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Identification of complex shear modulus from measured shear strains on a circular disc subjected to transient torsion at its centre
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid Mechanics.
2008 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 313, no 3-5, 567-580 p.Article in journal (Refereed) Published
Abstract [en]

A method for identification of complex shear modulus from measured shear strains on a circular disc subjected to a transient torque at its centre has been established. It is based on the evolution of an outgoing shear wave between two radial positions at which the associated shear strains are measured. The two-dimensional shear wave solutions used are exact in the sense of three-dimensional theory. Therefore, in principle, there is no frequency beyond which they are not valid. The method requires a minimum disc size, which is related to the duration of the load. The non-parametric results become inaccurate at frequencies near zero and at certain problematic frequencies where the excitation of the disc is weak or non-existent. These frequencies may be moved outside the frequency range of interest by sufficiently decreasing the duration of the load. If there are problematic frequencies within this range, the results of parametric identification become more accurate than those of non-parametric identification. Parametric results from experimental tests with loads having different amplitudes and durations agree well with each other in accord with the assumed linearity of the tested polypropylene material.

Place, publisher, year, edition, pages
2008. Vol. 313, no 3-5, 567-580 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-96484DOI: 10.1016/j.jsv.2007.12.010ISI: 000255790600014OAI: oai:DiVA.org:uu-96484DiVA: diva2:171071
Available from: 2007-11-07 Created: 2007-11-07 Last updated: 2016-04-13Bibliographically approved
In thesis
1. Identification of Viscoelastic Materials by Use of Wave Propagation Methods
Open this publication in new window or tab >>Identification of Viscoelastic Materials by Use of Wave Propagation Methods
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Complex moduli and Poisson’s ratio have been estimated using extensional and torsional wave experiments. The data were used for assessment of linearity and isotropy of two polymers, polymethyl methacrylate (PMMA) and polypropylene (PP). The responses of both materials were found to be close to linear and isotropic. A statistical analysis of different estimation approaches for complex modulus and Poisson’s ratio was conducted. It was shown that a joint estimation of complex modulus and Poisson’s ratio improves the estimated results. Considerable improvement was achieved in the frequency range 5-15 kHz for Poisson’s ratio.

A non-equilibrium split Hopkinson pressure bar (SHPB) procedure for identification of complex modulus has been developed. Two simplified procedures were also established. Both overestimated the magnitude of the complex modulus. The complex modulus of PP was identified using PMMA and aluminium bars, and the estimated complex modulus was in good agreement with published results. The procedure was found to be accurate regardless of the specimen size or the specimen-to-bar impedance ratio. The procedure was also used to analyze the mechanical response of four compacted pharmaceutical tablet materials. A Debye-like relaxation was observed for all tested materials.

Utilizing SHPB effectively requires knowledge about the impact process that is normally used for excitation. Therefore the impact between a cylindrical striker and a long cylindrical bar of viscoelastic material was studied theoretically and experimentally. Strains measured at three locations along a PMMA bar impacted by strikers of the same material agreed well with the theoretical results.

A method for identification of complex shear modulus from measured shear strains on a disc subjected to a transient torque at its centre has been established. The two-dimensional wave solutions used are exact in the sense of three-dimensional theory. The results from experimental tests with different load amplitudes and durations agree well with each other.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 56 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 369
Keyword
Engineering physics, Identification, Viscoelastic, Complex modulus, Complex Poisson's ratio, wave, Impact, Teknisk fysik
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-8324 (URN)978-91-554-7033-3 (ISBN)
Public defence
2007-12-14, Å2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
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Available from: 2007-11-07 Created: 2007-11-07 Last updated: 2009-08-14Bibliographically approved

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Lundberg, Bengt

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