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Gerrit Peters

Eindhoven University of Technology, Mechanical Engineering, Faculty Member

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Papers by Gerrit Peters

Continuous Cooling Curves Diagrams of Propene/Ethylene Random Copolymers. The Role of Ethylene Counits in Mesophase Development

by Giancarlo Alfonso and Gerrit Peters

Macromolecules, 2010

A simple method to investigate polymer crystallization during fast cooling, based on in situ temp... more A simple method to investigate polymer crystallization during fast cooling, based on in situ temperature acquisition and ex-situ structural characterization, is proposed. The approach enables one to obtain the continuous cooling curve (CCC) diagrams, widely used in metallurgy but seldom adopted for semicrystalline polymers. This method is here exploited to gain new insights on polymorphic behavior of quenched polypropylene and its copolymers with ethylene. Experimental CCC diagrams, covering a wide range of crystallization temperatures in the domains of monoclinic structure and mesophase, are obtained for the first time. The role of counits in affecting the development of the mesophase upon fast cooling is assessed: the critical cooling rate above which a predominant fraction of mesomorphic form is generated significantly decreases with increasing comonomer concentration. This is due to the remarkable hindrance of ethylene counits on the crystallization kinetics of the R-form, which indirectly favors the development of the less affected mesophase. We expect that this concept can be extended to any kind of defects that disturbs the structuring of the monoclinic phase.

Design and numerical implementation of a 3-D non-linear viscoelastic constitutive model for brain tissue during impact

by Dave Brands and Gerrit Peters

Journal of Biomechanics, 2004

Finite Element (FE) head models are often used to understand mechanical response of the head and ... more Finite Element (FE) head models are often used to understand mechanical response of the head and its contents during impact loading in the head. Current FE models do not account for non-linear viscoelastic material behavior of brain tissue. We developed a new non-linear viscoelastic material model for brain tissue and implemented it in an explicit FE code. To obtain sufficient numerical accuracy for modeling the nearly incompressible brain tissue, deviatoric and volumetric stress contributions are separated. Deviatoric stress is modeled in a non-linear viscoelastic differential form. Volumetric behavior is assumed linearly elastic. Linear viscoelastic material parameters were derived from published data on oscillatory experiments, and from ultrasonic experiments. Additionally, non-linear parameters were derived from stress relaxation (SR) experiments at shear strains up to 20%. The model was tested by simulating the transient phase in the SR experiments not used in parameter determination (strains up to 20%, strain rates up to 8 s À1). Both time-and strain-dependent behavior were predicted accurately ðR 2 > 0:96Þ for strain and strain rates applied. However, the stress was overestimated systematically by approximately 31% independent of strain(rate) applied. This is probably caused by limitations of the experimental data at hand.

Comparison of the dynamic behaviour of brain tissue and two model materials

by Dave Brands and Gerrit Peters

Stapp car crash : conference : proceedings, 43rd, San Diego, Cal., October 25-27, 1999, Oct 1, 1999

Linear viscoelastic material parameters of porcine brain tissue and two brain substitute material... more Linear viscoelastic material parameters of porcine brain tissue and two brain substitute materials for use in mechanical head models (edible bone gelatin and dielectric silicone gel) were determined in small deformation, oscillatory shear experiments. Frequencies to 1000 Hertz could be obtained using the Time/Temperature Superposition principle. Brain tissue material parameters (i.e. dynamic modulus (phase angle) of 500 (10 degrees) and 1250 Pa (27 degrees) at 0.1 and 260 Hz respectively) are within the range of data reported in literature. The gelatin behaves much stiffer (modulus on the order of 100 kPa) and does not show viscous behavior. Silicone gel resembles brain tissue at low frequencies but becomes more stiff and more viscous at higher frequencies (dynamic modulus (phase angle) 245 Pa (7 degrees) and 5100 Pa (56 degrees) at 0.1 and 260 Hz respectively). Furthermore, the silicone gel behaves linearly for strains up to at least 10%, whereas brain tissue exhibits non-linear behavior for strains larger than 1%.

