Artigos de revistas sobre o tema "Universal viscosity curve"
Siga este link para ver outros tipos de publicações sobre o tema: Universal viscosity curve.
Crie uma referência precisa em APA, MLA, Chicago, Harvard, e outros estilos
Veja os 30 melhores artigos de revistas para estudos sobre o assunto "Universal viscosity curve".
Ao lado de cada fonte na lista de referências, há um botão "Adicionar à bibliografia". Clique e geraremos automaticamente a citação bibliográfica do trabalho escolhido no estilo de citação de que você precisa: APA, MLA, Harvard, Chicago, Vancouver, etc.
Você também pode baixar o texto completo da publicação científica em formato .pdf e ler o resumo do trabalho online se estiver presente nos metadados.
Veja os artigos de revistas das mais diversas áreas científicas e compile uma bibliografia correta.
1
Arrabal-Campos, Francisco M., Luis M. Aguilera-Sáez e Ignacio Fernández. "A diffusion NMR method for the prediction of the weight-average molecular weight of globular proteins in aqueous media of different viscosities". Analytical Methods 11, n.º 2 (2019): 142–47. http://dx.doi.org/10.1039/c8ay01817k.
Texto completo da fonteResumo:
We have introduced for the first time, a non-viscosity dependent universal calibration curve (UCC) for the successful prediction of the weight-average molecular weights of globular proteins in the range of 8.5–66.2 kDa with no dependence on the solvent viscosity.
2
Ramaswamy, Meera, Itay Griniasty, Danilo B. Liarte, Abhishek Shetty, Eleni Katifori, Emanuela Del Gado, James P. Sethna, Bulbul Chakraborty e Itai Cohen. "Universal scaling of shear thickening transitions". Journal of Rheology 67, n.º 6 (5 de outubro de 2023): 1189–97. http://dx.doi.org/10.1122/8.0000697.
Texto completo da fonteResumo:
Nearly, all dense suspensions undergo dramatic and abrupt thickening transitions in their flow behavior when sheared at high stresses. Such transitions occur when the dominant interactions between the suspended particles shift from hydrodynamic to frictional. Here, we interpret abrupt shear thickening as a precursor to a rigidity transition and give a complete theory of the viscosity in terms of a universal crossover scaling function from the frictionless jamming point to a rigidity transition associated with friction, anisotropy, and shear. Strikingly, we find experimentally that for two different systems—cornstarch in glycerol and silica spheres in glycerol—the viscosity can be collapsed onto a single universal curve over a wide range of stresses and volume fractions. The collapse reveals two separate scaling regimes due to a crossover between frictionless isotropic jamming and frictional shear jamming, with different critical exponents. The material-specific behavior due to the microscale particle interactions is incorporated into a scaling variable governing the proximity to shear jamming, that depends on both stress and volume fraction. This reformulation opens the door to importing the vast theoretical machinery developed to understand equilibrium critical phenomena to elucidate fundamental physical aspects of the shear thickening transition.
3
Sripathi, Sriharsha, e K. A. Padmanabhan. "Universality of the Phenomenology of Structural Superplasticity". Materials Science Forum 838-839 (janeiro de 2016): 84–88. http://dx.doi.org/10.4028/www.scientific.net/msf.838-839.84.
Texto completo da fonteResumo:
The equation σ=Kέm, where σ is the applied stress, έ is the strain rate, K and m are material constants that depend on stress / strain rate, temperature and grain size is often used to describe structural superplasticity. The general shape of the logσ-logέ curve is sigmoidal. Based on limited data, it was suggested by us earlier that a universal σ-έ curve could exist in a properly normalized space. έ and m are normalized with respect to έopt and mmax, the strain rate at which m is a maximum and the maximum m value respectively. Here a multi-dimensional relationship involving σ/σopt-έ/έopt-m/mmax-ΔF0/kT-η/ηopt is developed; σopt corresponds to έopt, ΔF0 is the free energy of activation for the rate controlling mechanism, k the Boltzmann constant, T the absolute test temperature, η the (apparent) viscosity of the superplastic alloy and ηopt is the viscosity of the same alloy for m=1 in a dimensionless σ-έ space. Using data concerning many systems, the phenomenology of structural superplasticity in all classes of materials is shown to be unique.
4
BĂLĂU, OANA, DOINA BICA, MARTINA KONERACKA, PETER KOPČANSKY, DANIELA SUSAN-RESIGA e LADISLAU VÉKÁS. "RHEOLOGICAL AND MAGNETORHEOLOGICAL BEHAVIOUR OF SOME MAGNETIC FLUIDS ON POLAR AND NONPOLAR CARRIER LIQUIDS". International Journal of Modern Physics B 16, n.º 17n18 (20 de julho de 2002): 2765–71. http://dx.doi.org/10.1142/s0217979202012967.
Texto completo da fonteResumo:
Rheological and magnetorheological behaviour of monolayer and double layer sterically stabilized magnetic fluids, with transformer oil (UTR), diloctilsebacate (DOS), heptanol (Hept), pentanol (Pent) and water (W) as carrier liquids, were investigated. The data for volumic concentration dependence of dynamic viscosity of high colloidal stability UTR, DOS, Hept and Pent samples are particularly well fitted by the formulas given by Vand (1948) and Chow (1994). The Chow type dependence proved its universal character as the viscosity data for dilution series of various magnetic fluids are well fitted by the same curve, regardless the nonpolar or polar charcater of the sample. The magnetorheological effect measured for low and medium concentration water based magnetic fluids is much higher, due to agglomerate formation process, than the corresponding values obtained for the well stabilized UTR, DOS, Hept and Pent samples, even at very high volumic fraction of magnetic nanoparticles.
5
Panton, Ronald L., e Gilles Robert. "The Wavenumber-Phase Velocity Representation for the Turbulent Wall-Pressure Spectrum". Journal of Fluids Engineering 116, n.º 3 (1 de setembro de 1994): 477–83. http://dx.doi.org/10.1115/1.2910301.
Texto completo da fonteResumo:
Wall-pressure fluctuations can be represented by a spectrum level that is a function of flow-direction wavenumber and frequnecy, Φ (k1, ω). In the theory developed herein the frequency is replaced by a phase speed; ω = ck1. At low wavenumbers the spectrum is a universal function if nondimensionalized by the friction velocity u* and the boundary layer thickness δ, while at high wavenumbers another universal function holds if nondimensionalized by u* and viscosity ν. The theory predicts that at moderate wavenumbers the spectrum must be of the form Φ+ (k+1, ω+ = c+ k+1) = k+1 − 2 P+ (Δc+) where P+ (Δc+) is a universal function. Here Δc+ is the difference between the phase speed and the speed for which the maximum of Φ+ occurs. Similar laws exist in outer variables. New measurements of the wall-pressure are given for a large Reynolds number range; 45,000 < Re = Uoδ/ν < 113,000. The scaling laws described above were tested with the experimental results and found to be valid. An experimentally determined curve for P+ (Δc+) is given.
