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- Hillström, L., et al.
(författare)
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Identification of complex modulus from measured strains on an axially impacted bar using least squares
- 2000
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 230:3, s. 689-707
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Tidskriftsartikel (refereegranskat)abstract
- The complex modulus of a material with linearly viscoelastic behaviour is identified on the basis of strains which are known, from measurements and sometimes from a free end boundary condition, at three or more sections of an axially impacted bar specimen. The aim is to improve existing identification methods based on known strains at three uniformly distributed sections by increasing the number of sections considered and by distributing them non-uniformly. The increased number of sections results in an overdetermined system of equations from which an approximate solution for the complex modulus is determined using the method of least squares. Through the non-uniform distribution of sections, critical conditions with accompanying large errors at certain frequencies are largely eliminated. Experimental tests were carried out at room temperature with two materials, viz., polypropylene and polymethyl methacrylate, five strain gauge configurations and two kinds of impact excitation. Substantial improvement in the quality of the results for complex modulus was obtained.
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- Mahata, K., et al.
(författare)
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On the use of flexural wave propagation experiments for identification of complex modulus
- 2003
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Ingår i: IEEE Transactions on Control Systems Technology. - : IEEE. - 1063-6536 .- 1558-0865. ; 11:6, s. 863-874
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate the nonparametric estimation of the frequency dependent complex modulus of a viscoelastic material. The strains due to flexural wave propagation in a bar specimen are registered at different cross sections. The time domain data is transformed into frequency domain using discrete Fourier transform and a nonlinear least squares algorithm is then employed to estimate the complex modulus at each frequency. Inherent numerical problems due to associated ill-conditioned matrices are treated with special care. An analysis of the quality of the nonlinear least squares estimate is also carried out. The validity of the theoretical results are confirmed by numerical studies and experimental tests
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