Evaluation of Fiber‐Matrix Debonding in Glass, Carbon, and Hybrid Fiber Composites Under Transverse Loading by Full‐Field Measurements

ABSTRACT This study aims to experimentally quantify fiber‐matrix debonding and transverse crack evolution in single‐fiber and double‐fiber composite specimens, with particular emphasis on hybrid glass/carbon configurations. Neat epoxy, single macro fiber, and double macro fiber model composites with controlled inter‐fiber spacing, orientation, and fiber material are fabricated and tested. A full‐field experimental measurement framework, enabled by digital image correlation (DIC), has been developed to quantify local displacement and strain fields at and in the vicinity of fiber‐matrix interfaces as functions of inter‐fiber distance, orientation angle, and fiber material. Novel aspects of this experimental approach include in situ, high‐resolution strain measurements enabling direct visualization of damage initiation, shear band formation and crack coalescence, and fiber‐to‐fiber interaction effects. The experimental findings suggest that carbon macro fibers exhibit highly localized strain fields and delayed debonding, while glass macro fibers lead to more diffuse and rapid debonding initiation. The approximate global stress levels at the onset of fiber‐matrix debonding were determined to be 12 MPa and 8 MPa for carbon and glass macro fibers, respectively. In double‐fiber specimens, inter‐fiber distance and angle strongly influenced shear band formation and microcrack coalescence. In double‐fiber specimens fabricated with the same fiber material, shear band coalescence was observed at shorter inter‐fiber distances and orientation angles below 45°. In contrast, hybrid glass/carbon configurations promote shear band coalescence at larger inter‐fiber distances and orientation angles exceeding 45°. This study provides new experimental insights into interfacial mechanics and fiber‐fiber interactions in hybrid composites, enabling robust validation of micromechanics‐based models.