Search

This paper presents results from an experimental study on the dynamic mechanical and viscoelastic properties of Biopolymer (BP) from Waste vegetable oils (WVO) blended with two types of thermoplastic polyethylene (PE) which are Low Density Polyethylene (LDPE) and High Density Polyethylene (HDPE). BP blended containing 10–30wt.% of BP were injection moulded. MDI were used as crosslinker agent for modifying the matrices. Dynamic mechanical analysis (DMA) of the blended were performed over a temperature range of 30–120°C for BL and 30-140°C for BH under frequency of 1 Hz. DMA revealed no noticeable changes in a-transition temperature when the BP content was increased or were added. The BP blended revealed better temperature resistance at higher BP content. However, the increase in storage modulus was negligible at BL10 and BH20; due to the agglomeration of the BP. The results of the damping ratio analysis revealed that higher interfacial bonding was achieved by addition of MDI crosslinker agent.

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.

A constitutive material model suitable for capturing the biaxial deformation response of poly-ether-ether-ketone (PEEK) films is presented. During the forming of thin PEEK films, a multi-axial state of stress is imposed when the thermally softened sheet is forced to take the desired shape of the mould. Simulation and optimization of the forming of products are capable through the use of modern computational tools, however can only be performed with accurate knowledge and modelling of the constitutive material response subject to process variables. Load-controlled biaxial testing of specimens at conditions analogous to the forming process highlighted the anisotropic, nonlinear viscoelastic material stress-strain behaviour. The Buckley material model accounts for the temperature and strain rate dependence of the biaxial yield behaviour, and further modified to represent inherent anisotropy within samples. The modelled stress-strain results show that the adapted material model is accurate in reproducing the observed biaxial deformation behaviour of PEEK films, providing future promise as a platform for the development of finite element simulations of the forming process.

Polyvinyl alcohol (PVA) hydrogels have desirable characteristics for use as a soft tissue substitute. However, their low mechanical strength and biocompatibility hinder the wide range of biomedical application. Herein, hydroxyapatite blended PVA/HAp composite hydrogel was developed by freeze-thawing and annealing method. The microstructure and rheological properties such as storage and loss modulus are investigated. Samples showed a porous structure with interconnected porosity and HAp distributed uniformly in a PVA matrix. Further, the composite hydrogel showed favorable viscoelastic properties and is suitable for artificial articular cartilage replacement.

Vibration damping gels were developed and characterized for their application as damping material for underwater applications. In the present work, a polydimethyl siloxane (SIL) based gel material and its nanocomposites with graphene nanopowder were prepared in varying compositions and its rheological properties were investigated. Effect of fillers on viscoelastic properties was studied. Rheological measurements were carried out to study effect of temperature and frequency on the viscoelastic properties using stress rheometer. In the oscillation mode, the instrument can give storage and loss moduli (G’ and G”) and tano. The frequency dependent modulus and damping properties were generated in the low frequency range (0.3 - 300 Hz) and using time temperature superposition (TTS) technique the material properties in the high frequency range (in kHz) which are significant for underwater applications, were obtained. Time dependent behaviour of the materials were investigated using creep and stress relaxation experiments.

Bipolar plates (BPPs) are the main component in proton exchange membrane fuel cells. In the last years, different manufacturing processes have been proposed as alternative to the traditional graphite BPPs, including the manufacture of thin stamped BPPs using the rubber pad forming process. In this context, the numerical simulation of the forming process is used to optimize of the process parameters. Thus, in addition to the modelling of the elastoplastic behavior of the metallic sheet, it is also necessary to describe the hyper-viscoelastic behavior of the rubber pad. The main objective of this study is to evaluate the importance of the viscous effect on the global behavior of two different polyurethanes, since the modelling of the viscoelastic behavior is significantly more complex than the hyperelastic one. Uniaxial compression and stress relaxation tests are carried out both experimentally and numerically, considering three loading/unloading velocities. The hyperelastic behavior is described by the Mooney-Rivlin model, while the viscoelasticity is modelled by a series of Maxwell elements. The results show that the viscous effect can be neglected in the numerical modelling of the rubber pad forming, if the rubber hardness value is low.