6
Shibaev, Andrey V., Alexander S. Ospennikov, Elizaveta K. Kuznetsova, Alexander I. Kuklin, Teimur M. Aliev, Valentin V. Novikov e Olga E. Philippova. "Universal Character of Breaking of Wormlike Surfactant Micelles by Additives of Different Hydrophobicity". Nanomaterials 12, n.º 24 (14 de dezembro de 2022): 4445. http://dx.doi.org/10.3390/nano12244445.
Texto completo da fonteResumo:
Wormlike surfactant micelles are widely used in various applications including fracturing technology in oil industry, template synthesis of different nanoobjects, micellar copolymerization of hydrophilic and hydrophobic monomers, and so forth. Most of those applications suggest the solubilization of different additives in the micelles. The present paper is aimed at the comparative study of the effect of the solubilization of hydrophobic (n-decane and 1-phenylhexane) and hydrophilic (N-isopropylacrylamide and acrylamide) substances on the rheological properties and structure of the micelles using several complementary techniques including rheometry, small angle neutron scattering, dynamic light scattering, and diffusion ordered NMR spectroscopy. For these studies, mixed micelles of potassium oleate and n-octyltrimethylammonium bromide containing the excess of either anionic or cationic surfactants were used. It was shown that hydrophobic additives are completely solubilized inside the micelles being localized deep in the core (n-decane, 1-phenylhexane) or near the core/corona interface (1-phenylhexane). At the same time, only a small fraction of hydrophilic additives (14% of N-isopropylacrylamide and 4% of acrylamide) penetrate the micelles being localized at the corona area. Despite different localization of the additives inside the micelles, all of them induce the breaking of wormlike micelles with the formation of either ellipsoidal microemulsion droplets (in the case of hydrophobic additives) or ellipsoidal surfactant micelles (in the case of hydrophilic additives). The breaking of micelles results in the drop of viscosity of the solution up to water value. The main result of this paper consists in the observation of the fact that for all the additives under study, the dependences of the viscosity on the volume fraction of additive lie on the same master curve being shifted along the volume fraction axis by a certain factor depending on the hydrophobicity of the added species. Those data are quite useful for various applications of wormlike surfactant micelles suggesting the solubilization of different additives inside them.
7
Grosch, K. A. "Goodyear Medalist Lecture. Rubber Friction and its Relation to Tire Traction". Rubber Chemistry and Technology 80, n.º 3 (1 de julho de 2007): 379–411. http://dx.doi.org/10.5254/1.3548172.
Texto completo da fonteResumo:
Abstract Rubber friction differs from that of hard solid materials in that it is not linearly related to the normal load and it depends strongly on sliding speed and temperature. There exists an interrelation between these two variables on their effect on the friction coefficient, first observed for the viscosity of liquids and generally described by the universal WLF transformation equation. The friction coefficient at a constant load is then described by a so-called master curve. Such master curves have been obtained on different types of surface and for gum rubbers as well as filled rubbers on wet and dry surfaces and it is shown that they may also be obtained on ice. The shape of the curve and position on the log(aTv) axis depends on the polymer and the track surface structure indicating that two distinct processes determine the friction: adhesion friction akin to a molecular relaxation process and a deformation process in which energy is lost due to the cyclic deformation of the rubber by the surface asperity. To obtain such a master curve it is necessary to keep the experimental speeds so low that the temperature rise in the contact area can be neglected. In practical tire tests, sliding speeds are high and hence the temperature rises with speed. Since the WLF equation is a negative function of temperature, the range of log(aTv) is limited. If thermocouples are used as sliders on rubber, it is shown that the experimental curves as function of speed can be transformed into a part of a master curve. For compound development friction tests, a limited range of track temperatures and speeds are sufficient to ensure a high correlation with road test data. A single point laboratory measurement may correlate with road tests if carefully chosen. More usually, it leads to misleading conclusions. Side force measurements at a reasonably large slip angle also reflect the friction coefficient and are a useful laboratory tool to evaluate the traction properties of tread compounds.
8
Sheng, Shaoyang, Aimin Shi e Junjie Xing. "A Systematical Rheological Study of Maize Kernel". Foods 12, n.º 4 (8 de fevereiro de 2023): 738. http://dx.doi.org/10.3390/foods12040738.
Texto completo da fonteResumo:
In this study, the rheological behavior of maize kernel was systematically investigated using a dynamic mechanical analyzer. The loss in toughness caused by drying resulted in a downward shift in the relaxation curve and an upward shift in the creep curve. The long relaxation behavior became obvious when the temperature was above 45 °C, resulting from the weakening of hydrogen bonds with temperature. The maize kernel relaxed more rapidly at high temperatures, caused by a reduction in the cell wall viscosity and polysaccharide tangles. The Deborah numbers were all much smaller than one, suggesting that the Maxwell elements showed viscous behavior. Maize kernel, as a viscoelastic material, showed a dominant viscous property at high temperatures. The decline in β with increasing drying temperature indicated an increase in the width of the relaxation spectrum. A Hookean spring elastic portion made up the majority of the maize kernel creep strain. The order–disorder transformation zone of maize kernel was about 50–60 °C. Due to the complexity of maize kernel, the William–Landel–Ferry constants differed from the universal values; these constants should be ascertained through experiments. Time-temperature superposition was successfully used to describe the rheological behavior. The results show that maize kernel is a thermorheologically simple material. The data acquired in this study can be used for maize processing and storage.
9
Ma, Xiao Lin, e Yu Run Fan. "Aging and Shear Rejuvenation Behavior of Printing Ink". Advanced Materials Research 641-642 (janeiro de 2013): 132–35. http://dx.doi.org/10.4028/www.scientific.net/amr.641-642.132.
Texto completo da fonteResumo:
The aging and shear rejuvenation behavior of a commercial printing ink have been studied experimentally using creep and oscillation modes. We observed that the printing ink has typical rheological characteristics: time-dependent, reversible and shear-thinning viscosity. Meanwhile, these properties are very strongly influenced by shear history, thus employing pre-shearing to obtain a standard test state is of vital importance. After pre-shearing, the quiescent ink undergoes structural evolution, i.e., aging, including a sol-gel (liquid-solid) transition on the early stage at room temperatures, the higher the temperature, the earlier the sol-gel transition occurs. The degree of aging and shear rejuvenation can be characterized by the waiting time after pre-shearing and the stress dependence of the power-law index. Finally, we use a time-stress superposition to obtain a universal master curve which is able to describe the aging behaviors of the printing ink. This study shows that the aging processes of printing ink for different waiting times are self similar, variation of waiting time just change the time scale and elastic modulus.
