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Micro polishing is a process used when a fine surface quality is desired. In optics, it represents the key process to achieve low surface roughness and form error required for optics application. Automated micro polishing with polymer-based tools requires a better understanding of the interaction between tool and workpiece than conventional polishing, and an important phenomenon that has to be taken into account is polymer relaxation. Stress relaxation is due to the non-linear viscoelastic behaviour of polymers. This relaxation is a time-dependent phenomenon that causes a decrease in stress, although the strain is kept constant. In this work, the effect of polymer stress relaxation on polishing is studied. While this effect can be neglected in conventional polishing, it becomes an essential and dominant factor in micro polishing. Characterization tests are conducted on a very common extruded polyurethane (LP-66) used in polishing. Subsequently, bonnet polishing using a spherical tool with a diameter of 1 mm is performed for 8 minutes on a nickel sample. Due to relaxation, the induced stress on the tool decreases during polishing, causing a reduction in the polishing pressure. This implies a reduction in the material removal rate in accordance with Preston’s law. Experimental results are in accordance with the physical phenomenon. The polymer relaxation characteristics can be used to compensate the tool path to achieve uniform removal along the polished surface.

Studies on rheology and processing of wood-polymer composites are very limited in the literature [1]. These are pseudoplastic and viscoelastic materials that exhibit yield stress and wall slipping. Slip effects and flow with yield stress have been investigated numerically for single screw extrusion using ANSYS-Polyflow software. Fully three-dimensional non-Newtonian analysis has been performed both in the extruder (slip on the screw/barrel surfaces) and in the die. The model of Ostwald-de Waele has been used for flow modeling, the generalized law of Navier has been applied for a slip analysis, and Bingham law has been used for an analysis of the flow with yield stress. An effect of the parameters of these models on the flow in the extruder/die system has been studied. Screw pumping characteristics and die characteristics (i.e. flow rate vs. pressure gradient) have been computed and implemented into the recently developed [2] global model of the single screw extrusion process of wood-polymer composites. This model allows to predict various process parameters, e.g. flow rate, pressure and temperature profiles, melting profile. The effect of slipping and yield stress on the extruder operation, i.e. location of the operating point on the screw/die characteristics has been discussed.Studies on rheology and processing of wood-polymer composites are very limited in the literature [1]. These are pseudoplastic and viscoelastic materials that exhibit yield stress and wall slipping. Slip effects and flow with yield stress have been investigated numerically for single screw extrusion using ANSYS-Polyflow software. Fully three-dimensional non-Newtonian analysis has been performed both in the extruder (slip on the screw/barrel surfaces) and in the die. The model of Ostwald-de Waele has been used for flow modeling, the generalized law of Navier has been applied for a slip analysis, and Bingham law has been used for an analysis of the flow with yield stress. An effect of the parameters of these models on the flow in the extruder/die system has been studied. Screw pumping characteristics and die characteristics (i.e. flow rate vs. pressure gradient) have been computed and implemented into the recently developed [2] global model of the single screw extrusion process of wood-polymer composites. Th...

In the present work, an attempt was made to explore the effect of polystyrene-b-poly (ethylene-butylene)-b-polystyrene (SEBS) block copolymer morphology on carbon nanotube (CNT) dispersion in SEBS with cylindrical and spherical morphology which were melt mixed with different amounts of CNT. Microstructure of nanocomposite samples were studied by using both melt linear and nonlinear viscoelastic measurements. The frequency sweep test results showed a pronounced enhancement in storage modulus in low frequency region with greater extent for the SEBS with spherical morphology. This result could be explained in terms of lower viscosity and/or melt elasticity of SEBS with spherical morphology compared to that of cylindrical one. Lower viscosity and/or melt elasticity lead to greater diffusion of polymer chains into nanoparticle agglomerates and better dispersion. The startup flow test results evidenced the existence of a 3D network due to block copolymer phase separated microdomains in cylindrical SEBS and its nanocomposites which intensified through addition of CNT.

Our long-term goal is to quantify changes in the viscoelastic behavior of the uterine cervix during pregnancy using Shear Wave Elasticity Imaging. In this study we compared the sensitivity of two quantitative imaging biomarkers of viscosity extracted from either a time-domain or a frequency-domain analysis of shear wave dispersion. The time-domain descriptor was the ratio R of the group speed obtained from particle velocities and particle displacements. The frequency domain descriptor was the slope S of the phase speed vs. frequency. We observed that R and S are sensitive not only to shear wave dispersion but also to the width and rate of acoustic radiation force impulse (ARFI) excitation. However, S showed the biggest contrast to changes in the tissue viscosity than R, as well as more dependence on the width and pulse duration of the ARFI. Future studies will investigate the tradeoff between contrast and noise.

Quantitative ultrasound (QUS) has shown a great potential in the assessment of bone characteristics in the recent research. However, wave propagation in bones is very challenging due to the nature of multi-layer, anisotropic, and viscoelastic behaviors. Therefore, our knowledge of wave interaction with bone structures is far from complete and the resulting wave modes have not been fully explained. The aim of the current study is to develop a model for propagation of ultrasonic guided waves in a soft-tissue layer over a cortical bone layer. The amplitudes of wave modes generated by time- harmonic loads in the bilayered plate are theoretically computed by reciprocity consideration.