In this study, heat and mass transfer flow of a viscoelastic (Walter’s liquid-B model) nanofluid over a stretching/shrinking sheet with slip velocity condition is considered. The governing equations for the model which is non-linear partial differential equations are first transformed by using similarity transformation. Runge-Kutta-Fehlberg (RKF) method is employed to solve the transformed ordinary differential equations. Numerical solutions are obtained for the reduced Nusselt number, the Sherwood number and the skin friction coefficient. It is found that the Walter’s viscoelastic nanofluid provided the higher heat and mass transfer rate compared to the ordinary nanofluid and the presence of the velocity slip reduces the effects of the stretching parameter on the skin friction coefficient.

Fiber metal composites made up of alternative layers of metallic and composite are now widely used in Aircraft structures are result of one such effort which bring in the combined strengths of composites and metals. In a similar way, the use of metal fiber composites made up of composite material laminates sandwiched between metallic sheets firmly bonded with high quality adhesives can become an effective replacement of conventional metallic components in high speed machinery such as gas turbines. The benefits of this hybrid form of composite material has the potential of use in areas where fiber reinforced composite material cannot be directly exposed due to the harsh environment of gas turbines. In addition, the metallic surfaces can easily interface into their respective metallic assemblies. Such hybrid composite materials used in static structures can push some of the structural natural frequencies beyond the operating speeds. Composite material used in supporting structures can effectively dampen the excessive vibrations and to further improve the damping capacity the viscoelastic material can also be strategically inserted between the layers. In rotating systems hybrid composite material can be used for some of the long slender shafts to push the critical speeds away from the operating speeds. But unlike supporting structures the damping present in the composite material can induce rotor dynamic instability of rotor-bearing systems. Hence the right combination of metal and fiber reinforced composites can effectively avoid or place the resonances and drastically reduce the vibrating stresses to improve the overall fatigue life of rotating machinery.

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.

Metal/polymer/metal sandwich sheets have recently attracted the interests of industries like automotive industry. These sandwich sheets have superior properties over single-layer metallic sheets including good sound and vibration damping and light weight. However, the formability of these sandwich sheets should be enhanced which requires more research. In this paper, the formability of Bondal sheet (DC06/viscoelastic polymer/DC06 sandwich sheet) was studied through different types of experiments. The mechanical properties of Bondal were determined by uniaxial tensile tests. Hemispherical punch stretching and hydraulic bulge tests were carried out to determine the forming limit diagram (FLD) of Bondal. Furthermore, cylindrical and square cup drawing tests were performed in dry and oil lubricated conditions. These tests were conducted at different blank holding forces (BHFs). An interesting observation about Bondal sheet deep drawing was obtaining of higher drawing depths at dry condition in comparison with oil-lubricated condition.

In the present study, a composite material consisting of a polymeric epoxy resin matrix, reinforced with forty layers of non-woven cotton fiber fabric was manufactured. The method used to manufacture the composite was the Resin Vacuum Infusion technique. This is a technique widely used for high-performance, defect-free, composite materials. Composites and neat polymers are subjected to stresses during their function, while at the same time being influenced by environmental conditions, such as temperature and humidity. The main goal of this study was the investigation of the degradation of composite’s viscoelastic behavior, after saline absorption. At this point, it should be mentioned, that this material could be used in biomedical applications. Therefore, a sealed container full of saline was used for the immer s ion of the specimens manufactured, and was placed in a bath at 37°C (body temperature). The specimens remained there for five different immersion periods (24, 72, 144, 216, 336 hours). The viscoelastic behavior of the composite material was determined through stress relaxation under flexure conditions, and the effect of immersion time and amount of saline absorption was studied. It was observed that after 24 hours of immersion a 42% decrease in stress was observed, which in the sequence remained almost constant. The stress relaxation experimental results were predicted by using the Residua l Property Model (RPM), a model developed by Papanicolaou et al. The same model has been successfully applied in the past, to many different materials previously subjected to various types of damage, in order to predict their residual behavior. For its application, the RPM predictive model needs only two experimental points. It was found that in all cases, predictions were in good agreement with experimental findings. Furthermore, the comparison between experimental values and theoretical predictions formed the basis of useful observations and conclusions.

