Detection and Identification of Hidden Defects in Layered Polymer Composites Using Combination of Acoustic Resonance and Interferometric Monitoring of Surface Displacements

Abstract

Method of detection and identification of hidden defects in the structural elements made of layered composite materials is presented in this study. Such defects occur during production of composite materials, composite structures and during their operation. A proposed method of non-destructive testing combines the acoustic load of the test object and the interferometric testing of its surface displacements, which arise as a result of resonance of the acoustic wave in the defect. The defect is considered as an acoustic resonator filled with a medium (under normal conditions – by air) in which only a longitudinal acoustic wave propagates. The novelty of the method is that it allows not only to detect and locate a hidden defect, but also to determine its dimensions. And its advantage is that it does not require knowledge about the mechanical properties of the material, as a result, it is not necessary to determine the speed of sound propagation in the composite; it allows to test materials with arbitrary parameters of its surface roughness (from optically rough to mirror-smooth ISO 4287:2012); uses acoustic waves with frequencies 3...5 times lower than similar methods. Authors presented in this work experimental results that confirm the effectiveness of the proposed method.