Changes In Orientation Distribution Research Articles

The effect of aqueous NaCl solution on methane hydrate nucleation and growth

Electrolyte solution can effectively inhibit the formation of hydrate. In this work, molecular dynamics simulations of hydrate nucleation and growth in aqueous NaCl solutions were performed to study the effect of ions on hydrate formation. We found that the electrolyte ions can inhibit hydrate formation on both the nucleation and the growth stage. Hydrates prefer nucleation in a region with low ionic concentration because the availability of water molecules in the ionized hydration layer is reduced. The slight change in orientation distribution of water around methane molecules in a NaCl solution system may be another factor to inhibit nucleation. The induction time is approximately proportional to the ionic strength, indicating that the charge has a more obvious inhibitory effect on hydrate formation. In hydrate growth stage, ions are excluded from the hydrate phase and a certain amount of free water molecules exist around the hydrate cluster. The ions near the hydrate can reduce its growth rate, causing a higher crystallinity of hydrate formed in salt solution. Finally, a dual influence of the ions on methane mass transfer was found to be that the ions increase the apparent concentration of methane to facilitate nucleation, but inhibit their diffusion at the same time.

On Structural Aspects of Texture Changes During Rolling of Zr-2.5%Nb Alloy

Using X-ray structural analysis, features of changes in characteristics of crystallographic texture during cold working of Zr-2.5%Nb alloy plates by longitudinal and cross rolling has been investigated. To make original plates, longitudinal fragments and rings of Æ15.0´1.5 mm² tube annealed at 580 °C were used. The plates were rolled at room temperature to the degrees in the range from 6 to 56% with 5…7% per pass and the rate of 5...10s-1. Using the method of inverse pole figures with measuring by the Bragg-Brentano optical scheme, densities of reflections along normal to plane of the plates (pole densities) was determined. Based on this, distributions of orientations of c-axes of hcp lattice of the material have been analyzed. Local features of the distributions, which were attributed to signs of twinning effects in texture changes in the alloy, are revealed. At subsequent analysis, an effect of strain non-uniformity associated with prehistory of the plates was taken into account. It is established that the second stage of (moderate) changes in Kearns textural coefficient of the plates with the deformation degrees differs from the initial stage of accelerated changes by activation of compression twins. By the method of tilt scanning (of rocking curves) around the Bragg-Brentano position at registration of (0004) reflection intensities, changes in orientation distributions of c-axes in longitudinal and cross section of the plates for both parties were investigated. It is noted that the main textural changes in process of deformation of the plates occur in the cross-sectional plane of the original tube and are most expressed on the cross-rolling plates. The doublet in the distributions of c‑axes, characteristic for rolling texture of hcp metals of titanium subgroup, was noted just at the second stage of the texture changes in the material. Its directionality is mainly associated with the plane of cross-section of the original tube. A connection is revealed between features of the pole density distributions and expression degree of the textural doublet on the rocking curves. According to the results obtained and analysis of other publications, twinning nature of the textural doublet was confirmed and a schematic sequence of its formation was proposed with participation of compression twins of{112-2}{1-1-23} system and tensile twins of {101-2}{1-011} and{112-1}{1-1-26} systems.

Dynamics of cylindrical particles in the contraction flow of a second-order fluid

The finite volume method is used to numerically simulate the dynamics of cylindrical particles in the contraction flow of a second-order fluid. The effects of Stokes number, Deborah number, particle aspect ratio and contraction ratio on the spatial and orientation distributions of cylindrical particles are analyzed. Some numerical results are compared with the available experimental results in the contraction flow of Newtonian fluids. The results show that the spatial and orientation distributions of the particles are dependent on the competition among the inertia, viscoelasticity and effect of confined wall. The result of competition is responsible for the force and torque inducing a cross-streamline migration and rotation of particles. Along the flow direction, the particle spatial distribution in the cross section changes non-monotonically. The particle orientation distribution changes monotonically and particles gradually align themselves with the flow direction, and this phenomenon is more obvious than the case of the Newtonian fluid under the same conditions. High shear rate makes the particles align with their major axis near to the flow direction. With the increase of the Stokes number, the particle spatial distribution becomes more uniform, and orientation distribution function of particles becomes flatter and wider. With the increase of Deborah number and the contraction ratio, the particle spatial distribution becomes more non-uniform, in the meantime, more particles tend to align themselves with the flow direction. With the increases of the particle aspect ratio, the particle spatial distribution in the cross section becomes more uniform, and more particles align with their major axis near to the flow direction. In the parameter region studied here, the particle aspect ratio has a weaker effect on the spatial and orientation distributions of particles than Stokes number, Deborah number and contraction ratio.

