Shear Frequency Research Articles

Uniaxial Shear Tester – new test method to determine shear properties of asphalt mixtures

The main focus of the paper is to present the concept of a newly developed Uniaxial Shear Tester (UST) and to investigate the correlation between results from the UST and the Superpave Shear Tester (SST), a tool broadly recognised for asphalt mix design and rutting susceptibility evaluation. In this study, the UST testing principles, finite element analysis of stresses and comparison of measured data are presented. The correlation was assessed on the basis of two tests, the repeated shear test and the small amplitude oscillation test also referred as the shear frequency sweep test. It was shown that the material characteristics determined from UST and SST are highly correlated. The dependencies are discussed in the sense of linear correlation and correlation coefficients. Test variability is discussed in the paper.

Amido‐Amine‐Based Cationic Gemini Surfactants: Thermal and Interfacial Properties and Interactions with Cationic Polyacrylamide

AbstractExperimental studies were conducted to investigate thermal and interfacial properties of two in‐house synthesized amido‐amine‐based cationic gemini surfactants namely: dodecanoic acid [3‐({4‐[(3‐dodecanoylamino‐propyl)‐dimethyl‐amino]‐butyl}‐dimethyl‐amino)‐propyl]‐amide dibromide (12‐4‐12) and dodecanoic acid [3‐({6‐[(3‐dodecanoylamino‐propyl)‐dimethyl‐amino]‐hexyl}‐dimethyl‐amino)‐propyl]‐amide dibromide (12‐6‐12). Thermogravimetric analysis showed the excellent thermal stability of surfactants and no structural degradation was observed at temperatures up to 250 °C. The long‐term thermal stability of the surfactants was investigated with the aid of spectroscopic techniques such as nuclear magnetic resonance (NMR (1H and13C) and Fourier transform infrared (FTIR) spectroscopy. Both surfactants were found to be thermally stable, and no changes in structure were observed after aging for 10 days at 90 °C. The interfacial tension of the surfactants was measured at three different temperatures (30, 60, and 80 °C), and the results showed a decrease in interfacial tension with increasing temperature and increasing spacer length of the surfactants. Rheological measurements were used to assess the interactions between the cationic gemini surfactant and cationic polyacrylamide. The addition of cationic surfactant reduced the viscosity and storage modulus of the polymer at low shear rate and frequency due to surfactant–polymer interactions and charge screening. The investigated surfactant–polymer system has great potential in high‐temperature carbonate reservoirs, where conventional anionic surfactants are not recommended due to high adsorption.

Tailoring the Static and Dynamic Mechanical Properties of Tri-Block Copolymers through Molecular Dynamics Simulation.

Although the research of the self-assembly of tri-block copolymers has been carried out widely, little attention has been paid to study the mechanical properties and to establish its structure-property relation, which is of utmost significance for its practical applications. Here, we adopt molecular dynamics simulation to study the static and dynamic mechanical properties of the ABA tri-block copolymer, by systematically varying the morphology, the interaction strength between A-A blocks, the temperature, the dynamic shear amplitude and frequency. In our simulation, we set the self-assembled structure formed by A-blocks to be in the glassy state, with the B-blocks in the rubbery state. With the increase of the content of A-blocks, the spherical, cylindrical and lamellar domains are formed, respectively, exhibiting a gradual increase of the stress-strain behavior. During the self-assembly process, the stress-strain curve is as well enhanced. The increase of the interaction strength between A-A blocks improves the stress-strain behavior and reduces the dynamic hysteresis loss. Since the cylindrical domains are randomly dispersed, the stress-strain behavior exhibits the isotropic mechanical property; while for the lamellar domains, the mechanical property seems to be better along the direction perpendicular to than parallel to the lamellar direction. In addition, we observe that with the increase of the dynamic shear amplitude and frequency, the self-assembled domains become broken up, resulting in the decrease of the storage modulus and the increase of the hysteresis loss, which holds the same conclusion for the increase of the temperature. Our work provides some valuable guidance to tune the static and dynamic mechanical properties of ABA tri-block copolymer in the field of various applications.

