Graphene-doped polymer nanofibers are fabricated by taper drawing of solvated polyvinyl alcohol doped with liquid-phase exfoliated graphene flakes. Nanofibers drawn this way typically have diameters measured in hundreds of nanometers and lengths in tens of millimeters; they show excellent uniformity and surface smoothness for optical waveguiding. Owing to their tightly confined waveguiding behavior, light-matter interaction in these subwavelength-diameter nanofibers is significantly enhanced. Using approximately 1350-nm-wavelength femto-second pulses, we demonstrate saturable absorption behavior in these nanofibers with a saturation threshold down to 0.25 pJ pulse 21 (peak power ,1.3 W). Additionally, using 1064-nm-wavelength nanosecond pulses as switching light, we show all-optical modulation of a 1550-nm-wavelength signal light guided along a single nanofiber with a switching peak power of ,3.2 W.

A finite element model implemented with a progressive damage propagation mechanism was generated to study the mechanical behavior of stiffened composite panels under uniaxial tension. Typical damage modes including fiber breakage, matrix crushing and delamination were considered in the model. Failure criteria with corresponding stiffness degradation technologies was used to predict the initiation and evolution of intra-laminar damage modes by a user-defined subroutine. Cohesive elements with thickness of 0.01mm were defined along the interface areas between the filler and the adjacent laminate layers for predicting the initiation and propagation of delamination. Corresponding tests on composite stiffened panel with a web cut-out were conducted. A good correlation between the numerical results and test data was obtained, which validated the finite element models. Both the numerical and experimental results conclude that the delamination in the flange around the cut-out region is the most critical failure mode for the composite stiffened panel under the uniaxial tensile load.