Numerical predictions of fiber orientation and mechanical properties for injection‐molded long‐carbon‐fiber thermoplastic composites

The use of long carbon fiber‐reinforced thermoplastic composites as lightweight automotive materials offers superior mechanical performance compared to glass fibers. However, the anisotropic fiber orientation distribution with shell–core structure is critical to determine mechanical properties. Recently, both theoretical models of fiber orientation—Anisotropic Rotary Diffusion and Reduced Strain Closure and Improved Anisotropic Rotary Diffusion and Retarding Principal Rate—have been significantly developed in the field of fiber suspension rheology. From injection molding simulations, numerical predictions of fiber orientation are derived with related experimental validations, while dramatic changes in orientation distribution are discussed at various fiber concentrations and different polymer matrices. More importantly, the reinforcing ability is discussed in regard to the tensile modulus and the stress–strain response for a variety of long carbon fiber composites. POLYM. COMPOS., 39:3726–3739, 2018. © 2017 Society of Plastics Engineers

Influence of the Hot Deformation Conditions on the Texture Evolution in Mg-8Li-5Zn-2Re Alloy

Abstract The microstructure and texture evolution in the hot-deformed Mg-8Li-5Zn-2Re alloy were investigated by optical micrography, SEM and X-ray diffraction. In the hot-extruded Mg-8Li-5Zn-2Re alloy, α phase is elongated approximately parallel to the extruding direction and exhibits a deformed structure. During hot compression, α phase is transformed to β phase with increasing of temperature. At the stage of hot extrusion, {001} and {110} textures of β phase are exhibited, while {0001} 0> texture in α phase is detected due to basal slip. As a result of the frequent changes of compression condition, grain orientation distribution changes obviously. The evolution of deformation texture was analyzed using the XRD analysis in the hot compression test under different deformation temperatures and strain rates.

The orientational behavior of multiwall carbon nanotubes in polycarbonate in simple shear flow

This paper describes the changes in the orientation of multiwall carbon nanotubes (MWCNT) in polycarbonate as determined by transient and oscillatory shear rheology. It is well known from rheological studies on composites with macroscopic fibers that the overshoot in transient shear viscosity is caused by the change in orientation distribution of these fibers. This study shows that although an overshoot in transient shear viscosity of MWCNT/polycarbonate is measured at shear rates as low as 0.1 s − 1, the MWCNT network is disturbed only at considerably higher shear rates. Scanning electron microscopy micrographs and oscillatory shear show that MWCNT in thermoplastic composites will only be oriented at high shear rates. Simultaneous measurements of the electrical conductivity during rheological start-up shear and oscillatory measurements show large differences between electrical and mechanical relaxation behaviors. The viscosity of the composite seems to depend strongly on the MWCNT network density, whereas the proximity of the tubes at the network points seems to determine the electrical properties of the MWCNT composite.

Evolution of microstructure and texture in an ultrafine-grained Al6082 alloy during severe plastic deformation

The evolution of microstructure and texture in Al6082 precipitation-hardened alloy during equal-channel angular pressing (ECAP) was studied. It was found that although the dislocation density and the subgrain size saturated after 1 pass, the size of grains bounded by high angle boundaries reached its minimum value only after 4 passes. Furthermore, the grain orientation distribution changes between 4 and 8 passes, indicating the development of grain boundary structure even after the saturation of the parameters of the microstructure. As a result of this evolution, the initial texture of the commercial alloy was diminished after 8 passes and the grain orientation distribution became to be close to random case.

Mechanical behavior of amorphous polymers in shear

Based on the non-equilibrium thermodynamic theory, a new thermo-viscoelastic constitutive model for an incompressible material is proposed. This model can be considered as a kind of generalization of the non-Gaussian network theory in rubber elasticity to include the viscous and the thermal effects. A set of second rank tensorial internal variables was introduced, and in order to adequately describe the evolution of these internal variables, a new expression of the Helmholtz free energy was suggested. The mechanical behavior of the thermo-viscoelastic material under simple shear deformation was studied, and the “viscous dissipation induced” anisotropy due to the change of orientation distribution of molecular chains was examined. Influences of strain rate and thermal softening produced by the viscous dissipation on the shear stress were also discussed. Finally, the model predictions were compared with the experimental results performed by G' Sell et al., thus the validity of the proposed model is verified.

