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1
Khine, Yu Yu, e John S. Walker. "Thermocapillary convection in a cylinder with a strong non-uniform axisymmetric magnetic field". Journal of Fluid Mechanics 276 (10 ottobre 1994): 369–88. http://dx.doi.org/10.1017/s0022112094002600.
Testo completoAbstract (sommario):
This paper treats a surface-tension-driven liquid-metal flow in a cylinder with a steady externally applied non-uniform axisymmetric magnetic field. The top boundary consists of an annular free surface around a solid disk, modelling the Czochralski growth of silicon crystals. A radial temperature gradient produces a decrease of the surface tension from the disk edge to the vertical cylinder wall. The magnetic flux density is sufficiently large that inertial effects and convective heat transfer are negligible. First we present large-Hartmann-number asymptotic solutions for magnetic fields with either a non-zero or a zero axial component at the free surface. The asymptotic solutions indicate that a purely radial magnetic field at the free surface represents a singular limit of more general magnetic fields. Secondly we present numerical solutions for arbitrary values of the Hartmann number, and we treat the evolution of the thermocapillary convection as the axial magnetic field at the free surface is changed continuously from the full field strength to zero.
2
Mironov, Boris, e Yuriy Mironov. "Torsion of anisotropic and non-uniform cylindrical rods with elliptical section". MATEC Web of Conferences 251 (2018): 04037. http://dx.doi.org/10.1051/matecconf/201825104037.
Testo completoAbstract (sommario):
In work the limit state of cylindrical and prismatic rods from anisotropic ideal rigid-plastic material is investigated under torsion for arbitrary condition of plasticity, and the torsion of anisotropic and non-uniform rods with elliptic section under the condition of Mises-Hill plasticity is considered. The integrals determining the stressed state of an anisotropic rod under arbitrary condition of plasticity are obtained, the field of characteristics of the basic ratios for anisotropic and composite rods under the condition of Mises-Hill plasticity is constructed, the ratios along characteristics are obtained, the envelopes of the family of characteristics and lines of tension rupture are found.
3
Shao, Mingyue, Miao Zhang, Jimei Wu, Xuxia Guo, Qiumin Wu e Jiajuan Qing. "Vibration and stability analysis of tensioned moving printed electronic laminated membrane under multiple working conditions". AIP Advances 12, n. 10 (1 ottobre 2022): 105017. http://dx.doi.org/10.1063/5.0110799.
Testo completoAbstract (sommario):
In this paper, the thermoelastic coupled vibration of roll-to-roll printed electronic laminated membrane under multiple working conditions, such as in a thermal environment, air resistance, and non-uniform tension are investigated. First, a mathematical model of a moving electronic laminated membrane was established, which takes into account the non-uniform tension at each end of the membrane and the non-uniform temperature field. The vibration differential equation of the moving electronic laminated membrane is derived considering the air resistance based on Hamilton’s principle; the differential quadrature method is used to calculate and analyze the effect of the moving electronic laminated membrane aspect ratio, thermoelastic coupling coefficient, air resistance, and other parameters on its vibration and stability. The results show that different parameters of the moving electronic laminated membrane have different effects on its stability, and some parameters are not positively correlated with stability. This study can serve as a theoretical guide for improving the transmission stability and high-precision fabrication of roll-to-roll, flexible electronic laminated membranes.
4
Керестень, И. А., И. А. Попов e М. В. Ховайко. "Numerical simulation of underwater cable laying with account of non-uniform hydrostatic force at Arctic basin condition". MORSKIE INTELLEKTUAL`NYE TEHNOLOGII), n. 3(53) (27 agosto 2021): 267–73. http://dx.doi.org/10.37220/mit.2021.53.3.032.
Testo completoAbstract (sommario):
Статья посвящена моделированию динамического равновесия установившегося движения протяженной кабельной линии с учетом действия гидродинамических сил сопротивления и неоднородной гидростатической силы. Учитывая различные условия и глубины укладки, а также требования функционального назначения и защиты от враждебных факторов морского дна, необходимо рассмотреть широкий диапазон кабелей с различными механическими характеристиками: трехжильный кабель с одиночным бронированием 2XS2YRAA, одножильный кабель с одиночным бронированием ZS-YJQ41 и одножильный кабель с двойным бронированием – аналог GASLMLTV. Целью работы является развитие цифровой технологии по моделированию укладки подводных коммуникационных и силовых кабелей, позволяющей учитывать многочисленные физико-механические явления, имеющие место при проведении реальных морских работ. Для достижения поставленной цели работы используется программная среда Matlab Math Works с использованием разработанного комплекса программ для инженерной оценки формы и натяжения провисающего участка кабеля. Научная новизна состоит в апробации модели подводной укладки кабеля, учитывающей действие неоднородной гидростатической силы. Результаты моделирования представлены в виде формы и натяжения провисающей части кабеля при различных углах схода кабеля с движущегося судна при различных механических параметрах кабелей. Практическое значение работы состоит в повышении эффективности освоения перспективных месторождений, путем определения характеристик укладки кабеля в условиях Арктического бассейна: газовое месторождение Лудловское, газоконденсатное месторождение Ленинградское, нефтяное месторождение Медынское-море. This article studies the numerical simulation of underwater steady motion of the cable line with account of hydrodynamic water resistance forces and non-uniform hydrostatic force. It is necessary to consider distinctive types of cables due to various depths, laying conditions, functional requirements and protection requirements against adverse factors of seabed. Three-core single armoured cable 2XS2YRAA, one-core single armoured cable ZS-YJQ41 and one-core double armoured cable – analogue GASLMLTV are considered in this article. The aim of the research consists in digital technology development for underwater cable laying modeling, which allows taking into account numerous physical and mechanical features. These features occur during real marine operations for communication and power cables. Programming and numeric computing platform Matlab Math Works with developed software package is chosen as the research method. Simulation results are presented in dimensionless form for cable shape and tension for engineering purposes. The novelty of the work consists in approbation of underwater cable laying analytical model considering non-uniform hydrostatic force. Simulation results are presented for underwater cable laying during reeling from spool mounted on the vessel, moving with constant speed for distinctive types of cables. The influence of the cable run-off angle on the investigated characteristics was also considered. The practical value of the research consists in increasing of efficiency of exploration of oil, gas and condensate fields by determining underwater cable laying characteristics for perspective fields. At the end of the paper, the results of estimation of the shape and tension of the cable being laid undersea were presented for several fields at Arctic basin condition: gas field Ludlovskoe, condensate field Leningradskoe and oil field Medinskoe sea.
5
Liu, Jie, e Sheng Liu. "Dynamics Behaviors of Droplet on Hydrophobic Surfaces Driven by Electric Field". Micromachines 10, n. 11 (14 novembre 2019): 778. http://dx.doi.org/10.3390/mi10110778.
Testo completoAbstract (sommario):
Droplet microfluidic technology achieves precise manipulation of droplet behaviors by designing and controlling the flow and interaction of various incompatible fluids. The electric field provides a non-contact, pollution-free, designable and promising method for droplet microfluidics. Since the droplet behaviors in many industrial and biological applications occur on the contact surface and the properties of droplets and the surrounding environment are not consistent, it is essential to understand fundamentally the sessile droplet motion and deformation under various conditions. This paper reports a technique using the pin-plate electrode to generate non-uniform dielectrophoresis (DEP) force to control sessile droplets on hydrophobic surfaces. The electrohydrodynamics phenomena of the droplet motion and deformation are simulated using the phase-field method. It is found that the droplet moves along the substrate surface to the direction of higher electric field strength, and is accompanied with a certain offset displacement. In addition, the effect of pin electric potentials, surface contact angles and droplet volumes on the droplet motion and deformation are also studied and compared. The results show that higher potentials, more hydrophobic surfaces and larger droplet volumes exhibit greater droplet horizontal displacement and offset displacement. But for the droplet vertical displacement, it is found that during the first revert process, the release of the surface tension can make the droplet with low potentials, small contact angles or small droplet volumes span from negative to positive. These results will be helpful for future operations encountered in sessile droplets under non-uniform electric fields towards the droplet microfluidics applications.
6
Umeno, Yoshitaka, e Takayuki Kitamura. "Criterion of Mechanical Instability in Inhomogeneous Atomic System". Materials Science Forum 482 (aprile 2005): 127–30. http://dx.doi.org/10.4028/www.scientific.net/msf.482.127.
Testo completoAbstract (sommario):
The mechanical stability of a material is a fundamental issue in strength of atomic systems. Although the criterion of the mechanical stability of homogeneous structures such as perfect crystals have been successfully investigated so far, the criterion has not been able to be precisely evaluated in the cases of non-uniform deformations or bodies of inhomogeneous atomic structures. Now we present an instability criterion of an arbitrary atomic structure based on the energy balance of the whole system. This method gives the mathematically rigorous condition for the onset of an unstable deformation in any inhomogeneous atomic system. Furthermore, the method can be applied to any type of potential field, which means that ab initio evaluations of the mechanical instability of inhomogeneous structure under non-uniform deformation will be possible. The validity of the method is clarified by the application to tension of a cracked body. The onsets of unstable deformations and their deformation modes are precisely evaluated by the method.