10
Vaqif Gurbanov, Safa Mustafayev, Zuleykha Eyvazova, Vaqif Gurbanov, Safa Mustafayev, Zuleykha Eyvazova. "IMPROVEMENT OF THE OPERATION PROCESS OF WATERED DEEP OIL PUMP WELLS BY APPLICATION OF POLYFUNCTIONAL MEASURES". ETM - Equipment, Technologies, Materials 07, n.º 03 (6 de junho de 2021): 22–33. http://dx.doi.org/10.36962/etm0703202122.
Texto completo da fonteResumo:
The article shows the types of complications that occur mainly in the fields of the Absheron archipelago in Azerbaijan and in the oil fields of the Azerbaijani sector of the Caspian Sea; the most common and frequent of them are the watering of the production of sucker rod pumping wells and the intensity of sand manifestations. It is noted that methods that prevent complications or reduce their negative impact are more appropriate than methods for their elimination. It is proposed to isolate formation water in flooded sucker-rod pumping oil wells using a universal hydrodynamic method; In this method, a liquid barrier should be created in front of the water in the formation, and not a solid barrier, and high-viscosity dead (non-gaseous) oil should be taken as a separating fluid, the specific gravity of which should be equal to the specific gravity of the formation water. The article uses the following five functions of multifunctional measures when carrying out various well survey methods: I. Pouring clean fluid into the annulus to increase the amount of fluid in the wellbore and reduce the concentration of sand particles in it. II. Without stopping the operation of the pumping unit, adding clean oil to the annulus with the help of a unit, raise its static level several meters higher. III. Determination of values of Pk, Po and G in rod deep well pumping wells producing viscous-plastic oil without stopping the operation of the pumping unit. IV. To determine the reservoir pressure in the simplest way, all well production is drained with a hose into the annulus. V. When removing the first lower curve by the method of two-sided restoration of curves without stopping the operation of the pumping unit VI. When applying the extraction method without changing the indicator diagrams S and n of water-cut oil wells. Thus, the use of multifunctional measures improves the performance of the considered wells and provides great economic benefits. Keywords: polyfunctional measure, irrigated well, sand manifestation, corrosion, erosion, wear, complication, pipe space, sand concentration in liquid, recovery curve.
11
Li, Yong, Xunhua Sun, Shoudong Zhang, Yanan Miao e Shanling Han. "Experimental Investigation and Constitutive Modeling of the Uncured Rubber Compound Based on the DMA Strain Scanning Method". Polymers 12, n.º 11 (16 de novembro de 2020): 2700. http://dx.doi.org/10.3390/polym12112700.
Texto completo da fonteResumo:
Existing research tends to focus on the performance of cured rubber. This is due to a lack of suitable testing methods for the mechanical properties of uncured rubber, in particular, tensile properties. Without crosslinking by sulfur, the tensile strength of uncured rubber compounds is too low to be accurately tested by general tensile testing machines. Firstly, a new tensile stress testing method for uncured rubber was established by using dynamic thermomechanical analysis (DMA) tensile strain scanning. The strain amplitude was increased under a set frequency and constant temperature. The corresponding dynamic force needed to maintain the amplitude was then measured to obtain the dynamic force-amplitude curve observed at this temperature and frequency. Secondly, the Burgers model is usually difficult to calculate and analyze in differential form, so it was reduced to its arithmetic form under creep conditions and material relaxation. Tensile deformation at a constant strain rate was proposed, so the Burgers model could be modified to a more concise form without any strain terms, making mathematical processing and simulating much more convenient. Thirdly, the rate of the modified Burgers model under constant strain was in good agreement with the test data, demonstrating that the elastic stiffness was 1–2 orders of magnitude less than the tensile viscosity. In the end, it was concluded that large data dispersion caused by the universal tensile test can be overcome by choosing this model, and it may become an effective way to study the tensile modeling of uncured rubber compound.
12
Grubin, S. E., e V. N. Trigub. "The asymptotic theory of hypersonic boundary-layer stability". Journal of Fluid Mechanics 246 (janeiro de 1993): 361–80. http://dx.doi.org/10.1017/s0022112093000175.
Texto completo da fonteResumo:
In this paper the linear stability of the hypersonic boundary layer is considered in the local-parallel approximation. It is assumed that the Prandtl-number ½ < σ < 1 and the viscosity-temperature law is a power function: μ/μ∞ = (T/T∞)ω. The asymptotic theory in the limit M∞ → ∞ is developed.Smith & Brown found for the Blasius base flow and Balsa & Goldstein for the mixing layer that, in this limit, the disturbances of the vorticity mode are located in the thin region between the boundary layer and the external flow. The gas model with σ = 1, ω = 1 was exploited in these studies. Here it is demonstrated that the vorticity mode also exists for gas with ½ < σ 1, ω < 1, but its structure and characteristics are considerably different. The nomenclature is discussed, i.e. what an acoustic mode and a vorticity mode are. The numerical solution of the inviscid instability problem for the vorticity mode is obtained for helium and compared with the solution of the complete Rayleigh equation at finite Mach numbers.The limit M∞ → ∞ in the local-parallel approximation for the Blasius base flow is considered so as to understand the viscous structure of the vorticity mode. The viscous stability problem for the vorticity mode is formulated under these assumptions. The problem contains only a single similarity parameter which is a function of the Mach and Reynolds numbers, the temperature factor and wave inclination angle. This problem is numerically solved for helium. The universal upper branch of the neutral curve is obtained as a result. The asymptotic results are compared with the numerical solutions of the complete problem.
13
Gvetadze, R. S., N. V. Yarigin, S. A. Muslov, A. Y. Ovchinnikov, S. D. Arutyunov e P. Y. Sukhochev. "Biomechanical properties of nasal tissues". Molekulyarnaya Meditsina (Molecular medicine) 22, n.º 1 (31 de janeiro de 2024): 52–59. http://dx.doi.org/10.29296/24999490-2024-01-07.
