Stress concentrations in an impregnated fibre bundle with random fibre packing

The stress redistribution after a single fibre break is a fundamental issue in longitudinal strength models for unidirectional composites. Current models assume hexagonal or square fibre packings. In the present work, random fibre packings were modelled using 3D finite element analysis and compared to ordered fibre packings. Significant differences in the stress redistribution are found. Compared to square and hexagonal packings, random fibre packings result in smaller stress concentration factors for fibres at the same distance from the broken fibre. These random packings, however, also show higher maximal stress concentration factors. The influence of the fibre breakage is more localised, which results in lower ineffective and overload lengths. The presence of fibres at smaller distances from the broken fibre explains these phenomena. For an accurate representation of the stress redistribution after a fibre breakage, random fibre packings should be used.