Mesomechanical modeling of braided cords

Braided-cord reinforced textile composites have the potential to be a material system choice that can offer comparable specific-strength and specific-stiffness properties as woven and uniaxial fabric-reinforced composites with the added benefit of higher specific-energy absorption. This increase in energy absorption is a result of tube crushing at the mesoscale, i.e. analogous to the macroscale crushing of the braided tubes that are used for crash rails in cars. Much research has been devoted to understanding the mechanical behaviors of fabrics during forming. However, the same level of understanding for the mechanical behavior of braided cords during preforming does not yet exist. The current work seeks to gain an understanding of the contributing factors to the mechanical behavior of a braided cord during the forming process. In the current work, a mesomechanical finite element model of a polyethylene braided cord is investigated. CT-scans of the cord were taken under various preloads. The CT-scan data of the cord under zero load is used to create a geometric FEA model of the cord using the Virtual Textile Morphology Suite (VTMS) software. Tensile and transverse compression tests are performed on the individual tows to characterize the axial and transverse stiffnesses, and these data are used in an orthotropic material model. The finite element model of the cord is then pulled in tension, and the deformation of the cord is compared with the deformations in the CT-scan. Once the model is shown to represent the mechanical behavior of the braided cord, it can be numerically characterized and insight into certain properties such as the bending stiffness and torsional stiffness can be gained. The mesomechanical model can then be adjusted (number of tows, braid angle, etc.) to understand how braid design choices effect the deformation behavior of the braid during a preforming process.