The effect of variable fiber diameters in unidirectional fiber-reinforced bundles on stress redistributions around fiber breaks

Abstract

Finite element modeling is conducted to simulate the stress redistribution around a broken fiber (BF) in a bundle with experimentally measured fiber diameter distributions (FDD), followed by a parametric study of the influence of the FDD coefficient of variation on the stress concentration factor (SCF) and ineffective length (IL). Two variants of the SCF definition are considered: based on average, SCF_avg, and maximum, SCF_max, stress in the fiber cross-section. Results demonstrate that bigger fiber diameters show higher SCF and clustering of such fibers increases SCF in nearest neighbor fibers (NNFs). Critically, maximum stress-based SCF (${\mathrm{maxSCF}}_{\max }$​) significantly exceeds average stress-based SCF (${\mathrm{maxSCF}}_{\mathrm{avg}}$​), with differences about 40–75% in NNFs for FDD bundles compared to fiber constant diameter (FCD) bundles. This emphasises the necessity of prioritizing maximum stress criteria over conventional average stress models in failure predictions. The findings challenge benchmark models that rely on averaged SCF values, offering critical insights for improving accuracy in predicting fiber break propagation and composite strength.