7
Gao, Yang. "Singular Problems of Spherically Uniform Anisotropic Piezoelectric Solids". Advanced Materials Research 415-417 (dicembre 2011): 19–24. http://dx.doi.org/10.4028/www.scientific.net/amr.415-417.19.
Testo completoAbstract (sommario):
A material is radially anisotropic piezoelectric when its generalized Hooke’s law at each material point referred to a spherical coordinate system is the same everywhere. In a recent paper by Ting, the remarkable nature at the center of a sphere has been shown when a spherically uniform linear anisotropic elastic material is subjected to a uniform traction at the surface of the sphere. This paper extends elastic material for piezoelectric material, and shows that the singular problems also prevail in piezoelectric material. When a sphere of piezoelectric material is subjected to a uniform traction and electric potential at the surface of the sphere, for a certain range of material parameter, the stress, the electric field and the electric potential at the center of the sphere are infinite. When the sphere is subjected to a uniform tension, a cavitation occurs at the center of the sphere. If the applied traction is a uniform pressure, a black hole occurs at the center of the sphere. The singular problems depend only on one non-dimensional material parameter and the direction of the applied traction, while is independent of the magnitude of the traction.
8
Syngellakis, Stavros. "Stress amplification in three-dimensional narrow zones created by cavities". Theoretical and Applied Mechanics 39, n. 1 (2012): 71–97. http://dx.doi.org/10.2298/tam1201071s.
Testo completoAbstract (sommario):
The paper is concerned with a particular case of stress amplification arising from the proximity of a spherical cavity to the boundary of a loaded elastic solid. The performed approximate analysis yields distributions of stresses and displacements in the narrow region formed between a spherical cavity and the faces of a thin flat layer subjected to a far field uniform radial tension. The narrow region is modelled as a circular plate of non-uniform thickness undergoing coupled membrane and flexural deformation. Series solutions are obtained for both membrane forces and bending moments leading to estimates for the stress concentration factor at minimum thickness. These predictions are found consistent with those obtained from both the exact analytical solution and finite element modelling of the problem. Cross-validated results from the two latter methods also provide trends for the stress amplification due to the narrowness of the region.
9
Sun, Peng, Jin Huang, Jiaying Zhang e Fanbo Meng. "Wrinkling Patterns and Stress Analysis of Tensile Membrane with Rigid Elements". Applied Sciences 12, n. 13 (30 giugno 2022): 6630. http://dx.doi.org/10.3390/app12136630.
Testo completoAbstract (sommario):
Heterogeneous membrane structures with rigid elements are often used in flexible electronic and aerospace structures. In heterogeneous membrane structures under tension, the disturbance stress caused by the rigid element changes the stress distribution of the membrane, and it is difficult to calculate the stress distribution of the heterogeneous membrane structure using the traditional stress functions method. In this article, we propose a method for calculating the non-uniform stress field based on the Eshelby elastic inclusion theory, which states that tension membrane structures contain square rigid elements. The wrinkle distribution of the rigid element at different positions is predicted by a stress analysis, and the influence of the position and size of the rigid element on the wrinkle distribution of the membrane is studied by a finite-element simulation. The research results show that the wrinkle pattern of the stretched membrane can be controlled by changing the position of the rigid element to meet some special needs.
10
Siva, Dr M. M. "Elevated Percentage Mechanical Properties of in-situ Synthesized TiB2/Al Matrix Composites". International Journal for Research in Applied Science and Engineering Technology 10, n. 6 (30 giugno 2022): 2172–76. http://dx.doi.org/10.22214/ijraset.2022.44199.
Testo completoAbstract (sommario):
Abstract: Make use of TiB2 salts with Al-2011 fabricated by stir cast method. In the composites of Particulate reinforced varies in non-uniform microstructure and the composition in a 5 and 10 percentage of TiB2 in functional performance of a component with continuously changing properties. In mechanical, aeronautical and marine field Al 2011 is used due to its good mechanical and corrosion resistance. TiB2 is combined with Al 2011 also increases the mechanical corrosion resistance properties. MMc of Al-2011 by stir cast method titanium and boride salt were used. InTiB2 5% and 10% the tension tests and hardness tests were performed on the as cast or after heat treated samples to find the microstructure and the effect of reinforcement on the mechanical properties.
11
Sumithra, R., e B. Komala. "The study of effects of surface tension, magnetic field and non-uniform salinity gradients on the onset of double diffusive convection in composite system". Malaya Journal of Matematik 8, n. 3 (giugno 2020): 730–37. http://dx.doi.org/10.26637/mjm0803/0001.
Testo completo
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Liu, Zhao, Shusen Cheng, Yong Liu, Pengbo Liu e Weiyang Zhang. "Effect of slag properties and non-uniform bottom blowing gas supply mode on fluid flow and mixing behavior in converter". Metallurgical Research & Technology 120, n. 5 (2023): 506. http://dx.doi.org/10.1051/metal/2023064.
Testo completoAbstract (sommario):
Bottom blowing plays an important role in improving the physical and chemical reaction speed in the molten bath of combined blowing converter. In this paper, physical and numerical simulations were performed to study the influence of slag properties and non-uniform bottom blowing gas supply mode on flow and mixing behavior of molten bath in a 210 t converter. Compared with the two-phase case, the average velocity in the three-phase case is lower and the flow field is asymmetric. The increase of slag thickness, viscosity and surface tension will reduce the average velocity of the molten bath and make the mixing time longer. The numerical simulation of ten cases is carried out to study the effect of partial blockage of the tuyere on the overall mixing. The results showed that the existence of the central vortex and the long horizontal flow are beneficial to promote the overall mixing, while the central collision and the vortex at the edge play the opposite role in the non-uniform mode. The smaller flow difference between the tuyeres is unfavorable to the mixing of the molten bath. Reasonable tuyere flow difference can promote the horizontal flow of the molten bath and improving the stirring force.
13
Zabarankin, Michael. "Small deformation theory for two leaky dielectric drops in a uniform electric field". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 476, n. 2233 (gennaio 2020): 20190517. http://dx.doi.org/10.1098/rspa.2019.0517.
Testo completoAbstract (sommario):
A small deformation theory for two non-identical spherical drops freely suspended in an ambient fluid and subjected to a uniform electric field is presented. The three phases are assumed to be leaky dielectric (slightly conducting) viscous incompressible fluids and the nonlinear effects of inertia and surface charge convection are neglected. The deformed shapes of the drops are linearized with respect to the electric capillary number that characterizes the balance between the electric stress and the surface tension. When the two drops are sufficiently far apart, their deformed shapes are predicted by Taylor’s small deformation theory—depending on Taylor’s discriminating function, the drops may become prolate, oblate or remain spherical. When the two drops get closer to each other, in addition to becoming prolate/oblate, they start translating and developing an egg shape. (Since there is no net charge, the centre of mass of the two drops remains stationary.) The extent of each of these ‘modes’ of deformation depends on the distance between the drops’ centres and on drop-to-ambient fluid ratios of electric conductivities, dielectric constants and viscosities. The predictions of the small deformation theory for two drops perfectly agree with the existing results of two-drop dynamics simulation based on a boundary-integral equation approach. Moreover, while previous works observed only three types of behaviour for two identical drops—the drops may either become prolate or oblate and move towards each other or become prolate and move away from each other—the small deformation theory predicts that non-identical drops may, in fact, become oblate and move away from each other when the drop-to-ambient fluid conductivity ratios are reciprocal and the drop-to-ambient fluid viscosity ratios are sufficiently large. The presented theory also readily yields an analytical insight into the interplay among different modes of drop deformation and can be used to guide the selection of the phases’ electromechanical properties for two-drop dynamics simulations.
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Bostwick, J. B. "Spreading and bistability of droplets on differentially heated substrates". Journal of Fluid Mechanics 725 (17 maggio 2013): 566–87. http://dx.doi.org/10.1017/jfm.2013.196.
Testo completoAbstract (sommario):
AbstractAn axisymmetric drop spreads on a radially heated, partially wetting solid substrate in a rotating geometry. The lubrication approximation is applied to the field equations for this thin viscous drop to yield an evolution equation that captures the dependence of viscosity, surface tension, gravity, centrifugal forces and thermocapillarity. We study the quasi-static spreading regime, whereby droplet motion is controlled by a constitutive law that relates the contact angle to the contact-line speed. Non-uniform heating of the substrate can generate both vertical and radial temperature gradients along the drop interface, which produce distinct thermocapillary forces and equivalently flows that affect the spreading process. For the non-rotating system, competition between surface chemistry (wetting) and thermocapillary flows induced by the thermal gradients gives rise to bistability in certain regions of parameter space in which the droplets converge to an equilibrium shape. The centrifugal forces that develop in a rotating geometry enlarge the bistability regions. Parameter regimes in which the droplet spreads indefinitely are identified and spreading laws are computed to compare with experimental results from the literature.