High performance composites for aviation-related structures are prone to constant aging by environmental agents. Previous data from our work reported on the stiffening behaviour of glass fibre polyester composites used in the manufacturing of wind turbine blades. Airplanes from such composites are already on service nowadays. This justifies the detailed study of the exposure of high performance materials to environmental conditions such as varying temperature, humidity, ultraviolet radiation, in order to assess the impact of these important aging factors on their mechanical behaviour. The dramatic changes in the dynamic mechanical response of polymer matrix carbon fibre composites upon exposure to acceleration aging has been assessed in the present study. In order to assess the synergistic effect action of temperature and humidity on composites subjected to changes of temperature from −35 to +40 °C and humidity variations from

Polyamides are engineering thermoplastics which exhibit good mechanical and barrier properties. However, the viscoelastic behavior over the complete range of polyamide relaxation is a topic rarely mentioned in the literature due to the presence of a crystalline phase and lack of thermal stability.The rheological behavior of amorphous PA 6I with increasing molecular weight was studied. As molecular weight increases, a clear rubbery plateau appears and the longest relaxation time is shifted to lower frequencies, as expected by the Rouse and reptation models.Interactions were added to the PA by copolymerizing PA 6I’s monomers with different substituted isophthalic acids. Ionic copolyamides were synthesized in molar fractions from 5 to 20 mol%, inciting an increase of about 10 to 40°C in the glass transition temperature. Master curves of unentangled PA 6I and substituted polyamides, with similar molecular weight, overlap in the complete frequency range using an appropriate reference temperature, which is close to, but not identical to Tg. Ionic groups have an effect on the Angell’s dynamical fragility, i.e. on the temperature variation of the rheological response close to Tg. Dynamic moduli of unentangled polyamides were fitted with Rouse model, showing no effect of hydrogen bonds or ionic groups on the shape of the rheological master curves. The molecular weight between entanglements increases for ionic copolyamides due to an increase of chain rigidity. Small-angle X-ray scattering shows that no segregation of ionic domains occurs in unentangled ionic copolyamides, while entangled copolyamides show only weak segregation.Stronger hydrogen bonding resulted in a decrease of the molecular weight between entanglements. Nevertheless no significant difference was observed in the shape of master curves, which were fitted using the Rouse model.The effect of interacting groups on the local dynamics in the solid state (below Tg) was studied by dielectric spectroscopy. Ionic groups have no effect on secondary relaxations, while alpha-relaxation is shifted accordingly to Tg. No difference was observed between ionic copolyamides and PA 6I during aging experiments, as ionic groups do not act as dynamic heterogeneities, i.e., zones where the local dynamics are heterogeneous due to different local ionic fractions

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.

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.

During thermoforming process, the consolidation deformation mode of thermoplastic prepregs is one of the key deformation modes especially in the consolidation step, where the two resin flow phenomena: resin percolation and transverse squeeze flow, play an important role. This occurs a viscosity behavior for consolidation mode. Based on a visco-hyper-elastic model for the characterization of thermoplastic prepregs proposed by Guzman, which involves different independent modes of deformation: elongation mode, bending mode with thermo-dependent, and viscoelastic in-plan shearing mode with thermo-dependent, a viscoelastic model completed with consolidation behavior will be presented in this paper. A completed three-dimensional mechanical behavior with compaction effect for thermoplastic pre-impregnated composites is constituted, and the associated parameters are identified by compaction test. Moreover, a seven-node prismatic solid-shell finite element approach is used for the forming simulation. To subdue transverse shear locking, an intermediate material frame related to the element sides is introduced in order to fix nodal transverse shear strain components. Indeed, the enhanced assumed strain method and a reduced integration scheme are combined offering a linear varying strain field along the thickness direction to circumvent thickness locking, and an hourglass stabilization procedure is employed in order to correct the element’s rank deficiency for pinching. An additional node is added at the center providing a quadratic interpolation of the displacement in the thickness direction. The predominance of this element is the ability of three dimensional analysis, especially for the transverse stress existence through the thickness of material, which is essential for the consolidation modelling. Finally, an intimate contact model is employed to predict the evolution of the consolidation which permits the microstructure prediction of void presented through the prepreg. Several tests including a thermoforming test are launched to evaluate the consolidation model and the accuracy of the proposed element.

