A one-dimensional theoretical model is developed to predict the acoustic waves generated by rapid thermal expansion caused by electromagnetic microwave absorption in viscoelastic rods. The theoretical acceleration at the end of the irradiated rod is predicted. The comparison between the experimental and the theoretical accelerations leads to the evaluation of viscoelastic characteristics. Parameters related to the electromagnetic absorption can be also obtained. A procedure to find approximate values of the different parameters is developed. Since it is considered in the model that the distribution of the temperature rise along the rod is exponential, very absorbing materials can be tested. Consequently, the influence of the moisture content on viscoelastic properties of a porous material can be investigated. The method is applied to study the influence of the moisture content on viscoelastic characteristics of medium density fiberboard materials.

Issue Section:
Technical Papers
Keywords:
viscoelasticity, wood, fibres, porous materials, thermal expansion, electromagnetic wave absorption, thermoacoustics, nondestructive testing, moisture measurement
Topics:
Acoustics, Electromagnetic wave absorption, Medium density fiberboard, Microwaves, Porous materials, Rods, Temperature, Thermal expansion, Viscoelasticity, Waves, Absorption, Spectra (Spectroscopy), Wood products, Accelerometers
1.
Nolle
,
A. W.
,
1948
, “
Methods for Measuring the Dynamic Mechanical Properties of Rubber-Like Materials
,”
J. Appl. Phys.
,
19
, pp.
753
–
774
.
2.
McSkimin
,
H. J.
,
1964
, “
Ultrasonic Methods for Measuring the Mechanical Properties of Liquids and Solids
,”
Phys. Acoust.
,
E. P.
Mason
, ed,
1A
, pp.
271
–
334
.
3.
Ferry, J. D., 1970, Viscoelastic Properties of Polymers, John Wiley and Sons, New York.
4.
Nowick, A. S., and Berry, B. S., 1972, Anelastic Relaxation in Crystalline Solids, Academic Press, New York.
5.
Hillier
,
K. W.
, and
Kolsky
,
H.
,
1949
, “
An Investigation of the Dynamic Mechanical Properties of Some High Polymers
,”
Proc. Phys. Soc. London
,
B62
, pp.
111
–
121
.
6.
Hillier
,
K. W.
,
1949
, “
A Method of Measuring Some Dynamic Elastic Constants and Its Application to the Study of High Polymers
,”
Proc. Phys. Soc. London
,
B62
, pp.
701
–
713
.
7.
Kolsky
,
H.
,
1957
, “
The Propagation of Stress Pulses in Viscoelastic Solids
,”
Philos. Mag.
,
1
(
8
), pp.
693
–
711
.
8.
Norris
,
D. M.
, and
Young
,
W. C.
,
1970
, “
Complex Modulus Measurement by Longitudinal Vibration Testing
,”
Exp. Mech.
,
10
, pp.
93
–
96
.
9.
Madigosky
,
W. M.
, and
Lee
,
G. F.
,
1983
, “
Improved Resonance Technique for Materials Characterization
,”
J. Acoust. Soc. Am.
,
73
(
4
), pp.
1374
–
1377
.
10.
Pritz
,
T.
,
1982
, “
Transfer Function Method for Investigating the Complex Modulus Acoustical Materials: Rod-Like Specimen
,”
J. Sound Vib.
,
81
, pp.
359
–
376
.
11.
Buchanan
,
J. L.
,
1987
, “
Numerical Solution for the Dynamic Moduli of a Viscoelastic Bar
,”
J. Acoust. Soc. Am.
,
81
, pp.
1775
–
1786
.
12.
Blanc, R. H., 1971, “De´termination de l’e´quation de comportement des corps viscoe´lastiques line´aires par une me´thode d’impulsion,” Ph.D. thesis, Universite´ d’Aix-Marseille.
13.
Lundberg
,
B.
, and
Blanc
,
R. H.
,
1988
, “
Determination of Mechanical Material Properties From the Two-Point Response of an Impacted Linearly Viscoelastic Rod Specimen
,”
J. Sound Vib.
,
126
(
1
), pp.
97
–
108
.
14.
Trendafilova
,
I. N.
,
O¨deen
,
S.
, and
Lundberg
,
B.
,
1994
, “
Identification of Viscoelastic Materials From Electro-Optical Displacement Measurements at Two Sections of an Impacted Rod Specimen
,”
Eur. J. Mech. A/Solids
,
13
(
6
), pp.
793
–
802
.
15.
O¨deen
,
S.
, and
Lundberg
,
B.
,
1993
, “
Determination of Complex Modulus From Measured End-Point Accelerations of an Impacted Rod Specimen
,”
J. Sound Vib.
,
165
(
1
), pp.
1
–
8
.
16.
Hosten
,
B.
, and
Bernard
,
P. A.
,
1998
, “
Ultrasonic Wave Generation by Time-Gated Microwaves
,”
J. Acoust. Soc. Am.
,
104
(
2
), pp.
860
–
866
.
17.
Bacon
,
C.
,
Hosten
,
B.
, and
Bernard
,
P. A.
,
1999
, “
Acoustic Wave Generation in Viscoelastic Rods by Time-Gated Microwaves
,”
J. Acoust. Soc. Am.
,
106
(
1
), pp.
195
–
201
.
18.
Hosten, B., and Bacon, C., 2000, “Measurement of Complex Young Moduli of Composite Materials by Time-Gated Microwaves,” Review of Progress in Quantitative Non Destructive Evaluation, D. O. Thompson and D. E. Chimenti, eds., Plenum Press, New York, 19(1), pp. 1113–1120.
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