15
Stone, H. A., e L. G. Leal. "The effects of surfactants on drop deformation and breakup". Journal of Fluid Mechanics 220 (novembre 1990): 161–86. http://dx.doi.org/10.1017/s0022112090003226.
Testo completoAbstract (sommario):
The effects of surface-active agents on drop deformation and breakup in extensional flows at low Reynolds numbers are described. In this free-boundary problem, determination of the interfacial velocity requires knowledge of the distribution of surfactant, which, in turn, requires knowledge of the interfacial velocity field. We account for this explicit coupling of the unknown drop shape and the evolving surfactant distribution. An analytical result valid for nearly spherical distortions is presented first. Finite drop deformation is studied numerically using the boundary-integral method in conjunction with the time-dependent convective–diffusion equation for surfactant transport. This procedure accurately follows interfacial tension variations, produced by non-uniform surfactant distribution, on the evolving interface. The numerical method allows for an arbitrary equation of state relating interfacial tension to the local concentration of surfactant, although calculations are presented only for the common linear equation of state. Also, only the case of insoluble surfactant is studied.The analytical and numerical results indicate that at low capillary numbers the presence of surfactant causes larger deformation than would occur for a drop with a constant interfacial tension equal to the initial equilibrium value. The increased deformation occurs owing to surfactant being swept to the end of the drop where it acts to locally lower the interfacial tension, which therefore requires increased deformation to satisfy the normal stress balance. However, at larger capillary numbers and finite deformations, this convective effect competes with ‘dilution’ of the surfactant due to interfacial area increases. These two different effects of surface-active material are illustrated and discussed and their influence on the critical capillary number for breakup is presented.
16
Huo, Y., e B. Q. Li. "Surface Deformation and Convection in Electrostatically-Positioned Droplets of Immiscible Liquids Under Microgravity". Journal of Heat Transfer 128, n. 6 (30 novembre 2005): 520–29. http://dx.doi.org/10.1115/1.2188460.
Testo completoAbstract (sommario):
A numerical study is presented of the free surface deformation and Marangoni convection in immiscible droplets positioned by an electrostatic field and heated by laser beams under microgravity. The boundary element and the weighted residuals methods are applied to iteratively solve for the electric field distribution and for the unknown free surface shapes, while the Galerkin finite element method for the thermal and fluid flow field in both the transient and steady states. Results show that the inner interface demarking the two immiscible fluids in an electrically conducting droplet maintains its sphericity in microgravity. The free surface of the droplet, however, deforms into an oval shape in an electric field, owing to the pulling action of the normal component of the Maxwell stress. The thermal and fluid flow distributions are rather complex in an immiscible droplet, with conduction being the main mechanism for the thermal transport. The non-uniform temperature along the free surface induces the flow in the outer layer, whereas the competition between the interfacial surface tension gradient and the inertia force in the outer layer is responsible for the flows in the inner core and near the immiscible interface. As the droplet cools into an undercooled state, surface radiation causes a reversal of the surface temperature gradients along the free surface, which in turn reverses the surface tension driven flow in the outer layer. The flow near the interfacial region, on the other hand, is driven by a complimentary mechanism between the interfacial and the inertia forces during the time when the thermal gradient on the free surface has been reversed while that on the interface has not yet. After the completion of the interfacial thermal gradient reversal, however, the interfacial flows are largely driven by the inertia forces of the outer layer fluid.
17
PRIEDE, JĀNIS. "Oscillations of weakly viscous conducting liquid drops in a strong magnetic field". Journal of Fluid Mechanics 671 (10 febbraio 2011): 399–416. http://dx.doi.org/10.1017/s0022112010005781.
Testo completoAbstract (sommario):
We analyse small-amplitude oscillations of a weakly viscous electrically conducting liquid drop in a strong uniform DC magnetic field. An asymptotic solution is obtained showing that the magnetic field does not affect the shape eigenmodes, which remain the spherical harmonics as in the non-magnetic case. A strong magnetic field, however, constrains the liquid flow associated with the oscillations and, thus, reduces the oscillation frequencies by increasing effective inertia of the liquid. In such a field, liquid oscillates in a two-dimensional (2D) way as solid columns aligned with the field. Two types of oscillations are possible: longitudinal and transversal to the field. Such oscillations are weakly damped by a strong magnetic field – the stronger the field, the weaker the damping, except for the axisymmetric transversal and inherently 2D modes. The former are overdamped because of being incompatible with the incompressibility constraint, whereas the latter are not affected at all because of being naturally invariant along the field. Since the magnetic damping for all other modes decreases inversely with the square of the field strength, viscous damping may become important in a sufficiently strong magnetic field. The viscous damping is found analytically by a simple energy dissipation approach which is shown for the longitudinal modes to be equivalent to a much more complicated eigenvalue perturbation technique. This study provides a theoretical basis for the development of new measurement methods of surface tension, viscosity and the electrical conductivity of liquid metals using the oscillating drop technique in a strong superimposed DC magnetic field.
18
Guo, Ju, Xiao-Lei Cui, Wen-Kai Zhao, Cheng-Zhong Chi, Xiao-Qing Cao e Peng Lin. "The tensile deformation behavior of AZ31B magnesium alloy sheet under intermittent pulse current". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 236, n. 1 (29 settembre 2021): 471–80. http://dx.doi.org/10.1177/09544062211024280.
Testo completoAbstract (sommario):
In this paper, to investigate the effect of loading method of pulse current on the tensile deformation behavior of AZ31B magnesium alloy sheet, the intermittent pulse current with short-time and high-frequency was introduced in uniaxial tensile tests and the influence of duty ratio and loading time of pulse current on the deformation behavior of AZ31B magnesium alloy sheet was discussed. The strain and temperature field distributions on the specimens were measured during the intermittent pulse electrically-assisted tension (IPEAT), and the microstructure and fracture morphology under different pulse current conditions were observed. Results shows appropriate pulse current parameters can effectively improve the elongation of AZ31B magnesium alloy sheet. The strain of the sample is closely related to temperature distribution. With the deformation of the sample, the temperature on the sample increases gradually and the temperature distribution is non-uniform along the tensile direction, resulting in an inhomogeneous strain distribution of the sample. In addition, grain growth and dynamic recrystallization were observed on the AZ31B magnesium alloy sheet in different degrees under intermittent pulse current. Fracture morphology analysis shows that the number of dimples and tearing edges increased on the fracture obtained under IPEAT. The microhardness analysis shows that when intermittent pulse current is applied in the tensile test, the hardness of the sheet may change. This research provides an effective idea for the forming process of magnesium alloy sheets, which can be used to form large size thin-walled sheet components, and can significantly improve the forming quality of the sheets.
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Yan, Ying, Jiarun Li, Qiuyu Liu e Ping Zhou. "Evaporation Effect on Thickness Distribution for Spin-Coated Films on Rectangular and Circular Substrates". Coatings 11, n. 11 (29 ottobre 2021): 1322. http://dx.doi.org/10.3390/coatings11111322.
Testo completoAbstract (sommario):
Spin-coating is widely applied in the field of thin-film fabrication due to its simplicity and high film uniformity. To prepare thin films on rectangular substrates by spin-coating, the simulation and experimental methods were used to study the characteristics of the film thickness in this work. The two-phase flow simulations of spin-coating on a rectangular substrate and circular substrate were carried out with the volume of fluid (VOF) method. The simulation results showed that the airflow field and the substrate geometry had little effect on the evolution of spin-coated film thickness. However, in the experimental results, there was a significant difference in the thickness of the spin-coated film on the rectangular substrate and the circular substrate. According to further study, the solvent evaporation that was neglected in the simulation was the dominant factor of the differences. In addition, it was concluded that the non-uniform evaporation caused by the surface tension and edge accumulation in the later spin-coating stage was the main reason for the film accumulation of the windward area on the rectangular substrate. This work is useful to obtain a deeper understanding of the thin-film formation mechanism of spin-coating.
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Poddar, Antarip, Shubhadeep Mandal, Aditya Bandopadhyay e Suman Chakraborty. "Electrorheology of a dilute emulsion of surfactant-covered drops". Journal of Fluid Mechanics 881 (24 ottobre 2019): 524–50. http://dx.doi.org/10.1017/jfm.2019.745.