The significant drop of the storage modulus under uniaxial deformation (Payne effect) restrains the performance of the elastomer-based composites and the development of possible new applications. In this paper molecular-dynamics (MD) computer simulations using LAMMPS MD package have been performed to study the mechanical properties of a coarse-grained model of this family of nanocomposite materials. Our goal is to provide simulational insights into the viscoelastic properties of filled elastomers, and try to connect the macroscopic mechanics with composite microstructure, the strength of the polymer-filler interactions and the polymer mobility at different scales. To this end we simulate random copolymer films capped between two infinite solid (filler aggregate) walls. We systematically vary the strength of the polymer-substrate adhesion interactions, degree of polymer confinement (film thickness), polymer crosslinking density, and study their influence on the equilibrium and non-equilibrium structure, segmental dynamics, and the mechanical properties of the simulated systems. The glass-transition temperature increases once the mesh size became smaller than the chain radius of gyration; otherwise it remained invariant to mesh-size variations. This increase in the glass-transition temperature was accompanied by a monotonic slowing-down of segmental dynamics on all studied length scales. This observation is attributed to the correspondingly decreased width of the bulk density layer that was obtained in films whose thickness was larger than the end-to-end distance of the bulk polymer chains. To test this hypothesis additional simulations were performed in which the crystalline walls were replaced with amorphous or rough walls.

In this work, polyethylene glycol (PEG) nanocomposites containing different nanofillers (namely boehmites and hydrotalcites) were prepared through melt compounding and their thermal and rheological behavior was thoroughly investigated. The obtained results showed that the two types of nanofillers interact in a different way with the polymer matrix; more specifically, the rheological analyses performed on the systems containing hydrotalcites revealed that the presence of well-dispersed nanofillers strongly affects the relaxation dynamics of the PEG macromolecular chains, resulting in a modification of the rheological functions of unfilled matrix. Furthermore, the nanocomposites containing higher loadings of organo-modified hydrotalcite exhibit an unusual rheological behavior as a function of temperature, showing an enhancement of the linear viscoelastic functions along with a more important solid-like feature with increasing the temperature. Finally, the thermo-oxidative stability of the obtained nanocomposites was enhanced in the presence of boehmites and unmodified hydrotalcite, while the high organic fraction content in modified hydrotalcite promoted an anticipated degradation of the polymer matrix.

It has been suggested that the decay constants of tectorial membrane (TM) traveling waves contribute to differences in the tuning of Tectb −/– mutant mice, wild-type mice, and humans. However, the experiments underlying these results were obtained in vitro, in the absence of cochlear loads. In this work, we analyze effects of cochlear loads on TM traveling waves using a viscoelastic model. Results demonstrate that hair bundle stiffness has little effect on TM waves, the limbal attachment tends to increase the wavelength of TM waves, and viscous loss to subtectorial fluid tends to decrease the wave decay constant. To understand how the TM is able to support traveling waves despite these loads we examined how TM wave decay constants depend on thickness of the TM. We observe that increasing TM thickness tends to moderate all effects of cochlear loads and that as TM thickness increases, the wave decay constant approaches an asymptotic limit that is independent of cochlear loads. For material properties corresponding to both the apical and basal turns of the mouse TM, the asymptotic limit in decay constant is achieved at roughly the physiological thickness – suggesting an evolutionary pressure for the TM to be just thick enough to allow for wave propagation in the presence of subtectorial fluid.

On-going research into the complexities of polyurea behavior under shock loading has led to some breakthroughs in the predictive simulation of how this nominally soft polymer responds under high velocity impact conditions. This work expands upon a previously reported modified pressure-dependent viscoelastic constitutive model for polyurea and its performance under ballistic impact. Specifically, we present recent enhancements to the model including nonlinearites in the Hugoniot and improvements in the high-temperature viscoelastic behavior, which substantially improves accuracy and extends the model’s range of applicable conditions. These improvements are demonstrated through correlation of computations for a suite of normal and pressure-shear plate impact experiments well documented in the open literature. Additionally, microparticle impact experiments were performed on polyurea using a laser-induced particle impact test (LIPIT) technique. High-speed imaging of the impact mechanics revealed elastic particle rebound at low velocity but penetration at high velocity. Simulation of these LIPIT experiments demonstrates good accuracy of the polyurea model under these conditions as well as provides insight into the mechanisms governing the results observed.

Knowledge of the mechanical properties of the tectorial membrane (TM) would improve the understanding of TM function in hearing mechanics. In recent years, several groups have used measurements of wave propagation on isolated TMs to estimate the mechanical properties of the TM at acoustic frequencies. However, these studies have ignored the curvature, finite dimensions and anisotropy of the TM. In this study, optical images of an isolated wild-type basal TM segment in response to harmonic radial excitation are used to determine the amplitude and phase of the motion at acoustic frequencies. Wave propagation on the TM segment is modeled using a finite element model that takes into account the geometry, anisotropy and viscoelasticity of the TM. An automated least-square fitting algorithm is used to find material parameters of the TM. The resulting material properties are compared to previous estimates.Knowledge of the mechanical properties of the tectorial membrane (TM) would improve the understanding of TM function in hearing mechanics. In recent years, several groups have used measurements of wave propagation on isolated TMs to estimate the mechanical properties of the TM at acoustic frequencies. However, these studies have ignored the curvature, finite dimensions and anisotropy of the TM. In this study, optical images of an isolated wild-type basal TM segment in response to harmonic radial excitation are used to determine the amplitude and phase of the motion at acoustic frequencies. Wave propagation on the TM segment is modeled using a finite element model that takes into account the geometry, anisotropy and viscoelasticity of the TM. An automated least-square fitting algorithm is used to find material parameters of the TM. The resulting material properties are compared to previous estimates.

