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Energy and phase velocity considerations required for attenuation and velocity measurements of anisotropic composites

Energy and phase velocity considerations required for attenuation and velocity measurements of anisotropic composites
Energy and phase velocity considerations required for attenuation and velocity measurements of anisotropic composites
Viscoelastic fibre-reinforced composite materials have a number of possible advantages for use in underwater acoustic applications. In order to exploit these materials it is important to be able to measure their complex stiffness matrix in order to determine their acoustic response. Ultrasonic transmission measurements on parallel-sided samples, employing broadband pulsed transducers at 2.25 MHz and an immersion method, have been used to determine the viscoelastic properties of a glass-reinforced composite with uniaxially aligned fibres. The composite measured was constructed from Cytecfiberite's CYCOM 919 E-glass. The theory of acoustic propagation in anisotropic materials shows that the direction of energy propagation is, in general, different from that given by Snell's Law. At 15° incidence, Snell's Law implies a refracted angle of 40±2°, whereas the energy direction is observed to be 70±2°. Despite this, the experimental data indicates that the position of the receiving transducer has relatively little effect on the apparent phase velocity measured. The phase velocities measured at positions determined from the refracted angle and energy direction are 3647 and 3652±50 m s?1, respectively. However, the amplitude of the received signal, and hence estimate of attenuation, is highly sensitive to the receiver position. This indicates that the acoustic Poynting vector must be considered in order to precisely determine the correct position of the receiving transducer for attenuation measurements. The beam displacement for a 17.6 mm sample at 15° incidence is 9.5 and 40 mm by Snell's Law and Poynting's Theorem, respectively. Measured beam displacements have been compared with predictions derived from material stiffness coefficients. These considerations are important in recovering the complex stiffness matrix.
anisotropic material, composite, attenuation estimation, velocity estimation
0041-624X
525-530
Carroll, N.L.
ebb6e85f-f853-4afa-b691-96661a9e3321
Humphrey, V.F.
23c9bd0c-7870-428f-b0dd-5ff158d22590
Smith, J.D.
36614739-504f-48d7-9455-afef5cc4663d
Carroll, N.L.
ebb6e85f-f853-4afa-b691-96661a9e3321
Humphrey, V.F.
23c9bd0c-7870-428f-b0dd-5ff158d22590
Smith, J.D.
36614739-504f-48d7-9455-afef5cc4663d

Carroll, N.L., Humphrey, V.F. and Smith, J.D. (2002) Energy and phase velocity considerations required for attenuation and velocity measurements of anisotropic composites. Ultrasonics, 40 (1-8), 525-530. (doi:10.1016/S0041-624X(02)00178-6).

Record type: Article

Abstract

Viscoelastic fibre-reinforced composite materials have a number of possible advantages for use in underwater acoustic applications. In order to exploit these materials it is important to be able to measure their complex stiffness matrix in order to determine their acoustic response. Ultrasonic transmission measurements on parallel-sided samples, employing broadband pulsed transducers at 2.25 MHz and an immersion method, have been used to determine the viscoelastic properties of a glass-reinforced composite with uniaxially aligned fibres. The composite measured was constructed from Cytecfiberite's CYCOM 919 E-glass. The theory of acoustic propagation in anisotropic materials shows that the direction of energy propagation is, in general, different from that given by Snell's Law. At 15° incidence, Snell's Law implies a refracted angle of 40±2°, whereas the energy direction is observed to be 70±2°. Despite this, the experimental data indicates that the position of the receiving transducer has relatively little effect on the apparent phase velocity measured. The phase velocities measured at positions determined from the refracted angle and energy direction are 3647 and 3652±50 m s?1, respectively. However, the amplitude of the received signal, and hence estimate of attenuation, is highly sensitive to the receiver position. This indicates that the acoustic Poynting vector must be considered in order to precisely determine the correct position of the receiving transducer for attenuation measurements. The beam displacement for a 17.6 mm sample at 15° incidence is 9.5 and 40 mm by Snell's Law and Poynting's Theorem, respectively. Measured beam displacements have been compared with predictions derived from material stiffness coefficients. These considerations are important in recovering the complex stiffness matrix.

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More information

Published date: 2002
Keywords: anisotropic material, composite, attenuation estimation, velocity estimation

Identifiers

Local EPrints ID: 10279
URI: http://eprints.soton.ac.uk/id/eprint/10279
ISSN: 0041-624X
PURE UUID: 765a31b6-8b52-412d-b604-b61e345e935f
ORCID for V.F. Humphrey: ORCID iD orcid.org/0000-0002-3580-5373

Catalogue record

Date deposited: 16 May 2005
Last modified: 20 Jul 2019 01:00

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