Top PDF Nonlinearly viscoelastic response of glassy polymers

Nonlinearly viscoelastic response of glassy polymers

Nonlinearly viscoelastic response of glassy polymers

According to the kinematic and constitutive descriptions of a linearly viscoelastic solid cylinder under torsion, the maximum surface shear strain and stress on the specimen, namely, E'm[r]

124 Read more

Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders

Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders

The master curves provide a useful interpretation of the influence of polymer and crumb rubber modification on the rheological properties of the modified binders. At high frequencies, the rheological behaviour of the modified binders (polymer and rubber) is dominated by the base bitumen used in their production. This results in the SBS and EVA PMBs together with the TRN and TRW MBs having similar G* values although the semi- crystalline EVA PMB is slightly higher due to its plastomeric nature. It is envisaged that all four modified binders (as with the three penetration grade bitumens) will all approach a similar upper limiting stiffness (glassy modulus) with similar rheological properties. However, at intermediate and particularly at low frequencies, there is a significant increase in complex modulus due to the stiffening effect of the polymers and crumb rubber. This results in the rheological behaviour shifting from that seen for an intermediate grade bitumen (40/60 pen) at intermediate frequencies (temperatures) to, at a minimum, a hard (10/20 pen) bitumen at low frequencies (high temperatures). This increased stiffness and reduced temperature (and time) susceptibility are key benefits of both polymer and crumb tyre rubber modification.
Show more

45 Read more

A toolbox for parameter free predictions of solid state properties of monodisperse glassy polymers with frozen in molecular orientation

A toolbox for parameter free predictions of solid state properties of monodisperse glassy polymers with frozen in molecular orientation

new, fully three-dimensional constitutive model that uses the linear viscoelastic spectrum in the melt and solid states to predict the nonlinear melt-state and solid-state constitutive response of glassy polymers. 15 By fitting this model to linear viscoelastic rheological data obtained from two monodis- perse linear polystyrenes (PS), the authors demonstrated a remarkable result: that it is possible to predict the optical birefringence, 14 the craze initiation stress, 10 and the solid- state mechanical response 15 of a polymer of given molar mass subjected to an arbitrary process history, with a small number of molar mass-independent material constants and experimental measurement of the molar mass-dependent melt-state linear viscoelastic spectrum.
Show more

9 Read more

NUMERICAL SIMULATION OF VISCOELASTIC MATERIALS

NUMERICAL SIMULATION OF VISCOELASTIC MATERIALS

as polymers, glassy materials, soils, biologic tissue, and textiles exhibit viscoelastic behavior. Material is viscoelastic if its stress response consists of an elastic part and viscous part. Upon application of a load, the elastic response is instantaneous while the viscous part changes over time. Generally, the stress function of viscoelastic materials can be de- fined in an integral form. Within the context of small strain theory, the constitutive equation for isotropic viscoelastic material can be written as follows:

9 Read more

Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders

Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders

The master curves provide a useful interpretation of the influence of polymer and crumb rubber modification on the rheological properties of the modified binders. At high frequencies, the rheological behaviour of the modified binders (polymer and rubber) is dominated by the base bitumen used in their production. This results in the SBS and EVA PMBs together with the TRN and TRW MBs having similar G* values although the semi- crystalline EVA PMB is slightly higher due to its plastomeric nature. It is envisaged that all four modified binders (as with the three penetration grade bitumens) will all approach a similar upper limiting stiffness (glassy modulus) with similar rheological properties. However, at intermediate and particularly at low frequencies, there is a significant increase in complex modulus due to the stiffening effect of the polymers and crumb rubber. This results in the rheological behaviour shifting from that seen for an intermediate grade bitumen (40/60 pen) at intermediate frequencies (temperatures) to, at a minimum, a hard (10/20 pen) bitumen at low frequencies (high temperatures). This increased stiffness and reduced temperature (and time) susceptibility are key benefits of both polymer and crumb tyre rubber modification.
Show more