Texto completo da fonteResumo:
Introduction. Plastic rhinosurgery and augmentation rhinoplasty are very relevant today. Especially in relation to patients with congenital saddle deformity of the nasal dorsum, as well as patients with iatrogenic disorders of the nose shape, which dramatically reduce the quality of human life. There are violations of the function of the nose. The purpose of the work. Purpose. Within the framework of the necessity of performing silicone implantation rhinoplasty, the strength, elastic and hyperelastic properties of the soft tissues of the nasal fascia and periosteum were studied, the dynamic viscosity of the tissues of the nasal fascia and periosteum was evaluated, determining their relaxation properties using elastic, hyperelastic and rheological models. Methods. Linear, bilinear (with two Young modules), exponential, hyperelastic (neohookean, Mooney-Rivlin, Ogden, Yeoh, polynomial and Veronda-Westmann) and elastic-viscous (Maxwell) models of biological tissues were used. We used the Mathcad 15.0 computer algebra system and the universal package of interdisciplinary programs ANSYS Multiphysics Software (version 2022 R2). The accuracy of replacing the properties of real tissues with the results of calculations was calculated on the basis of indicators of descriptive statistics (standard deviation, maximum absolute error, maximum relative error and correlation coefficient). Results. It is proved that the bilinear model for the exact reproduction of the stress-strain curve assumes at the molecular level of tissues an initial linear reaction of elastin fibers, passing at ε=εcr into the final linear reaction of the collagen matrix. It was found that the properties of the periosteum (correlation coefficient R=0.9999) and nasal fascia (correlation coefficient R=0.9999) are described most adequately by the 5-parametric polynomial model of the 2nd order and the Yeoh model of the 3rd order (R=0.999 and R=1, respectively), the least accurately by the simple 1-parameter neohookean model (R=0.898 for the periosteum and R=0.905 for the fascia). Among elastic models, the exponential dependence characterizes the behavior of nasal materials quite well. Conclusion. Biomechanically verified that the periosteum is thicker, stronger and more rigid than the fascia. The established very high viscosity values indicate the slowness of relaxation processes in tissues. The periosteum relaxes tension more slowly, which improves the result of implant fixation. On the contrary, the relaxation time of the periosteum is higher than that of the fascia, from which it is concluded that it is preferable not to cut the periosteum during subcostal implantation.
14
Wei, Ximei, Meng Wang, Hongwen Zhang, Lei Wang, Xintian Du, Lixin Chen e Shaohua Zhi. "Effect of Cyclic Loading Treatment on the Compression Energy and Creep Properties of Machine-Harvested Seed Cotton". Agriculture 14, n.º 2 (31 de janeiro de 2024): 239. http://dx.doi.org/10.3390/agriculture14020239.
Texto completo da fonteResumo:
Machine-harvested seed cotton was taken as the research object to further clarify its creep performance, minimize its power consumption during the loading process, and obtain a better loading method. The uniaxial compression creep test was carried out using the Instron universal material test bench to apply cyclic loading treatment. The test factors included cyclic loading times, cyclic stress peak, and cyclic loading frequency. The energy consumption curve of the machine-harvested seed cotton during cyclic loading was obtained through OriginPro 2019b software, and its energy change law was analyzed. Creep strain was divided into two parts, namely, initial creep strain and creep strain increment, to elucidate the creep mechanism. The Burgers model was chosen to describe the creep strain increment. Results show that machine-harvested seed cotton exhibits energy consumption hysteresis during cyclic loading. The compression energy rapidly decreases with increasing cyclic loading times and then stabilizes. Meanwhile, the compression energy increases with increasing cyclic stress peak and cyclic loading frequency. The creep strain mechanism is also the same, which first rapidly increases and then levels off. Cyclic loading times, cyclic stress peak, and cyclic loading frequency have different effects on creep strain increment, instantaneous elastic modulus, hysteresis elastic modulus, viscosity coefficient, delay time, and relative deformation index. Finally, disregarding power consumption and interaction, extending the cyclic loading time, and increasing the cyclic stress peak while simultaneously minimizing the cyclic loading frequency can reduce the relative deformation index in the creeping stage. Accordingly, the deformation retention ability in the creep is improved, but the compression energy in the cyclic loading increases. The results can provide theoretical and data support for studying the theoretical basis of the rheological properties of machine-harvested seed cotton, the design of seed cotton baling devices, and the study of bale (mold) forming quality.
15
Pyromali, Christina, Yanzhao Li, Flanco Zhuge, Charles-André Fustin, Evelyne van Ruymbeke e Dimitris Vlassopoulos. "Nonlinear shear rheology of single and double dynamics metal-ligand networks". Journal of Rheology 66, n.º 6 (1 de novembro de 2022): 1223–35. http://dx.doi.org/10.1122/8.0000429.
Texto completo da fonteResumo:
We present a systematic experimental study of the shear rheology of metallosupramolecular assemblies based on entangled telechelic star polymers comprising one (single dynamic network) or two (double dynamics network) types of physical bonds with the aim to unravel the role of concentration and strength of these bonds on the nonlinear response. Model dynamic networks functionalized with terpyridine ligands were formed by adding different metal ions with increasing bonding strength, zinc, copper, and cobalt. The dynamics are driven by entanglement/disentanglement processes and a ligand exchange mechanism. Steady-state viscosities of single and double dynamics networks collapse onto a universal curve over a wide range of Weissenberg numbers based on terminal time (up to about 300 for single and 1000 for double), exhibiting stronger shear thinning (with an exponent of −0.76) compared to entangled neutral star polymers. Double dynamics networks consisting of two different metal ions (with different lifetimes) exhibit stronger mechanical coherence (rate-dependent fractional viscosity overshoot) and accumulate larger strain at steady-state flow compared to single-ion counterparts. The shear stress growth function signals exhibit weak, albeit unambiguous shear strain hardening, which becomes more pronounced for stronger associations. They also exhibit double overshoot, which reflects the interplay of association strength and chain deformation. Increasing the strength of associations leads to the failure of the Cox–Merz rule, which is more severe for single dynamic networks. The markedly different behavior of double dynamics networks is attributed to the fact that at sufficiently high ion content, the weaker bond acts as a sacrificial component, which provides local energy dissipation and enhances the overall deformability. This bears analogies with their linear viscoelastic response, which has revealed that the arm disentanglement (delayed due to the reversible bonds) effectively interpolates between the two single dynamic network components, depending on composition. Our results suggest ways to tailor the mechanical properties of this class of materials by judicious choice of the type and content of the ion.
16
Lei, Cuiyue, e Peter E. Clark. "Crosslinking of Guar and Guar Derivatives". SPE Journal 12, n.º 03 (1 de setembro de 2007): 316–21. http://dx.doi.org/10.2118/90840-pa.