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.

A favorable gelling fluid for oil and gas industry is the one that have good rheological, thermally stable properties and environmental friendly. In the present study, a gelling agent, diutan gum (DG) was modified with N-(3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC) to enhance the rheological properties. The modified-diutan gum (MDG) were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and rheometer. FTIR result shows a significant decreasing of hydroxyl group intensity and the appearance of new peak at 1250 cm-1 attributed to the substitution of CHPTAC on the DG backbone. In addition, the rheological properties of the MDG fluid showed remarkable increases in apparent viscosity. The elastic modulus (G′) and viscous modulus (G″) also increases showing that the MDG have good viscoelastic properties which due to the strong electrostatic interaction between the chains after the modification. This finding showed that, with simple modification using CHPTAC, the rheological properties of MDG gelling agent can be tailored and expected to increase the thermal properties.

In the framework of linear stability analysis, the internal and boundary heating of top heavy non-Newtonian viscoelastic nanofluid layer is investigated. The model includes the Brownian diffusion and thermophoresis slip mechanisms which are responsible for nanoparticles migration. After applying normal mode, the Galerkin approach is employed to solve the eigenvalue problem under stress-free boundary conditions. The magnetic field is also applied to weak electrically conducting nanofluid along with rotation. The effect of other important parameters on the stability of the system has also been analyzed. Rayleigh number is found to be independent of non-Newtonian fluid parameters.

Finite Element (FE) forming simulation offers the possibility of a detailed analysis of the deformation behavior of multilayered thermoplastic blanks during forming, considering material behavior and process conditions. Rate-dependent bending behavior is a material characteristic, which is so far not considered in FE forming simulation of pre-impregnated, continuously fiber reinforced polymers (CFRPs). Therefore, an approach for modeling viscoelastic bending behavior in FE composite forming simulation is presented in this work. The presented approach accounts for the distinct rate-dependent bending behavior of e.g. thermoplastic CFRPs at process conditions. The approach is based on a Voigt-Kelvin (VK) and a generalized Maxwell (GM) approach, implemented within a FE forming simulation framework implemented in several user-subroutines of the commercially available FE solver Abaqus. The VK, GM, as well as purely elastic bending modeling approaches are parameterized according to dynamic bending characterizati...

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...

Pre-impregnated thermoplastic composites have recently attached increasing interest in the automotive industry for their excellent mechanical properties and their rapid cycle manufacturing process, modelling and numerical simulations of forming processes for composites parts with complex geometry is necessary to predict and optimize manufacturing practices, especially for the consolidation effects. A viscoelastic relaxation model is proposed to characterize the consolidation behavior of thermoplastic prepregs based on compaction tests with a range of temperatures. The intimate contact model is employed to predict the evolution of the consolidation which permits the microstructure prediction of void presented through the prepreg. Within a hyperelastic framework, several simulation tests are launched by combining a new developed solid shell finite element and the consolidation models.

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.

A method for determining rheological parameters of the Prony model describing the process of viscoelastic deformation of a material was developed based on the results of dynamic mechanical analysis. For the approbation of the method, static (uniaxial tension) and dynamic (three-point bending) mechanical tests of polymer composites were carried out. Based on the analytical dependence of the storage modulus on the parameters of the Prony model, the parameters of the shear function are determined. The results of the static and dynamic analysis are in good agreement. The proposed technique allows us to accelerate the determination of rheological parameters of polymer materials and recommend it to the calculation of the stress-strain state of structural elements and friction joints during their long operation at elevated temperature.A method for determining rheological parameters of the Prony model describing the process of viscoelastic deformation of a material was developed based on the results of dynamic mechanical analysis. For the approbation of the method, static (uniaxial tension) and dynamic (three-point bending) mechanical tests of polymer composites were carried out. Based on the analytical dependence of the storage modulus on the parameters of the Prony model, the parameters of the shear function are determined. The results of the static and dynamic analysis are in good agreement. The proposed technique allows us to accelerate the determination of rheological parameters of polymer materials and recommend it to the calculation of the stress-strain state of structural elements and friction joints during their long operation at elevated temperature.

