Acoustic Emission Monitoring and Damage Failure Behavior of Seawater-Aged Composites Under the Bending Load

To investigate the failure mechanism of carbon fiber-reinforced composites with different fiber orientations in the seawater environment, seawater aging and three-point bending tests were conducted. Acoustic emission technique was applied to establish the relationship between stress waves and damage signal characteristics. The experimental results showed that the specimen with [0°/45°/-45°/90°/0°/45°] had the best seawater aging resistance under seawater aging, and the failure load decreases by 3.89%. Furthermore, damage evolution behaviors were divided into three stages and the damage modes during the failure process were accompanied by matrix cracking, fiber/matrix debonding and fiber fracture. Besides, the modal acoustic emission and k-means clustering analysis were employed to confirm the existence of three damage modes. By analyzing the numbers of acoustic emission signals, it was discovered that the matrix cracking and fiber/matrix debonding resulted in the deterioration of the mechanical properties of the seawater-aged composites. Fiber/matrix debonding is more crucial compared with matrix cracking. Moreover, a semi-supervised model based on the random forest algorithm was established to predict the damage modes. Acoustic emission monitoring technology helps to explore the damage mechanism of seawater-aged composites and provides a reference for structural health monitoring of composites.