Texto completo da fonteResumo:
Summary Crosslinking of guar and guar derivatives has played a major role in improving stimulation of oil and gas wells. While crosslinking has been used for a number of years, many facets of crosslinked systems are still not well understood. Part of the problem is that the traditional methods of determining the properties of crosslinked fluids work well for obtaining the data necessary for treatment design, but yield little insight into the nature of the crosslinked system. A good example of this is found in the development of low polymer concentration crosslinked gels. These gels are important because they lower costs and help to minimize formation damage. In this paper, methods for predicting crosslinkability at low concentrations are reported. The polymer literature is filled with methods for characterizing polymer solutions almost none of which find wide use in the development of crosslinked fracturing fluids. Dawson et al. (2000) first reported that the concentration at which a polymer solution transitions from dilute to semidilute could be used as a method for determining the potential for low concentration crosslinking in guar or guar-derivative solutions. To test this assertion, we have conducted a series of experiments that not only shows that the dilute-semidilute transition concentration is an important indicator for the polymers used in this study, but also presents a framework for exploring the potential of other polymer systems. These experiments show conclusively that low-polymer concentration crosslinking is strongly related to the value of the critical overlap concentration, c*. Both the critical overlap concentration and the critical crosslinking concentration increase in the order guar-3 < CMG < CMHPG < guar < HPG. In addition, we show that the critical crosslinking concentration for the range of polymer-crosslinking systems studied is correlated to the critical overlap concentration (). A strong case is presented for the ability to crosslink at low concentrations is a strong function of the polymer type and a weak function of the crosslinker type. Introduction Water-soluble polymers have been used for a number of years as thickening agents for stimulation fluids. Crosslinking was developed to improve the performance of these materials without increasing polymer concentration. Over the years, a number of different crosslinking agents have been used with success. There are several good discussions of polymer and crosslinking systems available (Economides and Nolte 1989; Gidley et al. 1989), and it is not the purpose of this paper to expand these discussions. Rather, we will approach the problem of crosslinking from the prospective of the molecular or solution properties that control or influence crosslinking. When a water-soluble polymer is hydrated, the viscosity of the resulting solution increases as a function of concentration. Starting at low concentrations and building to high concentrations, the viscosity appears to exhibit an exponential increase. This phenomenon has been studied for a wide range of polymer—solvent systems and seems to be universal. Early work divided the viscosity—concentration curve into two regions (Menjivar 1986; Robinson et al. 1982) that were separated at a critical concentration labeled c*. As the understanding of polymer solution behavior progressed and more sensitive instruments and experimental techniques were developed, the solution behavior was determined to be more complex (Rubinstein and Colby 2003).
17
Karadimitriou, Nikolaos, Marios S. Valavanides, Konstantinos Mouravas e Holger Steeb. "Flow-Dependent Relative Permeability Scaling for Steady-State Two-Phase Flow in Porous Media: Laboratory Validation on a Microfluidic Network". Petrophysics – The SPWLA Journal of Formation Evaluation and Reservoir Description 64, n.º 5 (1 de outubro de 2023): 656–79. http://dx.doi.org/10.30632/pjv64n5-2023a4.
Texto completo da fonteResumo:
Conventionally, the relative permeabilities of two immiscible fluid phases flowing in porous media are considered and expressed as functions of saturation. Yet, this has been put into challenge by theoretical, numerical, and laboratory studies of flow in artificial pore network models and real porous media. These works have revealed a significant dependency of the relative permeabilities on the flow rates, especially when the flow regime is capillary to capillary-viscous dominated, and part of the disconnected nonwetting phase remains mobile. These studies suggest that relative permeability models should include the functional dependence on flow intensities. However, revealing the explicit form of such dependence remains a persistent problem. Just recently, a general form of dependence was inferred based on extensive simulations with the DeProF model for steady-state two-phase flows in pore networks. The simulations revealed a systematic dependence of the relative permeabilities on the local flow rate intensities. This dependence can be described analytically by a universal scaling functional form of the actual independent variables of the process, namely, the capillary number, Ca, and the flow rate ratio, r. The proposed scaling incorporated a kernel function, the intrinsic dynamic capillary pressure (IDCP) function, describing the transition between capillarity- and viscosity-dominated flow phenomena. In a parallel laboratory study, SCAL measurements provided a preliminary proof-of-concept on the applicability of the model. In the laboratory study presented here, we examine the applicability of the scaling model by taking extensive, ex-core measurements of relative permeabilities for steady-state co-injections of two immiscible fluids within an artificial microfluidic pore network, across different flow regimes in Ca and r. From these measurements, we calculate the values of the mobility ratio, and we compare these to the corresponding values of the flow rate ratio. We also extract the IDCP curve, the locus of critical flow conditions, whereby the process is more efficient in terms of energy utilization – accounted by the nonwetting phase flow rate per unit of total power provided to the process, as well as the locus of flow conditions of equal relative permeabilities. We show that the degree of consistency between flow rate ratio and mobility ratio values, the IDCP curve, the locus of critical flow conditions, and the locus of equal relative permeabilities, as well as some associated invariant characteristic values, can be used for assessing the extent of end effects and for characterizing the flow as capillary- or viscous-dominated. The proposed scaling introduces new opportunities for enhancing SCAL protocols and their associated applications. These include the characterization of systems and flow conditions, dynamic rock typing, evaluation of capillary end effects, as well as the advancement of more efficient field-scale simulators. Additionally, it paves the way in designing more energy-efficient EOR interventions.
18
KENDON, VIVIEN M., MICHAEL E. CATES, IGNACIO PAGONABARRAGA, J. C. DESPLAT e PETER BLADON. "Inertial effects in three-dimensional spinodal decomposition of a symmetric binary fluid mixture: a lattice Boltzmann study". Journal of Fluid Mechanics 440 (10 de agosto de 2001): 147–203. http://dx.doi.org/10.1017/s0022112001004682.
Texto completo da fonteResumo:
The late-stage demixing following spinodal decomposition of a three-dimensional symmetric binary fluid mixture is studied numerically, using a thermodynamically consistent lattice Boltzmann method. We combine results from simulations with different numerical parameters to obtain an unprecedented range of length and time scales when expressed in reduced physical units. (These are the length and time units derived from fluid density, viscosity, and interfacial tension.) Using eight large (2563) runs, the resulting composite graph of reduced domain size l against reduced time t covers 1 [lsim ] l [lsim ] 105, 10 [lsim ] t [lsim ] 108. Our data are consistent with the dynamical scaling hypothesis that l(t) is a universal scaling curve. We give the first detailed statistical analysis of fluid motion, rather than just domain evolution, in simulations of this kind, and introduce scaling plots for several quantities derived from the fluid velocity and velocity gradient fields. Using the conventional definition of Reynolds number for this problem, Reϕ = ldl/dt, we attain values approaching 350. At Reϕ [gsim ] 100 (which requires t [gsim ] 106) we find clear evidence of Furukawa's inertial scaling (l ∼ t2/3), although the crossover from the viscous regime (l ∼ t) is both broad and late (102 [lsim ] t [lsim ] 106). Though it cannot be ruled out, we find no indication that Reϕ is self-limiting (l ∼ t1/2) at late times, as recently proposed by Grant & Elder. Detailed study of the velocity fields confirms that, for our most inertial runs, the RMS ratio of nonlinear to viscous terms in the Navier–Stokes equation, R2, is of order 10, with the fluid mixture showing incipient turbulent characteristics. However, we cannot go far enough into the inertial regime to obtain a clear length separation of domain size, Taylor microscale, and Kolmogorov scale, as would be needed to test a recent ‘extended’ scaling theory of Kendon (in which R2 is self-limiting but Reϕ not). Obtaining our results has required careful steering of several numerical control parameters so as to maintain adequate algorithmic stability, efficiency and isotropy, while eliminating unwanted residual diffusion. (We argue that the latter affects some studies in the literature which report l ∼ t2/3 for t [lsim ] 104.) We analyse the various sources of error and find them just within acceptable levels (a few percent each) in most of our datasets. To bring these under significantly better control, or to go much further into the inertial regime, would require much larger computational resources and/or a breakthrough in algorithm design.