Testo completoAbstract (sommario):
We investigate the effects of surfactant coating on a deformable viscous drop under the combined action of shear flow and a uniform electric field. Employing a comprehensive three-dimensional approach, we analyse the non-Newtonian shearing response of the bulk emulsion in the dilute suspension regime. Our results reveal that the location of the peak surfactant accumulation on the drop surface may get shifted from the plane of shear to a plane orthogonal to it, depending on the tilt angle of the applied electric field and strength of the electrical stresses relative to their hydrodynamic counterparts. The surfactant non-uniformity creates significant alterations in the flow perturbation around the drop, triggering modulations in the bulk shear viscosity. Overall, the shear-thinning or shear-thickening behaviour of the emulsion appears to be greatly influenced by the interplay of surface charge convection and Marangoni stresses. We show that the balance between electrical and hydrodynamic stresses renders a vanishing surface tension gradient on the drop surface for some specific shear rates, rendering negligible alterations in the bulk viscosity. This critical condition largely depends on the electrical permittivity and conductivity ratios of the two fluids and orientation of the applied electric field. Also, the physical mechanisms of charge convection and surface deformation play their roles in determining this critical shear rate. As a consequence, we obtain new discriminating factors, involving electrical property ratios and the electric field configuration, which govern the same. Consequently, the surfactant-induced enhancement or attenuation of the bulk emulsion viscosity depends on the electrical conductivity and permittivity ratios. The concerned description of the drop-level flow physics and its connection to the bulk rheology of a dilute emulsion may provide a fundamental understanding of a more complex emulsion system encountered in industrial practice.
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Akhtar Shahia, Humaira, Muhammad Shahzad Shifa, Zeshan Mehboob, Muhammad Hashim e Faseeh Ur Raheem. "Characterization of Zr-Al Substituted M-Type Barium Hexaferrite Synthesized by Co-Precipitation Method". Journal of Materials and Physical Sciences 2, n. 1 (30 giugno 2021): 45–53. http://dx.doi.org/10.52131/jmps.2021.0201.00015.
Testo completoAbstract (sommario):
Structural properties of Zr-Al substituted M-type of barium hexaferrites, having compositions Ba1-xZr0.5xAl0.3Fe11.7O19, (x= 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) are studied, which were synthesized by using co-precipitation method. These prepared samples are characterized by X-RAY diffraction (XRD) to confirm hexaferrites structure. Fourier transform infrared spectroscopy is used to make tetrahedral (higher frequency band) and octahedral (lower frequency band) clusters of metal oxides in hexaferrites and confirmed the formation of hexaferrites structure. (FESEM) Field emission scanning electron microscopy was used to give micrographs to show that grains are platelet like shaped, which agrees very well with hexaferrites structure. The particle morphology is observed to be porous and non-uniform. The grain size is decreased initially, and then increased with Zirconium additions. Scherer’s formula is applied to calculate particle size, which is observed to change in the range of 18.86 nm-9.43 nm. The grains are bounded together due to interfacial surface tension forces. The optical properties are also studied by UV Vis spectrometer to find the energy band gap, in the range of 2.09ev - 5.15ev and absorbance peak having the range 237.9nm - 252.13nm. This change in energy band gap and absorbance peak is due to the change in the grain size on the zirconium substitution.
22
Manela, A., e M. Weidenfeld. "The ‘hanging flag’ problem: on the heaving motion of a thin filament in the limit of small flexural stiffness". Journal of Fluid Mechanics 829 (14 settembre 2017): 190–213. http://dx.doi.org/10.1017/jfm.2017.547.
Testo completoAbstract (sommario):
We investigate the fluid–structure interaction of a vertically hanging filament immersed in uniform incompressible high Reynolds number flow. The filament is subject to small-amplitude harmonic heaving at its upstream edge, and to a gravity-induced (‘hanging chain’) tension force. We focus on the limit of small bending rigidity to examine the differences between a highly elastic beam (where bending rigidity is small but finite) and a membrane (where bending rigidity vanishes). The problem is analysed by means of thin airfoil theory, in conjunction with a discrete vortex model for the downstream wake. Denoting the filament non-dimensional rigidity (normalized by the tension force) by $\bar{\unicode[STIX]{x1D700}}$, it is first verified that the beam deflection and associated flow field converge to the membrane solution at $\bar{\unicode[STIX]{x1D700}}\rightarrow 0$. At low actuation frequencies, the differences between the membrane and beam motions are small, and both follow a nearly rigid-body motion parallel to the upstream-edge actuation. With increasing frequency, the differences between the beam and membrane become visible at increasingly lower values of $\bar{\unicode[STIX]{x1D700}}$, and the stabilizing effect of beam flexural rigidity, resulting in reduced flapping amplitudes, is apparent. Examining the beam motion near its edge points at non-small frequencies, semi-analytic approximations for the associated time-periodic displacements are obtained. Close to the actuated end, a layer of width $\bar{\unicode[STIX]{x1D700}}^{1/2}$ is found, where the flexural rigidity term in the equation of motion is balanced by the tension term. Here, the differences between the beam and membrane deflections are attributed to the additional zero-slope condition satisfied by the former. In the vicinity of the free end, a local Taylor expansion is carried out. A balance between the bending and inertia terms results in a layer of width $\propto \bar{\unicode[STIX]{x1D700}}^{1/4}/\bar{\unicode[STIX]{x1D714}}_{h}^{1/2}$, where $\bar{\unicode[STIX]{x1D714}}_{h}$ denotes the scaled heaving frequency. The layer is therefore thicker than the upstream layer for $\bar{\unicode[STIX]{x1D714}}_{h}\approx 1$, and becomes thinner with increasing $\bar{\unicode[STIX]{x1D714}}_{h}$. Within the layer, the beam deflects linearly with the distance from the edge, in marked difference from a membrane and in accordance with the free-end conditions satisfied by the former.
23
Nicosia, Alessio, Francesco Giuseppe Carollo, Costanza Di Stefano e Vito Ferro. "New Stage–Discharge Relationship for Triangular Broad-Crested Weirs". Water 14, n. 19 (23 settembre 2022): 2993. http://dx.doi.org/10.3390/w14192993.
Testo completoAbstract (sommario):
Simple hydraulic structures, such as weirs, allow measuring flow discharge by using the upstream flow depth and a stage–discharge relationship. In this relationship, a discharge coefficient is introduced to correct all the effects neglected in the derivation (viscosity, surface tension, velocity head in the approach channel, flow turbulence, non-uniform velocity profile, and streamline curvature due to weir contraction). In this paper, the dimensional analysis and the incomplete self-similarity theory are used to investigate the outflow process of triangular broad-crested weirs, characterized by different values of the ratio between crest height p and channel width B, and to theoretically deduce a new stage–discharge relationship. A new theoretical stage–discharge relationship is suggested for the free-flow condition, and it is tested using experimental data available in the literature for the hydraulic condition p/B > 0. The obtained stage–discharge equation, characterized by low errors in discharge estimate, is useful for laboratory and field investigations. Finally, specific analysis for the triangular broad-crested weirs with p/B > 0 was developed to modify the stage–discharge relationship obtained for the case p/B = 0. This specific stage–discharge relationship allows to reduce the errors, which are generally less than ±5%, in the estimate of discharge for triangular broad-crested weirs with p/B > 0 and is also applicable for the case p/B = 0.
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Gissinger, Jacob R., Alexander Z. Zinchenko e Robert H. Davis. "Drops with insoluble surfactant squeezing through interparticle constrictions". Journal of Fluid Mechanics 878 (10 settembre 2019): 324–55. http://dx.doi.org/10.1017/jfm.2019.678.
Testo completoAbstract (sommario):
The interfacial behaviour of surfactant-laden drops squeezing through tight constrictions in a uniform far-field flow is modelled with respect to capillary number, drop-to-medium viscosity ratio and surfactant contamination. The surfactant is treated as insoluble and non-diffusive, and drop surface tension is related to surfactant concentration by a linear equation of state. The constriction is formed by three solid spheres held rigidly in space. A characteristic aspect of this confined and contaminated multiphase system is the rapid development of steep surfactant-concentration gradients during the onset of drop squeezing. The interplay between two physical effects of surfactant, namely the greater interface deformability due to decreased surface tension and interface immobilization due to Marangoni stresses, results in particularly rich drop-squeezing dynamics. A three-dimensional boundary-integral algorithm is used to describe drop hydrodynamics, and accurate treatment of close squeezing and trapped states is enabled by advanced singularity subtraction techniques. Surfactant transport and hydrodynamics are coupled via the surface convection equation (or convection–diffusion equation, if artificial diffusion is included), the interfacial stress balance and a solid-particle contribution based on the Hebeker representation. For extreme conditions, such as drop-to-medium viscosity ratios significantly less than unity, it is found that upwind-biased methods are the only stable approaches for modelling surfactant transport. Two distinct schemes, upwind finite volume and flow-biased least squares, are found to provide results in close agreement, indicating negligible numerical diffusion. Surfactant transport is enhanced by low drop-to-medium viscosity ratios, at which extremely sharp concentration gradients form during various stages of the squeezing process. The presence of surfactant, even at low degrees of contamination, significantly decreases the critical capillary number for droplet trapping, due to the accumulation of surfactant at the downwind pole of the drop and its subsequent elongation. Increasing the degree of contamination significantly affects surface mobility and further decreases the critical capillary number as well as drop squeezing times, up to a threshold above which the addition of surfactant negligibly affects squeezing dynamics.
