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Preparation of magnetorheological elastomers and their slip-free characterization by means of parallel-plate rotational rheometry

by jppelteret

Authors: B. L. Walter, J-P. Pelteret, J. Kaschta, D. W. Schubert and P. Steinmann

A systematic study is presented to highlight a methodology of sample preparation and subsequent slip-free characterization of magnetorheological (MR) elastomers in parallel-plate rotational rheometry. Focusing on the magnetic field-dependent nonlinear viscoelastic behavior an array of oscillatory strain sweep measurements is conducted with samples cured within the rheometer.
The examined nonlinear material response (i.e. the amplitude dependence of the storage and loss moduli) as a function of the applied magnetic field is found to be qualitatively similar to the amplitude dependence of particle reinforced elastomers (i.e. the Payne effect). Therefore, the experimental data (both moduli) is decomposed similar to that for reinforced elastomers and a phenomenological model is formulated for both the storage and loss modulus to account for the physical mechanisms governing the nonlinear material characteristics.
Parameter identification suggests that the material response at low magnetic fields is dominated by the polymeric network whereas the strong magneto-reinforced microstructure governs the linear and nonlinear viscoelastic behavior at high magnetic fields. The overall experimental outcome further suggests that the underlying concept of the phenomenological model for particle reinforced elastomers (i.e. destruction and reformation of the filler network) can be transfered to magnetorheological materials. Consequently, the proposed phenomenological model can be applied to quantify and further analyze the nonlinear response characteristics of MR elastomers (i.e. the amplitude dependence of the storage and loss modulus as a function of the applied magnetic field) that is closely linked to microstructural changes of the magnetizable particle network. [1]

[1] [doi] B. L. Walter, J-P. Pelteret, J. Kaschta, D. W. Schubert, and P. Steinmann, “Preparation of magnetorheological elastomers and their slip-free characterization by means of parallel-plate rotational rheometry,” Smart Materials and Structures, 2017.
[Bibtex]
@Article{walter2017c-preprint,
author = {Walter, B. L. and Pelteret, J-P. and Kaschta, J. and Schubert, D. W. and Steinmann, P.},
title = {Preparation of magnetorheological elastomers and their slip-free characterization by means of parallel-plate rotational rheometry},
journal = {Smart Materials and Structures},
year = {2017},
note = {Accepted},
abstract = {A systematic study is presented to highlight a methodology of sample preparation and subsequent slip-free characterization of magnetorheological (MR) elastomers in parallel-plate rotational rheometry. Focusing on the magnetic field-dependent nonlinear viscoelastic behavior an array of oscillatory strain sweep measurements is conducted with samples cured within the rheometer.
The examined nonlinear material response (i.e. the amplitude dependence of the storage and loss moduli) as a function of the applied magnetic field is found to be qualitatively similar to the amplitude dependence of particle reinforced elastomers (i.e. the Payne effect). Therefore, the experimental data (both moduli) is decomposed similar to that for reinforced elastomers and a phenomenological model is formulated for both the storage and loss modulus to account for the physical mechanisms governing the nonlinear material characteristics.
Parameter identification suggests that the material response at low magnetic fields is dominated by the polymeric network whereas the strong magneto-reinforced microstructure governs the linear and nonlinear viscoelastic behavior at high magnetic fields. The overall experimental outcome further suggests that the underlying concept of the phenomenological model for particle reinforced elastomers (i.e. destruction and reformation of the filler network) can be transfered to magnetorheological materials. Consequently, the proposed phenomenological model can be applied to quantify and further analyze the nonlinear response characteristics of MR elastomers (i.e. the amplitude dependence of the storage and loss modulus as a function of the applied magnetic field) that is closely linked to microstructural changes of the magnetizable particle network.},
doi = {10.1088/1361-665X/aa6b63},
file = {walter2017c-preprint.pdf:PDF/walter2017c-preprint.pdf:PDF},
keywords = {magnetorheological elastomers (MREs), field-responsive materials, large amplitude oscillatory shear (LAOS), magnetorheometry, magneto-induced Payne effect},
owner = {Jean-Paul Pelteret},
timestamp = {2017.03.07},
}

