Investigation of fatigue crack initiation facets in Ti‐6Al‐4V using focused ion beam milling and electron backscatter diffraction

In the very high cycle fatigue regime, internal crack initiation can occur in Ti‐6Al‐4V because of the formation of facets, which are α grains that have fractured in a transcrystalline and planar manner. Because this crack initiation phase occupies most of the fatigue life, it is essential to understand which mechanisms lead to facet formation. Fatigue tests have been performed on drawn and heat‐treated Ti‐6Al‐4V wires, and the facets at internal crack initiation sites have been analysed in detail in terms of their appearance, their spatial orientation and their crystallographic orientation. The facets were not smooth, but showed surface markings at the nanoscale. In nearly all cases, these markings followed a linear pattern. One anomalous facet, in a sample with the largest grain size, contained a fan‐shaped pattern. The facets were at relatively steep angles, mostly between 50° and 70°. Cross‐sections of the fracture surfaces have been made by focused ion beam milling and were used to measure the crystallographic orientation of facets by electron backscatter diffraction. Most facet planes coincided with a prismatic lattice plane, and the linear markings were parallel to the prismatic slip direction, which is a strong indication that prismatic slip and slip band formation led to crack initiation. However, the anomalous facet had a near‐basal orientation, which points to a possible cleavage mechanism. The cross‐sections also exposed secondary cracks, which had formed on prismatic lattice planes, and in some cases early stage facet formation and short crack growth phenomena. The latter observations show that facets can extend through more than one grain, and that there is crack coalescence between facets. The fact that drawn wires have a specific crystallographic texture has led to a different facet formation behaviour compared to what has been suggested in the literature.     

甚低频矢量水听器水池校准方法研究

为研究水池条件下甚低频矢量水听器的校准方法,利用水池声场理论建模仿真的方法研究了声源位置、水池尺寸等因素改变时近源声场的变化规律.研究表明:在连续信号激励条件下,近源声场分布呈准球面波扩展规律,满足甚低频矢量水听器的校准需求.进而详细阐述了校准方法并仿真评估了标准水听器和待测甚低频矢量水听器所在位置的声场对校准结果的影...     

弯曲元试验高精度测试土样剪切波速方法

在HX-100型多功能三轴仪上开发了压电陶瓷弯曲元剪切波速测试系统,研究了高精度测试不同种类和刚度土样剪切波速的方法以及剪切波速弥散性问题,并将弯曲元测试结果与DrnevichLong-Tor型共振柱试验结果进行了对比。研究结果表明,对不同种类和刚度的土样,通过选用合适的激发波形和频率就可以消除接收波形的近场效应和过冲现象,高精度地确定土样剪切波速和极小应变剪切模量;在所使用的激发频率范围内,剪切波速不具弥散性。     

750kV GIS用变压器端部的快速暂态过电压的研究

GIS内开关操作产生的快速暂态过电压(VFTO)对系统的变压器构成了很大的威胁,对于超高压GIS更是如此。参考多个GIS变电站,建立了750kVGIS系统,并确定了断路器、隔离开关、接地开关及电抗器的计算模型可简化为等值对地电容或入口电容,其参数分别为276pF、240pF、240pF和5000pF。利用EMTP计算了不同操作过程在变压器端部出现的VFTO。分析了系统运行方式、开关操作顺序、变压器入口电容以及变压器与GIS的连接方式对变压器端部VFTO的影响。研究了断路器、隔离开关的并联电阻以及MOA对变压器的保护效果。     

面向密集部署的超高吞吐率Wi-Fi融合应用技术

为了降低网络密集部署对超高吞吐率( VHT) Wi-Fi性能的影响,提出了VHT Wi-Fi基于软件定义网络( SDN)的网络架构、无线网络侧虚拟化和增强型认证与快速切换技术,以提高系统的共存性、抗干扰性和安全性。实验结果表明,VHT Wi-Fi与SDN、网络功能虚拟化、伽罗瓦/计数模式协议结合,吞吐率性能获得约10%的提升,在保证安全性同时平均切换时延降低至40 ms,可保障VHT Wi-Fi在密集部署网络中发挥重要作用。     

矿山特大型采空区全尾砂充填封闭工程实践

为了解决采空区安全隐患，同时为矿山生产中大量的尾砂寻找堆存场地，经充分论证，利用全尾砂对采空区进行充填处理.井下采空区的封闭是实施全尾砂充填的必要条件之一，本文简述了井下采空区全尾砂充填封闭工程封闭墙位置的选择、墙体结构型式与厚度的确定及施工过程和实施效果等。     

一种限制GIS暂态地电位升高的措施

用EMTP程序对用不同的氧化锌避雷器限制GIS内快速暂态过电压的效果进行了计算,并给出了快速暂态过电压与暂态地电位升高的简单算式。同时对某GIS的隔离开关操作引起的暂态地电位升高数值进行了现场测量。提出了用氧化锌避雷器阀片限制GIS暂态地电位升高的措施。     

VHF-PECVD制备微晶硅材料及电池

采用VHF-PECVD技术制备了不同功率系列的微晶硅薄膜和电池,测试结果表明：制备的适用于微晶硅电池的有源层材料的暗电导和光敏性都在电池要求的参数范围内．低功率或高功率条件下,电池从n和p方向的喇曼测试结果是不同的,在晶化率方面材料和电池也有很大的差别,把相应的材料应用于电池上时,这一点很重要．采用VHFPECVD技术制备的微晶硅电池效率为5%,Voc=0.45V,Jsc=22mA/cm2,FF=50%,Area=0.253cm2．     

弱硼掺杂补偿对氢化微晶硅薄膜制备与特性的影响

研究了弱硼掺杂补偿对甚高频等离子体增强化学气相沉积方法生长氢化微晶硅薄膜（μc-Si∶H）及材料特性的影响.实验发现,随着弱硼补偿剂量的增大,μc-Si∶H薄膜的沉积速率先减小后增加,变化范围约为0.7～0.8nm/s.相比较而言,材料的结晶度以及晶粒的平均颗粒尺寸则呈现出先增后减的变化,且变化的幅度较大,当弱硼补偿剂量大于2.5ppm时,过度的弱硼补偿将导致μc-Si∶H薄膜的结晶状况恶化.此外,光敏性、暗电导及电导激活能的测量结果进一步表明,弱硼补偿显著影响μc-Si∶H薄膜的光电特性,弱硼补偿剂量为2.5ppm左右时,材料的光电特性最为理想.因此,优化弱硼补偿剂量是获得器件级质量μc-Si∶H材料的有效途径.