Rheology Of Materials Research Articles

Effects of Material Rheology and Die Walls Translational Motions on the Dynamics of Viscous Flow during Equal Channel Angular Extrusion through a Segal 2θ-Die: CFD 2D Solution of a Curl Transfer Equation

The present article is focused on a phenomenological description of a polymer workpiece Equal Channel Angular Extrusion (ECAE) through 2θ-dies of Segal and Iwahashi geometries with a channel intersection angle 2θ = 105° with fixed and movable external inlet and outlet die walls. The local flow dynamics, including the formation of macroscopic rotation and a dead zone appearance during the flow of plasticine, paraffin, and wax workpiece models through the subject die configuration was studied using physical simulation techniques. The present article utilizes a Computational Fluid Dynamics (CFD) numerical approach to a theoretical description of 2D viscous flow of incompressible Newtonian continuum through the stated die geometries. The boundary value problem for the Navier-Stokes equations in the curl transfer form for the local viscous flow was formulated and numerically solved with a finite-difference method. Theoretical CFD-derived plots with computational flow lines, dimensionless flow and curl functions, flow velocities, and tangential stresses for viscous material flow through the stated die geometries have been generated and described. As a first rheological approximation the derived computational results provide the theoretical description of physical simulation experiments and visualize the formation of ECAE-induced rotational modes of large deformations like macroscopic rotation and rotational inhomogeneity.

The rheological and crystallization behavior of polyoxymethylene

In the polymer melt processing, the solidification has a huge importance on the properties of the resulting part. For a semi-crystalline resin, this phenomenon involves a complex interplay between crystallization and the material rheology. In this work, an investigation is carried out on the influence of thermal conditions on crystallization kinetics and rheology of two commercial polyoxymethylene (POM) copolymers. In particular, isothermal crystallization experiments using differential scanning calorimetry (DSC) and rotational rheometry to measure the dynamic viscosity are performed. The evolution of the relative crystallinity and Normalized Rheological Function (NRF) are correlated by a recent technique which allows simultaneous analysis of several measurements, even if they are not carried out at same temperatures. On this basis, a relationship between the crystallinity and the hardening, i.e. the sharp increase in the viscosity, is obtained.

Linking Internal Dissipation Mechanisms to the Effective Complex Viscoelastic Moduli of Ferroelectrics

Microstructural mechanisms such as domain switching in ferroelectric ceramics dissipate energy, the nature, and extent of which are of significant interest for two reasons. First, dissipative internal processes lead to hysteretic behavior at the macroscale (e.g., the hysteresis of polarization versus electric field in ferroelectrics). Second, mechanisms of internal friction determine the viscoelastic behavior of the material under small-amplitude vibrations. Although experimental techniques and constitutive models exist for both phenomena, there is a strong disconnect and, in particular, no advantageous strategy to link both for improved physics-based kinetic models for multifunctional rheological materials. Here, we present a theoretical approach that relates inelastic constitutive models to frequency-dependent viscoelastic parameters by linearizing the kinetic relations for the internal variables. This enables us to gain qualitative and quantitative experimental validation of the kinetics of internal processes for both quasistatic microstructure evolution and high-frequency damping. We first present the simple example of the generalized Maxwell model and then proceed to the case of ferroelectric ceramics for which we predict the viscoelastic response during domain switching and compare to experimental data. This strategy identifies the relations between microstructural kinetics and viscoelastic properties. The approach is general in that it can be applied to other rheological materials with microstructure evolution.

Spectral quasilinear numerical simulation of micropolar convective wall plumes in high permeability porous media

Laminar natural convection plume of a microstructural non-Newtonian fluid along a vertical surface about a line heat source in a saturated high permeability porous medium is studied. The transformed non-linear boundary value problem is solved numerically using a rigorously tested SQLM algorithm, which combines a spectral collocationmethod with the quasilinearization method (QLM). The effects of Grashof number, Prandtl number, Darcy number and Eringen micropolar rheological material parameters are examined. Excellent stability and convergence of the spectral method is demonstrated. Validation of solutions with the Keller box finite difference is included. Applications of the study arise in geological (petroleum) fluid dynamics.

