Viscoelastic Domain Research Articles

Effect of synthetic and functionalized waxes on bituminous binders: From the glassy state to the intermediate viscoelastic domain

A 50/70 bitumen was modified with five different commercial waxes, including Fischer-Tropsch, Montan and functionalized waxes. Thermal and morphological properties were investigated through Differential Scanning Calorimetry (DSC) and polarized optical microscopy (POM). Dynamic and continuous rheological tests were carried out to analyse the mechanical response of wax-modified bitumens (WMB). Theories behind possible mechanisms of asphalt/wax interaction are discussed. The entire frequency/temperature domain was divided into two macro-regions. The first one covers the glassy state, with independent waxy structures, where the bitumen mainly determines the mechanical response. The second macro region develops along the intermediate viscoelastic domain and propagates towards high temperatures/low frequencies. Within this domain, all WMB exhibits a complex mechanical response, with gel-like characteristics, thus suggesting the existence of physical networks and interconnections between contiguous wax crystalline segments.

Free damped vibration analysis of Mindlin plates with hybrid material-foundation viscoelasticity

Suppressed vibration of shear deformable plates with hybrid viscoelastic damping of material and foundation is investigated. Viscoelasticity of foundation is established by adopting Kelvin-Voigt model while viscoelasticity of materials is expressed by Boltzmann superposition integral, which uses dynamic mechanical analysis (DMA) results in terms of Prony series. Application of Laplace transformation and Mindlin plate theory with Hamilton principle led to a system of coupled integro-PDE of motions. Weighted residual method, numerical iterative algorithm and Fourier transform are implemented to achieve complex frequencies and transient responses of plates. Assessment of accuracy is carried out in the both elastic and viscoelastic domains. In the earlier, the frequencies are compared with counterparts obtained by p-version Ritz method and in the latter, dynamic characteristics of Mindlin and classic plates are examined that represent acceptable correlation. The influences of hybrid material-foundation damping, edge conditions, foundation characteristics and geometrical parameters on dynamic characteristics of plates are studied via a set of parametric study.

Application of Time-Temperature Superposition Principle on Fatigue Failure Analysis of Asphalt Binder

The linear amplitude sweep (LAS) test has been proposed for fatigue specifications of asphalt binders. Recently, a newly developed fatigue failure definition and energy-based failure criterion have been proposed for improving the LAS procedure and data interpreting; however, these improvements only affect LAS data conducted at a constant temperature. This paper, therefore, discusses the loading temperature effects on LAS-based binder fatigue, damage evolution, and final fatigue failure occurrence. Experimental results indicate that both damage characteristic curves (DCCs) and the failure criterion derived from the simplified-viscoelastic continuum damage (S-VECD) model are strongly affected by the testing temperature. However, the temperature shift factors determined from the dynamic shear modulus testing within the linear viscoelastic domain have been proven to be effective in eliminating the temperature influence for both fatigue DCCs and the failure criterion. The validation on binder phase demonstrates that the time-temperature superposition principle (TTSP) shift factor is only a function of temperature and is independent of strain level. TTSP application on both undamaged and damaged material behaviors is able to greatly improve the testing efficiency of the LAS-based binder fatigue characterization.

