Co-authors​ :

 Yiding LI (CHINA), Weijie ZHANG (CHINA), Shibo YAN (CHINA) 

The bending stiffness of yarn in textiles is significantly affected by external pressure, resulting in nonlinear bending behavior. Understanding the intricate mechanical behavior of yarns in textiles and subsequently defining a proper formulation and bending properties for the numerical model of yarns are essential for modeling the mechanical response of textiles during composite manufacturing using the so-called digital element method, which is also known as the virtual fiber modeling (VFM) method. While the existing experimental methods, such as Peirce’s cantilever-bending test and Kawabata’s Evaluation System, focused on the mechanical behavior of individual yarns, they neglected the interaction among yarns within fabrics. This limitation is insufficient for properly defining the formulation and bending properties of virtual fibers.
This paper introduces the effect of pressure on the bending behavior of yarns and evaluates this effect through both experimental and theoretical methods. In the experimental method, specimens are enclosed in sealing bags and vacuumed before the test to provide a steady external pressure and sealed to maintain the external pressure during the test. Results reveal that external pressure significantly influences slippage, causing yarn disintegration and subsequent degradation in bending stiffness. Based on the experimental results and the classical beam theory, a theoretical model is proposed to describe the yarn’s nonlinear bending behavior in consideration of the slippage and the effect of external pressure.
With the characterized nonlinear pressure-dependent bending stiffness, the formulation and properties of the virtual fiber element in the VFM method are rationally defined through a tailored beam user element for bending properties, in conjunction with a truss element providing axial properties and contact surface. Employing this new formulation, the original kinematic VFM method is extended with a physical basis and can be applied to predict the mechanical response of different types of textile fabrics. In the case of the through-thickness compression of 2D woven fabric, simulation results demonstrated a strong agreement with reported experimental findings, emphasizing the importance of adopting pressure-dependent nonlinear bending behavior for virtual fibers.
This paper presents an integrated modeling framework based on the virtual fiber modeling concept for both deformation and mechanical analysis of fabrics, with minimum requirements for testing or trial calculations of model input parameters. This method can be a valuable tool for modeling the mechanical response of textiles during the manufacturing process and generating realistic mesoscale geometries for textile composites.