Distribution and propagation mechanisms of debonding damage caused by combined loading in cruciform specimens

The accumulation mechanisms and spatial distribution of debonding damage in fiber-reinforced polymer composites under combined tension and shear loading are not well understood. To tackle this research gap, X-ray computed tomography has been utilized to observe the debonding damage between epoxy and CFPR rods in cruciform specimens. An in-situ loading rig was used to perform tension tests, with different combined stresses applied by varying the orientation of the embedded reinforcements. After loading, the damage volumes have been extracted and visualized in 3D to comprehensively examine the spatial distribution of debonding. The in-situ and ex-situ experimental results confirm that the distribution and propagation of interface cracks are largely dependent on the ratio of tension to shear and the position of adjacent reinforcements. Additionally, critical parameters such as debonding angles, crack opening displacements, and deflecting angles have been quantitatively analyzed. Based on the results, the authors proposed three representative models to describe the dimensional properties of interface cracks, and an empirical formula that reveals the positional correlation between interface cracks on adjacent reinforcements. Considering the universality of combined loading in engineering applications, a full understanding of the resulting debonding damage can significantly contribute to the optimization of composite design methodologies.