Characterizing fiber-matrix debond and fiber interaction mechanisms by full-field measurements

An experimental approach is developed and utilized to characterize the fiber-matrix interfacial debonding mechanism and its effect on matrix cracking in unidirectional (UD) fiber composites. Local deformation response at the fiber-matrix interface is first studied by analyzing the strain fields developed in the vicinity of macro fibers in single-fiber samples. A practical approach for the identification of normal cohesive behavior at the fiber-matrix interface is presented and implemented in a finite element model that replicates the experimental findings. Fiber-to-fiber interaction, debond formation, and failure mechanisms in multiple fiber systems are then studied by varying the distance and angle between adjacent fibers in double-fiber samples. The experimental results indicate that the spacing and angular orientation between adjacent fibers affect the interface debond initiation and propagation, as well as subsequent matrix failure mechanisms. It is also shown that compared with fiber spacing, angular distance has a more significant effect on matrix cracking in UD composites under transverse tension. Results presented in this work provide an experimental-based quantitative insight into the mechanics of fiber-matrix interface using in-situ full-field measurements.