On the wall slip phenomenon of elastomers in oscillatory shear measurements using parallel-plate rotational rheometry – II. Influence of experimental conditions

by jppelteret

Authors: B. L. Walter, J-P. Pelteret, J. Kaschta, D. W. Schubert and P. Steinmann

The use of parallel-plate rotational rheometery to characterize ex situ pre-prepared samples of rubber-like polymers is motivated by, for example, the investigation of magneto-rheological elastomers. When exceeding a critical excitation amplitude in oscillatory shear experiments, these elastomeric samples are prone to slip at the sample-plate contact interface. This phenomenon, known as wall slip, starts to occur at the sample’s outer rim and leads to an imperfect force transfer onto the sample. This results in a systematic error of measured rheological material quantities.
A thorough investigation is presented to reveal how this phenomenon is affected by selected experimental conditions, namely the static axial preload and measuring frequency. For this purpose disc-shaped samples composed of an unfilled silicone rubber are prepared by casting and examined by means of a controlled stress rotational rheometer equipped with a serrated rotor configuration.
The oscillatory strain sweep experiments suggest that wall slip, exclusively present at the serrated rotor surface, is significantly influenced by the static preload. In contrast, only a slight frequency dependence is observed within the examined experimental conditions.
Further insights into the wall slip mechanism were attained by two novel methodologies. It is shown that it is possible to produce a master curve for the various applied preloads. This demonstrates that the physical mechanism behind wall slip is independent of the axial force. Furthermore, we derive an empirical model for the criterion governing the onset of wall slip. This links the critical stress at which wall slip is initiated to the static friction condition and geometrical aspects of the rotor configuration. From this it is anticipated that the conditions for reliable experiments involving ex situ pre-prepared samples composed of low damping elastomers can, in the future, be estimated a priori. [1]

[1] [doi] B. L. Walter, J-P. Pelteret, J. Kaschta, D. W. Schubert, and P. Steinmann, “On the wall slip phenomenon of elastomers in oscillatory shear measurements using parallel-plate rotational rheometry — II. Influence of experimental conditions,” Polymer Testing, 2017.
[Bibtex]
@Article{walter2017b-preprint,
author = {Walter, B. L. and Pelteret, J-P. and Kaschta, J. and Schubert, D. W. and Steinmann, P.},
title = {On the wall slip phenomenon of elastomers in oscillatory shear measurements using parallel-plate rotational rheometry -- II. Influence of experimental conditions},
journal = {Polymer Testing},
year = {2017},
note = {Accepted},
abstract = {The use of parallel-plate rotational rheometery to characterize ex situ pre-prepared samples of rubber-like polymers is motivated by, for example, the investigation of magneto-rheological elastomers. When exceeding a critical excitation amplitude in oscillatory shear experiments, these elastomeric samples are prone to slip at the sample-plate contact interface. This phenomenon, known as wall slip, starts to occur at the sample's outer rim and leads to an imperfect force transfer onto the sample. This results in a systematic error of measured rheological material quantities.
A thorough investigation is presented to reveal how this phenomenon is affected by selected experimental conditions, namely the static axial preload and measuring frequency. For this purpose disc-shaped samples composed of an unfilled silicone rubber are prepared by casting and examined by means of a controlled stress rotational rheometer equipped with a serrated rotor configuration.
The oscillatory strain sweep experiments suggest that wall slip, exclusively present at the serrated rotor surface, is significantly influenced by the static preload. In contrast, only a slight frequency dependence is observed within the examined experimental conditions.
Further insights into the wall slip mechanism were attained by two novel methodologies. It is shown that it is possible to produce a master curve for the various applied preloads. This demonstrates that the physical mechanism behind wall slip is independent of the axial force. Furthermore, we derive an empirical model for the criterion governing the onset of wall slip. This links the critical stress at which wall slip is initiated to the static friction condition and geometrical aspects of the rotor configuration. From this it is anticipated that the conditions for reliable experiments involving ex situ pre-prepared samples composed of low damping elastomers can, in the future, be estimated a priori.},
doi = {10.1016/j.polymertesting.2017.05.036},
file = {walter2017b-preprint.pdf:PDF/walter2017b-preprint.pdf:PDF},
keywords = {wall slip, adhesive failure, measuring artifact, large amplitude oscillatory shear, parallel-plate rotational rheometry},
owner = {Jean-Paul Pelteret},
timestamp = {2017.03.07},
}

