Toward better understanding of the effect of fiber distribution on effective elastic properties of unidirectional composite yarns

• Evaluated effect of micro-fiber distribution on properties of UD composite yarns.
• Random unit cell modeling results were assessed against theoretical predictions.
• The transverse Poisson’s ratios were highly affected by fiber distribution.
• Shear-wall artifact in imaging yarns can cause deviations from actual behavior.

A combined X-ray micro-computed tomography (XMT) and micro-Finite Element Analysis study is presented to quantify the effects of micro-scale random fiber distributions on the effective (homogenized) elastic properties of unidirectional (UD) yarns, as often used by designers for component-level computational modeling of composite structures. In addition, it is shown how the XMT artefacts can yield unreliable FE homogenization of the composite yarns by overestimating the stress transfer capacity between the material constituents. Finally, the micro-FEA modeling results under fiber distribution randomness are compared to the macro-level predictions such as the classical rule of mixture and Halpin–Tsai equations.