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.

In this study, viscoelastic modeling of the extrusion film casting process, based on the lD membrane model and modified Leonov constitutive equation, was conducted and the effect of the viscoelastic stress state at the die exit (captured here via second to first normal stress difference ratio) on the unwanted neck-in phenomenon has been analyzed for wide range of Deborah numbers and materials having different level of uniaxial and planar extensional strain hardening. Relevant experimental data for LDPE and theoretical predictions based on multimode eXtended Pom-Pom model acquired from the open literature were used for the validation purposes. It was found that firstly, the predicting capabilities of both constitutive equations for given material and processing conditions are comparable even if the single mode modified Leonov model was used and secondly, the agreement between theoretical and experimental data on neck-in is fairly good. Results of the theoretical study revealed that the viscoelastic stress ...

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...

The paper is to describe the method for studying the rheological characteristics of elastomers using a multi-circuit electrical scheme of substitution, the synthesis of which is performed on the basis of experimental data obtained during the mechanical relaxation of loaded test samples at a fixed value of the relative deformation. In analyzing the fast and slow stages of the stress relaxation process in elastomer test specimens with significantly different viscoelastic properties, it is established that the number of relaxation mechanisms in the decomposition of the time dependence into exponentials does not exceed 6 (six).

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...

Although, circular or planar abrupt entry flows are geometrically very simple hydrodynamic problem highly viscoelastic polymer melts makes it very complex with extreme differences in velocities and stresses across the geometry. Despite these flows are very common in polymer melt extrusion industry their strongly non-viscometric and transient nature represents exceedingly challenging task for experimental as well as theoretical investigation and consequently complicates their fully understanding. Polymer melts flowing through abrupt entry contractions exhibit several unique features of which the vortices are one of them. Occurrence of infinitesimal stress singularity in the salient corner leads to presence of weak concave Newtonian viscous vortex. Moreover, polymer melts with increasing extensional to shear viscosity (Trouton) ratio as a function of flow rate exhibit strong convex elastic vortex caused by complete reorientation of stress field near the re-entrant corner (infinite stress singularity point) ...

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.

Injection stretch blow moulding has been extensively researched for numerous years and is a well-established method of forming thin-walled containers. This paper is concerned with validating the finite element analysis of the stretch-blow-moulding (SBM) process in an effort to progress the development of injection stretch blow moulding of poly(ethylene terephthalate). Extensive data was obtained experimentally over a wide process window accounting for material temperature, air flow rate and stretch-rod speed while capturing cavity pressure, stretch-rod reaction force, in-mould contact timing and material thickness distribution. This data was then used to assess the accuracy of the correlating FE simulation constructed using ABAQUS/Explicit solver and an appropriate user-defined viscoelastic material subroutine. Results reveal that the simulation was able to pick up the general trends of how the pressure, reaction force and in-mould contact timings vary with the variation in preform temperature and air flow rate. Trends in material thickness were also accurately predicted over the length of the bottle relative to the process conditions. The knowledge gained from these analyses provides insight into the mechanisms of bottle formation, subsequently improving the blow moulding simulation and potentially providing a reduction in production costs.

Pressure pulse propagation in a viscoelastic cylindrical tube filled with polymeric liquid, is investigated. The tube is considered as a thin circular cylindrical shell, made of material following Kelvin-Voight rheological model. The liquid rheology is described by Oldroyd equation. Dynamic interaction of liquid with the tube wall in the wave is described within quasi-one-dimensional approach. The initial-boundary value problem, modeling pressure pulse propagation in the waveguide, is solved by operational method. The solution is presented in explicit form in the s-domain. Plots of pressure distribution along the pipe at different moments of time are calculated by numerical inversion of Laplace transform for initial finite pulse, generated at the tube end. Results of simulations illustrate the tube and liquid rheology effect on the wave propagation; they indicate that attenuation of the wave in a viscoelastic tube can exceed essentially that one for a corresponding pure elastic tube. Liquid viscoelasticit...

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 ...