Anisotropy of bituminous mixture in the linear viscoelastic domain

Some anisotropic properties in the linear viscoelastic domain of bituminous mixtures compacted with a French LPC wheel compactor are highlighted in this paper. Bituminous mixture is generally considered as isotropic even if the compaction process on road or in laboratory induces anisotropic properties. Tension–compression complex modulus tests have been performed on parallelepipedic specimens in two directions: (i) direction of compactor wheel movement (direction I, which is horizontal) and (ii) direction of compaction (direction II, which is vertical). These tests consist in measuring sinusoidal axial and lateral strains as well as sinusoidal axial stress, when sinusoidal axial loading is applied on the specimen. Different loading frequencies and temperatures are applied. Two complex moduli, $E_{\mathrm{I}} ^{*}$ and $E_{\mathrm{II}}^{*}$ , and four complex Poisson’s ratios, $\nu_{\text{II-I}}^{*}$ , $\nu_{\text{III-I}}^{*}$ , $\nu_{\text{I-II}}^{*}$ and $\nu_{\text{III-II}}^{*}$ , were obtained. The vertical direction appears softer than the other ones for the highest frequencies. There are very few differences between the two directions I and II for parameters concerning viscous effects (phase angles $\varphi(E_{\mathrm{I}})$ and $\varphi(E_{\mathrm{II}})$ , and shift factors). The four Poisson’s ratios reveal anisotropic properties but rheological tensor can be considered as symmetric when considering very similar values obtained for the two measured parameters (I-II and II-I) In addition, an anisotropic 3 dimensional version of the “2S2P1D” (2 springs, 2 parabolic creep elements and 1 dashpot) model, developed at the University of Lyon—ENTPE laboratory, is presented and used to simulate experimental results. The model simulation provides a good fit to the data. Stability of the material could also be investigated on the whole frequency–temperature range.

Viscoelastic rough contact mechanics: A multiscale investigation

The full understanding of the viscoelastic contact mechanics between rough surfaces is a crucial issue in modern engineering research. This paper investigates the role that the number of rough scales, i.e. the cut-off of the power spectrum of the surface roughness, has on quantities like contact area, mean separation, and friction. Furthermore, an effective, though approximate, definition of an equivalent modulus is provided in order to reduce the viscoelastic contact domain to an elastic equivalent one.

Characterization of the three-dimensional linear viscoelastic behavior of asphalt concrete mixtures

Mechanistic-empirical pavement design methods typically require the identification of the complex Young’s modulus and Poisson’s ratio for the characterization of bituminous layers. However, since in small deformation the frequency-dependent shear and bulk responses of an isotropic body are decoupled, the complex shear and bulk moduli are generally considered fundamental response functions. The objective of this study was to perform the experimental characterization of the three-dimensional response of asphalt mixtures in the linear viscoelastic domain, through the simultaneous measurement of the complex moduli E∗, K∗ and G∗ and the complex Poisson’s ratio ν∗. The testing program consisted of cyclic compression and cyclic tension–compression uniaxial tests on cylindrical specimen, with the measurement of both axial and transverse strain. In particular, frequency sweeps were carried out at temperatures between 0, and 40°C and at axial strain levels between 15 and 60με. Experimental results highlighted that, for the tested mixture, the time–temperature superposition principle was applicable to both the bulk and shear response, and consequently to the axial response. E∗ and G∗ showed very similar trends in terms of both stiffness moduli and loss angle, whereas K∗ values highlighted smaller frequency dependence. The time–temperature superposition principle was also applicable to ν∗ whose master curves can be qualitatively described using the local approximation to the Kramers–Kronig relations. Results suggest that the simultaneous assessment of bulk and shear response may be a useful tool for the performance characterization of asphalt mixtures.

The Symplectic Method in Polar Coordinates for Linear Viscoelastic Materials

In this study, the symplectic method is applied to a two-dimensional annular-sector viscoelastic domain under the polar coordinate system. By applying variable separation approach, all fundamental solutions are derived in analytical form. Furthermore, using the method of variable substitution, lateral conditions are transformed into finding a particular solution for the governing equations, and this particular solution is derived with the use of eigensolution expansion. In the numerical example, the boundary condition problem is discussed in detail to analyze the stress response of viscoelastic solids.

Modelling asphalt concrete viscoelasticity with damage and healing

The behaviour under load of asphalt concrete (AC) was viewed as additively separable into viscoelastic and viscoplastic components, and the study focused on modelling the pre-peak response of the viscoelastic part under constant temperature conditions. Non-linear viscoelastic behaviour was first exposed in several test modes, and a constitutive theory was subsequently offered – potentially capable of capturing and reproducing the observations. The modelling was based on replacing applied stresses in the linear convolution formulation with effective stresses; it included a mechanism for simulating the following effects: (i) short-lasting damage, (ii) long-lasting damage, (iii) stiffening under compressive conditions and (iv) healing during recovery intervals. As an initial validation effort, the model’s reproducibility was assessed by calibration to a uniaxial compression experiment consisting of both small and medium strain levels. Next, the calibrated model was employed to forecast small-strain behaviour in a standard complex modulus test. The simulated results qualitatively agree with recently reported findings that challenge the existence of a linear viscoelastic domain for AC.