19
Ismail, Izwan, Saiful Amri Mazlan, Syarifah Nur Aqida e A. G. Olabi. "Full Factorial Design to Study Material Parameters of Magnetorheological Fluid". Key Engineering Materials 543 (março de 2013): 511–14. http://dx.doi.org/10.4028/www.scientific.net/kem.543.511.
Texto completo da fonteResumo:
This paper presents the effects of magnetorheological (MR) fluid parameters, bidisperse ratio, carrier fluid viscosity and particle volume fraction, on its mechanical behaviour using statistical investigation. Silicone oil-based MR fluid samples were compressed using universal testing machine (UTM) in a vertical direction. A set of eight experiments was designed by Design Expert 7 software in which was conducted at two levels for each factor. Stress-strain curves that obtained from the compression test were then analysed by testXpert analyser software. The responses in terms of maximum stresses at 0.75 of strain were extracted from the curves. The result indicated that a combination of high bidisperse ratio and particle volume fraction, and a low carrier fluid viscosity could produce a high compressive stress. The findings are important to be considered in designing squeeze mode MR fluid actuators.
20
Ananyin, V. M., P. V. Morokhov, B. A. Kalin, R. S. Kuzmin e O. N. Sevryukov. "Study of melting and crystallization of Cu – P alloy using a universal vacuum viscometer and thermal analysis". Industrial laboratory. Diagnostics of materials 84, n.º 7 (8 de agosto de 2018): 34–37. http://dx.doi.org/10.26896/1028-6861-2018-84-7-34-37.
Texto completo da fonteResumo:
Methods of differential thermal analysis (DTA) and measurement of the melt viscosity are widely used in studying the properties of alloys at high temperatures. We have made an attempt to combine those two complementary methods of research. In contrast to the single-stranded Shvidkovskii viscometer, a bifilar suspension on two thermocouple wires is used in the proposed construction of the installation. The system based on the bifilar suspension provides using thermocouple in contact with the crucible with a sample, thus ensuring measurements of the crucible temperature like the measuring cell in DTA. The adjusting thermocouple located near the coil of a bifilar heater is used as a reference thermocouple. Since thermal analysis requires linear heating at a constant rate, and the viscosity is usually measured in a steady-state (steady-state) regime with long exposures at each measurement temperature, a series of dynamic viscosity determinations with a heating rate of 1, 2, 3 and 5 °C/min is carried out, the heating rates of 1 and 2 °C/min being approximately equal to the average heating rate under steady-state conditions. It is shown that when measuring in a dynamic mode at a heating rate up to 3 °C/min, the viscosity curves coincide with the measurement data in a steady-state mode, and the results of the thermal analysis (experimental setup) are consistent with the data of DTA (STA 409 setup). Results of measuring the logarithmic decrement of vibrations for Cu – 7.3% P alloy and data of thermal analysis are presented. Data of thermal analysis obtained on our experimental setup coincide completely with the DTA results obtained on a STA 409 unit. A model experiment carried out to explain the delay of growth of the logarithmic damping decrement at the beginning of melting and sharp decrease at the beginning of crystallization indicates to the effect of blocking free flow of the liquid melt component by the solid skeleton having a higher melting point.
21
KLEBANOV, IGOR R. "QCD AND STRING THEORY". International Journal of Modern Physics A 21, n.º 08n09 (10 de abril de 2006): 1831–43. http://dx.doi.org/10.1142/s0217751x06032794.
Texto completo da fonteResumo:
This talk begins with some history and basic facts about string theory and its connections with strong interactions. Comparisons of stacks of Dirichlet branes with curved backgrounds produced by them are used to motivate the AdS/CFT correspondence between superconformal gauge theory and string theory on a product of Anti-de Sitter space and a compact manifold. The ensuing duality between semi-classical spinning strings and long gauge theory operators is briefly reviewed. Strongly coupled thermal SYM theory is explored via a black hole in 5-dimensional AdS space, which leads to explicit results for its entropy and shear viscosity. A conjectured universal lower bound on the viscosity to entropy density ratio, and its possible relation to recent results from RHIC, are discussed. Finally, some available results on string duals of confining gauge theories are briefly reviewed.
22
Barenblatt, G. I., e V. M. Prostokishin. "Scaling laws for fully developed turbulent shear flows. Part 2. Processing of experimental data". Journal of Fluid Mechanics 248 (março de 1993): 521–29. http://dx.doi.org/10.1017/s0022112093000886.
Texto completo da fonteResumo:
In Part 1 of this work (Barenblatt 1993) a non-universal scaling law (depending on the Reynolds number) for the mean velocity distribution in fully developed turbulent shear flow was proposed, together with the corresponding skin friction law. The universal logarithmic law was also discussed and it was shown that it can be understood, in fact, as an asymptotic branch of the envelope of the curves corresponding to the scaling law.Here in Part 2 the comparisons with experimental data are presented in detail. The whole set of classic Nikuradze (1932) data, concerning both velocity distribution and skin friction, was chosen for comparison. The instructive coincidence of predictions with experimental data suggests the conclusion that the influence of molecular viscosity within the main body of fully developed turbulent shear flows remains essential, even at very large Reynolds numbers. Meanwhile, some incompleteness of the experimental data presented in the work of Nikuradze (1932) is noticed, namely the lack of data in the range of parameters where the difference between scaling law and universal logarithmic law predictions should be the largest.
23
Zhang, Hua, Guangwu Zhou, Ping Zhong, Kepeng Wu e Xingwu Ding. "Experimental investigation on Stribeck curves of different elastic modulus materials under oil and water lubrication conditions". Industrial Lubrication and Tribology 72, n.º 6 (4 de março de 2020): 805–10. http://dx.doi.org/10.1108/ilt-08-2019-0305.
