NEW METHOD OF STUDYING THE BOUNDARY LAYERS IN POLYMER COMPOSITE FIBERS
USING ACOUSTICAL INTERFEROMETER, L. A. Bulavin, S. P. Senchurov and
Yu. F. Zabashta, Taras Shevchenko University, PO Box 163, 03191 Kyiv,
Ukraine
New method of non-destructive testing of boundary layers in polymer
composite fibers is proposed. The problem of axisymmetric normal
acoustical waves in composite fibers with homogeneous and periodical
discrete boundary layer was solved. The possibility of simultaneous
propagation of one or two normal axisymmetric waves depending on
mechanical properties of boundary layers was shown. First wave is
usual Young wave that also propagates in homogeneous fibers. The other
wave is specific to composite fibers with boundary layers. This wave
has cut-off frequency, the magnitude of which is determined by the
properties of the boundary layer.
Considering of discrete periodical boundary layer increases the number
of cut-off frequencies. These cut-off frequencies form the cut-off
zone when discretization step decreases.
The shapes of acoustical interferograms were calculated for different
cut-off frequencies and experimental frequencies. Three types of the
acoustical interferogram shapes can be distingushed depending on the
position of cut-off and experimental frequencies.
New method, based on this dependence of the interferogram shape on the
boundary layer properties, was experimentally verified. The agreement
of theoretical predictions and experimental results was found.

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