Journal articles: 'Viscoelasticity. Shear (Mechanics)'

1

Azaiez, J., and G. M. Homsy. "Linear stability of free shear flow of viscoelastic liquids." Journal of Fluid Mechanics 268 (June 10, 1994): 37–69. http://dx.doi.org/10.1017/s0022112094001254.

Full text

Abstract:

The effects of viscoelasticity on the hydrodynamic stability of plane free shear flow are investigated through a linear stability analysis. Three different rheological models have been examined: the Oldroyd-B, corotational Jeffreys, and Giesekus models. We are especially interested in possible effects of viscoelasticity on the inviscid modes associated with inflexional velocity profiles. In the inviscid limit, it is found that for viscoelasticity to affect the instability of a flow described by the Oldroyd-B model, the Weissenberg number, We, has to go to infinity in such a way that its ratio to the Reynolds number, G ∞ We/Re, is finite. In this special limit we derive a modified Rayleigh equation, the solution of which shows that viscoelasticity reduces the instability of the flow but does not suppress it. The classical Orr–Sommerfeld analysis has been extended to both the Giesekus and corotational Jeffreys models. The latter model showed little variation from the Newtonian case over a wide range of Re, while the former one may have a stabilizing effect depending on the product ςWe where ς is the mobility factor appearing in the Giesekus model. We discuss the mechanisms responsible for reducing the instability of the flow and present some qualitative comparisons with experimental results reported by Hibberd et al. (1982), Scharf (1985 a, b) and Riediger (1989).

APA, Harvard, Vancouver, ISO, and other styles

2

Luo, Zheng Yuan, and Bo Feng Bai. "Dynamics of capsules enclosing viscoelastic fluid in simple shear flow." Journal of Fluid Mechanics 840 (February 14, 2018): 656–87. http://dx.doi.org/10.1017/jfm.2018.88.

Full text

Abstract:

Previous studies on capsule dynamics in shear flow have dealt with Newtonian fluids, while the effect of fluid viscoelasticity remains an unresolved fundamental question. In this paper, we report a numerical investigation of the dynamics of capsules enclosing a viscoelastic fluid and which are freely suspended in a Newtonian fluid under simple shear. Systematic simulations are performed at small but non-zero Reynolds numbers (i.e. $Re=0.1$) using a three-dimensional front-tracking finite-difference model, in which the fluid viscoelasticity is introduced via the Oldroyd-B constitutive equation. We demonstrate that the internal fluid viscoelasticity presents significant effects on the deformation behaviour of initially spherical capsules, including transient evolution and equilibrium values of their deformation and orientation. Particularly, the capsule deformation decreases slightly with the Deborah number De increasing from 0 to $O(1)$. In contrast, with De increasing within high levels, i.e. $O(1{-}100)$, the capsule deformation increases continuously and eventually approaches the Newtonian limit having a viscosity the same as the Newtonian part of the viscoelastic capsule. By analysing the viscous stress, pressure and viscoelastic stress acting on the capsule membrane, we reveal that the mechanism underlying the effects of the internal fluid viscoelasticity on the capsule deformation is the alterations in the distribution of the viscoelastic stress at low De and its magnitude at high De, respectively. Furthermore, we find some new features in the dynamics of initially non-spherical capsules induced by the internal fluid viscoelasticity. Particularly, the transition from tumbling to swinging of oblate capsules can be triggered at very high viscosity ratios by increasing De alone. Besides, the critical viscosity ratio for the tumbling-to-swinging transition is remarkably enlarged with De increasing at relatively high levels, i.e. $O(1{-}100)$, while it shows little change at low De, i.e. below $O(1)$.

APA, Harvard, Vancouver, ISO, and other styles

3

Nashima, Takeshi. "Method of Viscoelasticity Measurement under Shear-Flow." Nihon Reoroji Gakkaishi 48, no. 5 (December 15, 2020): 251–57. http://dx.doi.org/10.1678/rheology.48.251.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

AGGARWAL, NISHITH, and KAUSIK SARKAR. "Deformation and breakup of a viscoelastic drop in a Newtonian matrix under steady shear." Journal of Fluid Mechanics 584 (July 25, 2007): 1–21. http://dx.doi.org/10.1017/s0022112007006210.

Full text

Abstract:

The deformation of a viscoelastic drop suspended in a Newtonian fluid subjected to a steady shear is investigated using a front-tracking finite-difference method. The viscoelasticity is modelled using the Oldroyd-B constitutive equation. The drop response with increasing relaxation time λ and varying polymeric to the total drop viscosity ratio β is studied and explained by examining the elastic and viscous stresses at the interface. Steady-state drop deformation was seen to decrease from its Newtonian value with increasing viscoelasticity. A slight non-monotonicity in steady-state deformation with increasing Deborah number is observed at high Capillary numbers. Transient drop deformation displays an overshoot before settling down to a lower value of deformation. The overshoot increases with increasing β. The drop shows slightly decreased alignment with the flow with increasing viscoelasticity. A simple ordinary differential equation model is developed to explain the various behaviours and the scalings observed numerically. The critical Capillary number for drop breakup is observed to increase with Deborah number owing to the inhibitive effects of viscoelasticity, the increase being linear for small Deborah number.

APA, Harvard, Vancouver, ISO, and other styles

5

AGGARWAL, NISHITH, and KAUSIK SARKAR. "Effects of matrix viscoelasticity on viscous and viscoelastic drop deformation in a shear flow." Journal of Fluid Mechanics 601 (April 25, 2008): 63–84. http://dx.doi.org/10.1017/s0022112008000451.

Full text

Abstract:

The deformation of a Newtonian/viscoelastic drop suspended in a viscoelastic fluid is investigated using a three-dimensional front-tracking finite-difference method. The viscoelasticity is modelled using the Oldroyd-B constitutive equation. Matrix viscoelasticity affects the drop deformation and the inclination angle with the flow direction. Numerical predictions of these quantities are compared with previous experimental measurements using Boger fluids. The elastic and viscous stresses at the interface, polymer orientation, and the elastic and viscous forces in the domain are carefully investigated as they affect the drop response. Significant change in the drop inclination with increasing viscoelasticity is observed; this is explained in terms of the first normal stress difference. A non-monotonic change – a decrease followed by an increase – in the steady-state drop deformation is observed with increasing Deborah number (De) and explained in terms of the competition between increased localized polymer stretching at the drop tips and the decreased viscous stretching due to change in drop orientation angle. The transient drop orientation angle is found to evolve on the polymer relaxation time scale for highDe. The breakup of a viscous drop in a viscoelastic matrix is inhibited for smallDe, and promoted at higherDe. Polymeric to total viscosity ratio β was seen to affect the result through the combined parameter βDeindicating a dominant role of the first normal stress difference. A viscoelastic drop in a viscoelastic matrix with matched relaxation time experiences less deformation compared to the case when one of the phases is viscous; but the inclination angle assumes an intermediate value between two extreme cases. Increased drop phase viscoelasticity compared to matrix phase leads to decreased deformation.

