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Non-equilibrium split Hopkinson pressure bar procedure for non-parametric identification of complex modulus
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, Nanotechnology and Functional Materials.
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, Solid Mechanics.
2005 (English)In: International Journal of Impact Engineering, ISSN 0734-743X, Vol. 31, no 9, 1133-1151 p.Article in journal (Refereed) Published
Abstract [en]

A split Hopkinson pressure bar procedure was developed for non-parametric identification of complex modulus under conditions of non-equilibrium and axially non-uniform stress. Two simplified procedures were also established. The first requires low frequency and/or short specimen. The second, identical to a classical procedure based on equilibrium, requires that also the specimen-to-bar characteristic impedance ratio be low. Both overestimate the magnitude of the complex modulus, the second even at low frequencies. Tests were carried out with polymethyl methacrylate and aluminium bars and with polypropylene specimens having diameter 20 mm and lengths 10, 20, 50 and 100 mm. The complex moduli identified are in good to fair agreement with published results up to 10 kHz for all specimens with polymethyl methacrylate bars and for the 10–50 mm specimens with aluminium bars. The quality of the results is sensitive to truncation and to imperfect contact at the bar-specimen interfaces.

Place, publisher, year, edition, pages
2005. Vol. 31, no 9, 1133-1151 p.
Keyword [en]
Split Hopkinson pressure bar, SHPB, Non-equilibrium, Non-parametric identification, Estimation, Complex modulus, Polypropylene
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:uu:diva-96481DOI: 10.1016/j.ijimpeng.2004.07.002OAI: oai:DiVA.org:uu-96481DiVA: diva2:171068
Available from: 2007-11-07 Created: 2007-11-07 Last updated: 2013-01-08
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
Supervisors
Available from: 2007-11-07 Created: 2007-11-07 Last updated: 2009-08-14Bibliographically approved

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Welch, Kenneth

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