Changes in the physicomechanical characteristics of a ceramic paste during drying

This paper is a contribution to the determination of the variations of the physical and rheological properties of a ceramic paste during drying. The ceramic's density was determined as a function of moisture content using the Archimedes' Principle. The shrinkage was derived from the experimental density data and also determined by measuring the variation of the sample's dimensions during drying. Compression tests were performed at different deformation rates in order to identify the linear and non-linear viscoelastic domains of the material. Relaxation tests were carried out and the results of fitting showed that the generalized Maxwell model could be used to describe the viscoelastic behavior of the samples. Rupture tests were also made to measure the strength of the material for different moisture contents and to study the influence of temperature on the strength of the dried product.

Molecular weight distribution of asphaltic paving binders from phase-angle measurements

Based on previous works on polymers and regular bitumens, a new method for determining the molecular weight distribution (MWD) of asphaltic paving binders, using the phase angle () of the complex modulus measured in the linear viscoelastic domain, has been developed in this paper. MWDs of pure petroleum bitumens, natural bitumens, modified bitumens and artificially aged bitumens are calculated by this method and compared with MWDs obtained by gel permeation chromatography. The two methods give comparable results, but the δ-method developed here is more sensitive to the molecular weight of species. This method is very simple to implement, and seems a powerful tool in the determination of MWD of bitumens, in the visualisation and repartition of modifiers in the bitumen matrix and in the ageing monitoring and quantification.

On the effects of thermal history on the development and relaxation of thermo-mechanical stress in cryopreservation

This study investigates the effects of the thermal protocol on the development and relaxation of thermo-mechanical stress in cryopreservation by means of glass formation, also known as vitrification. The cryopreserved medium is modeled as a homogeneous viscoelastic domain, constrained within either a stiff cylindrical container or a highly compliant bag. Annealing effects during the cooling phase of the cryopreservation protocol are analyzed. Results demonstrate that an intermediate temperature-hold period can significantly reduce the maximum tensile stress, thereby decreasing the potential for structural damage. It is also demonstrated that annealing at temperatures close to glass transition significantly weakens the dependency of thermo-mechanical stress on the cooling rate. Furthermore, a slower initial rewarming rate after cryogenic storage may drastically reduce the maximum tensile stress in the material, which supports previous experimental observations on the likelihood of fracture at this stage. This study discusses the dependency of the various stress components on the storage temperature. Finally, it is demonstrated that the stiffness of the container wall can affect the location of maximum stress, with implications on the development of cryopreservation protocols.

Bulk and shear characterization of bituminous mixtures in the linear viscoelastic domain

Traffic loads and temperature variations produce three-dimensional stress–strain fields inside road pavements, and therefore the characterization of bituminous mixtures in different deformation modes is important for prediction of the performance of pavement structures. This paper presents a methodology for the bulk and shear characterization of bituminous mixtures in the linear viscoelastic domain, under the hypothesis of material isotropy, by means of uniaxial harmonic tests with the measurement of axial and transverse strains. The theoretical approach was based on the application of the elastic–viscoelastic correspondence principle and was validated by performing tension–compression tests at selected frequencies and temperatures on asphalt concrete specimens characterized by different volumetric properties. The results showed that since uniaxial tests induced both volume and shape variations, the simultaneous measurement of the complex bulk and shear moduli was possible. The validity of the time–temperature superposition principle was also verified for both deformation modes, allowing the construction of master curves for the bulk and shear moduli. The results also showed that the total dissipated energy could be decomposed into its volumetric and deviatoric fractions with excellent accuracy.

Effects of Wheat Flour Dough’s Viscoelastic Level by Adding Glucose Oxidase on its Dynamic Shear Properties whatever the Strain Modes

The objective of this work was to study the effects of wheat flour dough’s viscoelastic level by adding glucose oxidase (Gox) on its rheological properties at dynamic shear strain mode to predict the final product quality. Dough does display a linear viscoelastic domain. Glucose oxidase (Gox) was added to dough in order to enhance its viscoelasticity and to take into account the possible effects of this viscoelasticity on the results. Whatever the types of dough strain used G’ increased, tan δ decreased and led to less sticky dough. Wheat flour dough, an increase in G’ with extension may be associated to a strain-hardening phenomenon but the role of dough viscoelasticity is discussed.

