The effect of longitudinal debonding on stress redistributions around fiber breaks: Incorporating fiber diameter distribution and fiber misalignment

This research explores the influence of interfacial debonding between a broken fiber and matrix on stress redistribution surrounding a fiber break within a unidirectional (UD) impregnated fiber bundle, accounting for misalignment of fibers and fiber diameter distribution in randomly packed fiber configurations. Finite-element modelling is conducted on carbon-reinforced epoxy UD bundles with one fiber broken for different combinations of the bundle parameters: aligned/misaligned fibers and constant/randomly distributed fiber diameters. Two definitions of stress concentration factor (SCF) are examined, based on average and maximum stress over the fiber cross-section. The study reveals a statistically significant difference for average SCF for misaligned bundles with both constant and variable diameters of fibers compared to the case of aligned bundles of fibers with constant diameter. When the calculated SCFs are incorporated in a bundle strength model, the failure strain of unidirectional composites can be more realistically predicted.