Capturing the multiscale effects in the response of coated woven fabrics

The microstructure of coated woven fabrics employed in inflatable structures presents particular difficulties in constructing homogenized models for their mechanical response unlike those associated with traditional woven composites. Specifically, the woven yarns in coated fabrics are comprised of small filaments that are not held in place by a polymeric matrix, but in fact are free to slide past each other as the yarns deform. While this mechanism provides desirable extensibility for inflatable structures applications, it complicates the analysis as the number of contacting filaments within a yarn is typically large and hence computationally prohibitive to be individually taken into account during structural simulations. Herein, we construct a finite-element unit cell model for this class of woven materials that captures the in situ response of yarns comprised of contacting filaments. The complex microstructure of the woven yarns is replaced by equivalent homogenized yarns appropriately partitioned to mimic the filament-scale deformation mechanism of the actual yarns. This yarn partitioning approach mimics the actual filament yarn response without requiring large computational resources, and is capable of simulating uniaxial tensile, biaxial tensile, shear, and combined inplane loadings. In order to validate the model and gain insight into the deformation mechanism of the woven yarns, the effects of varying the manner of yarn partitioning and cross-section shape on the unit cell response relative to experimental data were investigated in a parametric study. Under loading parallel to one set of yarns, the manner of partitioning the yarn set had the most bearing on the homogenized unit cell response, with little contribution from the orthogonal set of yarns. For this type of loading, excellent agreement with experiment was obtained when the yarn partitioning correctly captured the actual filament microstructure and the concomitant deformation mechanism accompanying yarn uncrimping through subdivision into several non-interacting horizontal layers. Under loading that involves shearing of the orthogonal set of yarns, appropriate partitioning into both horizontal and vertical layers is required, with the homogenized response exhibiting greater sensitivity to the manner of yarn partitioning.