Dynamic rheological behavior of polyfluorinated ethylene propylene/polypropylene blend melts

The polyfluorinated ethylene propylene (FEP)/polypropylene (PP) blend was compounded at melt state in a twin-screw extruder. The melt dynamic viscoelasticity of FEP/PP blends was measured using a Bohlin rheometer with the extended temperature option under experimental conditions with temperature scope from 270°C to 280°C and shear frequency ( ω) varying from 10−2 to 101 s−1. The results showed that the shear storage modulus ( G′) and shear loss modulus ( G″) increased nonlinearly, while the dynamic complex viscosity ( η*) decreased slightly with increasing ω. The G′ and G″ were an exponential function of ω. The G′, G″, and η* of the blend melts decreased with an addition of the PP weight fraction [Formula: see text], and the relationship between them might be expressed by a multinomial third-order equation. This phenomenon might be attributed to the difference in viscoelasticity between the FEP melt and PP melt. The value of tan δ of the blend melts achieved the maximum at about 100 s−1.

Observations of asymmetry in contrasting wave‐ and tidally‐dominated environments within a mesotidal basin: implications for estuarine morphological evolution

AbstractTides are often considered to be the dominant hydrodynamic process within mesotidal estuaries although waves can also have a large influence on intertidal erosion rates. Here, we use a combination of hydrodynamic measurements and sediment deposition records to determine the conditions under which observed waves are ‘morphologically significant’, in which case they influence tidal and suspended sediment flux asymmetry and subsequently infilling over geomorphological timescales. Morphological significant conditions were evaluated using data from contrasting arms in a dendritic mesotidal estuary, in which the orientation of the arms relative to the prevailing wind results in a marked difference in wave conditions, deposition rates and morphology. By defining the morphological significance of waves as a product of the magnitude of bed shear stress and frequency of occurrence, even small (but frequently occurring) winds are shown to be capable of generating waves that are morphologically significant given sufficient fetch. In the arm in which fetch length is restricted, only stronger but rare storm events can influence sediment flux and therefore tides are more morphologically significant over longer timescales. Water depth within this mesotidal estuary is shown to be a critical parameter in controlling morphological significance; the rapid attenuation of short period waves with depth results in contrasting patterns of erosion occurring during neaps and accretion during springs. Copyright © 2016 John Wiley & Sons, Ltd.

Application of Euler⿿Lagrange CFD for quantitative evaluating the effect of shear force on Carthamus tinctorius L. cell in a stirred tank bioreactor

The relationship between shear environment and physiological characteristics of plant cells is always a crucial and challenging aspect in the scale up of suspension cultivations. In this work, we propose a quantitative method for evaluating the lethal effects of hydrodynamic on Carthamus tinctorius L. cell with computational fluid dynamic (CFD) technology and online capacitance viable cell detection. The study towards the effect of short term shear force on C. tinctorius L. cells was carried out in 5L bioreactor under various overall shear intensities (0.02⿿1.82w/kg), in which an online capacitance electrode was applied to count the dynamic vital cell. A first order kinetic model was achieved to describe the death rate in a time span of 60min based on the capacitance. A product of the maximum shear stress and shear frequency (SSF) parameter, which is an evolution of energy dissipation/circulation function, was established to relate cell death rate to the shear environment. A good correlation between cell death kinetics and the SSF parameter was observed in the verification test in a 15L STR bioreactor. SSF can be used to determine the maximum operating range of hydrodynamic stress, and improve the design and optimization of the of C. tinctorius L. cultivation in scale-up process.

Dispersion and shear-induced orientation of anisotropic nanoparticle filled polymer nanocomposites: insights from molecular dynamics simulation

Although a large number of studies have been performed to study the dispersion behavior of spherical nanoparticles (NPs) in the polymer matrix, little effort has been directed to anisotropic NPs via simulation, which is convenient for controlling the physical parameters compared to experiment. In this work we adopt molecular dynamics simulation to study polymer nanocomposites filled with anisotropic NPs such as graphene and carbon nanotubes (CNTs). We investigate the effects of the grafting position, grafting density, the length and flexibility of the grafted chains on the dispersion of graphene and CNTs. In particular, we find that when the grafting position is located on the surface center of the graphene or the middle of the CNT, the dispersion state is the best, leading to the greatest stress–strain behavior. Meanwhile, the mechanical property can be further strengthened by introducing chemical couplings in the interfacial region, by chemically tethering the grafted chains to the matrix chains. To monitor the processing effect, we exert a dynamic periodic shear deformation in the x direction with its gradient in the y direction. Polymer chains are found to align in the x direction, graphene sheets align in the xoz plane and CNTs orientate in the z direction. We study the effects of the shear amplitude, the shear frequency, polymer–NP interaction strength and volume fraction of NPs on the stress–strain behavior. We also observe that the relaxation process following the shear deformation deteriorates the mechanical performance, resulting from the disorientation of polymer chains and NPs. In general, this work could provide valuable guidance in manipulating the distribution and alignment of graphene and CNTs in the polymer matrix.

