Stitched composite materials are emerging as a promising material due to their high interlaminar strength,combined performance and light weight.The mechanical properties of stitch yarns are very essential for stitched composite structures.In this study,the tensile behaviors of the twisted fiber yarn in stitched composites were investigated experimentally,analytically and numerically.Two kinds of cross-sectional area of twisted yarn are proposed and discussed.The paper presents an intersecting circle model to describe the cross-section of twisted fiber yarns,and a physics-based theoretical model to predict the effective tensile moduli.The numerical models take into account the cross-sectional characteristic and the twist architecture.The investigation shows that: the sum of each fiber area should be used for experimental analysis;and the cross-sectional area surrounded by the yarn profile should be used for theoretical predictions and finite element (FE) simulations.The relative errors of the prediction method and the FE simulation are less than 2％ and 1％,respectively.The friction between the fibers is derived,and the effect of friction on mechanical properties is discussed.The investigation method will serve as a fundamental component of twisted fiber bundle/yarn analysis.