Viscoelastic flows through microscale porous arrays exhibit complex path selection and switching phenomena. However, understanding this process is limited by a lack of studies linking between a ...single object and large arrays. Here, we report experiments on viscoelastic flow past side-by-side microcylinders with variable intercylinder gap. With increasing flow rate, a sequence of two imperfect symmetry-breaking bifurcations forces selection of either one or two of the three possible flow paths around the cylinders. Tuning the gap length through the value where the first bifurcation becomes perfect reveals regions of bistability and tristability in a dimensionless flow rate-gap length phase diagram.
Rheology of vitrimers Meng, Fanlong; Saed, Mohand O; Terentjev, Eugene M
Nature communications,
09/2022, Letnik:
13, Številka:
1
Journal Article
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Abstract
We describe the full rheology profile of vitrimers, from small deformation (linear) to large deformation (non-linear) viscoelastic behaviour, providing concise analytical expressions to ...assist the experimental data analysis, and also clarify the emerging insights and rheological concepts in the subject. We identify the elastic-plastic transition at a time scale comparable to the life-time of the exchangeable bonds in the vitrimer network, and propose a new method to deduce material parameters using the Master Curves. At large plastic creep, we describe the strain thinning when the material is subjected to a constant stress or force, and suggest another method to characterize the material parameters from the creep curves. We also investigate partial vitrimers including a permanent sub-network and an exchangeable sub-network where the bond exchange occurs. In creep, such materials can exhibit either strain thinning or strain thickening, depending on applied load, and present the phase diagram of this response.
A novel Eulerian approach is proposed for numerical simulations of wave propagation in viscoelastic media, for application to shocks interacting with interfaces between fluids and solids. We extend ...the five-equations multiphase interface-capturing model, based on the idea that all the materials (gases, liquids, solids) obey the same equation of state with spatially varying properties, to incorporate the desired constitutive relation; in this context, interfaces are represented by discontinuities in material properties. We consider problems in which the deformations are small, such that the substances can be described by linear constitutive relations, specifically, Maxwell, Kelvin–Voigt or generalized Zener models. The main challenge lies in representing the combination of viscoelastic, multiphase and compressible flow. One particular difficulty is the calculation of strains in an Eulerian framework, which we address by using a conventional hypoelastic model in which an objective time derivative (Lie derivative) of the constitutive relation is taken to evolve strain rates instead. The resulting eigensystem is analyzed to identify wave speeds and characteristic variables. The spatial scheme is based on a solution-adaptive formulation, in which a discontinuity sensor discriminates between smooth and discontinuous regions. To compute the convective fluxes, explicit high-order central differences are applied in smooth regions, while a high-order finite-difference Weighted Essentially Non-Oscillatory (WENO) scheme is used at discontinuities (shocks, material interfaces and contacts). The numerical method is verified in a comprehensive fashion using a series of smooth and discontinuous (shocks and interfaces), one- and two-dimensional test problems.
•The five-equations multiphase model is extended to viscoelastic fluids and solids.•A Lie derivative of the constitutive model transforms strains into strain rates.•We show how viscoelasticity modifies the eigensystem, and thus the wave speeds.•Our solution-adaptive approach is fourth-order accurate on smooth problems.•Spurious pressure/temperature errors at interfaces are prevented.
It has long been recognized that biofilms are viscoelastic materials, however the importance of this attribute to the survival and persistence of these microbial communities is yet to be fully ...realized. Here we review work, which focuses on understanding biofilm mechanics and put this knowledge in the context of biofilm survival, particularly for biofilm-associated infections. We note that biofilm viscoelasticity may be an evolved property of these communities, and that the production of multiple extracellular polymeric slime components may be a way to ensure the development of biofilms with complex viscoelastic properties. We discuss viscoelasticity facilitating biofilm survival in the context of promoting the formation of larger and stronger biofilms when exposed to shear forces, promoting fluid-like behavior of the biofilm and subsequent biofilm expansion by viscous flow, and enabling resistance to both mechanical and chemical methods of clearance. We conclude that biofilm viscoelasticity contributes to the virulence of chronic biofilm infections.