Versatile specimen-grating fabrication technique for moiré method based on solute-solvent separation soft lithography

A specimen-grating fabrication technique based on solute-solvent separation soft lithography (3S soft lithography) is reported. Both transfer and zero-thickness gratings can be fabricated using this approach. A two-layer hybrid polydimethylsiloxane (PDMS) stamp is designed to increase the stamp in-plane stiffness without degrading the off-plane flexibility. The frequency uniformity, micromorphology, thickness, and shear lag of each fabricated grating is characterized. The application ranges of the fabricated transfer and zero-thickness gratings are determined via experiments. As examples of typical applications, the fabricated gratings are used in moire interferometry and scanning moire experiments to determine the residual stress and crack opening displacement.

Turbulent Winds and Temperature Fronts in Large-Eddy Simulations of the Stable Atmospheric Boundary Layer

Abstract The nighttime high-latitude stably stratified atmospheric boundary layer (SBL) is computationally simulated using high–Reynolds number large-eddy simulation on meshes varying from 2003 to 10243 over 9 physical hours for surface cooling rates Cr = [0.25, 1] K h−1. Continuous weakly stratified turbulence is maintained for this range of cooling, and the SBL splits into two regions depending on the location of the low-level jet (LLJ) and . Above the LLJ, turbulence is very weak and the gradient Richardson number is nearly constant: . Below the LLJ, small scales are dynamically important as the shear and buoyancy frequencies vary with mesh resolution. The heights of the SBL and Ri noticeably decrease as the mesh is varied from 2003 to 10243. Vertical profiles of the Ozmidov scale show its rapid decrease with increasing , with over a large fraction of the SBL for high cooling. Flow visualization identifies ubiquitous warm–cool temperature fronts populating the SBL. The fronts span a large vertical extent, tilt forward more so as the surface cooling increases, and propagate coherently. In a height–time reference frame, an instantaneous vertical profile of temperature appears intermittent, exhibiting a staircase pattern with increasing distance from the surface. Observations from CASES-99 also display these features. Conditional sampling based on linear stochastic estimation is used to identify coherent structures. Vortical structures are found upstream and downstream of a temperature front, similar to those in neutrally stratified boundary layers, and their dynamics are central to the front formation.

Volcanic tremor at Mt Vesuvius associated with low frequency shear failures

Abstract Mt Vesuvius has been dormant since the eruption occurred in 1944, after which the conduit closed and the volcano entered a quiescent state. Only a minor seismic activity, characterized by low magnitude volcano-tectonic (VT) earthquakes, testifies that the magmatic system is still active. In this paper we report the fist quantitative analysis of volcanic tremor discovered at Vesuvius through the analysis of array data. A seismic array installed in 2012 improved the monitoring performance of the local network, permitting the identification of low amplitude coherent signals. Many of such coherent signals recorded during the last few years have been classified as volcanic tremor. We selected 22 tremor events based on their amplitude and on the number of available stations, and performed detailed analysis aimed at location and characterization of the source. They are characterized by low frequency, duration of a few minutes, and the strongest episodes are recorded at distance up to 90 km from the volcano. In many cases we could identify P–S wave pairs in the seismograms that allowed a precise location of the source depth, which is in the range between 5 km and 6.5 km below the crater. Waveform features, spectral analysis, and comparison with VT earthquakes located at the same depth indicate that the source mechanism of the Vesuvius non-eruptive tremor is a sequence of low frequency shear failures.

Viscoelastic properties of marginal networks in a solvent.

Polymer networks at the margins of mechanical stability are known to be highly sensitive to applied forces and fields and to exhibit an anomalously large resistance to deformation. In this paper, we study the effects of hydrodynamic interactions on the behavior of marginal networks using a hybrid molecular dynamics and multiparticle collision dynamics simulation technique. We examine how the filament and solvent properties affect the response of marginal networks to shear. We find that the stiffening of the network shows a stronger dependence on the shear frequency when hydrodynamic interactions are present than when they are not. The network shear modulus scales as G'∼ω(α(c)), with a critical stiffening exponent α(c) that can be controlled by varying the relative concentrations of the network and the solvent. Our results show that this arises due to the solvent aiding the relaxation of the network and suppressing the network nonaffinity, with the system deforming more affinely when hydrodynamic interactions are maximized.