Concomitant Crystallization in Propylene/Ethylene Random Copolymer with Strong Flow at Elevated Temperatures

Industrial & Engineering Chemistry Research, 2018

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Towards the Development of a Strategy to Characterize and Model the Rheological Behavior of Filled, Uncured Rubber Compounds

Polymers

In this paper, an experimental strategy is presented to characterize the rheological behavior of ... more In this paper, an experimental strategy is presented to characterize the rheological behavior of filled, uncured rubber compounds. Oscillatory shear experiments on a regular plate-plate rheometer are combined with a phenomenological thixotropy model to obtain model parameters that can be used to describe the steady shear behavior. We compare rate- and stress-controlled kinetic equations for a structure parameter that determines the deformation history-dependent spectrum and, thus, the dynamic thixotropic behavior of the material. We keep the models as simple as possible and the characterization straightforward to maximize applicability. The model can be implemented in a finite element framework as a tool to simulate realistic rubber processing. This will be the topic of another work, currently under preparation. In shaping processes, such as rubber- and polymer extrusion, with realistic processing conditions, the range of shear rates is far outside the range obtained during rheologi...

Influence of Shear Flow on the Specific Volume and the Crystalline Morphology of Isotactic Polypropylene

by maurice van der beek and Gerrit Peters

Macromolecules, 2006

ABSTRACT

Mixing behaviour in a cavity flow

Structure evolution during film blowing: An experimental study using in-situ small angle X-ray scattering

European Polymer Journal, 2016

The prediction of mechanical performance of isotactic polypropylene on the basis of processing conditions

Polymer, 2016

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Linear viscoelastic fluid characterization of ultra-high-viscosity fluids for high-frequency damper design

Rheologica Acta, 2015

This paper presents the use of a state of the art damper for high-precision motion stages as a sl... more This paper presents the use of a state of the art damper for high-precision motion stages as a sliding plate rheometer for measuring linear viscoelastic properties in the frequency range of 10 Hz-10 kHz. This device is relatively cheap and enables to obtain linear viscoelastic (LVE) fluid models for practical use in precision mechanics applications. This is an example of reversed engineering, i.e., turning a machine part into a material characterization device. Results are shown for a high-viscosity fluid. The first part of this paper describes the damper design that is based on a high-viscosity fluid. This design is flexure-based to minimize parasitic nonlinear forces such as hysteresis and stick-slip. In the second part of the paper, LVE fluid characterization by means of the damper setup is presented. Measurements are performed and model parameters are fitted by a non-convex optimization algorithm in order to obtain the frequency-dependent behavior of the fluid. The resulting fluid model is validated by comparison with a second measurement with a different damper geometry. This paper shows that LVE fluid characterization between 10 Hz and 10 kHz for elastic high-viscosity fluids is possible with a motion stage damper for which the undamped behavior is known.

A new approach for calculating the true stress response from large amplitude oscillatory shear (LAOS) measurements using parallel plates

Rheologica Acta, 2013

The parallel plates geometry is often deemed unsuitable for nonlinear viscoelasticity measurement... more The parallel plates geometry is often deemed unsuitable for nonlinear viscoelasticity measurements because the strain field, and thus the nonlinear response, varies across the sample. Although cone-plate and Couette geometries are designed to circumvent this problem by ensuring a uniform strain field, it is not always easy to shape the material to the complex shapes that is required for these geometries. This has motivated the development of techniques to accurately determine the nonlinear stress response using the more convenient plate-plate geometry. Here, we introduce a new approach to obtain this true material response in large amplitude oscillatory shear (LAOS) experiments using the plate-plate geometry. By tracing the Fourier components of the torque response and their derivatives with respect to the maximum applied deformation, we accurately obtain the material's true stress-strain response from parallel plate measurements. The approach does not require any assumptions about the material's viscoelastic behavior. We test our approach experimentally

Analysis of mixing in three-dimensional time-periodic cavity flows

Journal of Fluid Mechanics, 1999

A method to locate periodic structures in general three-dimensional Stokes flows with time-period... more A method to locate periodic structures in general three-dimensional Stokes flows with time-periodic boundary conditions is presented and applied to mixing cavity flows. Numerically obtained velocity fields and particle tracking schemes are used to provide displacement and stretching fields. From these the location and identification of periodic points can be derived. The presence or absence of these periodic points allows a judgement on the quality of the mixing process. The technique is general and efficient, and applicable to mixing flows for which no analytical velocity field is available (the case for all three-dimensional flows considered in this paper). Results are presented for three different mixing protocols in a three-dimensional time-periodic cavity flow, serving as an accessible test case for the methods developed. A major result is that periodic lines are obtained for these three-dimensional flows. These lines can be complex in geometry and their nature can change along...