Stress relaxation behavior of unidirectional AS4/8852 carbon/epoxy composites at high temperatures has been investigated. Specimens with an off axis angle of 90° and ±45° have been exposed to constant strain and high temperature. The mechanical results have been modeled by Standard Linear Solid model. The obtained parameters have been implemented in a finite element (FEM) model able to predict the residual stresses in carbon fiber reinforced composites, both in the elastic and in the viscoelastic field.Stress relaxation behavior of unidirectional AS4/8852 carbon/epoxy composites at high temperatures has been investigated. Specimens with an off axis angle of 90° and ±45° have been exposed to constant strain and high temperature. The mechanical results have been modeled by Standard Linear Solid model. The obtained parameters have been implemented in a finite element (FEM) model able to predict the residual stresses in carbon fiber reinforced composites, both in the elastic and in the viscoelastic field.

We report the results of a study on the ignition behavior of a novel concept and design of a heterogeneous energetic material system called ABX, or aluminum-bonded explosives. The idea is to replace the polymeric binder in polymer-bonded explosives (PBX) with aluminum. The motivation of this study is that a new design may have several desirable attributes, including, among others, electrical conductivity, higher mechanical strength, enhanced integrity, higher energy content, and enhanced thermal stability at elevated temperatures. The analysis carried out concerns the replacement of the Estane binder in a HMX/Estane PBX by aluminum. The HMX volume fraction in the PBX and HMX is approximately 81%. 2D mesoscale simulations are carried out, accounting for elasticity, viscoelasticity, elasto-viscoplasticity, fracture, internal friction, and thermal conduction. Results show that, relative to the PBX, the aluminum bonded explosives (ABX) show significantly less heating and lower ignition sensitivity under the s...

In a variety of biomedical applications, cavitation occurs in soft tissue. Although significant amounts of research have been performed on cavitation in water, bubble dynamics, and related bioeffects remain poorly understood. We use numerical simulations of spherical bubble dynamics in soft tissue to assess the extent to which viscoelasticity affects “known” and introduces “new” damage mechanisms. We find that deviatoric stresses – although not an important damage mechanism in water – are significantly enhanced and could be an important bioeffect mechanism in tissue. Both the viscoelastic properties and the nonlinear, large-collapse radius contribute to stress amplification in the surroundings. In addition, temperatures in the surrounding medium increase more in the Zener tissue than in water, due to viscous heating.

It has been shown experimentally that under many circumstances the strength limiting factor of Polymer Bonded Explosives (PBXs) is the adhesion which exists between the filler crystals and the polymer matrix. Experimental measurements of the Work of Adhesion between different binders and glass have been conducted using the JKR experimental technique, a reversible axisymmetric fracture experiment, during which the area of contact and the applied force are both measured during loading and unloading of the interface. The data taken with this technique show a rate dependence not present in the analytical JKR theory which is normally used to describe the adhesive contact of two elastic bodies, and which arises from the viscoelastic properties of the bulk polymer. The data is intended to inform the development, and validate the predictions of, microstructural models of PBX deformation and failure.

Pressure-shear plate impact (PSPI) experiments have been conducted to study the mechanical response of an elastomer (polyurea) at high pressures and high strain rate. The previously determined isentrope has been extended to 18 GPa. At this pressure, the high-strain-rate shearing resistance of polyurea is approximately 1 GPa. From the PSPI tests, it is evident that the shearing resistance of polyurea is quite sensitive to pressure. Based on the experimental results, a quasilinear viscoelasticity model is introduced and implemented in ABAQUS to simulate the response of polyurea P1000 under the impact conditions of the various PSPI experiments. Results of these simulations are compared with the experimental results to gain insight into the viability of the proposed model.

For a model describing the behaviour of one-dimensional viscoelastic medium, all conservation laws are constructed. From a nonlinear partial differential equation, which describes the model, the conservation laws are derived by using the multipliers method. Furthermore, the Lie point symmetries of the equation and the Lie point symmetries associated with the conserved vectors are determined. Then, the classical symmetries are obtained by the Lie classical method. Finally, in order to find potential symmetries, the associated auxiliary system is obtained. However, applying the classical method to the associated auxiliary system yields to the classical symmetries too.For a model describing the behaviour of one-dimensional viscoelastic medium, all conservation laws are constructed. From a nonlinear partial differential equation, which describes the model, the conservation laws are derived by using the multipliers method. Furthermore, the Lie point symmetries of the equation and the Lie point symmetries associated with the conserved vectors are determined. Then, the classical symmetries are obtained by the Lie classical method. Finally, in order to find potential symmetries, the associated auxiliary system is obtained. However, applying the classical method to the associated auxiliary system yields to the classical symmetries too.

Wave processes in a 2D blocky medium are under investigation. Considered continuum consists of rectangular elastic blocks divided by fluid-saturated porous interlayers. The interlayers are described in terms of modified Biot’s porous-flow model. Porous skeleton in the model has viscoelastic properties and takes pore collapsing effect into account. In order to analyse the fluid behavior in nodes between blocks, a hydrodynamic analogue of Kirchhoff’s law is used. To implement presented model nu-merically, a computational algorithm, based on a two-cyclic splitting by spatial variables, is developed. For the blocks equations Godunov’s gap decay scheme is used; for the interlayers equations a hybrid numerical method, based on the dissipationless Go- dunov’s and Ivanov’s schemes, is applied. Parallel software is designed for analysing stresses and velocity fields in a 2D blocky medium. Comparative study of the model with elastic interlayers and the model with fluid-saturated porous interlayers is carried out. I...

