Analysis of the torsional behaviour of carbon fibre-reinforced composite tubes based on acoustic emission and micro-CT

High demands have been placed on the torsional performance of composite tubes used as steering columns, making it important to understand the torsional properties. In order to qualitatively study the torsional performance of carbon fibre-reinforced composite tubes with minor off-axis angles caused by manufacturing errors, the torsional behaviour of carbon fibre-reinforced composite tubes with two different structures was investigated. Micro-CT and acoustic emission (AE) techniques were used to characterise the damage evolution during the torsion process of composite tubes. The results revealed that small angle deviations could reduce the mechanical properties (failure torque decreases by 18.10%), particularly the maximum failure angle (decreases by 31.50%). The damage morphology and location of the torsional failure composite tubes were observed, and different failure modes were identified by micro-CT and scanning electron microscopy (SEM). Furthermore, fuzzy c-means (FCM) was used for post-processing AE signals collected during the torsion process, and frequency characteristics of AE signals for different damage modes observed by CT and SEM were identified, including matrix cracking (<140 kHz), fibre debonding (140–250 kHz), fibre breakage (250–480 kHz). Based on the research, angle deviation should be avoided in the preparation of composite tubes.