High viscosity paste dosing for microelectronic applications

AbstractToday's microelectronics packaging especially for SiPs relies on the processing of a wide variety of materials Such as materials for components, substrates, contact materials (solder & adhesives) and encapsulants. Most materials are processed as bulk material but precision dosing of pastes is key to many assembly processes. Examples are dosing of solder paste, typically done by stencil printing, underfilling for Flip Chip encapsulation, typically done by dispensing or jetting, or glob top encapsulation of Chip on Board assemblies, where also dispensing is the typical process. When working with those paste materials, viscosity is one of the key parameters for processing, and viscosities too high do not allow dosing of the materials, not even to transport the material from a reservoir to the dosing head, which may be a simple needle or a jet valve. [1,2]To overcome this obstacle, i.e. to dose materials of high viscosity precisely and homogeneously from a syringe to the dosing head, a research program has been set up, where Vermes microdispensing as a valve manufacturer and TU Berlin/IZM as a research institute are cooperating. TU Berlin is working on material rheology effects and flow models; Vermes is researching valve modifications and material flow path optimization. Core of the research is to find methods that allow a reduction of paste viscosity without leading to irreversible changes in the material, as would be the case when simply applying heat to the paste.As reference process for material dosing, FO-WLP has been chosen, materials selected for the investigations are glob top dam and fill material and liquid molding compound – using both rheological experiments as well as actual material dosing and processing. Apart from temperature, mechanical and ultrasonic stimulation of the material have been evaluated to achieve optimized dosing of high viscous pastes,As a result, a first description of paste behavior during processing is given, being the basis for future work towards homogeneous precision dosing of high viscous pastes for microelectronic applications.

Renovation and Strengthening of Wooden Beams With CFRP Bands Including the Rheological Effects

The paper presents a work analysis of wooden beams reinforced with glued composite bands from the top and resin inclusions, taking into account the rheology of materials. The paper presents numerical model of the multimaterial beam work including rheological phenomena described by linear equations of viscoelasticity. For the construction of this model one used MES SIMULIA ABAQUS environment in which were prepared its own procedures containing rheological models. The calculation results were compared with the literature data. One has done an analysis of the advisability of the use of CFRP reinforcements bands in terms of rheological phenomena.

Distributive mixing of carbon nanotubes in poly(caprolactone) via solution and melt processing: Viscoelasticity and crystallization behavior versus mixing indices

Different mixing processes give rise to significant differences in the agglomeration and deagglomeration of nanoparticles and how they are mixed and distributed within a polymeric matrix. Here poly(caprolactone), PCL, was compounded with carbon nanotubes, CNTs, at a weight fraction of 0.5% (volume fraction, Φ = 0.0027), using both solution and melt processing methods. Microscopy, image analysis, and thermogravimetric analysis, TGA, were used to define and characterize the distributions of the CNT-rich domain sizes and to obtain quantitative mixing indices at different scales of examination. The presence of the CNTs led to the shear-induced crystallization of PCL under conditions at which pure PCL would not crystallize and the microstructures obtained upon shear-induced crystallization were documented via X-ray diffraction, differential scanning calorimetry, and rheological characterization. Shear-induced crystallization occurred at a faster rate (smaller induction times) when the nanocomposites exhibited greater mixing index values. The shear-induced crystallization behavior was found to be a more sensitive indicator of the distributive mixing states of the CNTs in comparison with the widely used linear viscoelastic rheological material functions. The demonstrated methodologies can be used as complementary tools for processing and development of nanocomposites to achieve consistent and reproducible microstructures at various scales of examination and functional properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2254–2268.

Rheometry of polymer melts using processing machines

The technology of slit-die rheometry came into practice in the early 1960s. This technique enables engineers to measure the pressure drop very precisely along the slit die. Furthermore, slit-die rheometry widens up the measurable shear rate range and it is possible to characterize rheological properties of complicated materials such as wall slipping PVCs and high-filled compounds like long fiber reinforced thermoplastics and PIM-Feedstocks. With the use of slit-die systems in polymer processing machines e.g., Rauwendaal extrusion rheometer, by-pass extrusion rheometer, injection molding machine rheometers, new possibilities regarding rheological characterization of thermoplastics and elastomers at processing conditions near to practice opened up. Special slit-die systems allow the examination of the pressure-dependent viscosity and the characterization of cross-linking elastomers because of melt preparation and reachable shear rates comparable to typical processing conditions. As a result of the viscous dissipation in shear and elongational flows, when performing rheological measurements for high-viscous elastomers, temperature-correction of the apparent values has to be made. This technique was refined over the last years at Montanuniversitaet. Nowadays it is possible to characterize all sorts of rheological complicated polymeric materials under process- relevant conditions with viscosity values fully temperature corrected.