Thermoplastic materials are extensively used as a light weight replacement for metal alloys, especially in automotive applications. Furthermore polymer materials can be used to enhance the safety of passengers and pedestrians in a car accident. The state of the art design process for plastics parts is based on Computer Aided Engineering (CAE). Using Finite Element Analysis (FEA), highly dynamic systems can be simulated with a very high accuracy. Considering crash applications, the influence of strain rate on the mechanical behaviour is of paramount importance. To determine the effect of strain rate on the mechanical behaviour, tensile impact tests are conducted at different haul-off velocities. With an increase of the haul-off velocity, the force-oscillation phenomenon becomes significant. The force-oscillation phenomenon is an artifact caused by the dynamic load application in highly dynamic tests. It can be monitored as a superimposition of measured force data with oscillations which increase in amplitude to higher impact velocities.This study looks at the phenomenon of force oscillation in tensile impact testing on viscoelastic materials and its dependency on longitudinal stress wave propagation. Aside a detailed analysis of its origin, a new approach is presented to measure a nearly oscillation free force signal in tensile impact testing on polymer materials, basically independent of the considered haul-off velocity. For this purpose a modification of a standard dumbbell specimen was designed.Thermoplastic materials are extensively used as a light weight replacement for metal alloys, especially in automotive applications. Furthermore polymer materials can be used to enhance the safety of passengers and pedestrians in a car accident. The state of the art design process for plastics parts is based on Computer Aided Engineering (CAE). Using Finite Element Analysis (FEA), highly dynamic systems can be simulated with a very high accuracy. Considering crash applications, the influence of strain rate on the mechanical behaviour is of paramount importance. To determine the effect of strain rate on the mechanical behaviour, tensile impact tests are conducted at different haul-off velocities. With an increase of the haul-off velocity, the force-oscillation phenomenon becomes significant. The force-oscillation phenomenon is an artifact caused by the dynamic load application in highly dynamic tests. It can be monitored as a superimposition of measured force data with oscillations which increase in amplitu...

Based on Frenkel’s Newtonian viscous flow approach [1] and Mackenzie and Shuttleworth’s [2] extension accounting for trapped gas, a model for the shrinkage of a gaseous pore in a viscoelastic polymer melt driven by surface tension was developed. The viscoelastic flow of polymeric materials was considered by using a simple viscoelastic model described by Bellehumeur [3]. In the simulation, the viscoelastic relaxation leads to a pronounced increase of the characteristic time of shrinkage but does not alter the final equilibrium gas sphere diameter. A first attempt at including gas diffusion into the polymer melt motivated by the works of Kontopoulou and Vlachopoulos [4] and Gogos [5] will be given. Numerical solutions of our simplified model show that gas diffusion leads to a complete collapse of the pore. The rate of diffusion can change the collapse mechanism and the time-dependence of pore radius and pressure tremendously.

We study the dynamics of small perturbations to the rest state of a viscoelastic rate type fluid with temperature dependent material parameters. We show that if the material parameters are chosen appropriately, then the quiescent state of the fluid filling an isolated (mechanically, thermally) vessel is a stable state. The outlined analysis explicitly documents the importance of thermodynamic analysis in the development of advanced models for complex fluids.

The melt blending of polymers is an effective and practical way to produce new materials for specific application. Properties of polymer blends depend strongly on their morphology which can be controlled and quantified by rheological properties of the components. In the present work, rheological properties of PP/HDPE blend were investigated at linear and nonlinear viscoelastic range. Relaxation of the step shear strain and morphology were studied at various HDPE concentrations as disperse phase and EPR amounts as a compatibilizer. The blends showed three relaxation stages; a first fast relaxation which was attributed to the relaxation of the components, second one with slower rate, named plateau, which related to droplets relaxation, and the last one with higher relaxation rate. The results showed that the length of the plateau increased with increasing of HDPE concentration, while it decreased with increasing of the compatibilizer content. These behaviors are related to the droplets size, as the smaller ...

Powder injection moulding (PIM) is a multi-stage process to manufacture metallic or ceramic complex, functional parts in large quantities and with high material requirements. The flow in PIM filling process is a complicated non-isothermal problem with viscoelasticity effects and instabilities. The exact description of the whole process of the flow is very difficult. The existence of a yield stress on PIM-feedstock depends on particle interactions within the polymer matrix. Further factors, like powder loading and dispersion during the measurements, are influencing the rheological characterisation of PIM-feedstocks. Additionally, inertial and gravitational effects can have an influence for systems with a very low viscous matrix. Quantifying yield stress, however, must be done carefully because the value obtained depends on the analytical technique used. Knowing the flow behaviour of PIM-feedstock is necessary for successful filling simulation of PIM. In this context, the yield behaviour of a stainless stee...

The paper deals with the evolution of the parameters of a fractional model for different values of temperature. An experimental campaign has been performed on epoxy resin at different levels of temperature. It is shown that epoxy resin is very sensitive to the temperature.