Stretchable Polyurethane Sponge Scaffold Strengthened Shear Stiffening Polymer and Its Enhanced Safeguarding Performance.

A simple and scalable "dip and dry" method was developed for fabricating stretchable polyurethane sponge-based polymer composite with excellent shear stiffening effect, creep resisting and adhesion property. The stiffness of the composite was tunable, the storage modulus (G') could automatically increase 3 orders of magnitude with the increasing of shear frequency, and the G'max could reach to as high as 1.55 MPa. Importantly, the composite with ideal damping capacity reduced the impact force by 2 orders of magnitude even under 26 cycles of consecutive dynamic impact loading with no obvious mechanical degradation. Moreover, an enhancing mechanism was proposed and it was found the "B-O cross bond" and the entanglement of polymer chains were attributed to the shear stiffening characteristic. Finally, the excellent adhesion ability and hydrophobicity guarantee the composite with reliable mechanical performance and longer lifespan.

Preparation, rheological properties and primary cytocompatibility of TPU/PLA blends as biomedical materials

A polymer blends containing thermoplastic polyurethane (TPU) and poly (lactic acid) (PLA) as a biomedical material were prepared by a process of modifying thermally induced phase separation (MTIPS) and melt blending. The influences of composition, shear frequency, and temperature on the rheological behaviors of the blends were investigated by small amplitude oscillatory shear rheology. The results revealed that the addition of TPU into PLA significantly decreased the non-Newtonian index of the blends, and increased the sensitivity of the blends on shear rate, suggesting that optimization of the shear rate and temperature could improve the flowability of the blend melts in the extrusion process. In addition, the results of SEM images revealed that TPU distributed well into PLA matrix and showed good compatibility between the TPU and PLA, which made the blends with good toughness. The primary cytocompatibility of the blends was evaluated using C2C12 cells. The results suggested that the TPU/PLA blends did not affect cell growth, showing no cytotoxicity. In short, the TPU/ PLA blends with excellent toughness had potential application as biomedical devices.

Study on the Dynamic Viscoelasticity of Bamboo Kraft Black Liquor

The dynamic viscoelasticity of bamboo kraft pulping black liquor under various temperatures (ranging from 50 to 80 °C) and solids concentrations (60 to 80 wt.%) was studied. Rotational rheometer analysis data indicated that the viscoelastic motion law with a high solids concentration in black liquor was in accordance with the Kelvin model, and black liquor with a medium concentration conformed to the Maxwell model. As a result, the temperature and solids concentration greatly influenced the dynamic viscoelasticity of bamboo kraft pulping black liquor. For instance, the modulus increased as the solids concentration increased, indicating that the viscous component of black liquor was prominent. For this reason, it was easier to soften the bamboo black liquor, providing a favorable condition for the pure viscosity of black liquor. Steady shear thinning was apparent during the frequency shear process. The dynamic viscosity, storage viscosity, and complex viscosity of the black liquor decreased as the shear frequency increased. The quantitative relationship between dynamic viscosity and angular frequency can be described using the Power Law model.

Viscoelasticity of Shear Thickening Fluid Based on Silica Nanoparticles Dispersing in 1-butyl-3-methylimidizolium Tetrafluoroborate

The viscoelasticity of shear thickening fluid (STF), a crucial property in the protective composite applications, with different silica nanoparticle concentrations in ionic liquid, 1-butyl-3-methylimidizolium tetrafluoroborate ([C4min]BF4), was studied at different temperatures and with shear frequencies through oscillatory shear, respectively. All STFs present strain thickening behavior. With increasing silica nanoparticle concentration, the critical shear strain for the onset of strain thickening decreased, while the complex viscosity, storage modulus, and loss modulus increased significantly. The critical shear strain increased with an increase of temperature, while the complex viscosity, storage modulus, and loss modulus decreased notably. The critical shear strain was constant with increasing the frequency of strain, while the complex viscosity decreases slightly. The storage modulus and loss modulus were independent with frequency in the strain thickening region. Nanoparticle clusters leading to strain thickening were demonstrated. The viscoelastic response of STFs to varying silica nanoparticle content, temperature, and frequency investigated here will help to design the specific application of STFs in soft protective composites and damping devices.