Axisymmetric boundary integral simulations of film drainage between two viscous drops

Journal of Fluid Mechanics, 2006

Film drainage between two drops with viscosity equal to that of the matrix fluid is studied using... more Film drainage between two drops with viscosity equal to that of the matrix fluid is studied using a numerical method that can capture both the external problem of two touching drops and the inner problem of pressure-driven local film drainage, without assumptions about the dimensions of the film or the use of lubrication approximations. We use a non-singular boundary integral method that has sufficient stability and accuracy to simulate film thicknesses down to and smaller than 10 −4 times the undeformed drop radius. After validation of the method we investigate the validity of various results obtained from simple film-drainage models and asymptotic theories. Our results for buoyancy-driven collisions are in agreement with a recently developed asymptotic theory. External-flow-driven collisions are different from buoyancy-driven collisions, which means that the internal circulation inside the drop plays a significant role in film drainage, even for small capillary numbers, as has been recently shown (Nemer et al., Phys. Rev. Lett., vol. 92, 2004, 114501). Despite that, we find excellent correspondence with simple drainage models when considering the drainage time only.

Numerical Study of the Effect of Thixotropy on Extrudate Swell

Polymers

The extrusion of highly filled elastomers is widely used in the automotive industry. In this pape... more The extrusion of highly filled elastomers is widely used in the automotive industry. In this paper, we numerically study the effect of thixotropy on 2D planar extrudate swell for constant and fluctuating flow rates, as well as the effect of thixotropy on the swell behavior of a 3D rectangular extrudate for a constant flowrate. To this end, we used the Finite Element Method. The state of the network structure in the material is described using a kinetic equation for a structure parameter. Rate and stress-controlled models for this kinetic equation are compared. The effect of thixotropy on extrudate swell is studied by varying the damage and recovery parameters in these models. It was found that thixotropy in general decreases extrudate swell. The stress-controlled approach always predicts a larger swell ratio compared to the rate-controlled approach for the Weissenberg numbers studied in this work. When the damage parameter in the models is increased, a less viscous fluid layer appea...

Effect of shear rate and pressure on the crystallization of PP nanocomposites and PP/PET polymer blend nanocomposites

Polymer, 2019

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Effect of Thermal History and Shear on the Viscoelastic Response of iPP Containing an Oxalamide-Based Organic Compound

Macromolecules, 2019

We report on the role of temperature and shear on the melt behavior of iPP in the presence of the... more We report on the role of temperature and shear on the melt behavior of iPP in the presence of the organic compound N1,N1′-(propane-1,3-diyl)bis(N2-hexyloxalamide) (OXA3,6). It is demonstrated that OXA3,6 facilitates a viscosity suppression when it resides in the molten state. The viscosity suppression is attributed to the interaction of iPP chains/ subchains with molten OXA3,6 nanoclusters. The exact molecular mechanism has not been identified; nevertheless, a tentative explanation is proposed. The observed viscosity suppression appears similar to that encountered in polymer melts filled with solid nanoparticles, with the difference that the OXA3,6 compound reported in this study facilitates the viscosity suppression in the molten state. Upon cooling, as crystal growth of OXA3,6 progresses, the decrease in viscosity is suppressed. Retrospectively, segmental absorption of iPP chains on the surface of micrometer-sized OXA3,6 crystallites favors the formation of dangling arms, yielding OXA3,6 crystallites decorated with partially absorbed iPP chains. In other words, the resulting OXA3,6 particle morphology resembles that of a hairy particle or a starlike polymer chain. Such hairy particles effectively facilitate a viscosity enhancement, similar to branched polymer chains. This hypothesis and its implications for the shear behavior of iPP are discussed and supported using plate−plate rheometry and slit-flow experiments combined with smallangle X-ray scattering analysis.