In the present work, the definition of memory dependent derivative (MDD) heat transfer in an infinite solid body was used to investigate the problem of wave characteristics in an unbounded ...thermoelectric viscoelastic solid caused by a continuous line heat source in the presence of a uniform magnetic field. Both Laplace and Hankel transform strategies are used to acquire the widespread answer in a closed form. Analytical findings were obtained for the distribution within the medium of various fields such as temperature, displacement, and stresses. For the inversion of the Laplace transformations, a computational approach is used. The distributions of the numerical consequences of the non-dimensional considered bodily variables are represented graphically. Detailed comparative evaluation is represented thru the numerical outcomes to estimate the results of the kernels, time-delay and magnetic number on the behavior of all variable. The effect offers a concept to research main thermoelectric viscoelastic materials as any other type of pertinent materials.
Fractional derivative models, which are expressed by combining standard dashpots, fractional dashpots and elastic springs in series or parallel, are often utilized to account for the behaviors for ...viscoelastic materials. Even with the models extended to finite deformation, the precise definition of objective fractional derivative remains challenging. The proposed fractional derivative model is expressed by the combination of an elastic spring in series with two parallel fractional dashpots. We extend the fractional derivative model to finite deformation through a new approach without defining an objective fractional derivative and assuming the decomposition of the deformation rate into the elastic and inelastic parts. This proposed model can be reduced to the Maxwell model for finite deformation. Such reduction results in a model that stands in between the two existing Maxwell models in which the objective rate of the Cauchy stress is taken as the material corotational rate and the relative corotational rate respectively. The proposed model is applied to the simple shear deformation.
Abstract
We describe the trapping and absorption of audible sound in centimeter-scale claddings of two-dimensional, locally resonant phononic crystals. In a square lattice of local resonators ...consisting of steel cores and cellulose shells, embedded in a viscous foam, dual acoustic-range band gaps extending from about 200 to
$$2850 \text { Hz}$$
2850
Hz
are achieved. The spectral range consists of a low-frequency, local resonance gap, separated from a higher frequency Bragg resonance gap, by narrow bands of slow-sound modes. We demonstrate that thin claddings of such phononic crystal, of only three unit cells in thickness, can effectively prevent sound transmission, by a combination of reflection and absorption, over much of the audible spectrum. Moreover, frequency-selective sound transmission can be enabled by engineering waveguide channels that transmit sound through the local resonance gap, the Bragg gap, or both. This offers a path to sound-sculpting claddings that can surround a noise-generating source. The viscoelastic foam in our cladding is treated using a fractional Voigt model, capable of describing experimentally observed responses.
Dispersion states are vital for fibrous nanocelluloses to be used as reinforcements for polymers, which is highly dependent on geometry of nanocelluloses. Three types of nanocelluloses with various ...fiber aspect ratios were used to prepare target composite samples with poly(β-hydroxybutyrate) in this work. Viscoelasticity/elastoplasticity were used as probes to detect the flexibility-morphology relations of nanocelluloses in polymer. Cellulose nanocrystals (aspect ratio = 8) were rigid in polymer, retaining their rod-like shape, whereas bacterial celluloses (aspect ratio = 600) fully flexible, forming closely networked structure, and cellulose nanofibers (aspect ratio = 70) semi-flexible, dispersing as loosely flocculated clusters. Owing to these differences, the viscoelastic flow and elastoplastic deformation of three kinds of composites differed from one another. The strain-scaling and hysteresis work-scaling behaviors were then used to establish relaxation scale-structure correlations of target samples. This work provides interesting information around regulating the dispersion of nanocelluloses in polymer composites by tailoring aspect ratios of nanocelluloses.
•Percolation thresholds of composites reduce with increased aspect ratios of fibers.•Stress-scaling is independent on the geometry or size of fibers during start-up flow.•Hysteresis energy-scaling is independent on the loading and aspect ratios of fibers.
A new micromechanically motivated theory is proposed to model dragline silk. A thorough review of the micro-structure of dragline silk is presented. Based on the review, a continuum framework is ...utilized to develop constitutive equation of dragline silk. Dragline silk is composed of a dominant soft amorphous phase (α-phase) and a reinforcing hard crystal phase, which is classified as rigid β-sheets and extremely soft β-spirals. These two different β-fillers have completely different effects on the mechanical behaviors of dragline silk. The former results in the Mullins effect while the latter produces plastic deformation. Both these effects result in energy dissipation. In addition to these effects, the damping effect due to finite viscoelasticity is accounted for by using a double network model. Moreover, the highly oriented chains in the amorphous phase are modeled as an anisotropic network model. It is found that the proposed model accurately captures the complex mechanical behavior of dragline silk subjected to cyclic loading with merely 7 “physically-based” material constants.
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