attainable), and small (S; MBV at 50% of the large step). Increase in shear rate (estimate of shear stress: MBV/BAD) was 76.8 ± 15.6 s−1 for L and 41.4 ± 8.7 s−1 for S. The peak %FMD was 14.5 ± 3.8% for L and 5.7 ± 2.1% for S ( P < 0.001). Both the L (all subjects) and the S step trials (12 of 15 subjects) elicited a biphasic diameter response with a fast initial phase (phase I) followed by a slower final phase. Relative contribution of phase I to total FMD when two phases occurred was not sensitive to shear rate magnitude ( r2 = 0.003, slope P = 0.775). Parameters quantifying the dynamics of the FMD response [time delay (TD), time constant (τ)] were also not sensitive to shear rate magnitude for both phases (phase I: TD r2 = 0.03, slope P = 0.376, τ r2 = 0.04, slope P = 0.261; final phase: TD r2 = 0.07, slope P = 0.169, τ r2 = 0.07, slope P = 0.996). These data support the existence of two distinct mechanisms, or sets of mechanisms, in the human conduit artery FMD response that are proportionally sensitive to shear stimulus magnitude and whose dynamic response is not sensitive to shear stimulus magnitude.

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