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GIANNAKIS, D., R. ROSNER e P. F. FISCHER. "Instabilities in free-surface Hartmann flow at low magnetic Prandtl numbers". Journal of Fluid Mechanics 636 (25 settembre 2009): 217–77. http://dx.doi.org/10.1017/s0022112009007824.
Testo completoAbstract (sommario):
We study the linear stability of the flow of a viscous electrically conducting capillary fluid on a planar fixed plate in the presence of gravity and a uniform magnetic field, assuming that the plate is either a perfect electrical insulator or a perfect conductor. We first confirm that the Squire transformation for magnetohydrodynamics is compatible with the stress and insulating boundary conditions at the free surface but argue that unless the flow is driven at fixed Galilei and capillary numbers, respectively parameterizing gravity and surface tension, the critical mode is not necessarily two-dimensional. We then investigate numerically how a flow-normal magnetic field and the associated Hartmann steady state affect the soft and hard instability modes of free-surface flow, working in the low-magnetic-Prandtl-number regime of conducting laboratory fluids (Pm ≤ 10−4). Because it is a critical-layer instability (moderately modified by the presence of the free surface), the hard mode exhibits similar behaviour as the even unstable mode in channel Hartmann flow, in terms of both the weak influence of Pm on its neutral-stability curve and the dependence of its critical Reynolds number Rec on the Hartmann number Ha. In contrast, the structure of the soft mode's growth-rate contours in the (Re, α) plane, where α is the wavenumber, differs markedly between problems with small, but non-zero, Pm and their counterparts in the inductionless limit, Pm ↘ 0. As derived from large-wavelength approximations and confirmed numerically, the soft mode's critical Reynolds number grows exponentially with Ha in inductionless problems. However, when Pm is non-zero the Lorentz force originating from the steady-state current leads to a modification of Rec(Ha) to either a sub-linearly increasing or a decreasing function of Ha, respectively for problems with insulating or perfectly conducting walls. In insulating-wall problems we also observe pairs of counter-propagating Alfvén waves, the upstream-propagating wave undergoing an instability driven by energy transferred from the steady-state shear to both of the velocity and magnetic degrees of freedom. Movies are available with the online version of the paper.
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Sevilla, Alejandro. "The effect of viscous relaxation on the spatiotemporal stability of capillary jets". Journal of Fluid Mechanics 684 (2 settembre 2011): 204–26. http://dx.doi.org/10.1017/jfm.2011.297.
Testo completoAbstract (sommario):
AbstractThe linear spatiotemporal stability properties of axisymmetric laminar capillary jets with fully developed initial velocity profiles are studied for large values of both the Reynolds number, $\mathit{Re}= Q/ (\lrm{\pi} a\nu )$, and the Froude number, $\mathit{Fr}= {Q}^{2} / ({\lrm{\pi} }^{2} g{a}^{5} )$, where $a$ is the injector radius, $Q$ the volume flow rate, $\nu $ the kinematic viscosity and $g$ the gravitational acceleration. The downstream development of the basic flow and its stability are addressed with an approximate formulation that takes advantage of the jet slenderness. The base flow is seen to depend on two parameters, namely a Stokes number, $G= \mathit{Re}/ \mathit{Fr}$, and a Weber number, $\mathit{We}= \rho {Q}^{2} / ({\lrm{\pi} }^{2} \sigma {a}^{3} )$, where $\sigma $ is the surface tension coefficient, while its linear stability depends also on the Reynolds number. When non-parallel terms are retained in the local stability problem, the analysis predicts a critical value of the Weber number, ${\mathit{We}}_{c} (G, \mathit{Re})$, below which a pocket of local absolute instability exists within the near field of the jet. The function ${\mathit{We}}_{c} (\mathit{Re})$ is computed for the buoyancy-free jet, showing marked differences with the results previously obtained with uniform velocity profiles. It is seen that, in accounting for gravity effects, it is more convenient to express the parametric dependence of the critical Weber number with use made of the Morton and Bond numbers, $\mathit{Mo}= {\nu }^{4} {\rho }^{3} g/ {\sigma }^{3} $ and $\mathit{Bo}= \rho g{a}^{2} / \sigma $, as replacements for $G$ and $\mathit{Re}$. This alternative formulation is advantageous to describe jets of a given liquid for a known value of $g$, in that the resulting Morton number becomes constant, thereby leaving $\mathit{Bo}$ as the only relevant parameter. The computed function ${\mathit{We}}_{c} (\mathit{Bo})$ for a water jet under Earth gravity is shown to be consistent with the experimental results of Clanet and Lasheras for the transition from jetting to dripping of water jets discharging into air from long injection needles, which cannot be properly described with a uniform velocity profile assumed at the jet exit.
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Seifarth, Volker, Joachim O. Grosse, Matthias Gossmann, Heinz Peter Janke, Patrick Arndt, Sabine Koch, Matthias Epple, Gerhard M. Artmann e Aysegül Temiz Artmann. "Mechanical induction of bi-directional orientation of primary porcine bladder smooth muscle cells in tubular fibrin-poly(vinylidene fluoride) scaffolds for ureteral and urethral repair using cyclic and focal balloon catheter stimulation". Journal of Biomaterials Applications 32, n. 3 (27 luglio 2017): 321–30. http://dx.doi.org/10.1177/0885328217723178.
Testo completoAbstract (sommario):
To restore damaged organ function or to investigate organ mechanisms, it is necessary to prepare replicates that follow the biological role model as faithfully as possible. The interdisciplinary field of tissue engineering has great potential in regenerative medicine and might overcome negative side effects in the replacement of damaged organs. In particular, tubular organ structures of the genitourinary tract, such as the ureter and urethra, are challenging because of their complexity and special milieu that gives rise to incrustation, inflammation and stricture formation. Tubular biohybrids were prepared from primary porcine smooth muscle cells embedded in a fibrin gel with a stabilising poly(vinylidene fluoride) mesh. A mechanotransduction was performed automatically with a balloon kyphoplasty catheter. Diffusion of urea and creatinine, as well as the bursting pressure, were measured. Light and electron microscopy were used to visualise cellular distribution and orientation. Histological evaluation revealed a uniform cellular distribution in the fibrin gel. Mechanical stimulation with a stretch of 20% leads to a circumferential orientation of smooth muscle cells inside the matrix and a longitudinal alignment on the outer surface of the tubular structure. Urea and creatinine permeability and bursting pressure showed a non-statistically significant trend towards stimulated tissue constructs. In this proof of concept study, an innovative technique of intraluminal pressure for mechanical stimulation of tubular biohybrids prepared from autologous cells and a composite material induce bi-directional orientation of smooth muscle cells by locally and cyclically applied mechanical tension. Such geometrically driven patterns of cell growth within a scaffold may represent a key stage in the future tissue engineering of implantable ureter replacements that will allow the active transportation of urine from the renal pelvis into the bladder.
28
Pererva, Evgeny. "Injury Rate of the Bronze Age Population from the Lower Volga Area". Vestnik Volgogradskogo gosudarstvennogo universiteta. Serija 4. Istorija. Regionovedenie. Mezhdunarodnye otnoshenija, n. 4 (ottobre 2020): 236–55. http://dx.doi.org/10.15688/jvolsu4.2020.4.16.
Testo completoAbstract (sommario):
Introduction. The research objective is to determine and analyze data on traumatic phenomena found in the bones of the Bronze Age population originating from the burial sites of the Lower Volga area. Methods. The identification of traumatic injuries in anthropological materials was based on the works and recommendations in the field of special traumatology and pathology used in forensic medicine and bioarchaeological reconstructions. Statistical analysis was carried out using one-dimensional methods and nonparametric Mann-Whitney and Kruskal-Wallis criteria. Analysis. The study of paleoanthropological materials of the Early Bronze Age shows that injuries are found only on skulls. The total injuries of the adult population in the group are at the level of 15.2%. Of the 5 injuries on the bones of the Early Bronze Age, 1 belongs to a woman and 4 – to men. Severe injuries are discovered in adult individuals. General injuries are not numerous and reach 24.8%. In the series of the Late Bronze Age, injuries on the bone remains of children are also not detected. The frequency of occurrence of traumatic objects on anthropological materials of II millennium BC is insignificant, only 18 cases, which is 16.1% of the total number of adult individuals. Results. In the studied series, sex dimorphism and differences in the nature of distribution of injuries between groups of different ages are not statistically revealed, which indicates similar social roles of the male and female population in the Bronze Age. No injuries are detected in children. The frequency of perimortem injuries is extremely low. Non-lethal (uniform, with traces of healing) injuries on the skull bones and postcranial skeleton dominate in the series, which indicates a similar level of technological development and medical knowledge in the Bronze Age population. Injuries of the Bronze Age of the Lower Volga region can be described as every day or civilian trauma due to the development of labor production or social tension in the groups.
