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BN and BN/SiC coatings were deposited on the surface of two typical domestic SiC fibers by CVI process, and the composition of coatings was analyzed. The tensile strength of monofilaments was evaluated by Weibull distribution, and the tensile fracture failure behaviors of the fiber before and after depositing coatings were studied. The results show that the carbon-rich layer with appropriate thickness (15 nm) can heal the defects on the surface of SiC fiber and reduce the possibility of fiber failure from the surface. The thickness of the coating prepared by the CVI process is uniform and the composition is stable. After depositing BN and BN/SiC coatings, the tensile strength and elastic modulus of the two kinds of SiC fibers are decreased. BN coatings can also repair the surface defects of the fiber, so that the fiber strength distribution tends to be concentrated. Different from the uncoated fibers, the tensile fracture failure sources of coated fibers are the surface defects of BN and SiC coatings, respectively.

Laminating method is one of the key factors affecting the thermal shock resistance of SiCf/SiC composites prepared by prepreg paving process. Based on the cohesion model, 1200 ℃ high temperature water quenching tests and finite element simulation studies were carried out on SiCf/SiC composite square samples with different orthogonal lay-up methods, which were prepared by the precursor immersion pyrolysis(PIP) process. The results show that the surface temperature of the sample drops sharply during the water quenching process, and there is a large temperature difference between the core and the surface. The temperature difference between the corner and the core can reach up to 1077 ℃. The main failure modes are interlaminar delamination and matrix cracking, and the delamination position is related to the layering method. Moreover, significant differences in the delamination displacement can be observed, due to the difference in the orthogonal lay-up mode: tacking displacement of the main interlaminar delamination of [0/90] and [0/90/0] can reach 0.61 mm, while the [0/0/90/90] layer cracking displacement is only 0.04 mm. In addition, the cracking displacement of the main interlaminar delamination increases gradually with the increase of water quenching time, while the secondary cracks will undergo crack closure after opening.

The output of wind and solar power stations is intermittent and fluctuating,but their complementarity can be fully realized with reasonable wind-solar capacity ratio. The inaccurate theoretical power calculation of power station affects the extraction of true features of wind and solar,and then leads to large capacity matching error. The model-generator method commonly used in theoretical power calculation of new energy power stations is improved in this study. The abnormal data are firstly identified and reconstructed,and then the abnormal model-generators are identified and updated. Furthermore,according to the actual operation of non-model-generators,the dynamic information window is selected. By using the measured power of model-generator and non-model-generator in the dynamic information window,the non-model-generators are grouped and the scale coefficient of each group of non-model-generator is dynamically identified,and thus the theoretical power of new energy power stations is calculated. Based on the calculation of historical theoretical power for many years,the characteristics of new energy power stations are analyzed. The random output scenario is simulated accordingly,and the optimization method of wind-solar capacity ratio based on the risk of source-load mismatching is established. The accuracy of the improved model-generator method is verified by examples. By using this method,the improved theoretical power data of wind farm and photovoltaic power stations in a certain area of northwest China are obtained,and the optimal ratio of wind-solar capacity in this area is optimized. The improved model machine method proposed in this paper can effectively improve the calculation accuracy of theoretical power of new energy power stations,and the optimal ratio of wind-solar capacity calculated based on this method can provide reference for wind-solar power generation capacity of regional power grid.

SiCf/SiC composites with the polycarbosilane and silicon carbide fiber of different pyrolytic carbon (PyC) interphase thicknesses as the reinforcement phase were fabricated by a polymer impregnation and pyrolysis (PIP) method. And SiC whisker was introduced into the SiCf/SiC composites to further improve its performance. It is found that the mechanical properties of SiCf/SiC composites have outstanding tensile strength, fracture toughness and flexural strength of 192.3 MPa, 446.9 MPa and 11.4 MPa·m1/2,, when the PyC interphase thickness is about 230 nm. After the introduction of SiC whisker, into the SiCf/SiC composite matrix, the toughening mechanisms such as whisker pull-out, whisker bridging and crack deflection increase the energy consumption when the crack is transferred in the matrix, and the fracture toughness and bending strength of the composite are increased by 22.9% and 9.1% respectively.

SiCf/SiC composites are consisted of SiC fibers, SiC matrix and interphase. The interphase can transfer stresses from matrix to SiC fibers and deflects microcracks, at the same time, it protects SiC fibers from chemical erosion during the preparation and use of materials, which plays a very important role in regulating the properties of SiCf/SiC composites. In this paper, the effects of precursor gas ratio, carrier gas, deposition pressure, temperature on the deposition rate and microstructure of interphase during the chemical vapor infiltration (CVI) process are summarized. It will be the key and difficult point in the research of SiCf/SiC composite interphase to select appropriate process conditions and prepare BN and its composite multilayer with ideal structure.