Elaboration and Rheological Investigation of Magnetic Sensitive Nanocomposite Biopolymer Networks

We propose the elaboration and study of rheological properties under continuous magnetic field of magnetic sensitive biopolymer-based nanocomposites. Magnetic iron oxide (maghemite) nanoparticles were synthesized by the polyol process and then functionalized by grafting organic bifunctional ligand for establishing electrostatic bonds between the sodium alginate chains of biopolymer and functionalized nanoparticles. The enhancement of rheological properties at low shear rate of these new magnetic soft nanocomposites was clearly demonstrated by the increase of yield stress and viscoelastic moduli in the linear viscoelastic domain with an increase of applied magnetic field, thus providing new functionality to these soft nanocomposites.

The Rheological Properties of κ-Carrageenan-Konjac Gum Mixed Gel

The rheological properties of κ-Carrageenan-Konjac Gum Mixed Gel were investigated by using dynamic rheological analysis. Results showed that the mixture of κ-Carrageenan and Konjac Gum had higher modulus of elasticity than single κ-Carrageenan or Konjac Gum. Blends solution has a good pseudo-plastic behavior at low concentrations, viscosity declined rapidly with shear rate increased. K+ and Ca2+ participated in the gelatin process and under the controlled condition might enhance force among molecules. With the temperature increasing G' and G" increased, and G' and G" presented suddenly change at 60-70 °C. Small amplitude oscillatory tests in the linear domain of viscoelasticity showed that κ-Carrageenan played the major role in the viscoelasticity of the mixture, and Konjac gum strengthened the gel-net configuration and stability.

Mechanical properties of filler-asphalt mastics

There has been an increasing awareness of the addition of ordinary Portland cement (OPC) rather than limestone filler into asphalt pavements in Taiwan. Filler interpaticle interaction and physicochemical interaction between cement filler particle and asphalt improved engineering properties of asphalt mixtures. Current Superpave parameters of G*/sinδ and G*sinδ were used to link the rheological properties of asphalt binders to the pavement performance of rutting and fatigue. However, the characteristics of asphalt binders were determined in the linear viscoelastic domain by performing frequency sweeps. The asphalt binder film might perform in the non-linear range due to the considerable difference between the stiffness modulus of aggregates and the modulus of binders. In addition, the filler-asphalt interaction might not be reflected by means of the Superpave parameters. Mechanical properties of stiffness, deformation and fatigue for filler-asphalt mastics may be more appropriate in terms of establishing a correlation with asphalt pavement performance. Oscillatory and creep tests using a dynamic shear rheometer (DSR) were performed to quantify the mechanical properties of cement and limestone filler-asphalt mastics at the same levels of filler contents by weight. The test results showed that the higher complex modulus and stiffening effect of the cement filler-asphalt mastics than those of the limestone filler-asphalt mastics within a linear viscoelastic domain. In terms of creep behavior, the addition of cement filler to base bitumen increases the viscosity at a steady state. The longer fatigue lives for the cement filler-asphalt mastics indicated the addition of active filler may provide a better pavement durability.

Influence of extracellular polymeric substances on rheological properties of activated sludge

Influence of extracellular polymeric substances (EPS) on rheological properties of activated sludge (AS) was conducted by comparing properties of AS before and after EPS extraction at a TSS of 54g/L. Slime, loosely and tightly bound EPS (LB- and TB-EPS) were stratified by centrifugation and ultrasound method. The results showed that sludge after LB-EPS extraction produced a higher hysteresis loop area (Hla), limiting viscosity (η∞), yield stress (τy), energy of cohesion of network sludge (Ec), and storage modulus (G′0), than three other sludge samples, indicating that sludge with TB-EPS exhibited stronger network structure. Strain amplitude sweep (SAS) and frequency sweep (FS) tests revealed that AS before and after EPS extraction produced a gel-like structure in the linear viscoelastic (LVE) domain. TB-EPS appeared to have a positive effect on the gel-like structure of AS.