29
Toyoizumi, R., e S. Takeuchi. "The behavior of chick gastrula mesodermal cells under the unidirectional tractive force parallel to the substrata". Journal of Cell Science 108, n. 2 (1 febbraio 1995): 557–67. http://dx.doi.org/10.1242/jcs.108.2.557.
Testo completoAbstract (sommario):
Advancement of leading lamellae of a migratory cell inevitably causes a strain inside the cell body. We investigated the effect of the tension arisen inside a mesodermal cell on its behavior by pulling the cell body unidirectionally along the substratum. Chick gastrula mesodermal cells, known as highly migratory, were dissociated into single cells in sodium citrate buffer, conjugated with paramagnetic beads activated by tosyl-residue (4.5 microns in diameter) and seeded onto coverglasses coated with fibronectin. After the cells spread on the substratum and protruded cellular processes in all directions, they were exposed to a non-uniform magnetic field by a magnet. Thus the cells bearing the beads were pulled with a force in the order of 10(−10) N. The behavior of such cells was recorded with a time-lapse video taperecorder and assessed quantitatively. Shortly after the magnetic force was applied, the beads stuck to the cells were aligned in tandem along the line of magnetic force at the site for the magnet. Subsequently, they frequently came to extend their leading lamella precisely counter to the traction on the line of the beads. Observation with scanning electron microscope revealed that a large part of the beads attached to the cells were wrapped in the cell membrane. In this condition, the cells were stretched locally between the attachment site of the beads and adhesion plaques beneath the leading edge, which was formed in a direction away from the traction. It was proved statistically that such cells tended to locomote away from the magnet at the 0.1% significance level with Hotelling's T2-test. In contrast, the mesodermal cells free of the artificial traction in three kinds of control experiments did not show such a preference in the direction of locomotion. These results proved that migratory cells tended to move in the direction away from the tractive force parallel to the substratum, suggesting that advancement of a leading lamella is accelerated when it is stretched along the direction of projection by a mechanical force of sufficient strength. Implication of this finding to the mechanism of cell locomotion will be discussed.
30
Taniguchi, Akito, Takatoshi Maeyama, Makoto Uchida e Yoshihisa Kaneko. "Macroscopic and Microscopic Non-Uniform Deformations of Polycrystalline Pure Copper during Uniaxial Tensile Test with High Stress Gradient". Key Engineering Materials 794 (febbraio 2019): 246–52. http://dx.doi.org/10.4028/www.scientific.net/kem.794.246.
Testo completoAbstract (sommario):
Metallic materials usually have microscopically heterogeneous structures, such as polycrystalline structures, affecting macroscopic mechanical characteristics. Both macroscopic and microscopic non-uniform deformations of polycrystalline pure copper under a moderate stress gradient were investigated. In this study, macroscopic and microscopic non-uniform deformations under higher stress gradients are investigated. Uniaxial tensile tests using three-curve specimens with different curvatures and grain sizes were performed. In order to evaluate the heterogeneous strain field in the specimen surface, the development of the displacement field was measured using the digital image correlation method (DIC). The stress field was evaluated by coupling the DIC and finite-element methods. In smaller-grain specimens, a strong strain concentration was generated in the minimum cross-section area. Although a strong strain concentration was also confirmed in a larger-grain specimen, the strain field depended not only on the specimen shape but also on the microscopic heterogeneity. This microstructure-driven non-uniform deformation was also observed in the specimen with a larger curvature radius. These results indicated that the macroscopic non-uniform deformation should be estimated by the material parameter related to the microscopic heterogeneity.
31
AFKHAMI, S., A. J. TYLER, Y. RENARDY, M. RENARDY, T. G. St. PIERRE, R. C. WOODWARD e J. S. RIFFLE. "Deformation of a hydrophobic ferrofluid droplet suspended in a viscous medium under uniform magnetic fields". Journal of Fluid Mechanics 663 (8 settembre 2010): 358–84. http://dx.doi.org/10.1017/s0022112010003551.
Testo completoAbstract (sommario):
The effect of applied magnetic fields on the deformation of a biocompatible hydrophobic ferrofluid drop suspended in a viscous medium is investigated numerically and compared with experimental data. A numerical formulation for the time-dependent simulation of magnetohydrodynamics of two immiscible non-conducting fluids is used with a volume-of-fluid scheme for fully deformable interfaces. Analytical formulae for ellipsoidal drops and near-spheroidal drops are reviewed and developed for code validation. At low magnetic fields, both the experimental and numerical results follow the asymptotic small deformation theory. The value of interfacial tension is deduced from an optimal fit of a numerically simulated shape with the experimentally obtained drop shape, and appears to be a constant for low applied magnetic fields. At high magnetic fields, on the other hand, experimental measurements deviate from numerical results if a constant interfacial tension is implemented. The difference can be represented as a dependence of apparent interfacial tension on the magnetic field. This idea is investigated computationally by varying the interfacial tension as a function of the applied magnetic field and by comparing the drop shapes with experimental data until a perfect match is found. This estimation method provides a consistent correlation for the variation in interfacial tension at high magnetic fields. A conclusion section provides a discussion of physical effects which may influence the microstructure and contribute to the reported observations.
32
van Rooyen, Melody, e Thorsten Hermann Becker. "High-temperature tensile property measurements using digital image correlation over a non-uniform temperature field". Journal of Strain Analysis for Engineering Design 53, n. 3 (23 gennaio 2018): 117–29. http://dx.doi.org/10.1177/0309324717752029.
Testo completo
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Wang, Xingxing, Zhenchao Qi, Mu Lu e Haicheng Pan. "A Non-Uniform Interference-Fit Size Investigation of CFRP/Al Alloys by Riveting Mold Design". Processes 11, n. 3 (21 marzo 2023): 962. http://dx.doi.org/10.3390/pr11030962.
Testo completoAbstract (sommario):
The interference-fit size has a significant effect on the riveted lap joints of CFRP/Al alloy laminates. The requirements for the interference-fit size are different because of the strengthening of heterogeneous materials. However, in the riveting process of CFRP/Al alloys, the heterogeneous laminates lead to poor structural strength because of the different interference-fit size requirements. Therefore, differently assembled riveting molds are designed to acquire a novel interference-fit size, and the tensile test is adopted to evaluate their tensile properties. In addition, the fracture failure of CFRP/Al alloy laminate riveted lap joints is observed with an ultra-depth-of-field microscope. Finally, the best assembly type is identified as the trapezoid riveting mold combined with an arc riveting die, and the sidewall intersection angle of the trapezoid riveting mold is 66°, which could achieve a suitable interference-fit size and a better mechanical performance.
34
Collini, Luca, e Alessandra Bonardi. "A micromechanical model of the evolution of stress and strain fields in ultrafine-grained metal structures under tension". Journal of Strain Analysis for Engineering Design 48, n. 2 (17 gennaio 2013): 91–102. http://dx.doi.org/10.1177/0309324712466550.
Testo completoAbstract (sommario):
In this study, the authors present a micromechanical finite element modelling approach to the analysis of a set of ultrafine-grained polycrystalline copper structures. The models take into account both realistic grain distribution and the number of refinement passes of the microstructure. The grain size effect is successfully predicted, with non-uniform deformation and shear localization reproduced during global plastic flow in agreement with experimental observations. The models provide a useful tool with which to interpret damage and fracture mechanisms occurring in ultrafine-grained structures.
35
Kumar, T. S., B. Rushi Kumar, Oluwole Daniel Makinde e A. G. Vijaya Kumar. "Magneto-Convective Heat Transfer in Micropolar Nanofluid over a Stretching Sheet with Non-Uniform Heat Source/Sink". Defect and Diffusion Forum 387 (settembre 2018): 78–90. http://dx.doi.org/10.4028/www.scientific.net/ddf.387.78.
Testo completoAbstract (sommario):
The objective of investigation is to study the hydro-magnetic boundary layer micropolar nanofluid steady flow past a stretching sheet with a non-uniform heat suction/sink by taking into account of nanofluids containing Cu– water, TiO2–water, Al2O3–water, and Ag–water. As per the geometry of the flow configuration the conservation laws are transformed into a non-linear model. Using the appropriate analoguestransformations, the resultant equations are employing order approach along with shooting technique to derive closed form solutions for momentum, angular velocity, and temperature fields as well as couple stress, skin friction, local Nusselt number, and then to analyse and physical insight of various flow parameters on these fields. Also the numerical computations are performed and plotted through graphs and tables. It is found that the effect of volume fraction of nanoparticles on the fluid velocity, it decreases due to the absence of surface tension forces and hence, the momentum boundary layer thickness reduced. Furthermore, comparisons with published results are in very good agreement. Nomenclature
36
He, Zhubin, Zhibiao Wang, Yanli Lin e Xiaobo Fan. "Hot Deformation Behavior of a 2024 Aluminum Alloy Sheet and its Modeling by Fields-Backofen Model Considering Strain Rate Evolution". Metals 9, n. 2 (18 febbraio 2019): 243. http://dx.doi.org/10.3390/met9020243.
