Effect of ultrasonic vibration on finished quality in ultrasonic vibration assisted micromilling of Inconel718

Inconel718 was machined with the traditional micromilling (TMM) and ultrasonic vibration assisted micromilling (UVAMM) with the different technology parameters, whose surface quality and burrs formation were studied. The results show that TMM often forms pits, bumps and gullies in the size effect range. UVAMM effectively improves the surface quality compared with TMM. The surface defects are significantly reduced with the increase of feed per tooth (ƒ_z). When ƒ_z exceeds 4 μm, the effect of ultrasonic vibration on the surface quality is no longer obvious. The minimum burr size on the down milling side and the up milling side are 50.23 μm and 36.57 μm, respectively. The feasibility of vibration cutting in improving surface quality and suppressing burr size was verified. UVAMM effectively suppresses the formation of built-up edge, which can significantly improve the micromilling process. The cutting force is obtained through simulation and experiment. They are agreement in the change trend. The finite element simulation can be used to predict the cutting force. Compared with TMM, feeding force (F_x), radial force (F_y) and axial force (F_z) of UVAMM decrease by 7.6%, 11.5% and 1.3%, respectively.     

Thermomechanical coupling effect on characteristics of oxide film during ultrasonic vibration-assisted ELID grinding ZTA ceramics

Ultrasonic vibration-assisted ELID (UVA-ELID) grinding is utilized as a novel and highly efficient processing method for hard and brittle materials such as ceramics. In this study, the UVA-ELID grinding ZTA ceramics is employed to investigate the influence of thermomechanical loading on the characteristics of oxide film. Based on the fracture mechanics of material, the model of internal stress for oxide film damage is proposed. The thermomechanical loading is composed of mechanical force and the thermal stress generating from grinding temperature. The theoretical model is established for the mechanical force, thermal stress and internal stress respectively. Then the finite element analysis method is used to simulate the theoretical model. The mechanical force and grinding temperature is measured during the actual grinding test. During the grinding process, the effect of grinding wheel speed and grinding depth on the thermomechanical force and the characteristics of oxide film is analyzed. Compared with the conventional ELID (C-ELID) grinding, the mechanical force decreased by 25.6% and 22.4% with the increase of grinding wheel speed and grinding depth respectively, and the grinding temperature declined by 10.7% and 12.8% during the UVA-ELID grinding. The thermal stress in the latter decreased by 16.3% and 20.8% respectively, and internal stress reduced by 12.3% and 15.6%. It was experimentally found that the topographies of oxide layer on the surface of the wheel and the machined surface in the latter was better than that in the former. The results indicate that the action of ultrasonic vibration establish a significant effect on the processing. Subsequently, it should be well considered for future reference when processing the ZTA ceramics.     

质子辐射带辐射中心区域模型

利用AP-8和CRRESPRO质子辐射带模式数据库, 比较了二者在磁赤道面上计算结果 的差异并给出其差异原因. 利用AP-8模式数据库数据, 建立起质子辐射带函数形式的辐射中心区域模式, 包括各能道全向微分通量峰值所对应的L值(L_c) 随能量E的变化模式以及各能道全向微分通量峰值J_max随能量E的变化模式. 利用RBSP A卫星REPT望远镜在磁赤道面上的高能质子观测数据, 分别与 AP-8模式、CRRESPRO模式及本文所得辐射中心区域模式计算结果进行比较, 发现在78.9, 102.6和208MeV三个能道上, RBSP A卫星观测所得各能道全向微分 通量明显偏大, 而L_c与AP-8或本文辐射中心模式所得结果基本一致; RBSP A卫星也观测到CRRESPRO Quiet模式所得的隐性第二质子辐射带结构.      

