New insights in understanding the fiber-matrix interface and its reinforcement behavior using single fiber fragmentation data

As the microscale size of fiber reinforcements limits the physical ability to measure adhesion and residual stresses, there exists an incomplete understanding of the mechanisms that improve composite performance, further compounded by the recent trends in advanced surface treatments that incorporate multi-functional nanofillers. Despite significant advances in the micromechanical analysis of single-fiber systems, revised methodologies to characterize the fiber interface have yet to be standardized, often due to the need for additional experiments. To address these challenges, we demonstrate a novel data processing approach for the single fiber fragmentation test, with the primary objective of maintaining practicality by using typical fragmentation data as-is while deriving interface cohesive parameters. Our twofold process uses Monte Carlo simulations to establish accurate boundary conditions for subsequent numerical analysis using cohesive zone models (CZM). The Monte Carlo simulation derives the average interface shear stress (τ_ave) and critical fiber length (l_c) to estimate the link between the fragmentation process and fiber-matrix properties. Then CZM—while incorporating sample fabrication stresses, interface friction, thermal/cure stresses, and plasticity effects—allows for the assessment of the maximum shear traction (τ_max) and Mode II critical energy release rate (G_IIC). Applying this analysis to the results of a surface treatment involving cellulose nanocrystals deposited at the sized glass fiber-epoxy interface, we reveal the reinforcement mechanisms of interface deposited nanofillers. Our study assists in reconciling the differences between the SFFT and other single fiber methodologies, to bridge the gap between experimental and computational micromechanics.