45 Read more

Glassy Carbons

Glassy Carbons

ments that glassy carbon is not a single material, even when made from the same starting polymer system, but rather a class of materials whose structure and resulting properties can be t[r]

91 Read more

Nonlinearly testing for a unit root in the presence of a break in the mean

Nonlinearly testing for a unit root in the presence of a break in the mean

Section 3 presents and discusses estimated distributions of the statistics for testing time series with a break for a unit root, comparing those based on the linear and nonlinear test eq[r]

33 Read more

Some observations of nonlinearly modified internal wave spectra

Some observations of nonlinearly modified internal wave spectra

Either spectra are dominated at tidal and/or inertial nonlinear higher harmonics superposed on a nearly white (noise) spectral continuum, the latter extending to supertidal frequencies u[r]

6 Read more

Host immune response to anti-cancer camptothecin conjugated cyclodextrin-based polymers

Host immune response to anti-cancer camptothecin conjugated cyclodextrin-based polymers

Although some proinflammatory factors or neutrophil- attracting factors, such as MMP3, CCL5, leptin and VEGF- A, were decreased in the IT-101-treated group, other factors like sCD30, sCD30L, sCD40 and sCD40L (that are reported inflammatory markers in cancer patients), were elevated in the circulation of IT-101-treated mice. In ovarian cancer pa- tients, an increase in sCD30, sCD30L and sCD40 could be early diagnostic indicators, and all of these factors may im- pair apoptosis and interrupt the immune response [23]. The expression levels of sCD30, as well as sCD30L, in circulation could also be used as a prognostic marker for Hodgkin lymphoma [24–26]. High levels of sCD40 have been found associated with advanced pathogenesis and poor prognosis in non-small cell lung cancer patients [27]. Similarly, reports have showed high levels of sCD40L in patients with neopla- sia and nasopharyngeal carcinoma (NPC); hence, sCD40L might be a prognostic biomarker for NPC [28, 29]. Add- itionally, sCD40L could be a diagnostic marker for hepatitis C virus-related hepatocellular carcinoma [30]. The CD40/ CD154 interaction plays critical functions in humoral and cellular immune responses. Elevated levels of the soluble form of CD40 (sCD40) have been observed in patients in uremic or hemodialyzed situations; of note, sCD40 is able to inhibit immunoglobulin generation from CD154-induced activated B cells [31].
Show more

12 Read more

Electrochemical Response of Glassy Carbon Electrodes Modified using Graphene Sheets of Different Sizes

Electrochemical Response of Glassy Carbon Electrodes Modified using Graphene Sheets of Different Sizes

In this study, we investigated the electrochemical behavior of reduced graphene oxide sheets (rGO) of different sizes deposited on glassy carbon electrodes. Graphene oxide sheets were produced by the exfoliation of graphite oxide in an aqueous solution by ultrasonication. Scanning electron microscopy and transmission-mode scanning electron microscopy results indicated a decrease in the size of the graphene oxide sheets with an increase in the exfoliation time or sonication power. The results of spectroscopic characterization corroborated with this behavior. X-ray diffraction analysis indicated a broadening of the peaks with crystallite size reduction while Raman spectroscopy results suggested an increase in the structural defects in the sp 2 framework of graphene oxide. Complementary X-ray photoemission spectroscopy analysis indicated a decrease in the sp 2 /sp 3 ratio with respect to the amount of sp 2 framework in graphene oxide sheets upon decreasing the sheet size. Electrochemical analysis showed that the response of the GO-modified glassy carbon electrodes increased significantly with a decrease in the graphene oxide sheet size.
Show more

17 Read more

Viscoelastic damping of beams

Viscoelastic damping of beams

because they neglected the on acting was primarily the modulus higher Based have [5,6], the the the elastic relation end conditions by Asnani and Nakra elastic the of and Ross, Kerwin, l[r]

78 Read more

SIR3: Dimension reduction in the presence of linearly or nonlinearly related predictors

SIR3: Dimension reduction in the presence of linearly or nonlinearly related predictors