APA, Harvard, Vancouver, ISO, and other styles

6

Korol, A. M., J. R. Valverde, and R. J. Rasia. "Viscoelasticity: Fractal parameters studied on mammalian erythrocytes under shear stress." Experimental Mechanics 42, no. 2 (June 2002): 172–77. http://dx.doi.org/10.1007/bf02410879.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Helgeson, Matthew E., Norman J. Wagner, and Dimitris Vlassopoulos. "Viscoelasticity and shear melting of colloidal star polymer glasses." Journal of Rheology 51, no. 2 (March 2007): 297–316. http://dx.doi.org/10.1122/1.2433935.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Yoshimura, Narihiko, Noboru Umemoto, and Tsunamitsu Nakahara. "Analysis of Traction Curve in Linear Region Considering Volume Viscoelasticity." Journal of Tribology 121, no. 2 (April 1, 1999): 252–58. http://dx.doi.org/10.1115/1.2833928.

Full text

Abstract:

Measurements of the gradient in the linear region of traction curve, where the effects of heat generation and nonlinearity of shear viscosity can be neglected were made for two kinds of synthetic oils, DOP and 5P4E, using a traction tester improved to a precision less than 0.01 percent in slip ratio. The measured results were compared with the theoretical results based on a viscoelastic model for shear stress and on an elastic model for compressibility using primary data of the rheological properties which were obtained not by means of traction test; they were markedly less than the theoretical results under low speed for both oils and also under high speed for DOP. A new analysis of the traction was performed considering volume viscoelasticity for compressibility which relates shear viscoelasticity under high pressure. The theoretical results agree fairly with the measured results.

APA, Harvard, Vancouver, ISO, and other styles

9

Mukherjee, Swarnajay, and Kausik Sarkar. "Effects of matrix viscoelasticity on the lateral migration of a deformable drop in a wall-bounded shear." Journal of Fluid Mechanics 727 (June 21, 2013): 318–45. http://dx.doi.org/10.1017/jfm.2013.251.

Full text

Abstract:

AbstractThe dynamics of a drop deforming, orienting and moving in a shear flow of a viscoelastic liquid near a wall is numerically investigated using a front-tracking finite-difference method and a semi-analytic theory. The viscoelasticity is modelled using the modified FENE-CR constitutive equation. In a Newtonian system, deformation in a drop breaks the reversal symmetry of the system resulting in a migration away from the wall. This study shows that the matrix elasticity reduces the migration velocity, the reduction scaling approximately linearly with viscoelasticity (product of the Deborah numberDeand the ratio of polymer viscosity to total viscosity$\beta $). Similar to a Newtonian system, for small Deborah numbers, the dynamics quickly reaches a quasi-steady state where deformation, inclination, as well as migration and slip velocities become independent of the initial drop–wall separation. They all approximately scale inversely with the square of the instantaneous separation except for deformation which scales inversely with the cube of separation. The deformation shows a non-monotonic variation with increasing viscoelasticity similar to the case of a drop in an unbounded shear and is found to influence little the change in migration. Two competing effects due to matrix viscoelasticity on drop migration are identified. The first stems from the reduced inclination angle of the drop with increasing viscoelasticity that tries to enhance migration velocity. However, it is overcome by the second effect inhibiting migration that results from the normal stress differences from the curved streamlines around the drop; they are more curved on the side away from the wall compared with those in the gap between the wall and the drop, an effect that is also present for a rigid particle. A perturbative theory of migration is developed for small ratio of the drop size to its separation from the wall that clearly shows the migration to be caused by the image stresslet field due to the drop in presence of the wall. The theory delineates the two competing viscoelastic effects, their relative magnitudes, and predicts migration that matches well with the simulation. Using the simulation results and the stresslet theory, we develop an algebraic expression for the quasi-steady migration velocity as a function ofCa,Deand$\beta $. The transient dynamics of the migrating drop is seen to be governed by the finite time needed for development of the viscoelastic stresses. For larger capillary numbers, in both Newtonian and viscoelastic matrices, a viscous drop fails to reach a quasi-steady state independent of initial drop–wall separation. Matrix viscoelasticity tends to prevent drop breakup. Drops that break up in a Newtonian matrix are stabilized in a viscoelastic matrix if it is initially far away from the wall. Initial proximity to the wall enhances deformation and aids in drop breakup.

APA, Harvard, Vancouver, ISO, and other styles

10

Murata, Shoichi, Akihiko Takada, and Yoshiaki Takahashi. "Structure and Viscoelasticity of Wormlike Micellar Solutions under Steady Shear Flows." Nihon Reoroji Gakkaishi 35, no. 4 (2007): 185–89. http://dx.doi.org/10.1678/rheology.35.185.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Ewoldt, Randy H., A. E. Hosoi, and Gareth H. McKinley. "New measures for characterizing nonlinear viscoelasticity in large amplitude oscillatory shear." Journal of Rheology 52, no. 6 (November 2008): 1427–58. http://dx.doi.org/10.1122/1.2970095.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Lim, Hyung Tag, Kyung Hyun Ahn, Joung Sook Hong, and Kyu Hyun. "Nonlinear viscoelasticity of polymer nanocomposites under large amplitude oscillatory shear flow." Journal of Rheology 57, no. 3 (May 2013): 767–89. http://dx.doi.org/10.1122/1.4795748.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Cao, Yifang, Randy Bly, Will Moore, Zhan Gao, Alberto M. Cuitino, and Wole Soboyejo. "Investigation of the viscoelasticity of human osteosarcoma cells using a shear assay method." Journal of Materials Research 21, no. 8 (August 1, 2006): 1922–30. http://dx.doi.org/10.1557/jmr.2006.0235.

Full text

Abstract:

This paper presents a shear assay method for the determination of the viscoelastic properties of biological cells. The method was applied to the measurement of the viscoelastic properties of human osteosarcoma (HOS) cells. It involves a combination of shear assay experiments and digital image correlation techniques. Following in situ observations of cell deformation during shear assay experiments, a digital image correlation (DIC) technique was used to determine the local displacement and strain fields. The creep curves were also extracted from multiple digital images that were used to extract the time dependence of local strain under constant stress conditions. The measured creep curves were well described by a generalized viscoelastic Maxwell model. The extracted elastic and viscous parameters were in good agreement with results obtained from prior studies with other techniques. The results also suggested that the nucleus is stiffer than the surrounding cytoplasm of HOS cells.

APA, Harvard, Vancouver, ISO, and other styles

14

Quintanilla, Ramon, and Giuseppe Saccomandi. "The Importance of the Compatibility of Nonlinear Constitutive Theories With Their Linear Counterparts." Journal of Applied Mechanics 74, no. 3 (May 24, 2006): 455–60. http://dx.doi.org/10.1115/1.2338053.

Full text

Abstract:

We show, by considering a special class of nonlinear viscoelastic materials, that consistency of a mechanical model with classical linear viscoelasticity, may be a fundamental condition to ensure a mathematical and physical well-posedness behavior. To illustrate our arguments we use a rectilinear class of shear motions that we investigate in the static and quasistatic case in the framework of a simple boundary value problem and the classical recovery phenomenon.

