Investigation Of Viscoelastic Properties Research Articles

Investigation of viscoelastic properties in composite sandwich panels subjected to low-velocity impact: Experimental and numerical approaches

This study investigates the effect of viscoelastic properties in the numerical modeling of foam-filled sandwich panels when their composite facesheets are exposed to low-velocity impact loading. A finite element (FE) model is developed using the software package of ABAQUS and used to investigate the effect of both considering and ignoring the time-dependent behavior of composite laminate facesheets as well as the foam core. Material constitutive equations, damage characteristics, and failure modes are defined in a FORTRAN user-subroutine VUMAT. To characterize the material behavior of both polyurethane foam and glass/epoxy composite material, a set of experimental tests are conducted under compression, tension, and stress relaxation modes. To validate the numerical results, low-velocity impact tests at two energy levels of 9.81 and 17 joules are carried out on sandwich panels with foam core. The results of numerical simulations are found to be in good agreement with the experimental test results. It is shown that ignoring the viscoelastic properties in the composite laminate and the foam core can lead to deviations of up to 7% and 25%, respectively, from experimental results. The analysis reveals that, ignoring the viscoelastic behavior along the fiber-direction in the composite facesheets does no change the results considerably. The viscoelastic properties perpendicular to the fibers, however, has a more noticeable effect on the results due to the prevalence of the properties of the polymeric resin in that direction.

Ultrasonic Investigation of Viscoelastic Properties in Silver Nanofluids

Silver nanofluids have been prepared by a one-step simple, green and cost-effective method using tannic acid as both reducing and stabilizing agent. The physical parameters such as ultrasonic velocity, density and viscosity of silver nanofluids were measured at (298.15 K, 303.15 K, 308.15 K and 313.15 K) and derived parameters like adiabatic compressibility (β), mean free path (Lmfp), bulk modulus (E), ultrasonic attenuation coefficient (α/f2), diffusion coefficient (D) and relaxation time (t) were computed. The variation of ultrasonic velocity with temperature, concentration and frequency shows anomalous behaviour and the parameters β, Lmfp, E too reflected this behaviour. Viscosity variation as a function of temperature and concentration is also studied and correlated with particle size. Ultrasonic attenuation coefficient (α/f2), diffusion coefficient and relaxation time exhibited a similar pattern as that of viscosity of samples confirming the significant role of viscosity in transport phenomena and flow characteristics of fluids. Results are interpreted in terms of nanoparticlenanoparticle and nanoparticle-fluid interactions.

Characterization of SPN Pickering emulsions for application in enhanced oil recovery

Abstract Emulsion, stabilized by solid particles that get adsorb on to the surface of the interface is known as Pickering emulsion, which has potential application in enhanced oil recovery (EOR). In present study, a stable oil-in-water surfactant–polymer–nanoparticle (SPN) Pickering emulsion has been formulated using light mineral oil, carboxy methyl cellulose (CMC) and silica nanoparticles (SiO 2 ) in presence of anionic surfactant, for use in EOR. The nanoparticles (NPs) show synergetic effect in presence of surfactant and polymer thus prevents the droplets from coalescence and lowers the interfacial tension (IFT) at the oil–water interface. The emulsion was characterized in terms of particle size, creaming behavior and zeta potential measurements. The viscosity remains stable in wide range temperature (30–100 °C) indicating thermal stability of the Pickering emulsion. The emulsion exhibits pseudo-plastic behavior in wide range of shear rate (1–1000 s −1 ). The investigation of viscoelastic properties (G′ and G″) of the Pickering emulsion as a function of pressure (0–5 MPa) and temperature (30–100 °C) shows a stable value of G″ indicating better flow ability of the emulsion. The emulsions show viscous behavior below the specific frequency (SF) indicated by the crossing point between G′ and G″ on the viscoelastic curve and elastic behavior above the SF. Flooding experiment was conducted on sand pack system to study the efficiency of Pickering emulsion in EOR and additional recovery of more than 24% was observed after conventional water flooding.

Investigation of viscoelastic properties and thermal behavior of photocurable epoxy acrylate nanocomposites

Abstract In this study, the dynamic-mechanical properties and thermal behavior of the nanocomposites of a photocurable epoxy-acrylate resin and CuO nanohybrid were determined. In order to improve the dispersion of CuO nanoparticles and prevention of nanoparticle migration to the surface coating, the surface of commercial nanoparticles was modified by triethoxymethylsilane (TEMS) and vinyltrimethoxysilane (VTMS) as silane-coupling agents. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) tests were then performed on CuO-filled epoxy-acrylate resins to identify the loading effect on the properties of material. The thermal stability of nanocomposites was affected slightly after incorporation of CuO nanoparticles. DMA studies revealed that filling the CuO nanoparticles into epoxy-acrylate resin can produce a significant enhancement in storage modulus, as well as a shift in the glass transition temperature. The films reinforced with the modified CuO exhibit the most significant enhancements in properties.

