4 - AE tests and signal analysis on delamination of composite laminates under three-point bending and hygrothermal environments

Abstract

This chapter performs three-point bending experiments and acoustic emission (AE) tests of single-leg bending and over-leg bending T700/9916 composite laminates with an initial delamination crack under room temperature and hygrothermal environment (relative humidity 95% and temperature 70°C). By analyzing the load–displacement curve and the responses of AE feature parameters, and combining with the observation and identification of failure modes by scanning electron microscope (SEM), the degradation of mechanical properties and the variable of AE signals corresponding to different failure modes in the delamination failure process of composite materials are studied. The crack tip position is located in real time based on the AE amplitude–location diagram, and the damage of laminates is evaluated according to the load–displacement–energy curve. Combined with SEM observation, the dominant failure mode of composites is analyzed. Finally, the AE source signals obtained during the test are decomposed by the fast Fourier transform (FFT) and the wavelet packet, and their characteristics and difference in the time domain and frequency domain are analyzed in order to provide more comprehensive AE information for studying failure modes.