Currently the development of a new generation of polyketone materials offers an interesting technical property profile primarily characterized by excellent chemical resistance, impact resistance and gas barrier properties. Various fields of structural applications such as automotive and electronics as well as pipe and film applications are in prime focus for the practical use of polyketone competing well established technical plastics such as polyamides or polyoxymethylene among others. Besides the excellent physical properties mentioned above, particularly the viscoelastic performance of the polymers is decisive for a successful use in structural applications. Regarding this, especially the mechanical behavior under dynamic and/or long term loading conditions is of major interest. Therefore, a sound and comprehensive dynamic mechanical test methodology under consideration of the time and temperature dependent deformation behavior is required for reliable materials comparison and characterization. In this...

For developing the new engineering materials such as structural materials and tribomaterials based on all plants-derived materials, we investigated the effect of processing sequence on the dynamic viscoelastic properties of the ternary biomass composites: 5mm cut hemp fiber (HF) filled polymer blend of plants-derived polyamide 1010 (PA1010) and polyamide 11 elastomer (PA11E) composites in the molten state. PA1010 and PA11E, which contain the polyether groups as soft segment, were made from plant-derived castor oil. The composition of the polymer blend of PA1010 and PA11E was fixed with 60/40 weight fraction. HF was surface-treated by two types of treatment: alkali treatment by NaOH solution and surface treatment by ureido silane coupling agent. The volume fraction of HF in the composites was fixed with 20vol.%. Five different processing sequences: (1) HF, PA1010 and PA11E were mixed simultaneously (Process A), (2) Re-mixing (second compounding) of the materials prepared by Process A (Process AR), (3) PA11E was blended with PA1010 (PA1010/PA11E blends) and then these blends were mixed with HF (Process B), (4) HF was mixed with PA1010 (HF/PA1010 composites) and then these composites were blended with PA11E (Process C), and (5) HF were mixed with PA11E (HF/PA11E composites) and then these composites were blended with PA1010 (Process D) were attempted for preparing the ternary biomass composites (HF/PA1010/PA11E) composites. These ternary biomass composites were extruded by a twin screw extruder and compression-molded. Their dynamic viscoelastic properties in the molten state were evaluated by oscillatory flow testing using a parallel plate type rheometer. It was found that those properties of the ternary biomass composites in the molten state are influenced so much by processing sequence. This is attributed to the change of internal microstructure of these composites such as the distribution and dispersion of HF. © 2016 Author(s)., JSPS, Japan Society for the Promotion of Science

The Butyl Glycidyl Ether (bge) is selected as a branch mononers and correspondingly poly(butylene succinate) PBS-bge copolymers is synthesised by polymerization. In this study, the dynamic viscoelastic is employed to study the rheological properties of homogeneous PBS and PBS-bge copolymers. The results indicated that all copolymers showed high mole weight and well matched the reaction mole ratio. But the PBS-bge copolymers exhibited a higher shear thinning behaviors than homogeneous PBS. And all PBS-bge copolymers exhibited a higher complex viscosity at low frequency indicating network-like structures were formed at the low shear frequency. In addition, the tanδ is remarkable decreased with the introducing of bge, which reflects that the elasticity of polymer is significantly improved. As a result, the branched modification has improved the ductility and toughness of the material obviously, especially when the branched ratio is more than 5%.

In order to develop the new engineering materials such as structural materials and tribomaterials based on all plants-derived materials, the influence of silane coupling agent on the rheological properties of hemp fiber (HF) filled polyamide 1010 (PA1010) biomass composites in molten state was investigated for one step of the fabrication of these materials. PA1010 was made from sebacic acid and decamethylenediamine, which are obtained from plant-derived castor oil. Hemp fibers were surface-treated by two types of surface treatment: a) alkali treatment by NaOH solution and b) surface treatment by silane coupling agents with different concentrations. Three types of silane coupling agents: aminosilane, epoxysilane and ureidosilane were used for surface treatment. HF/ PA1010 composites were extruded by a twin screw extruder and compression-molded. Rheological behavior in molten state were evaluated by oscillatory flow testing using a parallel plate type rheometer. It was found that the silane coupling agents remarkably influence on: 1) rheological properties such as storage modulus, loss modulus, loss tangent and complex viscosity in low angular frequency region in molten state, 2) temperature dependences of rheological properties, and 3) relationship between phase angle and complex modulus (van Gurp - Palmen plots). These rheological behavior were also strongly influenced by the type of silane coupling agents. The viscoelastic properties (both storage and loss moduli) of aminosilane and epoxysilane treated composites were lower, however, those of ureidosilane treated ones were higher than the moduli of only alkali treated composites. Ureidosilane treated composites were the least temperature sensitive in the surface treated composites investigated here.

This work reports the implementation and verification of a new solver in OpenFOAM® open source computational library, able to cope with integral viscoelastic models based on the integral upper-convected Maxwell model. The code is verified through the comparison of its predictions with analytical solutions and numerical results obtained with the differential upper-convected Maxwell model.

Rolling resistance contributes to 6-10% of the overall fuel consumption. In an effort to provide tunable rolling resistance and tunable damping rubbers, smart fluids are introduced to composites to fabricate smart composites. The subsequent composites will possess unique mechanical properties in response to an externally applied voltage. This paper discusses the measurement of rolling resistance of poly(vinylidene fluoride) (PVDF) using a wooden pendulum roller, crafted in our lab. All fibers can be submerged in the electro rheological fluids (ERF) and become impregnated with barium titanyl oxalate with urea coated particles. Under the influence of electric field strength, the properties such as damping coefficient, rolling force and viscoelastic properties are altered. A comparison between the properties of different PVDF samples was made. PVDF3 with 0.17 g/ml concentration is best aligned and shows the highest change in properties as a function of electric field strength.