APA, Harvard, Vancouver, ISO, and other styles

15

GAGNON, D. A., and T. D. MONTENEGRO-JOHNSON. "THRIFTY SWIMMING WITH SHEAR-THINNING: A NOTE ON OUT-OF-PLANE EFFECTS FOR UNDULATORY LOCOMOTION THROUGH SHEAR-THINNING FLUIDS." ANZIAM Journal 59, no. 4 (April 2018): 443–54. http://dx.doi.org/10.1017/s1446181118000032.

Full text

Abstract:

Microscale propulsion is integral to numerous biomedical systems, including biofilm formation and human reproduction, where the surrounding fluids comprise suspensions of polymers. These polymers endow the fluid with non-Newtonian rheological properties, such as shear-thinning and viscoelasticity. Thus, the complex dynamics of non-Newtonian fluids present numerous modelling challenges. Here, we demonstrate that neglecting ‘out-of-plane’ effects during swimming through a shear-thinning fluid results in a significant overestimate of fluid viscosity around the undulatory swimmer Caenorhabditis elegans. This miscalculation of viscosity corresponds with an overestimate of the power the swimmer expends, a key biophysical quantity important for understanding the internal mechanics of the swimmer. As experimental flow-tracking techniques improve, accurate experimental estimates of power consumption in similar undulatory systems, such as the planar beating of human sperm through cervical mucus, will be required to probe the interaction between internal power generation, fluid rheology, and the resulting waveform.

APA, Harvard, Vancouver, ISO, and other styles

16

Park, Seungman, Jiaxiang Tao, Li Sun, Cheng-Ming Fan, and Yun Chen. "An Economic, Modular, and Portable Skin Viscoelasticity Measurement Device for In Situ Longitudinal Studies." Molecules 24, no. 5 (March 5, 2019): 907. http://dx.doi.org/10.3390/molecules24050907.

Full text

Abstract:

A indentation-based device to measure tissue mechanical property was designed and built using over-the-counter and 3D-printed parts. The device costs less than 100 USD and is capable of measuring samples of various geometry because of its modular design. The device is light-weight, thus portable, for measurements that can be performed at different sites. It was demonstrated that the measurement results obtained using our device are comparable to previous observations. The elastic shear modulus of the human skin was in the range of 2 kPa to 8 kPa, and skin tissues in old mice were stiffer than young mice. Mechanical properties of the skin tissues belonging to the same test subject varied depending on the location of the measurement. In conclusion, because our device is economic, modular, portable, and robust, it is suitable to serve as a standard measurement platform for studying tissue mechanics.

APA, Harvard, Vancouver, ISO, and other styles

17

Shiromoto, Seiji, and Kiyohito Koyama. "Study on Morphology Change and Viscoelasticity of PP/PE Blend under Shear Flow." Nihon Reoroji Gakkaishi 31, no. 5 (2003): 313–19. http://dx.doi.org/10.1678/rheology.31.313.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Bechtel, Toni M., and Aditya S. Khair. "Nonlinear viscoelasticity of a dilute suspension of Brownian spheroids in oscillatory shear flow." Journal of Rheology 62, no. 6 (November 2018): 1457–83. http://dx.doi.org/10.1122/1.5040258.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Dai, Jun, Zhao-Dong Xu, and Pan-Pan Gai. "Dynamic analysis of viscoelastic tuned mass damper system under harmonic excitation." Journal of Vibration and Control 25, no. 11 (March 11, 2019): 1768–79. http://dx.doi.org/10.1177/1077546319833887.

Full text

Abstract:

The purpose of this paper is to investigate the contribution of viscoelastic material (VEM) to the control performance of the viscoelastic tuned mass damper (VTMD). Firstly, the equivalent fractional derivation Kelvin model is used to describe the frequency dependence of viscoelasticity in VTMD, and an index is proposed to characterize the level of frequency dependence. Then the effects of the high loss factor of VEM and frequency dependence of viscoelasticity on the effectiveness and robustness of VTMD control are analyzed by numerical examples. At last, a design strategy for VTMD is proposed to select the type of VEM and optimize its stiffness contribution. The results show that the frequency dependence of shear storage modulus of VEM is beneficial to further reduce the dynamic response of the primary structure equipped with VTMD, and the loss factor of VEM determines the optimum frequency ratio and control effect of VTMD. Compared to the conventional tuned mass damper, VTMD has a better robustness for the positive error of the natural frequency of VTMD but has a worse robustness for the negative error. The frequency dependence of shear storage modulus of VEM is beneficial to the robustness of VTMD for both the positive and negative errors of the natural frequency of the primary structure. The VEM with a strong frequency dependence of shear storage modulus is the ideal VEM for VTMD, and the proposed design strategy can deal with the trade-off between the control effectiveness and control robustness of VTMD.

APA, Harvard, Vancouver, ISO, and other styles

20

Wineman, Alan. "Dimensional changes during shear without normal tractions (the Poynting effect) in nonlinear viscoelastic fiber-reinforced solids." Mathematics and Mechanics of Solids 25, no. 3 (November 17, 2019): 582–96. http://dx.doi.org/10.1177/1081286519885162.

Full text

Abstract:

When a rectangular block of a nonlinear material is subjected to a simple shearing deformation, specific normal tractions are required to ensure that the distances between the faces of the block, i.e. its dimensions, do not change. This work investigates the time-dependent dimensional changes during shear in the absence of these normal tractions (the Poynting effect) that occur in a block composed of an incompressible nonlinearly viscoelastic fiber-reinforced solid. The material is modeled using the Pipkin–Rogers nonlinear single integral constitutive equation for viscoelasticity. This constitutive equation is used because (1) it exhibits the essential features of nonlinear viscoelasticity; (2) it is straightforward to include the material symmetry restrictions due to the reinforcing fibers. A system of nonlinear Volterra integral equations is formulated for the dimensional changes in the block. Numerical solutions are presented for the case when the standard reinforcing model for nonlinearly elastic fiber-reinforced materials is incorporated in the Pipkin–Rogers constitutive framework. The results illustrate how the time-dependent dimensional changes depend on the fiber orientation and the viscoelastic properties of the fibers relative to those of the matrix.

APA, Harvard, Vancouver, ISO, and other styles

21

Huang, Hu, Fu, Cheng, Wang, and Wang. "Molecular Morphology and Viscoelasticity of ASP Solution under the Action of a Different Medium Injection Tool." Polymers 11, no. 8 (August 2, 2019): 1299. http://dx.doi.org/10.3390/polym11081299.