Testo completoAbstract (sommario):
The deformation behavior of a 2024 aluminum alloy sheet at elevated temperatures was studied by uniaxial hot tensile tests over the nominal initial strain rate range of 0.001–0.1 s−1 and temperature range of 375–450 °C. In order to analyze the deformation behavior with higher accuracy, a digital image correlation (DIC) system was applied to determine the strain distribution during hot tensile tests. Local stress-strain curves for different local points on the specimens were calculated. The strain rate evolution of each point during the tensile tests was investigated under different deformation conditions. Then, an improved Fields–Backofen (FB) model, taking into account the local strain rate evolution instead of the fixed strain rate, was proposed to describe the constitutive behaviors. It has been found that obvious non-uniform strain distribution occurred when the true strain was larger than 0.3 during hot tensile tests. The strain rate distribution during deformation was also non-uniform. It showed increasing, steady, and decreasing variation tendencies for different points with the increasing of strain, which led to the local flow stress being different at different local points. The flow stresses predicted by the improved FB model showed good agreement with experimental results when the strain rate evolutions of local points during tensile tests were considered. The prediction accuracy was higher than that of traditional FB models.
37
Guo, Lei, e GuoHua Nie. "Elastic fields induced by non-elastic eigenstrains in a plane elliptical inhomogeneity existing in orthotropic media under uniform tension at infinity". Science in China Series G: Physics, Mechanics and Astronomy 51, n. 2 (febbraio 2008): 206–18. http://dx.doi.org/10.1007/s11433-008-0015-8.
Testo completo
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Bakhtiari, Reza, Bashir S. Shariat, Fakhrodin Motazedian, Zhigang Wu, Junsong Zhang, Hong Yang e Yinong Liu. "Complex transformation field created by geometrical gradient design of NiTi shape memory alloy". Functional Materials Letters 10, n. 01 (febbraio 2017): 1740011. http://dx.doi.org/10.1142/s1793604717400112.
Testo completoAbstract (sommario):
Owing to geometrical non-uniformity, geometrically graded shape memory alloy (SMA) structures by design have the ability to exhibit different and novel thermal and mechanical behaviors compared to geometrically uniform conventional SMAs. This paper reports a study of the pseudoelastic behavior of geometrically graded NiTi plates. This geometrical gradient creates partial stress gradient over stress-induced martensitic transformation, providing enlarged stress controlling interval for shape memory actuation. Finite element modeling framework has been established to predict the deformation behavior of such structures in tensile loading cycles, which was validated by experiments. The modeling results show that the transformation mostly propagates along the gradient direction as the loading level increases.
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Tyas, A., A. V. Pichugin e M. Gilbert. "Optimum structure to carry a uniform load between pinned supports: exact analytical solution". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, n. 2128 (20 ottobre 2010): 1101–20. http://dx.doi.org/10.1098/rspa.2010.0376.
Testo completoAbstract (sommario):
Recent numerical evidence indicates that a parabolic funicular is not necessarily the optimal structural form to carry a uniform load between pinned supports. When the constituent material is capable of resisting equal limiting tensile and compressive stresses, a more efficient structure can be identified, comprising a central parabolic section and networks of truss bars emerging from the supports. In the current article, a precise geometry for this latter structure is identified, avoiding the inconsistencies that render the parabolic form non-optimal. Explicit analytical expressions for the geometry, stress and virtual-displacement fields within and above the structure are presented. Furthermore, a suitable displacement field below the structure is computed numerically and shown to satisfy the Michell–Hemp optimality criteria, hence formally establishing the global optimality of this new structural form.
40
Matveenko, Valerii, Natalia Kosheleva, Grigorii Serovaev e Andrey Fedorov. "Measurement of Gradient Strain Fields with Fiber-Optic Sensors". Sensors 23, n. 1 (30 dicembre 2022): 410. http://dx.doi.org/10.3390/s23010410.
Testo completoAbstract (sommario):
The results of measuring gradient strain fields by embedded or mounted point fiber-optic sensors based on Bragg gratings and distributed fiber-optic sensors based on Rayleigh scattering are discussed. Along with the experiment, the results of numerical modeling of strain measurement errors associated with the assumption of uniaxial stress state in the area of the embedded Bragg grating and measurement errors by distributed fiber-optic sensors associated with gage length are presented. Experimental results are presented for 3D printed samples and samples made of polymer composite material. The geometry of the samples was chosen based on the results of numerical simulations, and provides different variants of non-uniform strain distribution under uniaxial tension, including the variant in which the derivative of the strain distribution function changes its sign. A good agreement of numerical results and experimental data obtained by distributed and point fiber-optic sensors in areas where the derivative of the strain distribution function keeps a sign and an increase in the error of strain measurement results by distributed fiber-optic sensors in areas where this derivative changes sign are demonstrated.
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Takahashi, Shun, Sanichiro Yoshida, Tomohiro Sasaki e Tyler Hughes. "Dynamic ESPI Evaluation of Deformation and Fracture Mechanism of 7075 Aluminum Alloy". Materials 14, n. 6 (20 marzo 2021): 1530. http://dx.doi.org/10.3390/ma14061530.
Testo completoAbstract (sommario):
The deformation and fracture mechanism in 7075 aluminum alloy is discussed based on a field theoretical approach. A pair of peak-aged and overaged plate specimens are prepared under the respective precipitation conditions, and their plastic deformation behaviors are visualized with two-dimensional electronic speckle pattern interferometry (ESPI). The in-plane velocity field caused by monotonic tensile loading is monitored continuously via the contour analysis method of ESPI. In the plastic regime, the peak-aged specimen exhibits a macroscopically uniform deformation behavior, while the annealed specimen exhibits non-uniform deformation characterized by a localized shear band. The occurrence of the shear band is explained by the transition of the material’s elastic resistive mechanism from the longitudinal force dominant to shear force dominant mode. The shear force is interpreted as the frictional force that drives mobile dislocations along the shear band. The dynamic behavior of the shear band is explained as representing the motion of a solitary wave. The observed decrease in the solitary wave’s velocity is accounted for by the change in the acoustic impedance with the advancement of plastic deformation.
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Kerchman, Vladamir, e Cheng Shaw. "Experimental Study and Finite Element Simulation of Heat Build-Up in Rubber Compounds with Application to Fracture". Rubber Chemistry and Technology 76, n. 2 (1 maggio 2003): 386–405. http://dx.doi.org/10.5254/1.3547750.
Testo completoAbstract (sommario):
Abstract IR thermography was used to measure surface temperature profiles of cylindrical rubber specimens during cyclic compression. A linearized constitutive approach and finite element analysis were used to evaluate heat generation and associated transient temperature fields. Modeled temperatures compared well with the IR measurements. This led to extended simulation efforts on lab fracture samples. IR thermography was used to measure temperature of filled NR and filled SBR specimens during tensile fatigue cut growth tests. Temperature gradients are expected to relate to kinetics of rubber fracture and identify regions within the sample that are undergoing accelerated damage. The following cut growth issues were addressed: 1) crack propagation direction in a non-uniform stress field; 2) crack propagation direction as a function of the angle of initial cuts; 3) initiation of crack branching; and 4) catastrophic failure. The nonlinear coupled mechanical and thermal FEA was used to evaluate the energy dissipation in the non-homogeneous cyclic deformation of cracked samples. Modeled and measured surface temperatures are in good agreement. Accounting for heat build-up ahead of an advancing crack can improve numerical models that quantify fatigue cut growth behavior in rubber compounds.
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Feng, Guangjie, Hu Wang, Yifeng Wang, Dean Deng e Jian Zhang. "Numerical Simulation of Residual Stress and Deformation in Wire Arc Additive Manufacturing". Crystals 12, n. 6 (7 giugno 2022): 803. http://dx.doi.org/10.3390/cryst12060803.
Testo completoAbstract (sommario):
In this paper, multi-layer and multi-pass arc additive manufacturing experiments were carried out on the Q345 substrate using Y309L welding wire. Based on MSC. Marc software, a thermal-elastic-plastic finite element method was developed to numerically simulate the temperature field, stress field, and deformation during the additive manufacturing process. The effects of the substrate thickness and interpass temperature on the temperature field, stress field, and deformation were discussed. The results indicated that the deposition materials at different positions experienced different thermal cycles, which might lead to the non-uniform microstructure and mechanical properties within the workpiece. The interpass temperature and the thickness of the substrate influenced the residual stress distribution in the additive manufactured structure. A low interpass temperature and thin substrate was able to effectively reduce the tensile residual stress. The thick substrate resulted in a small angular deformation of the substrate during the additive manufacturing process.
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Sankar, M., e M. Venkatachalappa. "Numerical Investigation of Combined Buoyancy and Surface Tension Driven Convection in an Axi-Symmetric Cylindrical Annulus". Nonlinear Analysis: Modelling and Control 12, n. 4 (25 ottobre 2007): 541–52. http://dx.doi.org/10.15388/na.2007.12.4.14685.