The design and development of a novel category of bi-component polymeric fibers, made of a polymeric sheath and a liquid core is described. To understand and to analyze the flow of molten polymer and liquid within a spin pack, we built a macroscale analogon where co-flow of polymer and liquid is investigated systematically. The macroscale analogon is composed of a glass cylinder with a finite length and a coaxial capillary. The inner fluid flows in the capillary and at its outlet meets the outer fluid flowing inside the glass cylinder. The fluids are pumped into the setup using pressurized bottles with controlled flow rates. A high-speed camera is placed in front of the glass cylinder to record the transient and the steady flow of the two phases and the morphology of their interface during co-flow. We systematically analyzed the combination of various fluids and different injection channel geometries, and used these findings to design a customized spin pack. Extrusion trials with molten polymers and specific liquids resulted in the production of liquid filled polymeric fibers (LFF) with different amounts of liquid from 3% to 33%vol. and diameters from 150μm to 1mm. Fiber morphology has been investigated with the help of optical microscopy and computer tomography, in order to analyze both surface and core morphology. Mechanical characterization of fibers has been carried out with special care to the damping capacity of such fibers using two different methods: two point bending tests to evaluate the energy dissipation of fibers upon bending at low frequency values (0.005-0.5Hz), and analysis of vibration reduction to determine the quality factor at the resonance frequency of the 1st and 3rd vibration mode.

Viscoelasticity of entangled semiflexible polymers in the plateau frequency regime is investigated. We combine computer simulations and scaling arguments to develop a unified view of polymer entanglement based on primitive path analysis. The plateau modulus is obtained as a function of the dimensionless segment density. Our theoretical and numerical results agree well with the experimental data over a wide range of stiffness/density.

Gas-gun driven plate impact experiments were performed on High Performance Propellant (HPP) to measure the shock compression behavior and Hugoniot. HPP is a proprietary blend of ammonium-perchlorate (AP), aluminum, and plastic binder. A small amount of FeO2 gives the propellant a rust color. The primary diagnostic was embedded magnetic particle velocity gauges. The Hugoniot was determined by performing multiple experiments using different impactors and a range of impact velocities. Impact stresses ranged from 0.3 GPa to 15 GPa. Even at the highest stress no reaction was observed; none was expected. At low stress HPP exhibits viscoelastic behavior with rounded wave profiles. Hugoniot data can be described using a model based on a Murnaghan isotherm with a small amount of porosity.

Numerical studies of PBXs are important for understanding the relationship between their mechanical properties and explosive behavior. The objective of this research is to analyze the thermomechanical response of HMX/Estane, a Polymer-Bonded Explosive (PBX), over a range of grain volume fractions at room temperature (300 K) and ϵ = 16,667 s-1. The analysis focuses on the correlation between grain-level failure mechanisms and the overall response using a Lagrangian cohesive finite element method (CFEM) framework. Digitized micrograph of an actual PBX is used in the analysis. The results indicate a transition in heating mechanism from viscoelastic dissipation in the binder to frictional heating at fractured surfaces. The delay time which signifies the time at which the transition occurs, is found to decrease linearly with increases in grain volume fraction. The results are useful in obtaining microstructure-performance relations that can be used in the design of advanced energetic materials.

Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a recently developed high-intensity focused ultrasound (HIFU) treatment monitoring method with feasibilities demonstrated in vitro and in vivo. Here, a multi-parametric study is performed to investigate both elastic and acoustics-independent viscoelastic tissue changes using the Harmonic Motion Imaging (HMI) displacement, axial compressive strain and relative phase-shift during high energy HIFU where tissue boiling occurs. Forty three (n=18) thermal lesions were formed in ex vivo canine liver specimens. Two dimensional (2D) transverse HMI displacement maps were also obtained before and after lesion formation. The same method was repeated in 10-, 20-and 30-s HIFU durations at three different acoustic powers of 8, 10, and 11W. For the 10-, 20-, and 30-s treatment cases, a steady decrease in the displacement (−8.67±4.80, −14.44±7.77, 24.03±12.11μm), compressive strain −0.16±0.06, −0.71±0.30, −0.68±0.36 %, and phase shift +1.80±6.80, −15.80±9.44, −18.62±13.14 ° were obtained, respectively, indicating overall increase of relative stiffness and decrease of the viscosity-to-stiffness ratio during heating. After treatment, 2D HMI displacement images of the thermal lesions showed an increased lesion-to-background contrast of 1.34±0.19, 1.98±0.30, 2.26±0.80 and lesion size of 40.95±8.06, 47.6±4.87, and 52.23±2.19 mm2, respectively, which was validated again with pathology 25.17±6.99, 42.17±1.77, 47.17±3.10 mm2. Additionally, studies also investigated the performance of mutli-parametric monitoring under the influence of boiling and attenuation change due to tissue boiling, where discrepancies were found such as deteriorated displacement SNR and reversed lesion-to-background displacement contrast with indication on possible increase in attenuation and tissue gelatification or pulverization. Despite the challenge of the boiling mechanism, the relative phase shift served as consist biomechanical tissue response independent of changes in acoustic properties throughout the HIFU treatment. In addition, the 2D HMI displacement images were able to confirm and quantify the change in dimensions of the thermal lesion site. Therefore, the multi-parametric HMIFU was shown capable of monitoring and mapping tissue viscoelastic response changes during and after HIFU treatment.Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a recently developed high-intensity focused ultrasound (HIFU) treatment monitoring method with feasibilities demonstrated in vitro and in vivo. Here, a multi-parametric study is performed to investigate both elastic and acoustics-independent viscoelastic tissue changes using the Harmonic Motion Imaging (HMI) displacement, axial compressive strain and relative phase-shift during high energy HIFU where tissue boiling occurs. Forty three (n=18) thermal lesions were formed in ex vivo canine liver specimens. Two dimensional (2D) transverse HMI displacement maps were also obtained before and after lesion formation. The same method was repeated in 10-, 20-and 30-s HIFU durations at three different acoustic powers of 8, 10, and 11W. For the 10-, 20-, and 30-s treatment cases, a steady decrease in the displacement (−8.67±4.80, −14.44±7.77, 24.03±12.11μm), compressive strain −0.16±0.06, −0.71±0.30, −0.68±0.36 %, and phase shift +1.80±6.80, −15.80±9.44, −18.6...