On the development of the <111> fiber texture in nanocrystalline gold during growth and annealing

ABSTRACTThe evolution during growth and subsequent annealing of the <111> fiber texture in magnetron-sputtered nanocrystalline Au films has been studied experimentally using X-ray diffraction with synchrotron radiation. To quantitatively investigate this fiber texture, grain orientation distributions were recorded in situ during growth and during subsequent annealing using Bragg-Brentano geometry. The (111) diffraction intensity was measured as a function of the sample tilt χ, the tilt axis lying at the intersection of the film surface and the scattering plane. As a quantitative measure of the texture, we used the width of the orientation distributions. The grain-orientation distributions narrowed during annealing. The activation energy for the process behind this texture change was found to be 0.64 ± 0.05 eV, close to the activation energy for grain boundary self-diffusion in nanocrystalline Au. This and the narrowing of the grain orientation distributions led us to suggest that the observed changes in texture originated from grain rotations and not from grain growth. Grain growth did not take place at the lower temperatures, where changes in orientation distributions were observed.

Orientation-insensitive methodology for second harmonic generation. 1. Theory

The use of second harmonic generation as a means to probe either adsorption isotherms or the kinetics of adsorption/desorption is limited by the fact that the detected signal is dependent upon both surface coverage and molecular orientation. Thus, the second harmonic intensity must be tediously corrected if either the mean orientation angle or the width of the orientation distribution changes as a function of surface coverage. In this study, a new mathematical view of the second harmonic intensity as a function of excitation polarization is developed. This new approach predicts an experimental geometry that is relatively insensitive to molecular orientation, such that appropriate choice of the excitation polarization rotation angle allows for direct measurement of surface coverage. The theory is presented for the three common dominant hyperpolarizability tensor elements, beta(z'z'z'), beta(x'x'x'), and beta(x'x'z').

Analysis of Fiber Orientation and Velocity Distribution in Flow of Short Fiber-Polymer Melt Mixture through Cooled-Mold Slit Channel in Consideration with Fiber-Mold Wall Interaction.

In injection molding of short fiber-polymer melt mixture, influence of the interaction between a fiber and a mold wall on fiber distribution and flow property cannot be neglected, when fiber length is not very short comparatively to the thickness of a mold cavity. In the flow through a cooled mold cavity, solidifying layer grows and it affects that relation further. In this paper, effiects of these causes on fiber orientation and velocity distribution have been made clear by using numerical analysis, in which each fiber motion is analyzed from equilibrium conditions and fiber orientation distribution is obtained by integrating frequency of orientation angles of each fiber over the whole angles, and the following results have been obtained. (i) Near a mold wall, mixture is cooled and no flow layer is generated. On the other hand, apparent viscosity increases in the region, apart from a mold wall by more than half of fiber length, because of high fiber concentration, and plug flow-like velocity distribution is generated. (ii) Pressure gradient increases toward downstream in low injection rate, because of cooling of mixture, whereas it decreases in high injection rate, because of viscosity decrease due to shear heating. (iii) As fiber length decreases, pressure gradient decreases. (iv) Fiber orientation distribution changes considerably with injection rate change.

Mechanism of Orientation Selectivity During Grain Growth of Secondary Recrystallization in Fe-3%Si Alloy

Selective growth of {110}〈001〉 grains in the temperature gradient annealing has been studied in Fe–3%Si alloy. As grains grow, the average deviation angle from the ideal {110}〈001〉 orientation becomes smaller and orientation distribution changes corresponding to that of coincidence grains in the matrix. Secondary recrystallization temperature depends on the orientation of secondary recrystallized grain and sharper {110} 〈001〉 grains grow preferentially at lower temperatures.These phenomena are explained by modified Hillert's model of grain growth. Interfacial energy of coincidence boundary is lower than that of general boundary. Therefore, sharper {110}〈001〉 grains, which have higher frequency of coincidence grains in the primary recrystallized matrix, suffer lower pinning effect from the second phase particles and thus grow preferentially at lower temperatures.

