M46J高模量碳纤维预浸QY8911纤维束性能研究

以航空发动机应用为背景，研究了M46J／QY8911缠绕复合材料的预浸纱制备方法及性能，根据M46J特性，对现有的GB3326中纤维束力学性能测试试样的加强方式进行了改进，制作了M46J浸渍QY8911树脂的纤维束试样并测试其力学性能，同时与M46J浸渍环氧树脂的纤维束的力学性能进行比较，研究表明，不同树脂特性，不同固化工艺以及制造中所施加的张力都会影响到纤维束的纤维利用率。     

基于电饱和模型的裂纹端部应力场分析

在非线性电弹性理论构架内,采用电饱和条带模型和复变函数方法,探讨了远场均匀载荷作用下无限大压电介质中裂尖附近的应力场,主要关注裂尖附近的应力场。所得解表明,裂尖附近任意一点处的各规格化应力分量均仅由这一点的角度决定,而与该点到坐标原点的距离无关。最后,基于PZT-5H的数值结果对其裂尖附近各面内的应力分量进行了分析,与相关研究结果比较,本文方法得到的解是有效的。     

喷丸强化10Ni3MnCuAl钢的表面性能

对10Ni3MnCuAl钢磨削表面进行不同强度的喷丸强化处理,分析了喷丸强化后10Ni3MnCuAl钢的金相组织及喷丸表层下微观结构的变化,测量了喷丸影响层的显微硬度以及喷丸强化所形成的残余压应力场, 研究了喷丸所造成显微硬度、金相组织和表面残余应力等表面完整变化.结果表明, 喷丸强化可显著改善10Ni3MnCuAl钢表面完整性及其疲劳寿命. 喷丸强度高时将产生过喷效应,导致疲劳寿命的降低,实验测得最佳喷丸强化弧高值为0.40 mm时表面质量最好,喷丸影响层的残余应力深度达450 μm.     

微粒对放电通道生长的影响机理研究

 混粉电火花加工相对于普通电火花加工能够在小脉冲能量下稳定地进行加工并实现较好的加工质量,是因为悬浮在工作液中的微粒改变了放电通道形成的机制。分析了粉末颗粒对放电间隙电场、放电通道轨迹形成的影响,得出了混粉电火花加工放电过程稳定性提高的重要原因,即悬浮的微粒以及微粒之间的作用增大局部电场强度、改变放电通道的生长模式,从而减少击穿时间和能量消耗,因此在加工稳定性和加工质量上有明显提高。     

Microstructure and Optical Characterization of Magnetron Sputtered NbN Thin Films

Some fundamental studies on the preparation, structure and optical properties of NbN films were carried out. NbN thin films were deposited by DC reactive magnetron sputtering at different N2 partial pressures and different substrate temperatures ranging from –50 ℃ to 600 ℃. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) were employed to characterize their phase com- ponents, microstructures, grain sizes and surface morphology. Optical properties inclusive of refractive indexes, extinction coefficients and transmittance of the NbN films under different sputtering conditions were measured. With the increase in the N2 partial pressure, δ-NbN phase structure gets forming and the grain size and lattice constant of the cubic NbN increasing. The deposited NbN film has relatively high values of refractive index and extinction coefficient in the wavelength ranging from 240 nm to 830 nm. Substrate tem- perature exerts notable influences on the microstructure and optical transmittance of the NbN films. The grain sizes of the δ-NbN film remarkably increase with the rise of the substrate temperature, while the transmittance of the films with the same thickness decreases. Ultra-fine granular film with particle size of several nanometers forms when the substrate is cooled to –50 ℃, and a remarkable aug- mentation of transmittance could be noticed under so low a temperature.     

Microstructure and Martensitic Transformation Behaviors of Explosively Welded NiTi/NiTi Laminates

The study is a first attempt to prepare bulk NiTi/NiTi shape memory alloy (SMA) laminates with a macroscopic heterogeneous composition by explosive welding and investigate their microstructures and martensitic transformation behaviors. After explosive weld- ing, a perfect interfacial bonding between the two components and a reversible martensitic transformation are realized in the tandem. Results show achievement of a fine granular structure and the maximum value of microhardness near the welding interface because of the excessive cold plastic deformation and the high impact velocity during the explosive welding. Meanwhile, the effects of aging on the transformation of the welded tandem are investigated by differential scanning calorimeter (DSC) and subject to discussion. The trans- formation temperatures of NiTi/NiTi SMAs increase with the rise of the aging temperature. The experimental results indicate the shape memory properties of NiTi/NiTi SMA fabricated by explosive welding can be improved by optimizing the aging technology.     

Analytical solutions for Earth discontinuous coverage of satellite constellation with repeating ground tracks

This paper presents an analytical model for calculating the Earth discontinuous coverage of satellite constellation with repeating ground tracks by integrating and extending the application of coverage region and route theory. Specifically, the visibility condition for a ground point is represented as a coverage region in the two-dimension map of visibility properties, and the trajectories of satellites with circular orbits and repeating ground tracks are converted to several inclined lines in t...     

高速走丝电火花线切割表面条纹的成因研究

分析了高速走丝电火花线切割加工时可通过电极丝空间位置稳定性的改善及选用具有良好洗涤能力的工作介质进行条纹消除的机理.并研究指出在大能量切割时,选用复合工作液以喷射的方式进行冷却,可以大大提高极间的洗涤性能,达到消除表面烧伤纹的目的.     

新型双凸极发电机数字控制原理与实现

电励磁双凸极电机是一种新型交流无刷电机,它具有结构简单、可靠性高、维修方便等优点,用作发电机具有调压控制简单、可故障灭磁等优点。文中首先介绍了电励磁双凸极发电机系统的控制原理,并分析了发电系统的控制规律。为优化控制P I参数,提高系统的动稳态性能,通过M atlab仿真获得根据输出电压与给定电压的偏差的变P I参数组合,并经试验优化该P I参数组合。然后,通过硬件构成与软件设计两方面介绍了基于DSP控制的电励磁双凸极发电机系统的设计方法。最后,以一台30 kW发电机为例,设计了一套数字调压器,并进行了系统试验。实验结果表明,电励磁双凸极发电系统采用变P I参数的控制方法具有良好的动稳态特性。     

血液及血液替代流体流变特性实验研究

发现和寻找一种透明的、流变特性与血液流体特性很好匹配的血液替代流体进行实验研究是非常迫切和必要的.运用美国brook 公司生产的 PVS Rheometer型旋流变仪对黄原胶溶液流变特性实验发现,黄原胶溶液是一种典型的剪切稀化流体,其剪切应力和剪切速率符合幂律分布;黄原胶溶液浓度越高,其剪切稀化特性越强;黄原胶溶液的表观粘度与溶液温度成反比,与溶液浓度成正比;人体血液的表观粘度介于0.4‰的黄原胶溶液(重量百分比)在温度为20℃和37℃之间的粘度值,在剪切速率介于10s-1~500s-1范围内,人体血液表观粘度随剪切速率的变化过程和0.4‰黄原胶溶液(温度30℃)基本重合.