Comparison of material properties in butt welds of used and unused polyethylene pipes for natural gas distribution

Abstract The main purpose of this work was to evaluate the long term performance of butt welded polyethylene (PE) pipes in comparison to non-welded counterparts. Therefore, old welded PE pipes with different ages that had been used in Algerian gas distribution systems for up to 30 years were investigated. Samples prepared by butt welding of unaged pipes were used as reference. Crystallinity, melt rheology and thermal stability of pipes materials were examined at the weld zone and at the pipe wall. In order to assess the mechanical strength of welds, tensile test was conducted on both welded and unwelded specimens and the results of the strain to failure were considered for the determination of the weld factor. Compared to the reference, the results revealed that the crystallinity of PE materials at the weld zone was not affected by ageing as at the pipe wall. However, a slight decrease of the melt viscosity was observed for both welded and non-welded samples. The welds were found to be more sensitive to thermal and oxidative degradation than the parent pipes while the remaining amount of antioxidants was sufficient for service continuation. The tensile results indicate that welds strength were almost unaffected by ageing.

Steady viscoelastic film flow over 2D Topography: II. The effect of capillarity, inertia and substrate geometry

We examine the two-dimensional, steady flow of a viscoelastic film under the action of gravity over a substrate with periodic topographical features. We account for the rheology of the viscoelastic material using the exponential Phan–Thien and Tanner (PTT) constitutive model. The conservation equations are solved via the mixed finite element method combined with a quasi-elliptic grid generation scheme, while the viscoelastic stresses are discretized using the EVSS-G/SUPG method. Our scheme allows the computation of accurate steady-state solutions up to high values of Deborah, Reynolds and capillary numbers. We perform a thorough parametric analysis to investigate the effect of the elastic, capillary and inertia forces on the flow characteristics. Our results indicate that surface tension and elasticity affect the film closer to the location with abrupt changes of the substrate topography; the sizes of the capillary ridge before a step down and of the depression before a step up are increased and move upstream as fluid elasticity or interfacial tension increase. It is shown that under creeping flow conditions the length scale of the capillary ridge increases with De following a power law of ¼, which can also be predicted by simple scaling arguments. Inertia has a more global effect on the film affecting larger portions of it, while in its presence the length scale of the capillary features is not affected significantly by the material elasticity. Moreover, it is shown that similarly to the case of Newtonian liquids, high inertia causes the formation of a ridge just after the step up. We also explore the effect of the geometrical characteristics of the substrate as well as its inclination angle and it is shown that the interface shape becomes more deformed as the topography appears wider, deeper or it approaches the vertical plane.

Impacts of yield-stress fluid drops on permeable mesh substrates

Viscoplastic fluids, also known as yield-stress fluids, can stick and accumulate where they impact. Here we experimentally study conditions for open surfaces to be impermeable to impacting yield-stress fluid drops, and the dynamic conditions for these drops to permeate and coat internal aspects of a complex topography. We experimentally study drops of model yield stress fluids (Carbopol microgel particles in water) impacting open solid meshes (rigid surfaces with small, evenly spaced openings). High speed video reveals dynamics across a range of behavior, from 0% to 100% transmittance, by varying drop size, impact velocity, mesh geometry, and rheological material properties. When inertial stresses are sufficiently high compared to the yield stress, a drop can pass through a mesh, breaking into smaller fluid particles with varying shapes, sizes, and velocities in the process. In contrast, when inertial stresses are sufficiently low compared to the yield stress, a drop can stick to the mesh as though it were a solid surface, inhibited from passing through the holes by the yield stress. Layers of multiple meshes are also examined, demonstrating a range of behaviors and the ability to coat internal aspects of complex topography. Dimensional analysis is performed to characterize material transmittance and velocity of transmitted droplets as a function of dimensionless input parameters. Behavior is found to be well governed by the ratio of inertial stress to the sum of yield and viscous stresses.

Influences of bacteria-based self-healing agents on cementitious materials hydration kinetics and compressive strength

Bacterially induced calcium carbonate precipitation has been proposed as an alternative and environmental technique to develop self-healing cementitious materials system in recent years. This study investigated the influences of bacteria-based self-healing agents on the rheology, hydration kinetics and compressive strength of cementitious materials to further verify the feasibility of bacteria-based self-healing agents for crack repairing. The results showed that the rheology of cement mortar was significantly improved by the addition of bacteria-based self-healing agents. Incorporation of bacteria-based self-healing agents in cement greatly influenced the hydration kinetics. The self-healing agent RB could delay the hydration of cement resulting in final setting time increase, however the self-healing agents JB and NB accelerated the hydration resulting in initial and final setting time decrease. In addition, compressive strength test results showed that incorporation of RB in cement mortar resulted in early age compressive strength decrease, but the 28d compressive strength increased compared to control. Incorporation of JB in cement mortar enhanced compressive strength, however incorporation of NB in cement mortar could result in unwanted compressive strength loss. Furthermore, MIP test results indicated that the pore size distributions were different between cement paste samples with and without bacteria-based self-healing agents. The addition of bacteria-based self-healing agents increased the porosity between 100 and 1000nm. The porosity between 100 and 1000nm of the sample with NB increased the most compared to the samples with RB and JB. The incorporation of JB increased the porosity between 100 and 1000nm, but at the same time the small pores with a diameter under 10nm increased. These results could be used to explain the compressive strength development.

