Multi‐Perspective Quantitative Analysis of Expansion Processes of Interface Crack Under Off‐Axis Loading

The variation in the dimensions of interface cracks during loading provides key information for the establishment of a micro‐mechanical model for composites. Nevertheless, existing microscopic observations are limited, particularly concerning the multi‐perspective examinations of interface debonding resulting from combined loading. To address this issue, off‐axis tension was applied, and the reflected‐light method and CT scanning were employed separately to investigate the propagation of interface cracks along the fiber axis direction and circumferential direction. The experimental findings suggested that the extension velocity of the interface crack in the longitudinal section remains substantially stable under transverse tension and gradually decreases under loading incorporating shear stress components. Additionally, the interface crack propagation on a transverse section includes a rapid propagation stage, a deceleration stage, and a stabilization stage. Moreover, a finite element analysis of interface debonding was developed using the ABAQUS/Standard platform. It was found that an increase in the proportion of the shear component may enhance the challenge of acquiring accurate data from both observations and simulations. Most crucially, the characteristics and formation mechanisms of unique ear‐shaped interface cracks and re‐closed regions were examined based on the observations and the calculated stress contour maps. In conclusion, this paper offers multi‐perspective observations on the interface crack propagation under various combined loading conditions.