Full text

Abstract:

In order to improve the oil displacement effect of alkali/surfactant/polymer (ASP) solution in low-permeability oil layers, Daqing Oilfield has proposed a separate injection technology. The objective of separate injection technology is to reduce the viscosity of ASP solution through a different medium injection tool and increase the injection amount of ASP solution in low permeability oil layer, thus improving the oil displacement effect. In order to study the effect of the different medium injection tool on ASP solution, SEM is used to observe the changes in molecular micromorphology before and after the ASP solution flows through the tool. Then, the influence of the tool on viscosity and the first normal stress difference of the solution are studied through static shear experiments. Finally, the storage and loss modulus of the solution are measured through dynamic mechanical experiments and the relaxation time and zero shear viscosity of the solution are verified and compared. The results show that molecular chains are obviously broken and the grid structure is destroyed after the ASP solution is acted on by the different medium injection tool. The viscosity and elasticity of ASP solution decrease, and the influence degree of the different medium injection tool on viscosity is greater than elasticity. The results of the steady shear experiment and dynamic mechanics experiment are consistent. Therefore, the different medium injection tool can achieve the purpose of use, which is conducive to the injection of displacement fluid into low-permeability oil layers and enhance the recovery ratio.

APA, Harvard, Vancouver, ISO, and other styles

22

Zhang, Chao, and H. S. Cheng. "Transient Non-Newtonian Thermohydrodynamic Mixed Lubrication of Dynamically Loaded Journal Bearings." Journal of Tribology 122, no. 1 (May 11, 1999): 156–61. http://dx.doi.org/10.1115/1.555338.

Full text

Abstract:

A transient non-Newtonian THD theory of dynamically loaded journal bearings in mixed lubrication is presented. A mass conserving cavitation is included and shear thinning and viscoelasticity are characterized by the power law and the upper convected Maxwell models, respectively. The 2-D energy equation is solved with ISOADI (isothermal shaft and adiabatic bushing inner surface) boundary conditions. The journal is treated as a quasi-steady and lumped thermal element. [S0742-4787(00)02001-4]

APA, Harvard, Vancouver, ISO, and other styles

23

Martínez-Calvo, A., and A. Sevilla. "Temporal stability of free liquid threads with surface viscoelasticity." Journal of Fluid Mechanics 846 (May 10, 2018): 877–901. http://dx.doi.org/10.1017/jfm.2018.293.

Full text

Abstract:

We analyse the effect of surface viscoelasticity on the temporal stability of a free cylindrical liquid jet coated with insoluble surfactant, extending the results of Timmermans & Lister (J. Fluid Mech., vol. 459, 2002, pp. 289–306). Our development requires, in particular, deriving the correct expressions for the normal and tangential stress boundary conditions at a general axisymmetric interface when surface viscosity is modelled with the Boussinesq–Scriven constitutive equation. These stress conditions are applied to obtain a new dispersion relation for the liquid thread, which is solved to describe its temporal stability as a function of four governing parameters, namely the capillary Reynolds number, the elasticity parameter, and the shear and dilatational Boussinesq numbers. It is shown that both surface viscosities have a stabilising influence for all values of the capillary Reynolds number and elasticity parameter, the effect being more pronounced at low capillary Reynolds numbers. The wavenumber of maximum amplification depends non-monotonically on the Boussinesq numbers, especially for very viscous threads at low values of the elasticity parameter. Finally, two different lubrication approximations of the equations of motion are derived. While the validity of the leading-order model is limited to small enough values of the elasticity parameter and of the Boussinesq numbers, a higher-order parabolic model is able to accurately capture the linearised behaviour for the whole range of values of the four control parameters.

APA, Harvard, Vancouver, ISO, and other styles

24

Duan, Jun-Sheng, and Lian Chen. "Oscillatory shear flow between two parallel plates for viscoelastic constitutive model of distributed-order derivative." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 3 (September 16, 2019): 1137–48. http://dx.doi.org/10.1108/hff-05-2019-0424.

Full text

Abstract:

Purpose The purpose of this study is to investigate viscoelastic properties for the constitutive equation in terms of distributed-order derivatives. Design/methodology/approach The authors considered the steady oscillatory shear flow between two parallel plates (one is fixed and another oscillates in its own plane), and then examined the effects of different forms of the order-weight functions. Findings The constitutive equation in terms of distributed-order derivatives can characterize viscoelastic properties. The order-weight functions can effectively describe viscoelasticity. Originality/value Model the viscoelastic constitutive equation in terms of distributed-order derivatives, where order-weight functions can select to respond viscoelastic properties.

APA, Harvard, Vancouver, ISO, and other styles

25

Snijkers, F., K. M. Kirkwood, D. Vlassopoulos, L. G. Leal, A. Nikopoulou, N. Hadjichristidis, and S. Coppola. "Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution." Journal of Rheology 60, no. 3 (May 2016): 451–63. http://dx.doi.org/10.1122/1.4944993.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Wei, Jinjia, Yasuo Kawaguchi, Bo Yu, and Ziping Feng. "Rheological Characteristics and Turbulent Friction Drag and Heat Transfer Reductions of a Very Dilute Cationic Surfactant Solution." Journal of Heat Transfer 128, no. 10 (February 24, 2006): 977–83. http://dx.doi.org/10.1115/1.2345422.

Full text

Abstract:

Turbulent friction drag and heat transfer reductions and rheological characteristics of a very dilute cationic surfactant solution, cetyltrimethyl ammonium chloride (CTAC)/sodium salicylate (NaSal) aqueous solution, were experimentally investigated at various temperatures. It was found that there existed a critical temperature above which drag and heat transfer reductions disappeared and shear viscosities rapidly dropped to that of water. It was surmised that drag and heat transfer reductions had a certain relationship with rheological characteristics and a rheological characterization of CTAC∕NaSal surfactant solutions was performed to clarify this relationship. The effects of Reynolds number and fluid temperature and concentration on drag and heat transfer reductions were qualitatively explained by analyzing the measured shear viscosity data at different shear rates and solution temperatures and concentrations. The Giesekus model was found to fit the measured shear viscosities reasonably well for different temperatures and concentrations of the surfactant solution and the model parameter values obtained by fitting were correlated with temperature at certain solution concentrations. From the correlation results, the temperature effect on viscoelasticity of surfactant solutions was analyzed to relate the rheological characteristics with drag and heat transfer reduction phenomena.

APA, Harvard, Vancouver, ISO, and other styles

27

Hamed, Ehab, and Yeoshua Frostig. "Nonlinear thermo-mechanical behaviour of soft core sandwich panels – Creep effects." Journal of Sandwich Structures & Materials 22, no. 8 (October 29, 2018): 2629–54. http://dx.doi.org/10.1177/1099636218807727.

Full text

Abstract:

Sandwich panels can be subjected to significant changes in ambient temperature, which develop and sustain over certain time periods and lead to creep of the core material, and consequently to changes in the internal stresses and deformations with time. This paper deals with this issue with focus on the geometrically nonlinear aspects of structural behaviour. A theoretical model is developed, which combines the concepts of the principle of superposition of viscoelasticity, with the high-order sandwich theory (HSAPT), and the temperature dependency of the viscoelastic material properties. The nonlinear HSAPT formulation accounts for the deformability of the core in shear and through its thickness and it is based on large displacement kinematics of the face sheets. The convolution integral of viscoelasticity is converted into a rheological generalized Maxwell model after the expansion of the relaxation moduli into Prony series with temperature-dependence terms, which enables the solution of the governing equations through an incremental step-by-step time analysis without the need to store the response history. The capabilities of the model are demonstrated through numerical examples. It is shown that the creep of the core material can lead to bifurcation buckling of the sandwich panel under sustained temperatures that are smaller than the critical temperature obtained under an instantaneous increase of temperature.

