# Influence of Elliptical Fiber Cross-Section Geometry on the Transverse Tensile Response of UD-CFRP Plies Based on Parametric Micromechanical RVE Analysis

## TL;DR

This study shows how the shape of carbon fiber cross-sections affects the strength of composite materials under tension.

## Contribution

A new micromechanical framework with elliptical fiber cross-sections is introduced for predicting transverse tensile properties of CFRP plies.

## Key findings

- Increasing fiber volume fraction increases transverse elastic modulus and peak stress by thinning matrix ligaments.
- Cross-sectional aspect ratio redistributes stress among ligaments and affects failure localization.
- Size variability in fibers reduces peak stress due to stress localization near thin ligaments.

## Abstract

Predicting the transverse tensile properties of unidirectional CFRP plies is often based on micromechanical representative volume elements (RVEs) with circular fiber cross-sections, whereas microscopic observations show pronounced ellipticity and size variability in actual fibers. A two-dimensional plane-strain micromechanical framework with elliptical fiber cross-sections is developed as a virtual testing tool to quantify how fiber volume fraction, cross-sectional aspect ratio and statistical fluctuations in the semi-minor axis influence the transverse tensile response. Random RVEs are generated by a hard-core random sequential adsorption procedure under periodic boundary conditions and a minimum edge-to-edge gap constraint, and the fiber arrangements are validated against complete spatial randomness using nearest-neighbor statistics, Ripley’s K function and the radial distribution function. The matrix is described by a damage–plasticity model and fiber–matrix interfaces are represented by cohesive elements, so that high equivalent-stress bands in matrix ligaments and the associated crack paths can be resolved explicitly. Parametric analyses show that increasing fiber volume fraction raises the transverse elastic modulus and peak stress by thinning matrix ligaments and promoting longer, more continuous high-stress bands, while the cross-sectional aspect ratio redistributes high stress among ligaments and adjusts the balance between peak strength and the degree of failure localization. The observed size variability is represented by modeling the semi-minor axis as a normal random variable; a larger variance mainly leads to a reduction in transverse peak stress through stronger stress localization near very thin ligaments, whereas the elastic slope and the strain at peak stress remain almost unchanged. The proposed framework thus provides a statistically validated and computationally efficient micromechanical basis for microstructure-sensitive assessment of the transverse behavior of UD-CFRP plies with non-circular fiber cross-sections.