Comparison of the Dynamic Behavior of Brain Tissue and Two Model Materials

SAE Technical Paper Series, 1999

... Subject Areas: Highways; Research; Safety and Human Factors; I84: Personal Injuries. Last Mod... more

Glass transition temperature versus structure of polyamide 6: A flash-DSC study

Thermochimica Acta, 2017

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Modeling Flow-Induced Crystallization

Advances in Polymer Science, 2016

A numerical model is presented that describes all aspects of flow-induced crystallization of isot... more A numerical model is presented that describes all aspects of flow-induced crystallization of isotactic polypropylene at high shear rates and elevated pressures. It incorporates nonlinear viscoelasticity, including viscosity change as a result of formation of oriented fibrillar crystals (shish), compressibility, and nonisothermal process conditions caused by shear heating and heat release as a result of crystallization. In the first part of this chapter, the model is validated with experimental data obtained in a channel flow geometry. Quantitative agreement between experimental results and the numerical model is observed in terms of pressure drop, apparent crystallinity, parent/daughter ratio, Hermans' orientation, and shear layer thickness. In the second part, the focus is on flow-induced crystallization of isotactic polypropylene at elevated pressures, resulting in multiple crystal phases and morphologies. All parameters but one are fixed a priori from the first part of the chapter. One additional parameter, determining the portion of β-crystal spherulites nucleated by flow, is introduced. By doing so, an accurate description of the fraction of β-phase crystals is obtained. The model accurately captures experimental data for fractions of all crystal phases over a wide range of flow conditions (shear rates from 0 to 200 s À1 , pressures from 100 to 1,200 bar, shear temperatures from 130 C to 180 C). Moreover, it is shown that, for high shear rates and pressures, the measured γ-phase fractions can only be matched if γ-crystals can nucleate directly on shish.

Nucleation Induced by ”Short-Term Pressurization” of an Undercooled Isotactic Polypropylene Melt

European Polymer Journal, 2016

Nucleation of semi-crystalline polymers is very sensitive to perturbations of the melt state. In ... more Nucleation of semi-crystalline polymers is very sensitive to perturbations of the melt state. In contrast to the case of flow, the influence of pressure changes on nucleation has been almost neglected so far. In this work we explore the effect of the pressure history on isotactic polypropylene crystallization by applying a brief step-like increase of pressure to the undercooled melt. Using dilatometry and synchrotron X-ray diffraction, an enhancement of crystallization kinetics proportional to the magnitude of the pressure pulse is revealed. This acceleration is linked to an increase of the number of active nuclei after the short term pressurization, as confirmed by ex-situ optical microscopy observations. Up to an order of magnitude increase in nucleation density is found, for pressure pulses around 600-700 bar. The pressure-induced nucleating effect is interpreted in the light of classical nucleation theory; although a non-classical "barrier-less" nucleation mechanism is also envisaged.

Continuous Cooling Curves Diagrams of Propene/Ethylene Random Copolymers. The Role of Ethylene Counits in Mesophase Development

by Giancarlo Alfonso and Gerrit Peters

Macromolecules, 2010

A simple method to investigate polymer crystallization during fast cooling, based on in situ temp... more A simple method to investigate polymer crystallization during fast cooling, based on in situ temperature acquisition and ex-situ structural characterization, is proposed. The approach enables one to obtain the continuous cooling curve (CCC) diagrams, widely used in metallurgy but seldom adopted for semicrystalline polymers. This method is here exploited to gain new insights on polymorphic behavior of quenched polypropylene and its copolymers with ethylene. Experimental CCC diagrams, covering a wide range of crystallization temperatures in the domains of monoclinic structure and mesophase, are obtained for the first time. The role of counits in affecting the development of the mesophase upon fast cooling is assessed: the critical cooling rate above which a predominant fraction of mesomorphic form is generated significantly decreases with increasing comonomer concentration. This is due to the remarkable hindrance of ethylene counits on the crystallization kinetics of the R-form, which indirectly favors the development of the less affected mesophase. We expect that this concept can be extended to any kind of defects that disturbs the structuring of the monoclinic phase.

Design and numerical implementation of a 3-D non-linear viscoelastic constitutive model for brain tissue during impact

by Dave Brands and Gerrit Peters

Journal of Biomechanics, 2004

Finite Element (FE) head models are often used to understand mechanical response of the head and ... more Finite Element (FE) head models are often used to understand mechanical response of the head and its contents during impact loading in the head. Current FE models do not account for non-linear viscoelastic material behavior of brain tissue. We developed a new non-linear viscoelastic material model for brain tissue and implemented it in an explicit FE code. To obtain sufficient numerical accuracy for modeling the nearly incompressible brain tissue, deviatoric and volumetric stress contributions are separated. Deviatoric stress is modeled in a non-linear viscoelastic differential form. Volumetric behavior is assumed linearly elastic. Linear viscoelastic material parameters were derived from published data on oscillatory experiments, and from ultrasonic experiments. Additionally, non-linear parameters were derived from stress relaxation (SR) experiments at shear strains up to 20%. The model was tested by simulating the transient phase in the SR experiments not used in parameter determination (strains up to 20%, strain rates up to 8 s À1). Both time-and strain-dependent behavior were predicted accurately ðR 2 > 0:96Þ for strain and strain rates applied. However, the stress was overestimated systematically by approximately 31% independent of strain(rate) applied. This is probably caused by limitations of the experimental data at hand.