APA, Harvard, Vancouver, ISO, and other styles

28

Horner, Jeffrey S., Matthew J. Armstrong, Norman J. Wagner, and Antony N. Beris. "Measurements of human blood viscoelasticity and thixotropy under steady and transient shear and constitutive modeling thereof." Journal of Rheology 63, no. 5 (September 2019): 799–813. http://dx.doi.org/10.1122/1.5108737.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Yakobson, É. É., and L. A. Faiteľson. "Viscoelasticity of liquid-crystal polymers in superposition of period and steady-state shear flow." Mechanics of Composite Materials 29, no. 5 (September 1994): 520–26. http://dx.doi.org/10.1007/bf00611957.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Farokhi, Hamed, and Mergen H. Ghayesh. "Viscoelastic resonant responses of shear deformable imperfect microbeams." Journal of Vibration and Control 24, no. 14 (March 22, 2017): 3049–62. http://dx.doi.org/10.1177/1077546317699345.

Full text

Abstract:

A viscoelastic model for the nonlinear analysis of the coupled transverse, longitudinal, and rotational oscillations of an imperfect shear deformable microbeam is developed, for the first time, based on the modified couple stress theory. An energy dissipation mechanism is developed via use of the Kelvin–Voigt internal energy dissipation mechanism. For the stress and deviatoric part of the symmetric couple stress tensors, the viscous components along with the corresponding work terms are obtained. The size-dependent elastic energy along with the kinetic energy of the viscoelastic microsystem is formulated in terms of the displacement field together with system geometric and physical parameters. The internal energy dissipation is developed via the work done by the viscous components of the stress and the deviatoric part of the symmetric couple stress tensors by means of the Kelvin–Voigt mechanism. These work and energy terms are inserted into Hamilton’s principle together with the work due to an external force in order to obtain three viscoelastically coupled equations governing the transverse, longitudinal, and rotational motions with cubic and quadratic nonlinear terms. A high-dimensional Galerkin approximation method is applied for all the three equations, yielding three sets of second-order coupled ordinary differential equations with cubic and quadratic nonlinearities. Upon application of a transformation, a continuation technique along with the backward differentiation formula (BDF) is employed in order to obtain the time-variant response of the system subject to a harmonic load. Special attention is paid to the effect of the Kelvin–Voigt type viscoelasticity on the system response in the presence of the length-scale parameter.

APA, Harvard, Vancouver, ISO, and other styles

31

Khatri, Kamal N. "Vibrations of Arbitrarily Laminated Fiber Reinforced Composite Material Truncated Conical Shell." Journal of Reinforced Plastics and Composites 14, no. 9 (September 1995): 923–48. http://dx.doi.org/10.1177/073168449501400902.

Full text

Abstract:

Governing equations of motion are presented for arbitrarily laminated fiber reinforced composite material truncated conical shell in which each layer is permitted an arbitrary fixed fiber orientation. Each layer has been considered to be of a specially orthotropic material with its directional elastic properties depending on the fiber orientation. Extension, bending, in-plane shear and transverse shear in all the layers have been considered and inertia effects due to transverse, meridional and rotary motions are taken into account. Convenient trigonometric series are used as solution functions in Galerkin's method to reduce the governing equations to sets of matrix equations. The correspondence principle of linear viscoelasticity has been used for evaluating the damping effectiveness of the shell. Computer programs have been developed for axisymmetric and antisymmetric vibrations of multi-layered conical shells with simply supported edges. The influence of apex angle upon the resonance frequencies and the associated system loss factors of laminated FRP conical shells is investigated.

APA, Harvard, Vancouver, ISO, and other styles

32

Jannapureddy, Suneal R., Nisha D. Patel, Willy Hwang, and Aladin M. Boriek. "Selected Contribution: Merosin deficiency leads to alterations in passive and active skeletal muscle mechanics." Journal of Applied Physiology 94, no. 6 (June 1, 2003): 2524–33. http://dx.doi.org/10.1152/japplphysiol.01078.2002.

Full text

Abstract:

The role of extracellular elements on the mechanical properties of skeletal muscles is unknown. Merosin is an essential extracellular matrix protein that forms a mechanical junction between the sarcolemma and collagen. Therefore, it is possible that merosin plays a role in force transmission between muscle fibers and collagen. We hypothesized that deficiency in merosin may alter passive muscle stiffness, viscoelastic properties, and contractile muscle force in skeletal muscles. We used the dy/dy mouse, a merosin-deficient mouse model, to examine changes in passive and active muscle mechanics. After mice were anesthetized and the diaphragm or the biceps femoris hindlimb muscle was excised, passive length-tension relationships, stress-relaxation curves, or isometric contractile properties were determined with an in vitro biaxial mechanical testing apparatus. Compared with controls, extensibility was smaller in the muscle fiber direction and the transverse fiber direction of the mutant mice. The relaxed elastic modulus was smaller in merosin-deficient diaphragms compared with controls. Interestingly, maximal muscle tetanic stress was depressed in muscles from the mutant mice during uniaxial loading but not during biaxial loading. However, presence of transverse passive stretch increases maximal contractile stress in both the mutant and normal mice. Our data suggest that merosin contributes to muscle passive stiffness, viscoelasticity, and contractility and that the mechanism by which force is transmitted between adjacent myofibers via merosin possibly in shear.

APA, Harvard, Vancouver, ISO, and other styles

33

Jeyaseelan, R. S., and A. J. Giacomin. "The Role of Temperature in the Entanglement Kinetics of a Polymer Melt." Journal of Applied Mechanics 62, no. 3 (September 1, 1995): 794–801. http://dx.doi.org/10.1115/1.2897016.

Full text

Abstract:

Large-amplitude oscillatory shear (LAOS) experiments were conducted at different temperatures on a molten low-density polyethylene standard, designated IUPAC LDPE X. Jeyaseelan et al. (1993) have successfully employed a simplification of transient network theory to describe the LAOS behavior of this polymer melt, at 150°C. The transient network is described by two kinetic rate constants, one for the formation of entanglements due to Brownian motion (k1), and another for the destruction of entanglements (k2) due to the imposed deformation. Upon comparison of the predictions of this transient network theory with the measured LAOS behavior of this polymer, we find that the kinetic rate constants k1 and k2 are invariant in the range of temperatures examined (150 to 190°C). The temperature dependence of departures from linear viscoelasticity is fully accounted for in the equilibrium entanglement kinetics.