Applications of shear-induced polarized light imaging (SIPLI) technique for mechano-optical rheology of polymers and soft matter materials

A new experimental method for studying the mechano-optical rheology of polymeric liquids and soft matter materials is presented. The method is based on a combination of rotational rheology and a recently developed optical technique—shear-induced polarized light imaging (SIPLI). The method provides a unique opportunity to monitor a complete sample view during rheological measurements in plate–plate and cone-and-plate geometry. Applications of the method are presented including simultaneous SIPLI and the rheology of the oriented lamellar phase of block copolymers and liquid crystals as well as a study of the thermally induced reversible transformation of worm-like micelles to spherical micelles. In addition, a direct relation between the shish formation and the polymer melt viscosity upturn during flow-induced crystallization of semi-crystalline polymers is demonstrated. An application of SIPLI for quantitative birefringence measurements is also shown. © 2016 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2151–2170

Actuating Soft Matter with Magnetic Torque

Here, recent significant developments are reviewed in manipulating soft matter systems through the use of magnetic torque. Magnetic torque enables the orientation, assembly, and manipulation of thermally fluctuating systems in broad material fields including biomaterials, ceramic and composite precursor suspensions, polymer solutions, fluids, foams, and gels. Magnetism offers an effective, safe, and massively parallel manufacturing approach. By exploiting magnetic torque, leading soft matter researchers have demonstrated new technologies in rheology, life sciences, optics, and structural materials. Specifically, magnetic torque has been used to assemble particle suspensions, to fabricate and actuate composite materials, and to control and manipulate biological materials. In each of these applications, there are energetic limitations to magnetic torque that need to be understood and characterized. However, magnetic torque offers a promising remote‐controlled approach to creating and enabling new soft matter technologies.

Rheology of granular materials with size distributions across dense-flow regimes

We investigate the dense-flow rheology of granular materials with various size distributions through discrete element simulations of simple shear flows of frictional, spherical particles with binary, linear, Gaussian, and lognormal distributions in size. Dense shear flows of monodisperse granular materials exhibit three regimes: quasistatic, inertial, and intermediate. It is found that these regimes persist for polydisperse granular materials as well. However, the critical volume fraction that separates the quasistatic and inertial regimes is found to increase when particles manifest size distribution. This increase in the critical volume fraction can be described with fair accuracy by polydispersity and skewness alone regardless of types of distributions. Furthermore, the inertial number model for stress ratio is found valid for particles with size distribution. A rheological model is proposed that captures the simulation results on stresses for all the size distributions studied.

Geo-mechanical Model Testing for Stability of Underground Gas Storage in Halite During the Operational Period

A 3D geo-mechanical model test is conducted to study the stability of underground gas storage in halite, modeled after the Jintan gas storage constructed in bedded salt rock in China. A testing apparatus is developed to generate long-term stable trapezoid geostresses onto the model cavity, corresponding to the actual gas storage cavern. The time-depending character of the material is simulated using a rheological material, which was tested using a self-developed apparatus. The model cavern is built using an ellipsoid wooden mold divided into small blocks which are assembled and placed into the designed position during the model construction. They are then pulled out one by one to form the cavern. The ellipsoid cavern wall is then lined within a latex balloon. Gas is injected into the cavity and extracted to simulate the operational process of gas injection and recovery. Optical sensors embedded into the model to measure the displacement around the cavity showed that the largest deformation occurs in the middle section of the cavity. The deformation rate increases with increasing gas pressure. At 11 MPa the cavity is in equilibrium with the geostress. The pressure is highest during the gas recovery stages, indicating that gas recovery can threaten the cavern’s operational stability, while high gas injection causes rock mass compression and deformation outward from the cavern. The deformation is the combination of cavern convergence and gas-induced rebound which leads to tensile and compression during gas injection and recovery. Hence, the fatigue properties of salt rock should be studied further.

