Characterization of the dissipative large deformation bending response of dry fabric composites as occurs during forming

Bending rigidity is known to play a significant role in the formability of composite fabrics, as it can affect wrinkles formation and reduce the mechanical properties of the final part. However, measuring the highly nonlinear dissipative bending behavior of unconsolidated fabrics undergoing large deformation, is an ongoing challenge. In this article, a customized setup is employed to capture the bending as well as reverse bending responses of unconsolidated fabrics under large deformation (up to ±90° bent angle). As a test case, a typical fiberglass fabric that is thick and has high areal density, as well as a carbon fiber fabric with lower thickness and areal density are considered and compared. In addition, the response of each fabric is compared to that of individual yarns, suggesting that the interlaced architecture and the dissipative behavior of yarns affect the effective bending rigidity, along with the ensuing hysteresis effects during loading-unloading. Furthermore, when the unconsolidated fabrics are oriented off-axis relative to the bending axis, the bending rigidity interacts with the in-plane trellising (reaching a maximum shearing angle of 3.3° at full bent angle), suggesting that the classical laminate theory would not apply in capturing shear-bending coupling in dry fabrics.