超高温陶瓷改性C/SiC复合材料的制备及其性能

以碳纤维为增强体,聚碳硅烷和聚烷基铪为前驱体,采用前驱体浸渍裂解(PIP)工艺制备C/Si C-HfC复合材料,将其与同种工艺所得C/SiC复合材料进行对比评价分析。发现C/SiC-HfC复合材料具有较低密度和较好的高温力学性能,且在1 650℃静态氧化实验中,含有HfC的基体对纤维具有更佳保护效果。C/SiC-HfC密度约为1.92 g/cm~3,常温弯曲强度为345 MPa,1 800℃高温无氧环境弯曲强度可达424 MPa。C/SiC-HfC复合材料表现出更加优异高温力学性能是由于HfC组分的添加抑制了SiC晶粒的生长,降低了基体内部较大裂纹产生的概率。在1 650℃空气环境下,含有HfC的基体对纤维具有更佳保护作用,主要是由于HfC组分的添加使材料表面的SiC及时氧化成SiO_2,SiO_2在纤维和基体表面形成包覆层,防止了材料内部的进一步氧化。     

A novel method of utilizing static mixer to obtain mixing homogeneity of multi-species powders in laser metal deposition

Real-time mixing of multi-species powder challenges Laser Metal Deposition (LMD) of Functionally Graded Materials (FGMs). The current work proposes a novel method of using a static mixer to realize rapid, uniform multi-species powder mixing. Firstly, copper powder and 316L stainless steel powder are selected to complete the powder mixing observation experiment with Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). Secondly, computational fluid dynamics and particle mixing simulation models are used to analyze the flow field and particle motion characteristics in the static mixer. Finally, LMD experiment and metallographic observation are carried out with 316L stainless steel powder and WC powder to verify the feasibility of the static mixer. This study provides a theoretical and practical basis for powder mixing in laser processing with a static mixer. The conclusions can also be applied to other processing fields requiring real-time and uniform mixing of multi-species powders.     

Static magnetic field analysis of hollow-cup motor model and bow-shaped permanent magnet design

The hollow-cup Permanent Magnet (PM) motors have the characteristics of low power consumption, and are widely used in the aerospace field. At present, the tile-shaped PMs used by hollow-cup PM motors have poor sinusoidal characteristics of the air gap magnetic flux density waveform, which will cause torque ripple. The existing method for improving the air gap magnetic flux density waveform is not very effective when applied to hollow cup, a special motor with no stator core and large air gap. A bow-shaped PMs structure is designed for the hollow-cup motor in this paper. First, the equivalent surface current method is used to calculate the analytical formula of the static magnetic field of the model. Then, the Finite Element (FE) method is used to calculate the static air gap flux density waveform of conventional tile-shaped PMs and bow-shaped PMs with different bow heights, and the corresponding harmonics and sine distortion are obtained by Fourier decomposition. The simulation results show that the bow-shaped PMs can effectively improve the sinusoidal characteristics of the static air gap flux density waveform. And the suitable bow height is determined. Finally, a prototype is made based on the suitable bow height for experiments, and compared with the analytical result and the FE result, and the accuracy and effectiveness of the bow-shaped PMs with the suitable bow height are verified.     

铺层区域划分对大展弦比机翼静气动弹性影响

为了研究铺层区域变量对大展弦比机翼静气动弹性的影响，本文在考虑几何非线性影响下，依据有限元分析，研究了外翼段铺层区域的划分以及90°铺层角度的个数对大展弦比机翼静气动弹性特性的影响。结果表明，0°、±45°、90°混合铺层的铺设效果优于只有0°、±45°铺层的区域；机翼变形情况随着外翼段铺层区域的增大而减小，且减小斜率逐步增大；外翼段铺层区域固定时，增加90°铺层角度个数会有效减小机翼变形，且机翼变形情况与增加的个数基本呈现负相关关系，其个数在铺层设计中可能存在一个最佳取值或最优占比。