| Twisted fiber-reinforced elastomer laminates that could exhibit stress stiffening, high Poisson's ratios and negative Poisson's ratios are explored in the current research. Some of the applications include solid-state actuators, passive and active vibration dampeners, and active stiffners for morphing aircraft structures.;Polyvinyl acetate (PVAC), cotton/polyurethane and cotton/PVAC specimens were fabricated and tested. Single helix fiber/resin finite element models and a series of models of composite tubes (approximate representation of double helix fibers) embedded in an elastomeric matrix were developed and analyzed in NEi Nastran. Linear and non-linear finite element analysis (FEA) was carried out on the models with and without contact elements. Finite element analysis of single twist systems showed stiffening due to twist. Test results of twisted fiber laminates with single twist strands showed up to 47% increase in axial stiffness over dry cotton fiber and Poisson's ratios as high as 0.7. If one end of the double helix FEA models were unconstrained in the transverse direction, they showed extremely negative Poisson's ratios (-66), but, if both ends were constrained transversely, only small positive Poisson's ratios were observed. The reason could be the small length-to-diameter ratio of the FEA models, but should be explored more. |
