Analysis of the torsional behavior of the aramid/carbon fiber-reinforced hybrid composites based on acoustic emission

Understanding the torsional property of hybrid composites is challenge. In this study, a series of torsional experiment were carried out on the aramid/carbon fiber-reinforced hybrid composite specimens to study the torsional behavior of different off-axis angles structures. Meanwhile, the influence of pre-delamination defects on composites with different off-axis angles was also investigated. The results showed that the pre-delamination specimens are more prone to delamination damage during the torsional process. However, for specimens with deep pre-delamination, the failure torque of the specimens with off-axis angle decreases by about 25%, while specimens without off-axis angle decreased by about 35%. Therefore, the off-axis angle structure has a certain protective effect on deep delamination defects under torsional loading. By using Micro-CT and Scanning Electron Microscope (SEM) technology, the damage modes of the composite specimens were displayed. Furthermore, the entire torsional process for the composite specimens was monitored by using Acoustic Emission (AE) technology in real time. As an effective unsupervised data analysis method, Fuzzy C-Means (FCM) cluster was applied for post-processing AE signals to realize the damage pattern recognition during the torsional process. AE signals were clearly divided into three categories and corresponded to three damage modes, a correlation between the damage mechanisms and the frequency characteristics of AE signals was identified. It can be found that the off-axis angle structure has an impact on the frequency range of AE signals in different damage modes and pre-delamination can change the show up time of different damage modes. Combining Micro-CT, SEM, and AE technology provides a basis for further research on damage evolution of composite materials.