A molecular structural mechanics approach combining with finite element analysis(MSM/FEA) was applied to study the microstructure and tensile behaviors of bamboo-like carbon nanotubes(BCNTs). The mathematical model of tensile behaviors of BCNTs was established based on molecular structural mechanics theory. The deformations of BCNTs, with different diameters and compartments set based on the experimental investigation on BCNT structures synthesized by chemical vapor depositon, under tensile load, were analyzed with ANSYS programmed. Results show that the BCNTs have good tensile properties, and those Young's modulus can reach 0.84 Tpa. Through the analysis, it can be found that the Young's modulus of BCNTs depends on the diameters and the length of compartment, which is in good agreement with our experimental tests for the tensile performances of individual BCNT.
To improve the anti-oxidation ability of silicon-based coating for carbon/carbon （C/C） composites at high temperatures, a ZrB2 modified silicon-based multilayer oxidation protective coating was prepared by pack cementation. The phase composition, microstructure and oxidation resistance at 1773, 1873 and 1953 K in air were investigated. The prepared coating exhibits dense structure and good oxidation protective ability. Due to the formation of stable ZrSiO4-SiO2 compound, the coating can effectively protect C/C composites from oxidation at 1773 K for more than 550 h. The anti-oxidation performance decreases with the increase of oxidation temperature. The mass loss of coated sample is 2.44% after oxidation at 1953 K for 50 h, which is attributed to the decomposition of ZrSiO4 and the volatilization of SiO2 protection layer.
In order to study the successive deposition and solidification processes of uniform alloy droplets during the drop-on-demand three dimensional（3D） printing method,based on the volume of fluid（VOF） method,a 3D numerical model was employed.In this model,the 7075 alloy with larger temperature range for phase change was used.The simulation results show that the successive deposition and solidification processes of uniform 7075 alloy droplets can be well characterized by this model.Simulated droplets shapes agree well with SEM images under the same condition.The effects of deposition and solidification of droplets result in vertical and L-shaped ridges on the surface of droplets,and tips of dendrites appear near the overlap of droplets due to rapid solidification.