Sufficient dimension reduction ( sdr ) is an effective tool for reducing high- dimensional predictor spaces in regression problems. sdr achieves dimen- sion reduction without loss of any regression information and without the need to assume any particular parametric form of a model. This is particularly useful for high-dimensional applications such as data min- ing, marketing, and bioinformatics. However, all sdr methods require a linearity condition on the predictor distribution, and that restricts the applications of sdr . In this article, we propose a new sdr method, sir 3 , which does not require the linearity condition, and which we show to be effective when nonlinearly-related predictors are present. sir 3 is an extension of a representative sdr method sliced inverse regression ( sir ), and it is shown that sir 3 reduces to sir when the linearity condition holds. A simulation study and a real data application are presented to demonstrate the effectiveness of the proposed method.
Show more

25 Read more

Review on Viscoelastic Materials used in Viscoelastic Dampers

Review on Viscoelastic Materials used in Viscoelastic Dampers

David W. Dinehart (2001) Twelve viscoelastic dampers were tested under static loading to failure. Half of the dampers were comprised of VE material and A36 steel, typical of most VE dampers, while the other half used wood in lieu of steel. Two wood and steel specimens were tested for each of the three different thicknesses of VE material used. Comparison of the replicate dampers showed that there was no difference between the performance of the steel and wood dampers. The damper tests indicated that VE material could be applied directly to wood. The initial fullscale results showed that the application of viscoelastic sheet material between the sheathing and wall frame could be an effective method for improving the energy dissipation characteristics of wood-frame shear walls. Furthermore, the installation of the sheet material was such that there was no impact to the dimensions of the wall. This innovative application of VE material could be used in new design or the retrofitting of wood-frame structures. However, it must be emphasized that only limited testing, on the dampers and wall, was conducted and that further testing is necessary to verify these initial results, and investigate such matters as environmental effects, optimal of material thickness and type, and repeatability.
Show more

7 Read more

Mechanical Characteristics of SPG-178 Hydrogels: Optimizing Viscoelastic Properties through Microrheology and Response Surface Methodology

Mechanical Characteristics of SPG-178 Hydrogels: Optimizing Viscoelastic Properties through Microrheology and Response Surface Methodology

Precise measurement of the viscoelastic properties of SApeptides is crucial for their optimization in different applications. Traditionally, viscoelastic properties are provided through rheological measurements, undertaken using rheometers. However, the traditional rheometers are limited to low frequencies. Even though low frequency range is appropriate for solid- or liquid-like behavior, there are many complex fluids with microstructural relaxations that occur at higher frequencies. On the other hand, these devices require milliliter-scale material samples, but most biological samples are available in much lower quantities. Since the stress or strain is applied from boundaries, the bulk viscoelastic properties are measured, and the heterogeneities are not probed. This is a serious limitation for non-homogeneous materials with various microstructural length scales. Moreover, the traditional rheometers are not applicable to non- conventional geometries, such as thin films or the interior of biological cells and membranes. Therefore, such limitations have motivated the development of a number of techniques to probe the viscoelastic properties of materials on microscopic length scales. These microrheological techniques can probe local viscoelastic properties from small sample volumes
Show more

9 Read more

Electrocatalytic Response of Hydroquinone and Catechol at Polyglycine Modified Glassy Carbon Electrode

Electrocatalytic Response of Hydroquinone and Catechol at Polyglycine Modified Glassy Carbon Electrode

Voltammetric measurements were performed with a CHI 440 electrochemical analyzer (CH Instruments, Chenhua Co. Shanghai, China). A conventional three-electrode cell was used, including a saturated calomel electrode (SCE) as reference electrode, a platinum wire counter electrode and a bare or modified glassy carbon disk working electrode (GCE). The pH values were measured with a PB-10 pH meter (Satorius). Unless otherwise stated, the electrolyte solutions were thoroughly degassed with N 2 and kept under a N 2 blanket.

10 Read more

Problematic stabilizing films in petroleum emulsions: shear rheological response of viscoelastic asphaltene films and the effect on drop coalescence.