APA, Harvard, Vancouver, ISO, and other styles

34

Costa-Júnior, J. F. S., M. A. D. Elsztain, A. M. F. L. M. de Sá, and J. C. Machado. "Characterization of Viscoelasticity Due to Shear Wave Propagation: a Comparison of Existing Methods Based on Computational Simulation and Experimental Data." Experimental Mechanics 57, no. 4 (February 13, 2017): 615–35. http://dx.doi.org/10.1007/s11340-017-0254-6.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Shishesaz, Mohammad, and Arash Reza. "The Effect of Viscoelasticity of Polymeric Adhesives on Shear Stress Distribution in a Single-Lap Joint." Journal of Adhesion 89, no. 11 (November 2, 2013): 859–80. http://dx.doi.org/10.1080/00218464.2012.750581.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

Wu, Jiayu, Hong Yuan, and Long-yuan Li. "Effect of viscoelasticity on interfacial stress transfer mechanism in the biocomposites: A theoretical study of viscoelastic shear lag model." Composites Part B: Engineering 164 (May 2019): 297–308. http://dx.doi.org/10.1016/j.compositesb.2018.11.086.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Zhao, Dong, and Ying Liu. "Effects of director rotation relaxation on viscoelastic wave dispersion in nematic elastomer beams." Mathematics and Mechanics of Solids 24, no. 4 (May 25, 2018): 1103–15. http://dx.doi.org/10.1177/1081286518773516.

Full text

Abstract:

In this paper, the transverse wave dispersion in a nematic elastomer (NE) Timoshenko beam is studied by considering anisotropy and viscoelasticity of NEs in the low frequency limit. Firstly, the characteristic equations of wave motion in an NE beam are derived, and then numerically solved to obtain the corresponding phase velocities and attenuation factors. The influences of anisotropic parameter, director rotation and rubber relaxation times on the wave dispersion in an NE beam are discussed. Results show that unlike the situation in general isotropic viscoelastic beam, non-classical viscoelastic wave dispersion is found in NE beams. Geometric dispersion is restrained with the vanishing of cut-off frequencies for shear waves due to director rotation relaxation of NEs. This unique property promises prospective applications of NE beams in optic or acoustic design.

APA, Harvard, Vancouver, ISO, and other styles

38

Walton, J. R. "The Dynamic Energy Release Rate for a Steadily Propagating Mode I Crack in an Infinite, Linearly Viscoelastic Body." Journal of Applied Mechanics 57, no. 2 (June 1, 1990): 343–53. http://dx.doi.org/10.1115/1.2891995.

Full text

Abstract:

An analysis is presented for the dynamic, steady-state propagation of a semi-infinite, mode I crack in an infinite, linearly viscoelastic body. For mathematical convenience, the material is assumed to have a constant Poisson’s ratio, but the shear modulus is only assumed to be decreasing and convex. An expression for the Stress Intensity Factor (SIF) is derived for very general tractions on the crack faces and the Energy Release Rate (ERR) is constructed assuming that a fully developed Barenblatt type failure zone with nonsingular stresses exists at the crack tip and the loadings have a simple exponential form. For comparative purposes, expressions for the ERR are derived for the special cases of dynamic steady-state crack propagation in elastic material and quasi-static crack propagation in viscoelastic material, both with and without a failure zone. Sample calculations are included for power-law material and a standard linear solid in order to illustrate the combined influence of inertial effects, material viscoelasticity, and a failure zone upon the ERR.

APA, Harvard, Vancouver, ISO, and other styles

39

Zamani, HA, and MM Aghdam. "Hybrid material and foundation damping of Timoshenko beams." Journal of Vibration and Control 23, no. 18 (January 13, 2016): 2869–87. http://dx.doi.org/10.1177/1077546315624077.

Full text

Abstract:

In this paper, vibration suppression of shear deformable beams with hybrid material-foundation viscoelastic damping is studied. The precise behavior of viscoelastic polymeric structures is taken into consideration by Boltzmann superposition integral and utilizing dynamic mechanical analysis (DMA) results while foundation viscoelasticity is adapted by Kelvin-Voigt model. The integro-partial differential equations of motion are derived based on the Timoshenko theory via Hamilton principle. Assessment of the solution procedure is carried out by comparison with elastic Timoshenko and viscoelastic Euler-Bernoulli cases. Transient response, natural frequency and modal loss factor are attained by Fourier transform, weighted residual method and numerical iterative algorithm. Influences of hybrid viscoelastic damping, foundation properties, geometrical parameters and boundary conditions on vibration characteristics and dynamic response are investigated via comprehensive parametric study. Due to the absence of similar results in the literature, this paper is likely to fill a gap in the state of the art of this problem.

APA, Harvard, Vancouver, ISO, and other styles

40

Chen, Dao-Long, Tz-Cheng Chiu, Tei-Chen Chen, Ping-Feng Yang, and Sheng-Rui Jian. "Interconversions between linear viscoelastic functions with a time-dependent bulk modulus." Mathematics and Mechanics of Solids 23, no. 6 (March 26, 2017): 879–95. http://dx.doi.org/10.1177/1081286517694935.

Full text

Abstract:

The interconversion relations for viscoelastic functions are derived with the consideration of the time-dependent bulk modulus, K( t), for both traditional and fractional Prony series representations of viscoelasticity. The application of these relations is to replace the fitting parameters of Young’s relaxation modulus, E( t), by the unknown parameters of K( t) and the known parameters of the shear relaxation modulus, G( t), and to fit the E( t) to the experimental data for obtaining the parameters of K( t). The fitting results show that only two experiments for measuring the viscoelastic functions of an isotropic material are not enough to determine the other viscoelastic functions. However, if we consider the relaxation rates of K( t) and G( t), we may conclude that the constant bulk modulus is a more reasonable assumption, and the corresponding Poisson’s ratio, ν( t), is a monotonic-increasing function.

APA, Harvard, Vancouver, ISO, and other styles

41

Shishesaz, Mohammad, and Arash Reza. "The effect of viscoelasticity of adhesives on shear stress distribution in a double-lap joint using analytical method." Journal of Adhesion Science and Technology 27, no. 20 (October 2013): 2233–50. http://dx.doi.org/10.1080/01694243.2013.769085.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Cai, Xia, Liu Chen, Qun Zhang, Bulu Xu, Weidong Huang, Xiaoming Xie, and Zhaonian Cheng. "Quantitative Mechanism of Significant Benefits of Underfill in Flip-Chip Assemblies." Journal of Electronic Packaging 125, no. 1 (March 1, 2003): 84–92. http://dx.doi.org/10.1115/1.1533802.

Full text

Abstract:

The thermal fatigue failure of SnPb solder joints of flip chip on board with and without underfill for two types of flip-chip packages was investigated by conducting thermal cycling test, scanning acoustic microscopy observation, and cross section inspection. The corresponding 3-D finite element simulation was performed to analyze the effects of underfill on thermomechanical behavior. The viscoelasticity of underfill and the viscoplasticity of solder were considered in the 3-D simulations. The Coffin-Manson equation with material constants C=5.54,β=−1.38 was fitted from the combination of the lifetime measured and the shear plastic strain range simulated by 3-D model. In the case with underfill, the plastic strain of every solder joint becomes very similar and little dependent on the position of solder joints. The modeled axial strain distribution coincided well with the distribution of microstructure coarsening visible in cross sections. The mismatch of thermal expansion resulted in an overall warpage of the assembly for the case with underfill, which decreased the shear deformation of the solder joints and increased the interface stress on the chip. The interface stress distribution from the 3-D simulation agreed very well with the experimental observations.