Optically and rheologically tailored polymers for applications in integrated optics

We demonstrate an epoxy acrylate based system on which various micro-optical applications can be realized. With this innovative and flexible material concept, it is possible to adjust viscosity (3mPas<η<46Pas) as required for different microstructuring processes e.g. inkjet printing, spin coating, and stereolithography and simultaneously precisely tailor refractive indices (1.518<nD,20<1.569) which is essential to implement optical sensor concepts. The practicability of this material system is demonstrated for optical waveguide production and selected applications. The fast and low cost modification of optical and rheological material properties is advantageous for the fabrication of micro-optical polymer devices including planar-optical polymer sensor networks.

Density and rheology of acid suspensions of peanut waste in different conditions: An engineering basis for bioethanol production

The current world-wide energetic situation implies in researches about new resources and technologies capable of producing biofuels, such as the peanut processing residues. To design operations associated to bioethanol processing, understanding material properties, as density and rheology, is necessary. In this study, peanut shells were firstly chemically characterized, showing 37.1% cellulose, 33.4% hemicellulose and 15.0% lignin. Aqueous acid suspensions of powdered peanut shell were prepared and their physical properties were determined. Rheological parameters and density could be correlated with solid content and temperature by exponential and quadratic equations, respectively, while pH did not present significant effect on these parameters. Dilute suspensions showed Newtonian behavior, but at concentration above 8% (w/w) of solids, a non-Newtonian behavior was observed, showing yield stress and shear thinning. By evaluating the relative viscosity behavior with increasing solids concentration, Farris effect was also evidenced in suspensions above 8% of solids due to the presence of fine particles. Such result indicates the possibility of processing peanut shells for biofuel production in solids concentration higher than 10%, without a significant influence on viscosity.

Waste-glass fume synthesized using plasma spheroidization technology: Reactivity in cement pastes and mortars

Using silica-based nanoparticles is one way to stimulate the hydration reactivity and improve the rheological properties of concrete, given their fineness and spherical shape. Based on its high content in amorphous silica ((SiO2>70wt.%), waste glass is an excellent material for valorization into pozzolanic nanoparticles or the so-called “glass fume” (GF). GF, produced using the radiofrequency induction-coupled-plasma (RF ICP) spheroidization technology, mainly consists of spherical and amorphous nanoparticles (dia. of 30–200nm). Given the scarcity and high cost silica fume (SF), its use in producing high-strength concrete is now limited. GF produced using the scalable plasma spheroidization process is currently being tested in cement-based products as an alternative for SF.The GF was characterized with field-emission-gun scanning electron microscopy (FEGSEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) specific surface, acoustic particle sizer (APS), X-ray fluorescence (XRF) and thermogravimetry coupled to mass spectrometry (TGA-MS). The hydration of GF in cement pastes and mortars was monitored in this study. The cement pastes were characterized at early age with isothermal calorimetry and as a function of curing time with X-ray diffraction (XRD) as well as with thermogravimetric analysis (TGA) and variable pressure scanning electron microscopy (VPSEM). Mortars were tested for compressive strength and their microstructure was observed with VPSEM. Also, their hydration was monitored with the electrical conductivity. The results indicate that GF offers nucleation sites for portlandite, alkalis for the activation of the cement hydration at early age, and a pozzolanic behavior for the long-term evolution of mortar properties. In mortars, the GF yielded compressive strengths equivalent to those obtained with SF used as a comparison. The GF mortars required a lower superplasticizer (SP) dosage than the SF mortar because of the ball-bearing effect induced by GF’s complete spherical morphology. In addition to spherical nanoparticles, SF contains silica-based nanofilaments, which affect the rheology of fresh cement-based materials.

Study of Transfer Properties on Fresh Cement Pastes; Laboratory Experiments: Discontinue Measurements using a Permeameter

&lt;p class="1Body"&gt;The study of hydraulic conductivity or permeability (k) of fresh cement pastes is a fundamental stage to understand the concrete&lt;strong&gt; &lt;/strong&gt;placement in their formworks, and for the more extended study of the rheology of cementitious materials at fresh state. The results here are obtained on fresh cement pastes (PC) PC30, PC36 and PC40 with water- to- cement ratio (w/c) of 0.30, 0.36 and 0.40 respectively with a classical permeameter traditionally used in geotechnical for soil permeability measurements: the constant head permeameter. It has the advantage of allowing accurate measurements and staggered over time. The analysis of results obtained are in agreement with those obtained elsewhere in the literature.&lt;/p&gt;