Failure mechanism and bearing force of CFRP strengthened square hollow section under compressive load.

Carbon fibre-reinforced polymer (CFRP) plates can efficiently repair or enhance the mechanical properties of the square hollow section. However, the loading end of such a CFRP-strengthened member is prone to local bearing failure under compressive load. Given this limitation, an innovative CFRP-plate-strengthened square hollow section composite member (CFRP-SHSCM) was raised, and the thick-walled section was welded on both ends of the thin-walled steel column. The mechanical properties of CFRP-SHSCMs were investigated through parameter finite element (FE) analysis, focusing on the influence of the amount of CFRP layers (nc), the slenderness ratio (λ), the initial geometric imperfections (v0), the CFRP layouts (2S and 4S) and the length of the exposed steel column (Le). The load-displacement curves, the bearing force, and typical failure modes were also acquired. Results indicated that with increasing nc and v0, and decreasing λ, the conventional CFRP-SHSCMs were prone to local bearing failure with poor ductility, leading to the insufficient use of the CFRP plate, in contrast, the improved CFRP-SHSCMs primarily underwent overall buckling failure and exhibited better bearing force and ductility. Finally, the modified Perry-Robertson formula was put forward to predict the ultimate load of the CFRP-SHSCMs. The coefficients of variation between the FE simulation and the theoretical results were 0.00436 and 0.0292, respectively.

[Research on spectral characteristics of Yb3+ doped double-cladding large-mode-area micro-structured optical fiber].

Yb3+ doped double-cladding large-mode-area micro-structured optical fibers (Micro-structured fibers, MSF) are the ideal medium for the super high-power optical fiber laser applications. In the present paper, the authors fabricated the Yb3+ doped silica-based glass using the method of non-chemical vapor deposition, and fabricated the Yb3+ doped double-cladding large-mode-area MSF by stack-drawing method using this glass as the core of MSF, according to the design requirements. Fluorescence spectrum of the MSF was obtained using Ti: sapphire femtosecond laser with the wavelength of 975 nm and LD laser with the wavelength of 980 nm as pumping source. The experimental results show that the optical fiber has strong fluorescence at the wavelength of 1 050 nm, and it can inhibit generation of cooperative luminescence effectively.