Comparison of the dynamic behaviour of brain tissue and two model materials

by Dave Brands and Gerrit Peters

Stapp car crash : conference : proceedings, 43rd, San Diego, Cal., October 25-27, 1999, Oct 1, 1999

Linear viscoelastic material parameters of porcine brain tissue and two brain substitute material... more Linear viscoelastic material parameters of porcine brain tissue and two brain substitute materials for use in mechanical head models (edible bone gelatin and dielectric silicone gel) were determined in small deformation, oscillatory shear experiments. Frequencies to 1000 Hertz could be obtained using the Time/Temperature Superposition principle. Brain tissue material parameters (i.e. dynamic modulus (phase angle) of 500 (10 degrees) and 1250 Pa (27 degrees) at 0.1 and 260 Hz respectively) are within the range of data reported in literature. The gelatin behaves much stiffer (modulus on the order of 100 kPa) and does not show viscous behavior. Silicone gel resembles brain tissue at low frequencies but becomes more stiff and more viscous at higher frequencies (dynamic modulus (phase angle) 245 Pa (7 degrees) and 5100 Pa (56 degrees) at 0.1 and 260 Hz respectively). Furthermore, the silicone gel behaves linearly for strains up to at least 10%, whereas brain tissue exhibits non-linear behavior for strains larger than 1%.

Concomitant Crystallization in Propylene/Ethylene Random Copolymer with Strong Flow at Elevated Temperatures

Industrial & Engineering Chemistry Research, 2018

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Towards the Development of a Strategy to Characterize and Model the Rheological Behavior of Filled, Uncured Rubber Compounds

Polymers

In this paper, an experimental strategy is presented to characterize the rheological behavior of ... more In this paper, an experimental strategy is presented to characterize the rheological behavior of filled, uncured rubber compounds. Oscillatory shear experiments on a regular plate-plate rheometer are combined with a phenomenological thixotropy model to obtain model parameters that can be used to describe the steady shear behavior. We compare rate- and stress-controlled kinetic equations for a structure parameter that determines the deformation history-dependent spectrum and, thus, the dynamic thixotropic behavior of the material. We keep the models as simple as possible and the characterization straightforward to maximize applicability. The model can be implemented in a finite element framework as a tool to simulate realistic rubber processing. This will be the topic of another work, currently under preparation. In shaping processes, such as rubber- and polymer extrusion, with realistic processing conditions, the range of shear rates is far outside the range obtained during rheologi...

Influence of Shear Flow on the Specific Volume and the Crystalline Morphology of Isotactic Polypropylene

by maurice van der beek and Gerrit Peters

Macromolecules, 2006

ABSTRACT

Mixing behaviour in a cavity flow

Structure evolution during film blowing: An experimental study using in-situ small angle X-ray scattering

European Polymer Journal, 2016

The prediction of mechanical performance of isotactic polypropylene on the basis of processing conditions

Polymer, 2016

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Linear viscoelastic fluid characterization of ultra-high-viscosity fluids for high-frequency damper design

Rheologica Acta, 2015

This paper presents the use of a state of the art damper for high-precision motion stages as a sl... more This paper presents the use of a state of the art damper for high-precision motion stages as a sliding plate rheometer for measuring linear viscoelastic properties in the frequency range of 10 Hz-10 kHz. This device is relatively cheap and enables to obtain linear viscoelastic (LVE) fluid models for practical use in precision mechanics applications. This is an example of reversed engineering, i.e., turning a machine part into a material characterization device. Results are shown for a high-viscosity fluid. The first part of this paper describes the damper design that is based on a high-viscosity fluid. This design is flexure-based to minimize parasitic nonlinear forces such as hysteresis and stick-slip. In the second part of the paper, LVE fluid characterization by means of the damper setup is presented. Measurements are performed and model parameters are fitted by a non-convex optimization algorithm in order to obtain the frequency-dependent behavior of the fluid. The resulting fluid model is validated by comparison with a second measurement with a different damper geometry. This paper shows that LVE fluid characterization between 10 Hz and 10 kHz for elastic high-viscosity fluids is possible with a motion stage damper for which the undamped behavior is known.

