Fiber-reinforced plastics (FRP) used in transportation equipment are required to have vibration damping performance in addition to strength and stiffness. In this study, we evaluated the vibration-damping behavior of FRPs that are made from three kinds of polyarylate-fibers (high strength type, conventional type), and aramid-fiber, which are expected to have excellent vibration-damping performance. In order to clarify the changes in vibration-damping performance and its mechanisms, we focused on the hysteresis loop obtained by the stress-strain curve under cyclic loading, and the change in dissipation energy and strain energy obtained from the hysteresis loop. The hysteresis loop characteristics under cyclic loading were compared for these three materials. Under high cyclic load, the damping ratio of polyarylate FRP (high strength type) was higher than that of other FRPs. It is considered that the specimens with delamination at low cycle loadings develop delamination at the intersection of the fiber bundle in the loading direction and the fiber bundle perpendicular to the loading direction as the number of cycles increases. At high cycle loadings, the specimens with delamination in the fiber bundle in the direction of the loading occurred as the number of cycles increased for polyarylate (high strength type) FRP and aramid FRP. Based on the observation of the fracture surface, it is considered that the delamination developed at the intersection and transverse cracks, which led to a decrease in the dissipation energy.

The objective of this study was to improve the utility of a shape-memory-alloy (SMA) knitted fabric actuator. To that end, we employed a double-sided knitting structure with excellent structural stability and high yarn density and fabricated samples with different total number of courses, wales, and diameters of SMA fibers. These samples were subjected to repeated heating tests during uniaxial elongation along the direction of the wale, and the generated contraction force was measured. Furthermore, by comparing the results of the measurements, the influence of each parameter on the contraction force was evaluated. By including the amount of deformation in the direction of the knitting fabric width and the bending rigidity of the yarn in our analysis, we were able to determine the trend followed by the contraction force generated by SMA double-sided knitted fabrics. The results of this study are expected to be applicable to the development of smart textile products.