Recrystallization and Related Phenomena. Mechanism of Orientation Selectivity of Secondary Recrystallization in Fe-3%Si Alloy.

Selective growth behavior of {110} <001> grains has been studied utilizing the temperature gradient annealing method. As grains grow, the average deviation angle from the ideal {110} <001> orientation becomes smaller and orientation distribution changes corresponding to that of coincidence grains in the matrix. Secondary recrystallization temperature depends on the orientation of secondary recrystallized grain and sharper {110} <001> grains grow preferentially at lower temperatures. These phenomena are explained by modified Hillert's model of grain growth, which takes the grain boundary characteristics into account. Sharper {110} <001> grains, which have higher frequency of coincidence grains in the primary recrystallized matrix, suffer lower pinning force from the precipitates and thus grow preferentially at lower temperatures.

Orientation Distribution of Whiskers under Uniaxial Elongational Flow

Change of orientation distribution of whiskers in polystyrene-potassium titanate whisker composite melts under uniaxial elongational flow was studied by using wide angle X-ray diffraction. The orientation distribution had a single peak in the flow direction at all elongational strain rates, and the peak monotonously became sharp as elongational strain increased. The distribution was found to be strongly dependent on strain. These experimental results were compared with prediction of Jeffery theory. Although Jeffery theory does not take account of interaction among fillers, we found that tendency of the theory resembles to that of the orientation distribution under elongational flow even in high concentration systems.

Modulation of Escherichia coli type 1 fimbrial expression and adherence to uroepithelial cells following exposure of logarithmic phase cells to quinolones at subinhibitory concentrations.

Quinolone antibiotics at sub-inhibitory concentrations have been shown to antagonize the adherence of Escherichia coli to urinary tract epithelium. This may be due either to reduced expression or to alterations to the structure of the fimbriae which mediate adherence. While E. coli cells in the stationary growth phase have previously been used to investigate quinolone-induced inhibition of adherence, the present study has demonstrated that bacteria in the logarithmic phase also produce type 1 fimbriae and that the adherence of these organisms is reduced following exposure to various quinolones. In all experiments, cells in the logarithmic phase were incubated for 3 h in the presence of ciprofloxacin, enoxacin, CI-960 or PD131628 at a concentration equivalent to 0.5 x MIC. An in-vitro adherence assay which used acid-washed uroepithelial cells and a type 1-fimbriated strain of E. coli showed reductions in adherence of 47%, 72% and 95% after exposure to enoxacin, ciprofloxacin and PD131628, respectively. The effects of ciprofloxacin, enoxacin, CI-960 and PD131628 on two phase variation controlling genes, fimB and fimE, and the main structural gene, fimA, were evaluated by quantifying beta-galactosidase production encoded by chromosomally-located fim::lacZ fusions. All four quinolones tested caused reductions in beta-galactosidase production by a fimA::lacZ fusion strain, but did not significantly affect production of this enzyme by fimB::lacZ and fimE::lacZ fusion strains; these agents also led to decreases in wild-type beta-galactosidase production. Amplification of the invertible element after exposure to enoxacin at 0.25, 0.5 or 1 x MIC revealed no changes in orientation distribution compared with the antibiotic-free control. In addition, a fluorescence assay specific for type 1 fimbriae showed only 23%, 21%, 25% and 11% reductions in the surface expression of the structural subunit after incubation in the presence of ciprofloxacin, enoxacin, CI-960 and PD131628, respectively, at 0.5 x MIC.

Memory impairment in flowing suspensions. II. Experimental results

Experiments on the reversibility of particle orientation distributions in suspensions of nearly monodisperse rigid rods and hardened red blood cells (HRBC) subjected to cyclic shearing are described.The orientation distributions of initially aligned rods measured by direct observation exhibited a gradual loss in memory as flow was reversed back and forth which was attributed mainly to non-reversible particle interactions. When an electric field was applied continuously during cyclic shear flow, the rate of memory loss was increased. However, if an electrical shock was applied momentarily between each reversal of flow, the suspension maintained some memory. These results are generally in agreement with the theory presented in the preceding paper.With suspensions of HRBC, the particles were initially randomly oriented and the light transmittance across the planes of shear was used to measure changes in orientation distribution. Since HRBC are small enough to exhibit appreciable rotary Brownian motion, memory loss was inevitable and increased with the duration of each shear cycle and the cell concentration.Memory loss was also observed for rods and HRBC in non-Newtonian media and was attributed to drift in the rotational orbit constants of the particles.

