Investigation of damages formed in polymer composite materials under bending loading and their identification by the acoustic emission technique

Polymer composite materials (PCM) reinforced with glass fibers are very important in many industries due to their unique properties (high chemical resistance and specific strength) with the economic efficiency of use. At the same time, the application of glass fabrics as reinforcing elements ensures high manufacturability. However, unlike crystalline materials, polymer composite materials are subject to the complex process of destruction, which requires the application of non-destructive control methods to get information about the nature of the resulting damage and the kinetics of their accumulation. The paper studies the deteriorations formed in the fiberglass samples molded using T-11-GVS-9 glass fabric and DION 9300 FR binder within static bending deformation accompanied by the acoustic emission (AE) method. In this work, the authors solved the problem of identifying the nature of damages in fiberglass using the Fourier spectra of the recorded AE signals. The authors used the clustering method to estimate their formation and development kinetics. Clustering was performed based on the Kohonen self-organizing map (SOM) algorithm using the values of peak frequencies of the Fourier spectra calculated for the recorded AE signals under static bending deformation of a fiberglass sample up to failure. To ensure the separability of the resulting damages according to the AE parameters, the authors used the loading rate that was ten times lower than that calculated according to the state standard. The study established that the application of frequency representation of AE signals recorded during the fiberglass destruction is effective when solving the task of identifying the nature of the resulting damages. As a result of the study, the authors found that the process of delamination formation during the bending of multilayer laminated plastics acts as a critical mechanism of destruction leading to a significant loss of the polymer composite strength properties.