Study on the initial damage in 3D woven composites using a novel high-capacity load-retention device suitable for in-situ CT

The onset of damage in 3D woven composites (3DWCs) is a critical factor in evaluating their structural performance. To eliminate the adverse effects of crack closure on initial damage detection while maintaining a high load capacity, a novel removable high-capacity load-retention (HCLR) device was developed for in-situ computed tomography (CT) systems. The HCLR device enables in-situ testing under loads of up to 200 kN, significantly surpassing the capacity of most existing in-situ CT setups. A testing method combing the HCLR device with acoustic emission (AE) technology was established to capture damage initiation in 3DWCs. AE technology serves as an effective indicator for identifying the onset of damage. Initial damage was investigated using both the HCLR and conventional ex-situ methods. The results demonstrate that the HCLR method allows for more accurate detection of initial cracks, which coincided with the appearance of the first high-energy AE signal. Notably, damage initiation occurred at only 35.8% of the material's ultimate strength, with matrix cracking identified as the dominant failure mode. These findings provide valuable guidance for the design and application of 3DWCs.