A new approach for calculating the true stress response from large amplitude oscillatory shear (LAOS) measurements using parallel plates

Rheologica Acta, 2013

The parallel plates geometry is often deemed unsuitable for nonlinear viscoelasticity measurement... more The parallel plates geometry is often deemed unsuitable for nonlinear viscoelasticity measurements because the strain field, and thus the nonlinear response, varies across the sample. Although cone-plate and Couette geometries are designed to circumvent this problem by ensuring a uniform strain field, it is not always easy to shape the material to the complex shapes that is required for these geometries. This has motivated the development of techniques to accurately determine the nonlinear stress response using the more convenient plate-plate geometry. Here, we introduce a new approach to obtain this true material response in large amplitude oscillatory shear (LAOS) experiments using the plate-plate geometry. By tracing the Fourier components of the torque response and their derivatives with respect to the maximum applied deformation, we accurately obtain the material's true stress-strain response from parallel plate measurements. The approach does not require any assumptions about the material's viscoelastic behavior. We test our approach experimentally

Analysis of mixing in three-dimensional time-periodic cavity flows

Journal of Fluid Mechanics, 1999

A method to locate periodic structures in general three-dimensional Stokes flows with time-period... more A method to locate periodic structures in general three-dimensional Stokes flows with time-periodic boundary conditions is presented and applied to mixing cavity flows. Numerically obtained velocity fields and particle tracking schemes are used to provide displacement and stretching fields. From these the location and identification of periodic points can be derived. The presence or absence of these periodic points allows a judgement on the quality of the mixing process. The technique is general and efficient, and applicable to mixing flows for which no analytical velocity field is available (the case for all three-dimensional flows considered in this paper). Results are presented for three different mixing protocols in a three-dimensional time-periodic cavity flow, serving as an accessible test case for the methods developed. A major result is that periodic lines are obtained for these three-dimensional flows. These lines can be complex in geometry and their nature can change along...

Axisymmetric boundary integral simulations of film drainage between two viscous drops

Journal of Fluid Mechanics, 2006

Film drainage between two drops with viscosity equal to that of the matrix fluid is studied using... more Film drainage between two drops with viscosity equal to that of the matrix fluid is studied using a numerical method that can capture both the external problem of two touching drops and the inner problem of pressure-driven local film drainage, without assumptions about the dimensions of the film or the use of lubrication approximations. We use a non-singular boundary integral method that has sufficient stability and accuracy to simulate film thicknesses down to and smaller than 10 −4 times the undeformed drop radius. After validation of the method we investigate the validity of various results obtained from simple film-drainage models and asymptotic theories. Our results for buoyancy-driven collisions are in agreement with a recently developed asymptotic theory. External-flow-driven collisions are different from buoyancy-driven collisions, which means that the internal circulation inside the drop plays a significant role in film drainage, even for small capillary numbers, as has been recently shown (Nemer et al., Phys. Rev. Lett., vol. 92, 2004, 114501). Despite that, we find excellent correspondence with simple drainage models when considering the drainage time only.

Numerical Study of the Effect of Thixotropy on Extrudate Swell

Polymers

The extrusion of highly filled elastomers is widely used in the automotive industry. In this pape... more The extrusion of highly filled elastomers is widely used in the automotive industry. In this paper, we numerically study the effect of thixotropy on 2D planar extrudate swell for constant and fluctuating flow rates, as well as the effect of thixotropy on the swell behavior of a 3D rectangular extrudate for a constant flowrate. To this end, we used the Finite Element Method. The state of the network structure in the material is described using a kinetic equation for a structure parameter. Rate and stress-controlled models for this kinetic equation are compared. The effect of thixotropy on extrudate swell is studied by varying the damage and recovery parameters in these models. It was found that thixotropy in general decreases extrudate swell. The stress-controlled approach always predicts a larger swell ratio compared to the rate-controlled approach for the Weissenberg numbers studied in this work. When the damage parameter in the models is increased, a less viscous fluid layer appea...