The viscoelastic material functions for the Becker and the Lomnitz rheological models, sometimes employed to describe the transient flow of rocks, are studied and compared. Their creep functions, which are known in a closed form, share a similar time dependence and asymptotic behavior. This is also found for the relaxation functions, obtained by solving numerically a Volterra equation of the second kind. We show that the two rheologies constitute a clear example of broadly similar creep and relaxation patterns associated with neatly distinct retardation spectra, for which analytical expressions are available., 7 pages, 4 figures

In this paper, we show how fractional viscoelastic models can be efficient in the modeling of linear viscoelastic behavior, increasing the fitting accuracy of classic generalized viscoelastic models, such as the Generalized Maxwell model. Experimental data (Loss and Storage modulus in the frequency domain) were retrieved from a Dynamic Mechanical Analysis test considering Carbon Fibre Reinforced Polymer samples. The estimated parameters, for the derived fractional viscoelastic models, were obtained through numerical optimization techniques that minimize the difference between model-predicted values and experimental data. An excellent correlation between analytical and experimental results was observed, minimizing numerical instabilities found on a previous work, for the same experimental setup., This work was financed by FEDER funds through COMPETE-Programa Operacional Fatores de Competitividade and by portuguese funds through FCT-Fundação para a Ciência e a Tecnologia within projects PEst-C/MAT/UI0013/ 2011.

We prepare well dispersed nanocomposites based on Graphite Nanoplatelets (GNPs) and polystyrene (PS) through a combination of solution and melt mixing techniques. The samples are subjected to morphological, electrical, and rheological investigations. Electron microscopy analyses show that GNPs are well dispersed, and the presence of few nanometers thick GNPs is noticed. The electrical conductivity of the polymer dramatically increases at a critical content of particles of Φ~4 wt.%, indicating that electrical percolation has occurred. The existence of a percolating network induces a marked elastic connotation in the melt state. We show that the elasticity of GNP networks in samples at different composition can be scaled on a single master curve. This allows for the accurate estimation of the rheological percolation threshold. In addition, using the master curve we can infer the elasticity of GNP networks which are too tenuous to be appreciated via conventional rheological measurements.

Taylor impact tests were conducted on plastic bonded explosives PBX 9501 and PBXN-9 for impact velocities between 80 and 214 m/s. High-speed photography was used to image the impact event at a rate of one frame for every 25 μs. For early times, PBXN-9 showed large-deformation mushrooming of the explosive cylinders, followed by fragmentation by an amount proportional to the impact speed, was observed at all velocities. PBX 9501 appeared to be more brittle than PBXN-9, the latter demonstrated a more viscoelastic response. The post-shot fragments were collected and particle size distributions were obtained. The constitutive model ViscoSCRAM was then used to model the Taylor experiments using the finite element code ABAQUS. Prior to the Taylor simulations, ViscoSCRAM was parameterized for the two explosives using uniaxial stress-strain data. Simulating Taylor impact tests validates the model in situations undergoing extreme damage and fragmentation.

PVP‐CMC and PVP‐CMC‐BA are designated as medicated hydrogels which are elastic in nature like other gels and solids. This present work was focused on the effect of strain on viscoelastic behavior of these medicated hydrogels. Dynamic frequency sweep test at 10% strain and dynamic strain sweep tests at different angular frequencies were performed on these hydrogels. Freshly prepared hydrogels and hydrogels swelled for 60 min from dry state were chosen for the experiments. These two experiments reveal that both PVP‐CMC and PVP‐CMC‐BA hydrogels (fresh and swelled) maintain elastic behavior from very low to medium strain, but at high strain they become viscous in nature.

The influence of silica nanoparticles on the elasticity of a polymethylmethacrylate (PMMA) melt was investigated. The extrudate swell obtained from the extrusion of the melt through a die and the recoverable deformation after a creep test were measured. As well known from other materials, the extrudate swell becomes smaller by adding fillers, i.e. the elasticity decreases. This is usually explained by the effect of substituting viscoelastic polymer molecules by rigid particles. The linear steady‐state recoverable compliance Je0, however, attains values which are significantly higher than those of the matrix indicating an increase of the elasticity. This effect is postulated to be due to interactions of the matrix molecules with the particle surface giving rise to longer retardation times and higher retardation strengths which lead to larger Je0 according to the theory of linear viscoelasticity. The apparent discrepancy between these two contrary effects is solved by the finding that the recoverable compli...

