OPTICAL-ACOUSTIC DIAGNOSTICS OF ORTHOTROPIC COMPOSITE STRUCTURES

Abstract

A new approach to estimating the sizes of circular and elliptical internal defects in orthotropic composite structures based on the theory of thin plates is proposed. To calculate the fundamental resonance frequencies of circular and elliptical orthotropic plates clamped around their entire perimeter and located directly above circular and elliptical defects, known relationships between the vibrational and elastic properties of orthotropic materials, obtained by the Rayleigh-Ritz and Galerkin methods, were used. In this case, the dimensions of the orthotropic plates match those of the defects. To experimentally verify the obtained working formulas for calculating the fundamental resonance frequencies, an optical-acoustic method for detecting and visualizing internal defects developed by the authors was used. This method involves exciting the test object with a frequency chirping elastic wave and recording a sequence of dynamic speckle patterns synchronously with the defect vibrations. The accumulated sequences are entered into a computer and form digital speckle patterns. After their high-speed processing, optical spatial responses from defects are extracted. Experiments with samples of adhesive joints “carbon fiber reinforced polymer tape-concrete” containing artificial circular and elliptical interfacial defects were performed using an optical-digital system prototype implementing the optical-acoustic method. We detected such defects under a carbon composite tape layer at the fundamental resonance frequencies and showed that the sizes of the optical spatial responses from them are close to their sizes. The experimentally determined fundamental resonance frequencies of defects are close to the corresponding frequencies calculated using the obtained working formulas. The indicated approach makes it possible to estimate the size of the defects and their depth under the orthotropic composite surface.