Diagnostics of polymer composites by acoustic methods

Abstract

The most dangerous flaws of polymer composite materials (PCMs) are the low matrix polymerization and the inadequate material composition throughout the whole volume or a considerable part of the product. Besides, such defects as the zones of material excessive porosity or lower density, the irregularity of fiber orientation (reinforcement angle deviation, curvature of fibers in layer planes) and the local inadequacy of material composition can be found in PCMs. These defects are detected by the diagnostic methods based on the correlation between the diagnostic parameters and the properties being sought for. The diagnostic parameters used are the acoustic properties of materials (transmission and damping coefficient of ultrasonic oscillations in the material) which, as well as the physico-mechanical properties (density, porosity, elastic and strength properties) depend on a material. But testing according to only these parameters does not always allow to get the acceptable accuracy of diagnostics and the reliability of the achieved results.
The spectrum analysis of signals having transmitted through the structure under test and carrying information of material structure and properties allows to increase the accuracy of diagnostics. But the application of conventional piezoelectric converters (in case of PCMs diagnostics) to excite high-power broadband ultrasonic impulses is often impossible due to the low efficiency of piezo-excitation of broadband acoustic signals, therefore it is worthwhile to use laser for these tasks. Laser excitation of short pulses with the smooth-time envelope allows to analyze the ultrasonics damping within the broad frequency band (from 0.1 to 20 MHz), which in turn allows to improve the reliability of diagnostics for polymer composite density, porosity, composition, elastic and strength properties.
The use of laser for the excitation of ultrasonics in parts and structures under test opens up new possibilities for the polymer composite diagnostics to determine the material physico-mechanical properties by means of excitation of high-power broadband impulses with the characteristics unattainable by using the conventional piezoelectric converters.