Problematic stabilizing films in petroleum emulsions: shear rheological response of viscoelastic asphaltene films and the effect on drop coalescence.

A second deformation mode of the interfacial material can be described as the deformation by shear applied to a constant interfacial area, as opposed to the variable area as encountered during the dilatation. 19 Kilpatrick and co-workers reinvigorated interest in the shear rheological response of petroleum films. 20, 21 Applying the bicone technique, the authors conducted an extensive study on the interfacial films of asphaltenes extracted from different crude oils. They concluded that asphaltenes of lower aromaticity and higher nitrogen and metal contents form stable emulsion as a result of film aging which increases yield stress as measured under shear. In higher aliphatic solvents the onset of asphaltene precipitation was observed to delay film formation and the development of microstructure elasticity. Below the onset of precipitation, film aging kinetics increased closer to the solubility limit. 20 Possibly due to the inertial contribution of the bicone, the authors did not report any effect of aging at relatively short aging time, < 2 hr.
Show more

31 Read more

Brownian Motion in Viscoelastic Media

Brownian Motion in Viscoelastic Media

The utility of the tracer microrheology technique in gaining a deeper insight into the viscoelastic response of complex fluids has been discussed thus far in the context of the polyethylene oxide (PEO) system and will later be discussed in the context of the more complex FCC forming triblock copolymer Pluronic™ F108. For the simple flexible polymer, PEO, it was observed that the Generalized Stokes-Einstein Equation adequately described the tracer Brownian motion in this system, as evidinced through the good quantitative agreement between the viscoelastic properties extracted from tracer microrheology and those extracted from mechanical rheometry. The sphere size sweeps carried out on this system also exhibited a complete collapse of the data into a single master J(t) curve. This was indicative that longitudinal compression modes did not affect the extracted rheological parameters. In order to extend the understanding of probe motion in viscoelastic media further, a systematic tracer/ mechanical rheometry investigation was extended to a worm like micellar system. The system that was chosen was the worm like micellar system-Cetyltrmethylammonium Bromide/ Sodium Salicylate. This system was chosen because wormlike micelles have striking similarities with polymeric systems, yet exhibits more interesting and complicated static and dynamic behavior(1- 15).
Show more

233 Read more

Arbitrary decays for a viscoelastic equation

Arbitrary decays for a viscoelastic equation

It is well known that viscoelastic materials have memory effects. These properties are due to the mechanical response influenced by the history of the materials themselves. As these materials have a wide application in the natural sciences, their dynamics are of great importance and interest. From the mathematical point of view, their memory effects are modeled by an integro-differential equations. Hence, questions related to the behavior of the solutions for the PDE system have attracted considerable attention in recent years. Many authors have focused on this problem for the last two decades and several results concerning existence, decay and blow-up have been obtained, see [1-28] and the reference therein.
Show more

14 Read more

Damping of elastic-viscoelastic beams

Damping of elastic-viscoelastic beams

LIST OF ILLUSTRATIONS Figure 1.1 Analog Model for Viscoelastic Behavior of Material Figure 1.2 Dependence Materials on of Dynamic Behavior Temperature and of 5 Viscoelastic Frequency 7 F[r]

123 Read more

Implementation of viscoelastic Hopkinson bars

Implementation of viscoelastic Hopkinson bars

tension or torsion, and true strains of 0.3 can be readily achieved in a single test. The most widely used techniques normally implement metallic Hopkinson bars [5], which can have a material impedance in the region of 40 MPa s/m. These metallic bars experience difficulties when testing materials which have a significantly lower impedance than the bar being used to test them, meaning that testing of soft materials with an impedance of 2 MPa s/m is not possible. One solution to over coming this problem has been to simply use a bar material which has an impedance closer to that of the material being tested. As a result polymers have been used as Hopkinson bars as they have an impedance in the region of 4 MPa s/m. This paper deals with the implementation of polymeric Hopkinson bars which will enable testing of soft materials on a Split Hopkinson Pressure Bar (SHPB) setup.
Show more

6 Read more

Show all 10000 documents...