Effect of shear rate and pressure on the crystallization of PP nanocomposites and PP/PET polymer blend nanocomposites

Polymer, 2019

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Effect of Thermal History and Shear on the Viscoelastic Response of iPP Containing an Oxalamide-Based Organic Compound

Macromolecules, 2019

We report on the role of temperature and shear on the melt behavior of iPP in the presence of the... more We report on the role of temperature and shear on the melt behavior of iPP in the presence of the organic compound N1,N1′-(propane-1,3-diyl)bis(N2-hexyloxalamide) (OXA3,6). It is demonstrated that OXA3,6 facilitates a viscosity suppression when it resides in the molten state. The viscosity suppression is attributed to the interaction of iPP chains/ subchains with molten OXA3,6 nanoclusters. The exact molecular mechanism has not been identified; nevertheless, a tentative explanation is proposed. The observed viscosity suppression appears similar to that encountered in polymer melts filled with solid nanoparticles, with the difference that the OXA3,6 compound reported in this study facilitates the viscosity suppression in the molten state. Upon cooling, as crystal growth of OXA3,6 progresses, the decrease in viscosity is suppressed. Retrospectively, segmental absorption of iPP chains on the surface of micrometer-sized OXA3,6 crystallites favors the formation of dangling arms, yielding OXA3,6 crystallites decorated with partially absorbed iPP chains. In other words, the resulting OXA3,6 particle morphology resembles that of a hairy particle or a starlike polymer chain. Such hairy particles effectively facilitate a viscosity enhancement, similar to branched polymer chains. This hypothesis and its implications for the shear behavior of iPP are discussed and supported using plate−plate rheometry and slit-flow experiments combined with smallangle X-ray scattering analysis.

Comparison of the Dynamic Behavior of Brain Tissue and Two Model Materials

SAE Technical Paper Series, 1999

... Subject Areas: Highways; Research; Safety and Human Factors; I84: Personal Injuries. Last Mod... more

Glass transition temperature versus structure of polyamide 6: A flash-DSC study

Thermochimica Acta, 2017

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

Modeling Flow-Induced Crystallization

Advances in Polymer Science, 2016

A numerical model is presented that describes all aspects of flow-induced crystallization of isot... more A numerical model is presented that describes all aspects of flow-induced crystallization of isotactic polypropylene at high shear rates and elevated pressures. It incorporates nonlinear viscoelasticity, including viscosity change as a result of formation of oriented fibrillar crystals (shish), compressibility, and nonisothermal process conditions caused by shear heating and heat release as a result of crystallization. In the first part of this chapter, the model is validated with experimental data obtained in a channel flow geometry. Quantitative agreement between experimental results and the numerical model is observed in terms of pressure drop, apparent crystallinity, parent/daughter ratio, Hermans' orientation, and shear layer thickness. In the second part, the focus is on flow-induced crystallization of isotactic polypropylene at elevated pressures, resulting in multiple crystal phases and morphologies. All parameters but one are fixed a priori from the first part of the chapter. One additional parameter, determining the portion of β-crystal spherulites nucleated by flow, is introduced. By doing so, an accurate description of the fraction of β-phase crystals is obtained. The model accurately captures experimental data for fractions of all crystal phases over a wide range of flow conditions (shear rates from 0 to 200 s À1 , pressures from 100 to 1,200 bar, shear temperatures from 130 C to 180 C). Moreover, it is shown that, for high shear rates and pressures, the measured γ-phase fractions can only be matched if γ-crystals can nucleate directly on shish.

Nucleation Induced by ”Short-Term Pressurization” of an Undercooled Isotactic Polypropylene Melt

European Polymer Journal, 2016

Nucleation of semi-crystalline polymers is very sensitive to perturbations of the melt state. In ... more Nucleation of semi-crystalline polymers is very sensitive to perturbations of the melt state. In contrast to the case of flow, the influence of pressure changes on nucleation has been almost neglected so far. In this work we explore the effect of the pressure history on isotactic polypropylene crystallization by applying a brief step-like increase of pressure to the undercooled melt. Using dilatometry and synchrotron X-ray diffraction, an enhancement of crystallization kinetics proportional to the magnitude of the pressure pulse is revealed. This acceleration is linked to an increase of the number of active nuclei after the short term pressurization, as confirmed by ex-situ optical microscopy observations. Up to an order of magnitude increase in nucleation density is found, for pressure pulses around 600-700 bar. The pressure-induced nucleating effect is interpreted in the light of classical nucleation theory; although a non-classical "barrier-less" nucleation mechanism is also envisaged.