Delamination Initiation Identification of Mode II Based on AE Characterization of Composite Damage Mechanism

In order to understand the delamination growth under mode II loading from the perspective of composite damage mechanisms, this study conducted in-depth research on the damage evolution of laminated plates using acoustic emission (AE) technology and signal analysis methods. Delamination mainly includes two stages: initiation and propagation, in which the initiation is the more important stage in the process of material delamination. Three damage modes of laminated materials during loading were identified by combining peak frequency statistics of AE signals with continuous wavelet transform (CWT). The initial time and stage of delamination can be determined by two methods. (1) The evolution process of damage mechanisms can be characterized by the fast fourier transform (FFT) of AE signals in several time periods. (2) The cumulative energy of three damage modes separated by variational mode decomposition (VMD) can be used to characterize the damage evolution process. The initial time determined by integrating several methods is much earlier than the occurrence time of the interlaminar fracture toughness value defined by ASTM standard. The strain energy release rate (SERR) determined at the initial time of delamination is taken as a design reference, which will be of guiding significance for ensuring the safety of laminates.