Nonequilibrium structure of colloidal dumbbells under oscillatory shear

We investigate the nonequilibrium behavior of dense, plastic-crystalline suspensions of mildly anisotropic colloidal hard dumbbells under the action of an oscillatory shear field by employing Brownian dynamics computer simulations. In particular, we extend previous investigations, where we uncovered nonequilibrium phase transitions, to other aspect ratios and to a larger nonequilibrium parameter space, that is, a wider range of strains and shear frequencies. We compare and discuss selected results in the context of scattering and rheological experiments. Both simulations and experiments demonstrate that the previously found transitions from the plastic crystal phase with increasing shear strain also occur at other aspect ratios. We explore the transition behavior in the strain-frequency phase and summarize it in a nonequilibrium phase diagram. Additionally, the experimental rheology results hint at a slowing down of the colloidal dynamics with higher aspect ratio.

The Hall-diffusion–driven shear instability of a magnetized collisional dusty plasma

If the relative drift between the charged dust and magnetised electrons and ions which give rise to the Hall diffusion in a dusty plasma dominates the dynamics, the plasma may become diffusively unstable in the presence of shear flow. The growth rate of the diffusive instability is the geometric mean of the whistler and the shear frequencies. The role of the magnetic field is important in destabilising the waves as the growth rate of the instability is dependent on both the ambient magnetic field strength as well as on the dust charge.

Colloidal and rheological behavior of aqueous graphene oxide dispersions in the presence of poly(ethylene glycol)

In this work, the effects of the concentration of graphene oxide (GO) and poly(ethylene glycol) (PEG) on the colloidal and rheological behavior of aqueous GO dispersions were investigated. The concentration of GO and PEG was varied from 0 to 20 mg/mL, respectively. Atomic force microscopy (AFM) images and zeta-potential measurements demonstrated that PEG chains were adsorbed on the colloidal GO sheets. The red-shift of D and G bands in the Raman spectra of GO/PEG compared with pure GO suggested that there was hydrogen bond interaction between GO and PEG. Steady state shear results indicated that GO aqueous dispersions changed from Newton fluids to pseudoplastic fluids as the concentration of GO increased. The critical concentration of isotropic–nematic phase transition of aqueous GO dispersions was about 6 mg/mL. Significantly, the aqueous GO/PEG dispersions presented a lowest viscosity and minimum linear storage modulus linear G′ at the saturation adsorbing concentration cp,s, which were determined by steady state shear and small amplitude oscillatory frequency sweep, respectively. Therefore, the PEG concentration had a significant effect on the linear and non-linear rheological behavior of GO/PEG dispersions. In addition, the concentrated aqueous GO dispersions showed typical yield flow behavior and the yield stress σy firstly decreased and then increased with the increasing of GO concentration. These results could contribute to understand the interplay between microstructure and mechanical behavior of GO/polymer in aqueous dispersions, and also provide some guidance for the processing of GO-based polymer nanocomposites.

The influences of particle–particle interaction and viscosity of carrier fluid on characteristics of silica and calcium carbonate suspensions-coated Twaron® composite

ABSTRACTThe effects of particle–particle interaction and viscosity of carrier fluid on steady and dynamic rheological responses and quasi-static penetration resistance of Twaron® fabrics treated with shear thickening and shear thinning suspensions have been investigated. The suspensions have been made by mechanically dispersing 60 nm silica (SiO2) and calcium carbonate (CaCO3) nanoparticles in poly ethylene glycol (PEG) with molecular weights of 200 and 400 g/mol. The CaCO3 suspensions display shear thinning behaviour along with the total dominance of the elastic state over the viscous state while the SiO2 suspensions exhibit shear thickening behaviour with the emergence of both the elastic and viscous states. With the increase of molecular weight of PEG, viscosity, viscoelastic modules and instability of the suspensions increase and critical shear rate and frequency of transition to elastic state diminish. The PEG200 and PEG400-contained SiO2 suspensions-treated Twaron® composites at 35 wt.% have quasi-static penetration resistances which are nearly 2.63 and 2.48 times and maximum absorbed energies which are about 1.54 and 1.55 times higher, respectively, than those of the corresponding CaCO3 ones. However, the influence of increasing the PEG's molecular weight is not as considerable as the effect of particle–particle interaction on the enhancement of penetration resistance performance.

Use of High Frequency Shear Wave™ Elastography (HFSWE) to identify and evaluate treatment of fascial adhesions

Use of High Frequency Shear Wave™ Elastography (HFSWE) to identify and evaluate treatment of fascial adhesions