Analytical prediction of the elastic properties of 3D braided composites based on a new multiunit cell model with consideration of yarn distortion

• A new analytical model based on a multiunit cell model (MCM) is developed to study the effects of the yarn distortion and the shell–core structure feature on the elastic properties of 3D four-directional braided composites.
• An idealized yarn model with consideration of the yarn distortion is proposed to calculate its elastic properties by introducing an average twist angle.
• Combined with the MCM, the stiffness-volume averaging theory is applied to consider the contribution of all unit cells to the elastic properties of the overall specimen.
• The variation of the average twist angle for the interior and surface-corner yarns has been accounted for appraising the elastic properties.
• The effects of the braiding angle, the fiber volume fraction, and the number of the yarn carriers on the elastic properties are discussed in detail.

A new analytical model based on a multiunit cell model (MCM) is developed to study the effects of the yarn distortion and the shell–core structure feature on the elastic properties of 3D four-directional braided composites. An idealized yarn model with consideration of the yarn distortion is proposed to calculate its elastic properties by introducing an average twist angle. Combined with the MCM, the stiffness-volume averaging theory is applied to consider the contribution of all unit cells to the elastic properties of the overall specimen. The variation of the average twist angle for the interior and surface-corner yarns has been accounted for appraising the elastic properties. The predicted elastic properties are in good agreement with the available experimental data, demonstrating the applicability of the analytical model. In addition, the effect of the average twist angle on the elastic properties is discussed and the comparison between the predicted values and the experimental results are conducted. Then the elastic properties of unit cells with their unique microstructure are analyzed. Finally, the effects of the braiding angle, the fiber volume fraction, and the number of the yarn carriers on the elastic properties are discussed in detail. Discussion results have proved that the present analytical model can be utilized to predict the elastic properties of 3D braided composites.