Texto completo da fonteResumo:
Purpose The purpose of this paper is to study the influence of friction coefficient of materials with different elastic modulus on the variation of velocity and load under water lubrication and oil lubrication conditions. Design/methodology/approach Low-viscosity lubricating oil and water were used as lubricants to test the friction performance of the ball-disc contact friction pair in the lubrication state on the universal micro-tribometer multi-functional friction and wear test system. Findings In the same speed range, the lubrication states from soft to rigid materials are not necessarily similar to each other. Generally, the material with low elastic modulus is suitable in low-viscosity lubricant environments, while the material with high elastic modulus has relatively smaller friction coefficients in oil-lubricated environments compared with water lubrication. However, the coefficients of polyethylene, polytetrafluoroethylen and polyoxymethylene are exceeded by rubber’s coefficients under water lubrication in the same experiment environments, and their lubrication states are not affected by lubricants. The friction coefficient of the friction pair decreases with the increase of loads; however, it does not apply to all materials. The friction coefficients of materials with smaller elastic modulus such as rubber under high loads are rather large. Therefore, the elastic modulus of the material under high loads is a factor to be considered. Originality/value The Stribeck curves study of the ball-disk contact friction pair comprising soft and rigid materials, whose elastic modulus is from hundreds of GPa to a few of MPa, was carried out. The influence of different speeds, loads and lubricants on the friction coefficient of the friction pair was revealed, which provided a research basis for the selection and matching of friction pair materials.
24
Lebedev, A. V. "Violation of the Brownian relaxation law for cobalt ferrite particles in water". ВЕСТНИК ПЕРМСКОГО УНИВЕРСИТЕТА. ФИЗИКА, n.º 4 (2023): 55–61. http://dx.doi.org/10.17072/1994-3598-2023-4-55-61.
Texto completo da fonteResumo:
In the temperature range 0–90°C, the dynamic susceptibility of three samples of a magnetic fluid based on cobalt ferrite particles stabilized in water with a double layer of a surfactant was meas-ured. The first layer of the stabilizer was formed of auric acid molecules. The second layer consisted of a mixture of lauric acid and sodium dodecyl sulfate. The liquid samples had a small (about 10%) volume fraction of particles in order to reduce the influence of interparticle interactions and eliminate non-Newtonian rheological properties. The main parameter in which the samples differed was viscosity. It was changed by adding a small amount of polyvinyl alcohol. For all samples, in the studied temperature range the frequency dependence of the dynamic susceptibility had a quasi-Debye form with a pronounced maximum for the imaginary part. The value of the magnetization relaxation time was determined from the frequency of the maximum on the imaginary part of the dynamic susceptibility. As a result, the dependences of themagnetization relaxation time on tem-perature were obtained. To analyze the results obtained, viscosities of the samples were measured. All samples exhibited the properties of Newtonian fluids –the value of dynamic viscosity did not depend on the shear rate. The obtained results on the dynamic susceptibility and viscosity were compared by plotting relaxation times as a function of the ratio ofdynamic viscosity to absolute temperature. The resulting dependences do not fit on one universal straight line, as it is supposed to be according to the theory. The actual graph looks like a family of three different curves that di-verge as viscosity increases. In order to assess the influence of Néel relaxation on the resulting sus-ceptibility, the dynamic susceptibility of a frozen sample of the magnetic fluid was measured. The resulting susceptibility value was about 3% of the initial susceptibility of the liquid sample. Thus, despite the insignificant contribution of the Néel mechanism of magnetization relaxation to the dy-namic susceptibility, it is impossible to explain the obtained measurement results on the basis of the Brownian relaxation mechanism alone.
25
Shan, Yao, Shiyuan Liu, Biao Wang, Ying Hong, Chao Zhang, C. W. Lim, Guangzu Zhang e Zhengbao Yang. "A gravity-driven sintering method to fabricate geometrically complex compact piezoceramics". Nature Communications 12, n.º 1 (18 de outubro de 2021). http://dx.doi.org/10.1038/s41467-021-26373-x.
Texto completo da fonteResumo:
AbstractHighly compact and geometrically complex piezoceramics are required by a variety of electromechanical devices owing to their outstanding piezoelectricity, mechanical stability and extended application scenarios. 3D printing is currently the mainstream technology for fabricating geometrically complex piezoceramic components. However, it is hard to print piezoceramics in a curve shape while also keeping its compactness due to restrictions on the ceramic loading and the viscosity of feedstocks. Here, we report a gravity-driven sintering (GDS) process to directly fabricate curved and compact piezoceramics by exploiting gravitational force and high-temperature viscous behavior of sintering ceramic specimens. The sintered lead zirconate titanate (PZT) ceramics possess curve geometries that can be facilely tuned via the initial mechanical boundary design, and exhibit high piezoelectric properties comparable to those of conventional-sintered compact PZT (d33 = 595 pC/N). In contrast to 3D printing technology, our GDS process is suitable for scale-up production and low-cost production of piezoceramics with diverse curved surfaces. Our GDS strategy is an universal and facile route to fabricate curved piezoceramics and other functional ceramics with no compromise of their functionalities.
26
Bhattacharyya, Tulika, Khushboo Suman e Yogesh Moreshwar Joshi. "Gel - Sol Transition of Thermoresponsive Poly(vinyl alcohol) Solution: Validation of the Universal Critical Scaling Relations". Physics of Fluids, 19 de janeiro de 2023. http://dx.doi.org/10.1063/5.0137753.
Texto completo da fonteResumo:
While undergoing gelation transition, a material passes through a distinctive state called the critical gel state. In the neighborhood of this critical gel state, how viscosity, equilibrium modulus, and relaxation times evolve are correlated by scaling relations, and their universality has been validated for materials undergoing the sol - gel transition. In this work, we extend this approach for the gel - sol transition of a thermoresponsive polymeric system of aqueous Poly(vinyl alcohol) (PVOH) gel that passes through the critical state upon increasing temperature. We observe that, in the neighborhood of the critical gel state, the equilibrium modulus and viscosity demonstrate a power law dependence on the relative distance from the critical state in terms of normalized temperature. Furthermore, the relaxation times in the gel and the sol state shows symmetric power law divergence near the critical state. The corresponding critical power law exponents and the dynamic critical exponents computed at the critical gel - sol transition state validate the scaling and hyperscaling relations originally proposed for the critical sol - gel transition very well. Remarkably, the dependence of complex viscosity on frequency at different temperatures shows a comprehensive master curve irrespective of the temperature ramp rate independently in the gel and the sol state. Since sol - gel as well as the gel - sol transitions are opposite to each other, the applicability of the scaling relations validated in this work suggests broader symmetry associated with how the structure evolves around the critical state irrespective of the direction.
27
Dixit, Shivsai Ajit, Abhishek Gupta, Harish Choudhary e Thara Prabhakaran. "Universal scaling of mean skin friction in turbulent boundary layers and fully developed pipe and channel flows". Journal of Fluid Mechanics 943 (16 de junho de 2022). http://dx.doi.org/10.1017/jfm.2022.463.