Complex Poisson’s ratio of bituminous mixtures: measurement and modeling

Mechanical characterization of bituminous mixtures in the linear viscoelastic (LVE) domain is commonly limited to the measurement of a single (mono-dimensional) material function, either the Young’s modulus or the shear modulus. Even under the additional hypothesis of isotropy, a complete (three-dimensional) description of the LVE response requires two material functions to be determined simultaneously and in the same experimental conditions. The measurement of viscoelastic Poisson’s ratio, though generally overlooked because of the high accuracy and precision required, offers the opportunity to put aside this limitation because it can be achieved in experimental conditions that are very similar to those employed to obtain the Young’s modulus. In the present experimental research the concurrent determination of the complex Poisson’s ratio (ν*) and the complex Young’s modulus (E*) of a bituminous mixture is presented. A rheological model is employed to fit the measured complex-valued material functions and the validity of the time–temperature superposition principle is investigated. The experimental program consists of cyclic compression tests performed on cylindrical samples, with the measurement of axial and transverse strains. A conventional frequency sweep procedure is followed in a range of intermediate service temperatures. Two strain levels are chosen focusing the attention on the linear domain. In addition, samples with different air voids content are tested to observe the effect of the aggregate skeleton. Results allowed to characterize frequency and temperature dependance of the complex Poisson’s ratio and make a comparison to that of the complex Young’s modulus on the basis of the selected rheological model. Experimental data confirm the validity of the time–temperature superposition principle but suggest that different shift factors may be required to correctly translate the time–temperature dependance of different material functions.

A simple and effective scheme for data reduction of stress relaxation incorporating physical-aging effects: An analytical and numerical analysis

A simple methodology for obtaining viscoelastic parameters from the stress relaxation tests incorporating physical-aging effects is presented. The method assumes that the experimental data are in the linear viscoelastic domain. Three different mathematical representations of the viscoelastic stress relaxation modulus are analysed and used. Experimental data obtained from literature and simulated data with a random error are used to evaluate the proposed methodology. It is proved that it can capture very well the relaxation modulus of polymers irrespective of the mathematical representation used for the relaxation modulus. Moreover, the methodology proved to be reasonably insensitive to random noise. Extrapolation predictions were also evaluated for the proposed models with very good results.

Models of Adhesive Bonding of Hybrid Structures

Adhesives are often based on polymers materials. They are good candidates in order to manufacture adhesives joint because of their thermomechanical properties and their processing which is easier than other materials. Epoxy resins are widely used as adhesives joint. We can meet them in various industrial areas like car, spatial and aerospace domains. Because of numerous combinations between epoxy and amine chemical functions, these joints may be efficient at high or at low temperature. Indeed, close to their glassy transition temperature (Tg), exists an elastic modulus / ductility couple for which, shear stress is optimum: the Optimum Stress Zone (OSZ)[ which is restricted on limited temperatures range. Our study consists in formulating an epoxy amine joint able to be efficient on an extended temperatures rangei.e.a joint able to ensure a stress continuity over a large range of temperatures, for example-50°C to 100°C. To reach this objective, we propose an evolution of the Multi Adhesive Joints (MAJ): an adhesive joint presenting a gradient of mechanical properties. To make this adhesive joint formulation possible, its necessary to control kinetics diffusion at the adhesive scale (200μm to 500μm) between the low temperature adhesive (LTA) and the high temperature adhesive (HTA). The diffusion study will be carried out by using a rheometer. For such adhesive thickness, the rheometer compliance may have an influence on the results. Therefore, this present work proposes to identify and to set up the key parameters, which allow following kinetics diffusion in a rheometer for dimensions similar to those of bonding assembly, by checking the measurements are performed in the linear viscoelastic domain. In a first part, the morphological, mechanical and thermomechanical properties of the nanostructured thermosets versus time are performed. And, the second part will deal with the optimization of the key parameters by performing dynamic shear tests versus time on HTA and LTA samples in sight of kinetics diffusion study.