Ultrasonic and Viscoelastic Properties of Small-Volume Mesogen Samples at the Phase Transition

The ultrasonic method is very informative for research of viscoelastic properties of mesogens at changing thermodynamic parameters of state. At phase transitions, anomalies of the velocity of propagation and coefficient of absorption of ultrasound waves as well as of viscoelastic properties are observed. These anomalies for liquid crystals are most pronounced at frequencies lower that 1 MHz. Up to now acoustic resonators with volumes of about 5 cm3 have been used, which considerably prevents the application of this method for science-based newly synthesized mesogenic compounds. This article presents experimental results obtained by means of a new resonator method with samples with volumes of 0.06 cm3 to 0.15 cm3. The velocity and coefficient of absorption of ultrasound were measured at frequencies from 0.68 MHz to 1.63 MHz for four mesogens: esters of alkyloxyphenylcyclo-hexane-2-carbonic acid and n-amylphenol. It has been shown that temperature dependencies of ultrasonic parameters obtained in small-volume cells correspond to those established previously by traditional methods using measuring cells with larger volumes. It is also shown that the temperature dependencies of the bulk viscosity and the bulk elasticity modulus derived from our ultrasonic measurements, in general features, duplicate the corresponding dependencies obtained by standard methods. It confirms that the proposed acoustic method is suitable for routine investigations of viscoelastic properties of small-volume samples of mesogenic compounds.

Saturated Liquid Viscosity and Surface Tension of Alternative Refrigerants

Light scattering by thermally excited capillary waves on liquid surfaces or interfaces can be used for the investigation of viscoelastic properties of fluids. In this work, we carried out the simultaneous determination of the surface tension and the liquid kinematic viscosity of some alternative refrigerants by surface light scattering (SLS) on a gas–liquid interface. The experiments are based on a heterodyne detection scheme and signal analysis by photon correlation spectroscopy (PCS). R23 (trifluoromethane), R32 (difluoromethane), R125 (pentafluoroethane), R143a (1,1,1-trifluoroethane), R134a (1,1,1,2-tetrafluoroethane), R152a (1,1-difluoroethane), and R123 (2,2-dichloro-1,1,1-trifluoroethane) were investigated under saturation conditions over a wide temperature range, from 233 K up to the critical point. It is estimated that the uncertainty of the present surface tension data for the whole temperature range is less than ±0.2 mN·m−1. For temperatures up to about 0.95Tc, the kinematic viscosity of the liquid phase could be obtained with an absolute accuracy of better than 2%. For the highest temperatures studied in this work, measurements for the kinematic viscosity exhibit a maximum uncertainty of about ±4%. Viscosity and surface tension data are represented by a polynomial function of temperature and by a van der Waals-type surface tension equation, respectively. The results are discussed in detail with comparison to literature data.

Biomechanics of the gastrointestinal tract.

As the function of the gastrointestinal tract is to a large degree mechanical, it has become increasingly popular to acquire distensibility data in motility research based on various parameters. Hence it is important to know on which geometrical and mechanical assumptions the various parameters are based. Currently, compliance and tone derived from pressure-volume curves are by far the most often used parameters. However, pressure-volume relations obtained in tubular organs must be carefully interpreted as they provide no direct measure of luminal cross-sectional area and other variables useful in plane stress and strain analysis. Thus, erroneous conclusions concerning tissue distensibility may be deduced. Other parameters, such as wall tension, stress and strain, give more useful information about mechanical behaviour. Distensibility data procure significance in fluid mechanics and in the study of tone, peristaltic reflexes, and mechanoreceptor kinematics. Such data are needed for the determination of the interaction between stimulus, electrical responses in neurons and the mechanical behaviour of the gut. Furthermore, from a clinical perspective, investigation of visco-elastic properties is important because GI diseases are associated with growth and remodelling. For example, prestenotic dilatation, increased collagen synthesis, dysmotility and altered distensibility are common features of obstructive diseases. The purpose of this review is to discuss the physiological and clinical importance of acquiring biomechanical data, distensibility parameters and interpretation of these results and their associated errors. We will also discuss some aspects of the relationship between morphology, growth and biomechanics. Finally, we will outline a number of techniques to study the mechanical properties of the GI tract.

Experimental investigation of viscoelastic properties of polymeric binder

Experimental investigation of viscoelastic properties of polymeric binder