Time‐frequency analysis of acoustic emission signals in composite materials under repeated impact conditions

Abstract In the service of composite materials, scenarios involving repeated impacts are frequently encountered. In our study, the time‐frequency characteristics of acoustic emission signals during repeated impact processes were investigated using wavelet packet transform. Principal Component Analysis was utilized to identify the frequency bands containing the most information. Shannon entropy was employed to select the optimal wavelet basis function. The terms DDD3, ADD3, and DAA3 correspond to matrix cracking, delamination, and fiber failure, respectively. The initial impact, due to the presence of numerous internal voids in the specimen, often leads to stress concentration, thus resulting in a prolonged duration of matrix cracking during the initial impact. Delamination becomes more active when matrix cracking initially occurs. Fiber failure typically accompanies unloading when it becomes active. Matrix cracking dissipates the most energy, followed by delamination and then fiber failure. When the final impact penetration occurs, the characteristic frequency band proportions for the quasi‐isotropic matrix cracking, delamination, and fiber failure are 48.99%, 22.39%, and 7.16%, respectively. For the cross‐ply laminate, the corresponding proportions of the characteristic frequency bands are 56.62%, 14.46%, and 6.98%, respectively. Highlights Multiple impact tests were conducted, and acoustic emission signals were recorded. Principal component analysis was performed to select the characteristic frequency bands. The time‐frequency characteristics of the two types of laminated composites during the impact process were analyzed. The trends of the characteristic frequency band proportions under multiple impacts on the composites were investigated.