This paper provides an extension to Cosserat mechanics of a recently proposed version of hypoplasticity [1], and this extension is achieved economically by means of a novel complex‐variable formulation of Cosserat theory.The present work represents a compact synthesis and theoretical framework for both non‐polar and polar hypoplasticity, and it encompasses various special cases considered in the literature, as discussed in the recent monograph by Tejchman [2].The current approach offers a perspective on granular dilatancy, elastoplastic yield, and energy dissipation which differs from the standard hypoplasticity and which serves to establish a connection to classical incremental plasticity. In contrast to the classical theory, the present approach, based entirely on the concept of pseudo‐linear forms, admits but does require elastoplastic potentials to describe plastic flow. When such potentials are assumed, it is shown that they can be related to the plastic moduli of the present formulation.It is also s...

Polymer melts experience complex, time variant, stress and deformation fields on their passage through fixed geometries in many conversion operations. Flow complexity is further increased in operations involving the co‐joining of two or more melt streams where one confining boundary is moving and viscoelastic. Such a complex situation arises in coextrusion processes. This work covers experimental studies on polyethylene melt flows in complex coextrusion geometries with a view to understanding the stress fields involved and their effects on flow stability.A 30° coextrusion geometry is studied using two extrusion arrangements. In one arrangement a single extruder is used to feed a ’bifurcated’ die design wherein the melt stream is split prior to, and rejoined after, a divider plate in the die. In the other design melt streams are delivered to, and converged at 30°, using two independent extruders. In a second die melt streams are brought together at 90°. In each die arrangement melt flow in the confluent re...

A simple technology based new hydrogel “PVP‐CMC‐BA” has been prepared by the scientists of Tomas Bata University in Zlin, Czech Republic. Its swelling property (in presence of water, human blood and different pH), antimicrobial property (in presence of skin infection causing agents like: Staphylococcus aureus; bacteria and Candida albicans; fungi) and viscoelastic properties such as storage modulus (G’), loss modulus (G”) and complex viscosity (η*) were investigated at room temperature (25–28° C) which demonstrate that PVP‐CMC‐BA hydrogel is maintaining requisite properties for health care application, specially as a wound dressing material. The elasticity and antimicrobial property of PVP‐CMC‐BA is directly correlated with percentage of boric acid, an antiseptic agent. The consequential values of viscoelastic properties of the hydrogel (before drying) enable us to understand its specific flexible condition to apply on the surface of human body.

In this work, novel patent pending orifice die design for precise extensional viscosity data determination from entrance pressure drop measurements has been developed and tested both, theoretically (through Finite Element Analysis) and experimentally. It has been demonstrated that the proposed novel orifice die allows much more precise extensional viscosity measurements for polymer melts in comparison with conventionally used orifice dies.

Polyurethane (PU) solved in dimethylformamide (DMF) was electrospun under one set of conditions on two different support textiles. The mechanical properties were measured and aerosol filtration tests were done. The hole size distribution was calculated with a new digital image analysis methodology on SEM images. It has been found that supporting textiles have very high effect on mechanical properties and filtration efficiency of nanofiber mats (even if their fiber diameter distributions were practically identical), which can be explained by different porosity of the prepared samples.

Experimental data of two low‐density polyethylene (LDPE) melts at 200° C for both shear flow (transient and steady shear viscosity as well as steady first normal stress coefficient) and elongational flow (transient and steady‐state elongational viscosity) as published by Pivokonsky et al. [1] were analyzed by use of the Molecular Stress Function (MSF) model for broadly distributed, randomly branched molecular structures. For quantitative modeling of melt rheology in both types of flow and in a very wide range of deformation rates, only three nonlinear viscoelastic material parameters are needed: While the rotational parameter, a2, and the structural parameter, β, are found to be equal for the two melts considered, the melts differ in the parameter fmax2 describing maximum stretch of the polymer chains.

The simulations present a first attempt to describe the rheological properties of thermotropic liquid crystalline polymers (LCP's), using recently developed thermodynamic theory of weakly viscoelastic nematodynamics. In this mono‐domain theory the complicated rheological properties of nematic LCP's are modeled by a set of quasi‐linear anisotropic viscoelastic constitutive equations (CE) with anisotropy described by director. The viscoelastic evolution of stress is coupled with the evolution of director. Although this theory has been developed for small values of elastic strains, it is still possible to compare the simulations with experimental data. There are 8 parameters in the theory: 3 viscosities, 3 elastic moduli, and 2 tumbling (elastic and viscous) parameters. We demonstrate that our simulations in monodomain, aligning case are in a semi‐quantitative agreement with experimental data for steady, start up shearing flows and relaxation for two industrial and two “academic” LCP's. Dependencies of fitte...

This study focuses on the preparation and testing of hydroxyapatite‐gelatine nano‐composite gels via a sol‐gel route and in situ formation of hydroxyapatite (HA) type salts. Four types of gels and foams were prepared with Ca/P molar ratio of 0.43 and 0.86 and hydroxyapatite/gelatine weight ratio of 0.50 and 0.70. Cross‐linking of gelatine chains was carried out in 1% glutaraldehyde and dynamic mechanical torsion tests were used to measure the viscoelastic properties of the gels and foams, optimize the cross‐linking time and assess their mechanical performance. Optical and atomic force microscopy were used to investigate the micro‐ and nano‐structure of the produced composites: in these studies, it was confirmed that the gels were nano‐composites with a nano‐structure very similar to that of bone and several similarities in the microstructural features. The best foams incorporated dual pore size distribution.