Testo completoAbstract (sommario):
A numerical study is conducted to understand the effect of surface tension on buoyancy driven convection in a vertical cylindrical annular cavity filled with a low Prandtl number fluid. The inner and outer cylinders are maintained at different uniform temperatures and the horizontal top and bottom walls are thermally insulated. The upper free surface is assumed to remain flat and non-deformable. A finite difference scheme consisting of the Alternating Direction Implicit method and the Successive Line Over Relaxation method is used to solve the vorticity stream function formulation of the problem. Detailed numerical results of heat transfer rate, temperature and velocity fields have been presented for a wide range of physical parameters of the problem. The flow pattern and temperature distribution in the annular cavity are presented by means of contour plots of streamlines and isotherms. The rate of heat transfer is estimated by evaluating the average Nusselt number. Further, the present numerical results are compared with the existing results and are found to be in good agreement.
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Van Puymbroeck, Evy, Wim Nagy, Ken Schotte, Zain Ul-Abdin e Hans De Backer. "Determination of Residual Welding Stresses in a Steel Bridge Component by Finite Element Modeling of the Incremental Hole-Drilling Method". Applied Sciences 9, n. 3 (5 febbraio 2019): 536. http://dx.doi.org/10.3390/app9030536.
Testo completoAbstract (sommario):
For welded bridge components, the knowledge of residual stresses induced by welding is essential to determine their effect on the fatigue life behavior resulting in optimal fatigue design and a better knowledge about the fatigue strength of these welded connections. The residual stresses of a welded component in an orthotropic steel bridge deck are determined with the incremental hole-drilling method. This method is specified by the American Society for Testing and Materials ASTM E837-13a and it can be used only when the material behavior is linear-elastic. However in the region of the bored hole, there are relaxed plastic strains present that can lead to significant error of the measured stresses. The hole-drilling procedure is simulated with three-dimensional finite element modeling including a simplistic model of plasticity. The effect of plasticity on uniform in-depth residual stresses is determined and it is concluded that residual stresses obtained under the assumption of linear-elastic material behavior are an overestimation. Including plasticity for non-uniform in-depth residual stress fields results in larger tensile and smaller compressive residual stresses. Larger tensile residual stresses cause premature fatigue failure. Therefore, it is important to take these larger tensile residual stresses into account for the fatigue design of a welded component.
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Venter, A. M., M. W. van der Watt, Robert C. Wimpory, Rainer Schneider, P. J. McGrath e M. Topic. "Neutron Strain Investigations of Laser Bent Samples". Materials Science Forum 571-572 (marzo 2008): 63–68. http://dx.doi.org/10.4028/www.scientific.net/msf.571-572.63.
Testo completoAbstract (sommario):
Bending of metal plates with high-energy laser beams presents a flexible materials forming technique where bending results from the establishment of a steep temperature gradient through the material thickness. This inevitably leads to non-uniform thermal expansion/contraction and subsequently residual stresses. Non destructive residual strain mapping with neutron diffraction through the 8mm thickness of a series WA 300 grade structural steel plate samples, focused on the region straddling the centerline of the heating bead location, shows the presence of large residual stress fields. Directly below the laser track the longitudinal strains are tensile and dominant, normal strains compressive and transverse strains slightly tensile. The magnitudes of the strains decrease outside the width of the laser beam footprint. The first laser pass induces throughthickness strains close to yield, whereafter their magnitudes decrease with increased number of laser beam passes. A comprehensive mapping of the longitudinal stresses as function of the number of laser passes is given.
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Castillo, Acelle Pearl T., Bianca Rae Pasela, Kyrien Jewel Janeena L. Tabucan e Ruth R. Aquino. "Analysis on the Influence of O-MMT in the Properties and Bacterial Count of PVDF Nanocomposite Membrane". Materials Science Forum 1015 (novembre 2020): 97–102. http://dx.doi.org/10.4028/www.scientific.net/msf.1015.97.
Testo completoAbstract (sommario):
Polymer nanocomposites have become an exciting field of research and have attracted interest in both academia and industry. In this study, the addition of Organo-Montmorillonite (O-MMT),an ideal polymer filler due to its non-toxicity, large availability, well-known intercalation/exfoliation chemistry, and reactivity in Poly (vinylidene fluoride) (PVDF) membrane, a widely used polymer in separation fields owing to its remarkable mechanical, thermal, and chemical properties produced via non-solvent induced phased separation is observed. Presence of both polymers were confirmed using Fourier transform infrared spectroscopy (FTIR). These membranes were subjected to Scanning Electron Microscopy (SEM) which revealed addition of the filler reduced the porosity and further increasing O-MMT’s concentration led to a relatively smoother membrane. Influence of O-MMT in the porosity made no uniform trend however reduction in pore sizes was observed. Membranes were able to elongate at an average of 80% of its original length however tensile strength of the membranes all showed brittleness behavior of the films. Sterility Bacterial count also revealed that there are no infiltration colonies in the membranes. Analysis of the study further showed other factors that needs to be accounted since they were observed to highly affect the structure and properties of the membranes.
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He, Chenglong, Yingkang Yao, Yaqing Liu, Xiang Mao e Qihui Chen. "Dynamic Mechanical Characteristics of Horseshoe Tunnel Subjected to Blasting and Confining Pressure". Applied Sciences 13, n. 15 (2 agosto 2023): 8911. http://dx.doi.org/10.3390/app13158911.
Testo completoAbstract (sommario):
The blast loading direction and in-situ stress field have an effect on the destruction process in the surrounding rock around the tunnel. Five blasting directions are considered in the experiment and simulation. The static stress distribution by confining pressure and the superposition stress waves process are discussed by simulation in LS-DYNA. Results indicated that the hoop stress accelerates the radial cracks growing, and the damage around the hole is not influenced by the blasting direction. The stress wave superposition and failure process along the tunnel are affected by the blasting direction. The distribution of static prestress is symmetrical under the uniform confining pressure (k = 1) and decelerates the crack extension by confining pressure. Under the non-uniform confining pressure loading (k ≠ 1), the tensile prestress is formed with a k increase and accelerates the horizontal crack propagation after blast loading. The concentrated stress is serious in the partial region along the tunnel, especially in the vault position under the static-dynamic coupling loading. Notably, the horizontal destruction area between the hole and the tunnel further expands when k increases.
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Dall’Asta, E., V. Ghizzardi, R. Brighenti, E. Romeo, R. Roncella e A. Spagnoli. "New experimental techniques for fracture testing of highly deformable materials". Frattura ed Integrità Strutturale 10, n. 35 (29 dicembre 2015): 161–71. http://dx.doi.org/10.3221/igf-esis.35.19.
Testo completoAbstract (sommario):
A new experimental method for measuring strain fields in highly deformable materials has been developed. This technique is based on an in-house developed Digital Image Correlation (DIC) system capable of accurately capturing localized or non-uniform strain distributions. Thanks to the implemented algorithm based on a Semi-Global Matching (SGM) approach, it is possible to constraint the regularity of the displacement field in order to significantly improve the reliability of the evaluated strains, especially in highly deformable materials. Being originally introduced for Digital Surface Modelling from stereo pairs, SGM is conceived for performing a one-dimensional search of displacements between images, but here a novel implementation for 2D displacement solution space is introduced. SGM approach is compared with the previously in-house developed implementation based on a local Least Squares Matching (LSM) approach. A comparison with the open source code Ncorr and with some FEM results is also presented. The investigation using the present DIC method focuses on 2D full-field strain maps of plain and notched specimens under tensile loading made of two different highly deformable materials: hot mix asphalt and thermoplastic composites for 3D-printing applications. In the latter specimens, an elliptical hole is introduced to assess the potentiality of the method in experimentally capturing high strain gradients in mixed-mode fracture situations.
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Veselý, Jakub, e Vít Šmilauer. "Hygro-mechanical model for concrete pavement with long-term drying analysis". Acta Polytechnica CTU Proceedings 40 (24 luglio 2023): 104–10. http://dx.doi.org/10.14311/app.2023.40.0104.
Testo completoAbstract (sommario):
Concrete pavements are subjected to the combination of moisture transport, heat transport and traffic loading. A hygro-mechanical 3D finite element model was created in OOFEM software in order to analyse the stress field and deformed shape from a long-term non-uniform drying. The model uses a staggered approach, solving moisture transfer weakly coupled with MPS viscoelastic model for ageing concrete creep and shrinkage. Moisture transport and mechanical sub-models are calibrated with lab experiments, long-term monitoring on D1 highway and data from 40 year old highway pavement. The slab geometry is 3.5×5.0×0.29 m, resting on elastic Winkler-Pasternak foundation. The validation covers autogenous and drying strain on the slab. The models predict drying-induced tensile stress up to 3.3 MPa, inducing additional loading on the slab, uncaptured by current design methods.