On the wall slip phenomenon of elastomers in oscillatory shear measurements using parallel-plate rotational rheometry – I. Detecting wall slip

by jppelteret

Authors: B. L. Walter, J-P. Pelteret, J. Kaschta, D. W. Schubert and P. Steinmann

A systematic study is presented in order to reveal the occurrence of wall slip of pre-prepared elastomeric samples characterized with the use of rotational rheometry. To exclude effects that could be attributed to additional functional fillers, both an unfilled (primarily used) and lightly silica reinforced (complementary system) silicone rubber are evaluated. Cylindrical samples are prepared by casting using a standardized methodology and examined by means of a stress-controlled parallel-plate rotational rheometer. As a control test, samples are also cured within the rheometer (in situ), thereby fixing them to the measuring plates and firmly establishing their response in “no-slip” conditions. The experiments suggest that wall slip, postulated to be caused by an adhesive failure at the sample-plate interface, may occur if the deformation is sufficiently large and no cohesive failure is present. It is detected by an increase in the loss modulus that is related to the adhesive failure associated with local dynamic friction, resulting in increased dissipated energy. Direct (via raw waveform data and normalized Lissajous figures) and indirect (via fast-Fourier-transformation) analysis of the overall system response for a single steady state deformation cycle provided further insights into the mechanism of wall slip. [1]

[1] [doi] B. L. Walter, J-P. Pelteret, J. Kaschta, D. W. Schubert, and P. Steinmann, “On the wall slip phenomenon of elastomers in oscillatory shear measurements using parallel-plate rotational rheometry — I. Detecting wall slip,” Polymer Testing, 2017.
[Bibtex]
@Article{walter2017a-preprint,
author = {Walter, B. L. and Pelteret, J-P. and Kaschta, J. and Schubert, D. W. and Steinmann, P.},
title = {On the wall slip phenomenon of elastomers in oscillatory shear measurements using parallel-plate rotational rheometry -- I. Detecting wall slip},
journal = {Polymer Testing},
year = {2017},
note = {Accepted},
abstract = {A systematic study is presented in order to reveal the occurrence of wall slip of pre-prepared elastomeric samples characterized with the use of rotational rheometry. To exclude effects that could be attributed to additional functional fillers, both an unfilled (primarily used) and lightly silica reinforced (complementary system) silicone rubber are evaluated. Cylindrical samples are prepared by casting using a standardized methodology and examined by means of a stress-controlled parallel-plate rotational rheometer. As a control test, samples are also cured within the rheometer (in situ), thereby fixing them to the measuring plates and firmly establishing their response in "no-slip" conditions. The experiments suggest that wall slip, postulated to be caused by an adhesive failure at the sample-plate interface, may occur if the deformation is sufficiently large and no cohesive failure is present. It is detected by an increase in the loss modulus that is related to the adhesive failure associated with local dynamic friction, resulting in increased dissipated energy. Direct (via raw waveform data and normalized Lissajous figures) and indirect (via fast-Fourier-transformation) analysis of the overall system response for a single steady state deformation cycle provided further insights into the mechanism of wall slip.},
doi = {10.1016/j.polymertesting.2017.05.035},
file = {walter2017a-preprint.pdf:PDF/walter2017a-preprint.pdf:PDF},
keywords = {wall slip, adhesive failure, measuring artifact, large amplitude oscillatory shear, silicone rubber, parallel-plate rotational rheometry},
owner = {Jean-Paul Pelteret},
timestamp = {2017.03.07},
}