APA, Harvard, Vancouver, ISO, and other styles

43

Rahimi, Alireza, and Akbar Alibeigloo. "High-Accuracy Approach for Thermomechanical Vibration Analysis of FG-Gplrc Fluid-Conveying Viscoelastic Thick Cylindrical Shell." International Journal of Applied Mechanics 12, no. 07 (August 2020): 2050073. http://dx.doi.org/10.1142/s1758825120500738.

Full text

Abstract:

High importance of fluid-conveying structures in multifarious engineering applications arises the necessity of enhancing the mechanical characteristics of these systems in an effective way. Accordingly, this paper is concerned with vibration performance of functionally graded graphene-platelets reinforced composite (FG-GPLRC) fluid-conveying viscoelastic cylindrical shell surrounded by two-parameter elastic substrate and exposed to temperature gradient and axial load within the context of refined higher order shear deformation theory (RHSDT) including trapezoidal shape factor. Generalized differential quadrature method (GDQM) is employed to solve differential equations of motion for different cases of boundary conditions. The fourth-order Runge–Kutta technique is utilized to determine the time response of the system. Validity of the results is verified through comparison with those presented in the published articles. Comprehensive parametric analysis is performed to reveal the impact of fluid-flow velocity, distribution patterns of GPL, different forms of applied temperature gradient, different boundary conditions, viscoelasticity coefficient, geometrical dimensions of the shell as well as graphene-sheets on the vibration of the system. The numerical results demonstrate that negative influence of applying compressive axial load and rising temperature gradient on the vibrational response of the system can be alleviated when the system is exposed to sinusoidal form of temperature rise with proper power-index.

APA, Harvard, Vancouver, ISO, and other styles

44

Bechtel, S. E., M. G. Forest, D. D. Holm, and K. J. Lin. "One-dimensional closure models for three-dimensional incompressible viscoelastic free jets: von Kármán flow geometry and elliptical cross-section." Journal of Fluid Mechanics 196 (November 1988): 241–62. http://dx.doi.org/10.1017/s0022112088002691.

Full text

Abstract:

In this paper we derive one-space-dimensional, reduced systems of equations (one-dimensional closure models) for viscoelastic free jets. We begin with the three-dimensional system of conservation laws and a Maxwell-Jeffreys constitutive law for an incompressible viscoelastic fluid. First, we exhibit exact truncations to a finite, closed system of one-dimensional equations based on classical velocity assumptions of von Kármán (1921). Next, we demonstrate that the three-dimensional free-surface boundary conditions overconstrain these truncated systems, so that only a very limited class of solutions exist. We then proceed to derive approximate one-dimensional closure theories through a slender-jet asymptotic scaling, combined with appropriate definitions of velocity, pressure and stress unknowns. Our non-axisymmetric one-dimensional slender-jet models incorporate the physical effects of inertia, viscoelasticity (viscosity, relaxation and retardation), gravity, surface tension, and properties of the ambient fluid, and include shear stresses and time dependence. Previous special one-dimensional slender-jet models correspond to the lowest-order equations in the present asymptotic theory by an a posteriori suppression to leading order of some of these effects, and a reduction to axisymmetry. We thereby: (i) derive existing one-dimensional models from the three-dimensional free surface boundary-value problem; (ii) clarify the sense of the one-dimensional approximation; (iii) deduce new one-dimensional closure models for non-axisymmetric viscoelastic free jets.

APA, Harvard, Vancouver, ISO, and other styles

45

Morvarid, Masoud, Ali Rezghi, Alireza Riasi, and Mojtaba Haghighi Yazdi. "3D numerical simulation of laminar water hammer considering pipe wall viscoelasticity and the arbitrary Lagrangian-Eulerian method." World Journal of Engineering 15, no. 2 (April 9, 2018): 298–305. http://dx.doi.org/10.1108/wje-08-2017-0236.

Full text

Abstract:

Purpose Analysis of fast transient flow in water pipe systems is an important issue for the prevention of unfavorable pressure oscillations and severe damage to the pipelines. This paper aims to present the performance of three-dimensional (3D) simulation of laminar water hammer caused by fast closure of valve. Design/methodology/approach The viscoelastic behavior of pipe wall is mathematically modeled by using the rheological model of Maxwell. The arbitrary Lagrangian–Eulerian (ALE) method is also used to simulate fluid–structure interaction. In this method, unlike the classical water hammer theory, the acoustic wave velocity is calculated during the numerical simulations and therefore it is not predetermined. Findings Investigating the velocity profiles and the shear stress diagrams for transient flow in elastic pipe showed that the strong effect of viscous forces on the near wall region in conjunction with the influence of inertial forces in the central region of the pipe leads to creation of reverse flow near the pipe wall. Comparing the numerical results obtained for elastic pipe with those of viscoelastic pipe revealed that during transient condition, the viscoelastic wall absorbs the energy of fluid and therefore pressure fluctuations of viscoelastic pipe are damped more quickly. Moreover, the 3D simulation of water hammer confirmed the plane wave hypothesis of water hammer. Originality/value The 3D Navier–Stokes equations are solved considering the viscoelasticity of the pipe and the ALE method using the software package of COMSOL Multiphysics.

APA, Harvard, Vancouver, ISO, and other styles

46

Kirichok, I. F., Y. A. Zhuk, O. A. Chernyshok, and A. P. Tarasov. "Formulation of the problem of thermomechanics for a flexible cylindrical shell with piezoactive layers with taking into account to displacements." Bulletin of Taras Shevchenko National University of Kyiv. Series: Physics and Mathematics, no. 1 (2019): 78–81. http://dx.doi.org/10.17721/1812-5409.2019/1.17.

Full text

Abstract:

The formulation of problem on the forced resonant vibration and dissipative heating of layered element of structure containing both piezoelectric and electrically passive layers is considered. The improved problem statement taking account of both shear strain and rotatory inertia as well as geometrical nonlinearity is developed. Particular statement of the problem of axisymmetric vibration and dissipative heating of three layer cylidrical shell is formulated. It is assumed that the core layer of the shell is composed of the electrically passive material while the outer layers are manufactured from the piezoceramics. Theory of coupled thermo-electro-viscoelasticity is used to derive the problem statement in the case of monoharmonic loading. Within this theory, the concept of complex-value modulae is applied to formulate the relations between main field characteristics. It is also supposed that the piezo-active material characteristics do not depend on the temperature. Then the coupled problem is reduced to the problem of mechanics on the forced nonlinear vibrations and dissipative heating of the layered plate. Complete set of complex analogs of motion equations, geometric equations and constitutive relations was used to derive the resolving system of equations. Numerical method to attack this nonlinear system of ordinary differential equations supplemented with necessary boundary conditions is developed.

APA, Harvard, Vancouver, ISO, and other styles

47

Benschop, H. O. G., A. J. Greidanus, R. Delfos, J. Westerweel, and W. P. Breugem. "Deformation of a linear viscoelastic compliant coating in a turbulent flow." Journal of Fluid Mechanics 859 (November 21, 2018): 613–58. http://dx.doi.org/10.1017/jfm.2018.813.

