Based on the microstructure, a novel theoretical method was proposed to predict the equivalent stiffness and failure strength for stitched foam-core sandwich composites. Experimental studies on stiffness and failure strength were also carried out. Considering the different thickness increment of the laminated face-panels for different stitching density and the influence of the stitching angle to the width of the resin pocket zone, a modified fiber distortion model was developed to evaluate the stiffness of stitching laminated face-panels by a combined series-parallel model. As for the prediction of failure strength, the composite face-panels were analyzed by the classical laminate theory and the local wrinkling failure of the face panel was also considered. A bridging model was adopted to analyze the stress of the stitched foam-core, and the failure strengths were predicted with proper failure criteria for different constitutive materials. The equivalent stiffness and failure strength of stitched foam-core sandwich composite panels were obtained under fat-wise loading, edge-wise loading, three point bending and transverse shear loading, respectively. The predicted results showed a good agreement with the experimental results and the finite element results, which demonstrated the validity of the present theoretical method.

A novel photonic crystal fiber (PCF) based on pure silica is designed to transmit 114 orbital angular momentum (OAM) modes in the wavelength range of 1.2 μm–1.8 μm. The PCF composed of a central round air-hole, ring-shaped core, and air-hole array ensures effective refractive index differences of the constituent vector modes above 10−4 and stable transmission of the OAM modes. The finite element method is implemented to analyze the PCF. The confinement losses and nonlinear coefficients of all the eigenmodes at 1550 nm are less than 3.03 × 10−7 dB m−1 and 1.30 w−1 km−1, respectively. In addition, the PCF shows higher effective refractive index difference, lower confinement loss, and nonlinear coefficient thus holding large promise in high-performance fiber communication systems.

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