Effect of Elastic Stresses in FRP Composite on the Frequency Characteristics of Acoustic Emission Signals Recorded by a Fiber-Optic Sensor

Abstract

The purpose of the work is to establish the influence of elastic stresses in fiberglass on the frequency characteristics of acoustic emission (AE) signals recorded by a piezoelectric and fiber-optic acoustic emission sensor. Samples of fibre reinforced plastic (FRP) composite were made in the form of plates using the vacuum infusion method. After that, samples were cut out from the plate for subsequent tensile testing on a tensile testing machine. The samples had the shape of a double blade. The fiber-optic sensor was made on the basis of an adaptive laser holographic interferometer. The sensitive element of the sensor is a multimode optical fiber, which was glued to the surface of the working part of the samples before testing. The piezoelectric transducer was installed on the non-working part of the sample. The sample was loaded with a tensile load in stages. At each loading stage, acoustic waves were excited in the middle part of the sample by a Hsu-Nielsen source. AE signals from propagating acoustic waves were recorded by both sensors. The analysis of changes in the AE signal spectra caused by elastic stresses in the FRP composite material is performed. At low-frequency harmonics of the Fourier spectrum, a shift in the spectrum to the high-frequency region is observed with an increase in the tensile load stress. However, at high frequencies up to 500 kHz, which are informative for recording AE, the effect of tensile stresses becomes nonlinear. The nature of the influence of external stresses on the signal spectrum as a whole is important in identifying the type of AE signal source caused by a certain type of destruction of the FRP composite.