气隙构型对高频交流SDBD防除冰激励器的温升影响

等离子体激励具有电离效应、气动效应和热效应,可被用于飞行器防除冰。背面电极的气隙构型对于交流供电的沿面介质阻挡放电（SDBD）防除冰激励器的单周期放电次数和放电电荷分布均有影响,电源频率也为影响激励器温升的重要因素。目前对于交流SDBD温升效果的研究均是基于背面电极无气隙的构型,且缺乏激励频率大于15 kHz的高频条件。为此制作了背面电极有气隙和无气隙的对照构型,在35~55 kHz的高频范围内,采用电学特性、红外测温、放电形态相结合的方式研究了交流SDBD防除冰激励器温升特性。结果表明：施加相同的电压或频率时,背面电极有气隙构型的SDBD激励器的裸露正面最高温度相比无气隙构型激励器可提高至151.51%;背面电极气隙的存在也可以使激励器正面尤其是正面等离子放电反方向的温升区域扩大;增加频率使交流SDBD激励器的温度非线性提高,有助于降低高压击穿风险。     

直升机红外辐射的理论计算

选取了适当的理论计算方法,给出了计算公式和计算步骤,进而在所假设的飞行状态下计算了直升机的红外辐射,包括直升机发动机的排气管辐射和直升机蒙皮辐射的全辐射量和红外波段辐射量,最后对计算结果进行了分析。从分析来看,计算结果是可信的。     

Zernike多项式在拟合光学表面面形中的应用及仿真

光学镜面在重力的作用下,会产生镜面变形,这种变形包括刚体位移和表面变形,将对光学系统的成像品质产生不同的影响。文章通过Matlab软件,对有限元分析后的数据进行处理,用Zernike多项式精确拟合变形后的镜面面形,并在Matlab中绘出镜面面形云图,最后计算出表面变形的表面变形均方根和表面变形最大值与最小值之差。实例计算表明,该方法能将镜面变形的刚体位移和表面变形分离,适合于光学自由曲面的镜面面形精度分析。     

辐射式热流测量系统及其应用

根据某型号发动机进行的地面模拟热真空环境试验要求,建立了热真空环境模拟系统,在分析热流测量原理的基础上,应用一套辐射式热流测量系统对试验时发动机周围的热流进行测量.着重介绍系统组成及工作原理,热流测量传感器的标定方法.通过热辐射装置热流分布的计算和实际测量结果对比,验证了热流测量系统获取数据真实.     

航天器充放电在轨探测试验的发展

介绍了航天器充放电中表面充电和深层介质充电的产生原因，以及充放电试验的发展。分析了国外瞬态脉冲监测仪（TPM）、充电电气效应分析仪（CEEA）、IDM装置、PASP Plus试验、集约环境异常传感器（CEASE）、DDE试验，以厦悬浮电位探测单元（FPMU）等充放电试验的原理厦其试验结果。最后，根据国外的经验和发展趋势，对国内航天器充放电在轨测试的目的、发展步骤，以及与各种空间物理量的关系等提出了相应的建议。     

航天器单粒子效应的防护研究

随着航天电子器件集成度的不断提高,其发生单粒子效应的风险越来越高,已经成为影响航天器可靠性和运行寿命的重要因素。文章首先介绍了单粒子效应的发生机理、研究方法和研究成果,在此基础上对现有的各种抗单粒子效应加固技术进行了总结,按照硬件加固技术、软件加固技术和轨道优化设计的思路较为系统地论述了单粒子效应的防护手段。     

低重力环境下三维液体非线性晃动的数值模拟

本文讨论低重力环境下三维液体非线性晃动问题。采用ＡＬＥ（任意的拉格朗日－欧拉）运动学描述跟踪自由液面；对于ＡＬＥ描述的Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程，在时间域上采用分步离散方法中的速度修正格式进行数值离散，在空间域上利用有限元方法进行了数值离散；推导了考虑表面引力效应时有限元边界条件的弱积分形式；给出了表面张力的数值计算公式。模拟了考虑表面张力情况下圆筒型贮腔中液体的非线性晃动，并得到了贮腔壁面处