Texto completo da fonteResumo:
A dynamically consistent scaling of mean skin friction in zero-pressure-gradient turbulent boundary layers and fully developed pipe and channel flows, is derived. Theoretical arguments are based on transfer of kinetic energy from mean flow to large eddies of turbulence. A single new velocity scale $M/\nu$ is shown to be dynamically relevant for scaling skin friction in all flows; $M$ is the planar kinematic momentum rate of the shear flow and $\nu$ is fluid kinematic viscosity. An asymptotic $-1/2$ power scaling law (in $M$ – $\nu$ scaling) is shown to be universally applicable. It is observed that the semi-empirical finite- $Re$ skin friction model, resulting from the asymptotic scaling law, applies well to individual flows, but fails to describe all flows in a universal fashion. This non-universality could be due to the differences in flow boundary conditions at finite Reynolds numbers and flow geometry, that affect the outer-layer structures in these flows. It is argued that these differences may be simply absorbed by considering differences in the shapes of mean velocity profiles amongst these flows. An empirical correction to $M$ – $\nu$ scaling is proposed based on Clauser's shape factor $G$ . It is demonstrated that data from all flows in this new, semi-empirical $M$ – $\nu$ – $G$ scaling collapse remarkably well onto a single universal curve. The corresponding universal finite- $Re$ model in $M$ – $\nu$ – $G$ scaling is shown to describe this curve to an excellent accuracy. These results underscore the importance of a dynamically consistent approach towards revealing universality of skin friction scaling in wall turbulence.
28
Vishvakarma, Vicky, Oskar Engberg, Daniel Huster e Sudipta Maiti. "The effect of cholesterol on highly curved membranes measured by nanosecond Fluorescence Correlation Spectroscopy". Methods and Applications in Fluorescence, 8 de agosto de 2022. http://dx.doi.org/10.1088/2050-6120/ac87ea.
Texto completo da fonteResumo:
Abstract Small lipid vesicles (with diameter ≤ 100nm) with their highly curved membranes comprise a special class of biological lipid bilayers. The mechanical properties of such membranes are critical for their function, e.g. exocytosis. Cholesterol is a near-universal regulator of membrane properties in animal cells. Yet measurements of the effect of cholesterol on the mechanical properties of membranes have remained challenging, and the interpretation of such measurements has remained a matter of debate. Here we show that nanosecond fluorescence correlation spectroscopy (FCS) can directly measure the ns-microsecond rotational correlation time (τr) of a lipid probe in high curvature vesicles with extraordinary sensitivity. Using a home-built 4-Pi fluorescence cross-correlation spectrometer containing polarization-modulating elements, we measure the rotational correlation time (τr) of Nile Red in neurotransmitter vesicle mimics. As the cholesterol mole fraction increases from 0 to 50 %, τr increases from 17 ± 1 to 112 ± 12 ns, indicating a viscosity change of nearly a factor of 7. These measurements are corroborated by solid-state NMR results, which show that the order parameter of the lipid acyl chains increases by about 50% for the same change in cholesterol concentration. Additionally, we measured the spectral parameters of polarity-sensitive fluorescence dyes, which provide an indirect measure of viscosity. The green/red ratio of Nile Red and the generalized polarization of Laurdan show consistent increases of 1.3x and 2.6x, respectively. Our results demonstrate that rotational FCS can directly measure the viscosity of highly curved membranes with higher sensitivity and wider dynamic range compared to other conventional techniques. Significantly, we observe that the viscosity of neurotransmitter vesicle mimics is remarkably sensitive to their cholesterol content.
29
Xiong, Xuhai, Jianxin Ai, Rong Ren, Jing Wang e Guiyang Li. "Curing behavior and properties of ultra-high temperature resistant RTM bismaleimide resin". High Performance Polymers, 22 de dezembro de 2022, 095400832211469. http://dx.doi.org/10.1177/09540083221146926.
Texto completo da fonteResumo:
The properties of a RTM bismaleimide resin with low viscosity and ultra-high temperature resistance were systematically investigated, including its curing kinetics and rheological properties, and the thermal and mechanical properties of its cured resins. The thermal curing kinetics was investigated by differential scanning calorimetry (DSC) method with multiple heating rates. DSC curves display a cure regime in the temperature range of 150∼300°C and the exothermic peaks shift from 194°C to 231°C with heating rate. The apparent activation energy of curing reaction is calculated as 78.2 kJ/mol. The rheological properties were studied in terms of the changes of the non-isothermal and isothermal viscosity tested using a rotary viscometer. The test results show that the RTM resin has a wide molding temperature window from 90°C to 200°C and long molding time at 110°C for 275 min with a flow viscosity less than 1000 mPas. Dual-Arrhenius model was established to predict the viscosity characteristics at different constant temperatures, showing a good agreement with the experimental data. Four curing cycles were designed to obtain cured networks with different microstructures, and the thermal and mechanical properties of the cured resins suffered from various curing cycles were characterized by dynamic mechanical analysis (DMA) and universal material testing machine. The results exhibit that the cured product has a ultra-high glass transition temperature of 373.5°C and larger flexural strength of 145.4 MPa after post-curing at 250°C for 10 h.
30
Malbranche, Nelya, Aritra Santra, Bulbul Chakraborty e Jeffrey F. Morris. "Scaling Analysis of Shear Thickening Suspensions". Frontiers in Physics 10 (11 de julho de 2022). http://dx.doi.org/10.3389/fphy.2022.946221.
Texto completo da fonteResumo:
Dense suspensions of particles in viscous liquid often demonstrate the striking phenomenon of abrupt shear thickening, where their viscosity increases strongly with increase of the imposed stress or shear rate. In this work, discrete-particle simulations accounting for short-range hydrodynamic, repulsive, and contact forces are performed to simulate flow of shear thickening bidisperse suspensions, with the packing parameters of large-to-small particle radius ratio δ = 3 and large particle fraction ζ = 0.15, 0.50, and 0.85. The simulations are carried out for volume fractions 0.54 ≤ ϕ ≤ 0.60 and a wide range of shear stresses. The repulsive forces, of magnitude FR, model the effects of surface charge and electric double-layer overlap, and result in shear thinning at small stress, with shear thickening beginning at stresses σ ∼ FRa−2. A crossover scaling analysis used to describe systems with more than one thermodynamic critical point has recently been shown to successfully describe the experimentally-observed shear thickening behavior in suspensions. The scaling theory is tested here on simulated shear thickening data of the bidisperse mixtures, and also on nearly monodisperse suspensions with δ = 1.4 and ζ = 0.50. Presenting the viscosity in terms of a universal crossover scaling function between the frictionless and frictional maximum packing fractions collapses the viscosity for most of the suspensions studied. Two scaling regimes having different exponents are observed. The scaling analysis shows that the second normal stress difference N2 and the particle pressure Π also collapse on their respective curves, with the latter featuring a different exponent from the viscosity and normal stress difference. The influence of the fraction of frictional contacts, one of the parameters of the scaling analysis, and its dependence on the packing parameters are also presented.