Conductimetric investigation of erythrocyte behaviour during shear flow of concentrated suspensions through a large tube.

The behaviour of canine erythrocytes in isotonic saline suspensions undergoing steady unidirectional shear flow in the vertical direction, at cell volume concentrations (ρ) ranging between 0.017 and 0.840, is studied by measuring suspension resistivities in three mutually orthogonal directions. Results are compared with the predicted behaviour of rigid spheroids and liquid drops. Analyses of suspension resistivities show that there are significant changes in erythrocyte shape with increasing shear rate ( k ) at all k covered (2.6 x 10 – 10 3 s -1 ) and at all ρ, very large changes occurring at ρ &gt; 0.65. However, the changes in the equivalent principal axis-ratios of erythrocytes with k deviate substantially from the flow behaviour expected of liquid drops, the average ‘shape factor’ for the cells decreasing rather than increasing with k . Neither the simple liquid drop nor the rigid spheroid model can adequately explain some aspects of the results obtained. Results show that cell concentration is a major determinant of erythrocyte behaviour and point to the existence of three concentration regimes in the range of flow rates investigated, with different mechanisms of particle orientation during shear flow predominating in each. At ρ &lt; 0.08 no significant change in orientation distribution with k is observed; but results show that erythrocytes tend to assume the orientation corresponding to the maximum dissipation of energy in a shear field or corresponding to the maximum energy dissipation of settling disks (the effect increasing as ρ is reduced) indicating a predominance of inertial effects. Between ρ ≃ 0.08 and ρ ≃ 0.65 the orientation distribution changes towards alignment of erythrocytes parallel to the plane of flow, the degree of alignment increasing with k and with ρ. Here, particle-particle interactions facilitate the orientation of erythrocytes by shear stresses. Above ρ ≃ 0.65 the change in cell shape with k increases sharply, suggesting that erythrocyte deformation becomes the principal mechanism of suspension flow.

Particle behavior in shear and electric fields. VII. Orientation distributions of cylinders

Transient orientation distributions of electrically conductive rods and discs in suspensions subjected to combined shear and electric fields were determined experimentally. In subcritical electric fields the orientation distribution oscillated at a frequency twice that of the individual particle's rotation; the orbit distribution drifted towards higher orbits with rods and lower orbits with discs, so that eventually the axes of rods and the faces of discs lay in planes normal to the vorticity axis. In supercritical fields the orientation distributions no longer oscillated, but changed gradually as each particle moved to a steady orientation. Monotonic changes in orientation distributions occurred in suspensions subjected to an electric field alone. All of these observations were as predicted from theory. The influence of electric fields on such rheological properties as the intrinsic viscosity and normal stress differences of the suspensions are discussed.

Particle behavior in shear and electric fields. VI. The microrheology of rigid spheroids

A general theory for the rotation of a single ellipsoidal particle without Brownian motion in a flowing dielectric Newtonian fluid subjected to an electric field is developed. The particle experiences hydrodynamic and electric torques (the latter resulting from permanent and induced polarization of the particle), which cause it to rotate in a manner which depends upon the relative magnitudes of the two torques. Demetriades' earlier analysis of the motion of a dielectric spheroid in a simple shear (Couette) flow and an electric field normal to velocity and vorticity vectors is a special case of the theory. The distribution functions of particle orientations in a dilute monodisperse and collision-free suspension of dielectric spheroids subjected to shear and electric fields are calculated for transient and steady states. When the electric field is below the critical value so that particles execute complete rotations about the vorticity axis, the orientation distribution function for an initially randomly oriented spheroid is an oscillating function of time. Above the critical field, when the particles no longer execute complete rotations, the orientation distribution changes monotonically with time. The significance of particle orientations to suspension rheology is discussed with particular reference to viscosity enhancement due to the electric field, and to the development of transient and permanent normal stress differences and other manifestations of non-Newtonian behavior. The extension of the theory to the case in which an electric field is replaced by a magnetic field is briefly considered.