Full text

Abstract:

We investigate the deformation of a linear viscoelastic compliant coating in a turbulent flow for a wide range of coating parameters. A one-way coupling model is proposed in which the turbulent surface stresses are expressed as a sum of streamwise-travelling waves with amplitudes determined from the stress spectra of the corresponding flow over a rigid wall. The analytically calculated coating deformation is analysed in terms of the root-mean-square (r.m.s.) surface displacement and the corresponding point frequency spectra. The present study systematically investigates the influence of five coating properties namely density, stiffness, thickness, viscoelasticity and compressibility. The surface displacements increase linearly with the fluid/solid density ratio. They are linearly proportional to the coating thickness for thin coatings, while they become independent of the thickness for thick coatings. Very soft coatings show resonant behaviour, but the displacement for stiffer coatings is proportional to the inverse of the shear modulus. The viscoelastic loss angle has only a significant influence when resonances occur in the coating response, while Poisson’s ratio has a minor effect for most cases. The modelled surface displacement is qualitatively compared with recent measurements on the deformation of three different coatings in a turbulent boundary-layer flow. The model predicts the order of magnitude of the surface displacement, and it captures the increase of the coating displacement with the Reynolds number and the coating softness. Finally, we propose a scaling that collapses all the experimental data for the r.m.s. of the vertical surface displacement onto a single curve.

APA, Harvard, Vancouver, ISO, and other styles

48

Sancaktar, Erol. "Constitutive Behavior and Testing of Structural Adhesives." Applied Mechanics Reviews 40, no. 10 (October 1, 1987): 1393–402. http://dx.doi.org/10.1115/1.3149541.

Full text

Abstract:

Material characterization of structural adhesives in the bulk and bonded forms is discussed. Constitutive relations used for describing stress–strain data are reviewed. The difficulties associated with adhesive characterization in the bonded form are cited. Common testing procedures for adhesive characterization in the bulk and bonded forms are reviewed. In presenting the constitutive relations used in material characterization of structural adhesives, deformation theories introduced by Hencky are reviewed first. The modifications made in this theory to render it rate dependent and bilinear are discussed and applications to adhesive characterization are cited. Application of linear viscoelasticity, mechanical model characterization, and its use in describing the dependence of adhesive and cohesive strengths on rate, temperature, and bond thickness are presented. The time–temperature superposition principle and three-dimensional stress–strain relations in integral and differential operator forms are reviewed. Frequent assumptions for dilatation and distortion operations are presented. Procedures for describing nonlinear viscoelastic behavior are reviewed. It is pointed out that the extent of nonlinearity is dependent on both the stress level and the time scale. The use of nonlinear spring and dashpot elements, nonlinear differential operators, and perturbation of elastic and viscous coefficients are cited. Prandtl’s incremental theory of plasticity and its extension in the form of over-stress theory is presented. The incorporation of this over-stress idea into the viscoelastic mechanical model characterization is discussed. The modified Bingham model and the Chase–Goldsmith model developed in this fashion and their application to adhesive material characterization are presented. The use of empirical relations for the description of creep behavior is discussed. Prediction of shear behavior based on bulk tensile data is demonstrated. It is suggested that characterization of adhesive behavior in the bonded form should include the application of stress analysis, fracture mechanics, polymer chemistry and surface analysis techniques. In testing bonded samples the use of thick adherend symmetric single lap geometry or napkin ring test geometry is advised and it is suggested that the specimens should be prepared with the same surface preparation and cure techniques.

APA, Harvard, Vancouver, ISO, and other styles

49

Wu, B., Y. Gan, E. Carrera, and W. Q. Chen. "Three-dimensional vibrations of multilayered hollow spheres submerged in a complex fluid." Journal of Fluid Mechanics 879 (October 1, 2019): 682–715. http://dx.doi.org/10.1017/jfm.2019.681.

Full text

Abstract:

Fluid–structure interaction is fundamental to the characteristics of the induced flows due to the motion of structures in fluids and also is crucial to the performance of submerged structures. This paper presents a three-dimensional analytical study of the intrinsic free vibration of an elastic multilayered hollow sphere interacting with an exterior non-Newtonian fluid medium. The fluid is assumed to be characterized by a compressible linear viscoelastic model accounting for both the shear and compressional relaxation processes. For small-amplitude vibrations, the equations governing the viscoelastic fluid can be linearized, which are then solved by introducing appropriate potential functions. The solid is assumed to exhibit a particular material anisotropy, i.e. spherical isotropy, which includes material isotropy as a special case. The equations governing the anisotropic solid are solved in spherical coordinates using the state-space formalism, which finally establishes two separate transfer relations correlating the state vectors at the innermost surface with those at the outermost surface of the multilayered hollow sphere. By imposing the continuity conditions at the fluid–solid interface, two separate analytical characteristic equations are derived, which characterize two independent classes of vibration. Numerical examples are finally conducted to validate the theoretical derivation as well as to investigate the effects of various factors, including fluid viscosity and compressibility, fluid viscoelasticity, solid anisotropy and surface effect, as well as solid intrinsic damping, on the vibration characteristics of the submerged hollow sphere. Particularly, our theoretically predicted vibration frequencies and quality factors of gold nanospheres with intrinsic damping immersed in water agree exceptionally well with the available experimentally measured results. The reported analytical solution is truly and fully three-dimensional, covering from the purely radial breathing mode to the torsional mode to any general spheroidal mode as well as being applicable to various simpler situations, and hence can be a broad-spectrum benchmark in the study of fluid–structure interaction.

APA, Harvard, Vancouver, ISO, and other styles

50

Li, Mei, Zhi Qiang Li, Jun Xu, Dun Sheng Wei, Hong Wei Zhu, and Dong Li. "Thermal Property, Morphology, Mechanical and Rheological Properties of a Modified Bio-Polymers Prepared by Blending Poly(3-Hydrobutyrate-Co-4-Hydrobutyrate) with Chain Extenders." Advanced Materials Research 152-153 (October 2010): 924–30. http://dx.doi.org/10.4028/www.scientific.net/amr.152-153.924.

Full text

Abstract:

Modified Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] was prepared by melt reactive blending P(3HB-co-4HB) with chain extenders (ADR-4367). Thermal transitions, spherulitic and freeze-fracture morphology, mechanical and rheological properties of the chain extended bio-materials were investigated. The results show that glass transition temperatures and crystallization temperatures increase, crystallinity and diameters of spherulites decrease, there are amorphous parts dispersed among the crystalline phase, and the bio-materials transfer from brittleness to toughness and ductility. Steady shear viscosity of the modified P(3HB-co-4HB) increases by about one order of magnitude, melts of the modified P(3HB-co-4HB) behave more viscoelasticity by storage modulus and loss modulus correlated with oscillatory shear frequency. Addition of ADR-4367 with contents of 4~6 wt% in the blends is enough to branching and coupling the co-polymer chains and brings remarkable effect on improving mechanical properties, steady shear viscosity and viscoelasticity.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Viscoelasticity. Shear (Mechanics)'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles