The precision machining of Ti-6Al-4V (TC4) micro-channels remains a challenge due to the poor surface integrity and limited tool life. Ultrasonic vibration-assisted grinding (UVAG) is a promising technique that is being employed to enhance the achieved quality of Ti-6Al-4V micro-channels. Taking the wheel’s wear and the springback of the workpiece into consideration, a new kinematic simulation model for the 3D surface generation process is first developed, and the material removal mechanism under different ultrasonic parameters during UVAG of Ti-6Al-4V is investigated based on the calculated grit-cutting trajectory and ground surface topography. Comparing the simulated and experimental results, it is found that the built surface topography prediction model can successfully capture the obtained surface characteristics of Ti-6Al-4V by CG and UVAG process. The condition for intermittent machining in UVAG is obtained by establishing the mathematical relation between grinding and ultrasonic parameters. Therefore, the model developed in this paper can be applied to predict surface roughness and optimize the UVAG process of Ti-6Al-4V.

Carbon fiber reinforced plastic (CFRP)/Ti6Al4V stacks are widely used in the aircraft industry, and drilling these stacks is essential during the assembly process. To solve the problem of high drilling temperatures in CFRP/ Ti6Al4V stacks, which lead to poor tool life and hole quality, the effects of three cooling strategies compose minimum quantity lubrication (MQL), water-based coolant, and internal air cooling, were investigated in this study. Tensile/compressive strength and fatigue-life tests were conducted to evaluate the applicability of the cooling medium before drilling. Then, low-frequency vibration-assisted drilling of CFRP/Ti6Al4V stacks was performed to investigate and analyze their machinability under the three cooling strategies by analyzing the drilling temperature, thrust force, tool wear, chip removal capacity, and hole quality. The results show that the selected cooling media, including Rhenus XT46 and Accu-Lube LB2000, are applicable in CFRP drilling, whereas the adopted media, compared with water, have little influence on the tensile/compressive strength and fatigue life of the CFRP. Compared with internal air cooling and MQL, water-based coolant can more effectively improve the machinability of CFRP/Ti6Al4V stacks, decreasing the CFRP drilling temperature by 41.6 % and 40.1 %, respectively, while the reductions in the Ti6Al4V drilling temperature are 76.7 % and 57.4 %, respectively. Meanwhile, under water-based coolants, the thrust force reductions in the drilling of CFRP are 13.1 % and 11.7 %, whereas those in the drilling of Ti6Al4V are 11.0 % and 7.8 %, respectively, compared with the internal air and MQL. In addition, under the water-based coolant condition, the tool wear rate is the slowest and the hole quality is the best among the three cooling strategies, whereas a high injection pressure further decreases the VBmax value. Furthermore, under the water-based coolant conditions, the Ti6Al4V exit burr height and CFRP exit delamination are the lowest. These findings provide useful insights into improving the machinability of CFRP/Ti6Al4V stacks in the aerospace industry, particularly for drilling that requires high-quality holes and a long tool life.

采用磨削和铣削(顺铣、逆铣)加工工艺获得不同表面粗糙度Sa的碳纤维增强树脂基(CFRP)复合材料试样并进行拉-拉疲劳试验,基于刚度退化模型分析了加工表面粗糙度对疲劳性能的影响.结果表明:磨削、顺铣和逆铣试样的Sa分别为1.2,3.2,5.9μm;磨削试样0°纤维铺层表面纤维缺失,存在空隙,铣削试样在45°纤维铺层表面存在较多凹坑,其中顺铣试样凹坑更多且更深;磨削试样的疲劳寿命最高,逆铣试样次之,顺铣试样最低;随着S a的增大,CFRP复合材料试样表面裂纹迅速萌生扩展,刚度退化初始阶段的退化速率升高,刚度退化I阶段更快结束,试样的疲劳寿命降低.

选用三维表面算术平均高度Sa表征CFRP的表面粗糙度,以磨削样件的拉伸和压缩强度为标准,研究CFRP多向层合板在不同铣削参数下所产生的加工表面粗糙度对力学性能退化的影响.结果表明:Sa对拉伸强度及压缩强度的影响不显著,Sa>15μm时拉伸强度退化量会增多,加工时温度过高会对CFRP基体造成损伤,进而影响压缩强度.

To solve the contradiction between high quality and high efficiency of CFRP machining surface, the quadratic regression models of 3D surface roughness Sa and surface damage layer depth Dd were established by using the response surface method, and the genetic algorithm was used for multi-objective optimization to obtain small Sa, Dd and maximum material removal rate VMRR. The results show that the regression models of Sa and Dd are explicit and reliable, and the feed speed vf has the most significant influence on Sa and Dd, followed by the grinding depth ap, the spindle speed n and the ultrasonic amplitude A. The results of response surface analysis show that the interactions of n and A, vf and ap, vf and A have significant effects on Sa. The interactions of n and A, vf and A, vf and ap, ap and A have significant effects on Dd. When the weight ratios of Sa, Dd and VMRR are 1/5, 1/5 and 3/5 respectively, compared with the central point results, the optimized Sa decreases by 11.01%, Dd decreases by 10.08%, and VMRR increases by 62.02%. The absolute values of the relative errors between the experimental and the predicted values of Sa and Dd under the optimized process parameters are 8.25% and 9.41% respectively, indicating that the prediction model has high accuracy and can be used for the optimization and prediction of the process parameters of CRFP ultrasonic vibration grinding.

为分析碳纤维增强树脂基复合材料(CFRP)/钛合金(TC4)叠层材料低频振动制孔工艺下刀具磨损状态,开展基于切削力信号的制孔刀具磨损状态研究.通过采集CFRP/TC4叠层材料低频振动制孔过程中的切削力信号,进行时域和频域分析,探讨各信号特征量与刀具磨损状态之间的联系.研究结果表明:CFRP/TC4叠层材料低频振动制孔轴向力信号的均值、标准差、方均根和峰度系数都与刀具磨损状态关系密切.轴向力信号频率主要集中在0 Hz、主轴旋转频率33 Hz及振动刀柄振动频率38 Hz处,且频率分布不会随着刀具的磨损而改变.

On the basis of combining the two concepts of digital coding metasurface and metasurface antenna, low radar cross-section (RCS) coding metasurface antenna array with dynamic scattering performances is presented in this paper. Extending scattering factor theory to coding metasurface antenna, by controlling the states of PIN diodes randomly, the scattering performances of coding metasurface antenna array can be tuned dynamically without degrading its radiation property. Based on phase cancellation principle, a 8 × 8 antenna array was finally simulated and fabricated. By comparing several different layouts, taking checkerboard layout, new chessboard layout, and “0101” square ring nested layout as examples, both monostatic and bistatic RCS of the antenna mentioned above can be reduced 10 dB or more in the frequency range of 9–10.5 GHz under the illumination of x-polarized incident wave. The measured data are consistent with the simulation data, which proves the effectiveness of the proposed method.

This paper presents a 2.5-dimensional switchable frequency selective surface based on the active device reed switch. This structure uses reed switches instead of PIN diodes to connect the upper and bottom metal patches on the basis of 2.5 dimensions. The structure can control the connection and disconnection of the reed inside the reed switch by controlling whether the external magnetic field is applied or not, thereby controlling the switching of the structural performance. When the external magnetic field is not applied, the internal reed remains disconnected. At this time, the structure has a pass band of 0-3GHz; when a certain strength of the external magnetic field is applied to connect the internal reeds, there will be a stop band ranging from 1.90 GHz to 2.12 GHz, and the center of the stop band is 2.028 GHz. In addition, the structure has good miniaturization performance, and the unit size is only 0.08 λ× 0.08 λ.

In this paper, the broadband near-field scattering characteristics of targets are analyzed. Plane wave and double-ridged horn antenna are used respectively in 13GHz for near-field scattering analysis. Time-domain response of scattering objects are investigated firstly, and the waveform and time-delay are presented. Furthermore, near-field scattering coefficient (NFSC) and Generalized RCS (GRCS) are also introduced to analyze the near-field scattering characteristics of objects. Finally, four time domain characterization parameters are designed to quantitatively analyze the time domain waveform of scattering objects.

碳纤维增强树脂基复合材料(Carbon fiber reinforced polymer,CFRP)是一种典型的难加工材料,其铣削加工存在表面质量差、表面形貌难以充分表征等问题,为解决该问题,开展了不同进给速度下的槽铣试验,研究了CFRP铣削表面形貌及其形成机理.结果表明,三维表面粗糙度较二维表面粗糙度能更加全面地反映CFRP铣削表面形貌,并选用了算术平均高度Sa、均方根高度Sq、偏斜度Ssk以及陡峭度Sku对CFRP表面形貌进行联合表征.随着进给速度的增大,三维表征参数中Sa、Sq逐渐增大,Ssk和Sku逐渐减小.为保证较好的加工表面质量,应选用顺铣的加工方式,且进给速度不大于1200mm/min.

在碳纤维增强树脂(CFRP)复合材料钻削过程中,随着刀具磨损量的累积,轴向力会逐渐增加,轴向力过大会导致CFRP复合材料一系列的加工缺陷.为实现在CFRP复合材料钻削过程中随刀具磨损量的累积轴向力变化的有限元分析及预测,建立了CFRP复合材料钻削仿真模型,通过对ABAQUS仿真软件二次开发,利用python语言开发子程序,将考虑磨损量累积的轴向力预测模型导入仿真软件,运用ABAQUS软件对CFRP复合材料钻削中轴向力进行研究,实现了随着刀具磨损量累积轴向力变化的预测功能.随后通过CFRP复合材料钻削试验,分析了轴向力随钻削孔数的变化规律,以验证轴向力的预测结果.结果 表明:3D钻削有限元模型能够良好地预测实际加工过程中刀具未磨损时轴向力的大小,其误差为9.10％;在考虑磨损量累积后,轴向力预测模型能够较准确地预测实际加工过程轴向力的大小,其最大误差不超过10％.

旋转整流器为同步发电机提供励磁,其可靠性十分重要.主要采用FPGA平台设计了一套故障监测系统,可以对发电机的整流器进行运行状态监测.实验采用三级式同步发电机进行了验证,结果表明,该系统具有较好的监测性能.

随着计算机技术发展和移动计算能力的提高,虚拟现实技术得到广泛应用.针对《计算机软件技术基础》理论课程和《计算机实践》实验课程要求,基于微软HoloLens全息智能眼镜和磁力驱动的力触觉交互模块,设计实现了视觉和力触觉融合的多模态虚拟现实实验系统,构建了符合课程教学要求的综合实验平台.基于这一综合实验平台,将计算机最新前沿技术引入课程教学,设计开发了综合性、创新性和开放性的实验项目,以此激发学生学习的积极性和主观能动性,巩固课程知识点,有效促进了学生计算机软件实践能力和创新能力的提高.

实验教学是提高大学生实践能力和创新精神的有效途径.该文以“电子技术”实验课程群为例,利用先进的信息技术和数据处理资源,构建一种过程反馈式实验课程教学新模式,通过实验教学的全过程、实时反馈,有利于持续提高实验教学质量和教学水平.

针对航空发动机整体叶盘结构复杂和材料难以加工的特性,在磁力研磨技术的基础上引入超声波作为辅助手段.磁性磨粒在磁场力和振动冲击产生的超声脉冲压力的复合作用下,加大了对叶盘表面纹理的去除.结果显示:加工前叶盘表面粗糙度值为Ra 1.38μm,单纯磁力研磨后表面粗糙度值降至Ra 0.52μm,超声波辅助磁力研磨后表面粗糙度值降至Ra 0.18μm.通过电镜观测叶盘表面形貌,纹理基本去除,表面更加细密、均匀.

《普通高中物理课程标准(2017年版)》第6部分"实施建议"中提出"要从培养物理学科核心素养的视角审视教学的目的 ,应通过习题教学,使学生在科学思维、探究能力、实践意识、科学态度等方面得到有效提升.习题教学的作用不仅仅是为了得到答案,而是要全面提高学生的问题解决能力.[1]"在物理习题教学过程中引导学生进行正确的问题表征,对提高学生的问题解决能力具有重要的促进意义.

In this paper, a circularly polarized microstrip antenna loaded with a polarization conversion metasurface(PCM) is presented , whose unit cell is composed of a double-head arrow-shaped metal film mounted on the single side of a FR-4 substrate. The radiating element of the antenna is a modified T-shaped metal patch. Simulated results indicate that with the proposed structure, the microstrip antenna can operate over a 10.7 GHz to 17 GHz range with a return loss less than -10 dB, while exhibit a 3-dB axial ratio bandwidth of 0.4 GHz from 11.4 GHz to 11.8 GHz and from 12.6 GHz to 13 GHz respectively. The gain across the circular polarization band ranges from 4.9 to 5.2 dB.

为了提高钛合金TC4表面质量,采用超声辅助磁粒研磨技术对TC4平面进行光整试验研究,研究了磁极开槽宽度与深度在不同比例下的磁场强度大小,及不同超声波振动幅度和磨粒粒径条件下对TC4表面粗糙度值的影响.结果表明:在磁极开槽宽度与深度比为1:1,超声波振动幅度为10μm,磨粒粒径为200μm时,研磨加工60 min,钛合金TC4平面研磨前后的表面粗糙度值Ra由原始3.00μm下降到0.12μm,表面纹理去除,形貌得到明显改善,TC4平板表面材料力学属性加强,表面摩擦系数降低.

姿态解算是四旋翼飞行器的关键技术,其精度直接影响飞行器控制的可靠性和稳定性.针对当前常用一阶互补滤波算法中阻带衰减速率慢和陀螺仪常值漂移产生的稳态误差问题,通过增加积分环节,设计了一种基于四元数的二阶互补滤波算法,能更好地利用加速度计和磁力计的稳态信息有效补偿陀螺仪常值漂移,从而减少姿态解算的累积误差.仿真结果表明,该算法具有更好的稳定性,提高了系统的姿态解算精度.通过飞行器真实飞行数据对算法进行了实验验证,结果显示姿态的俯仰角、横滚角精度<1°,偏航角精度<2°,能很好地满足飞行器控制系统对姿态解算的精度要求.

该试验研究为提高玉石材料表面加工质量和加工效率,去除工件表面微裂纹、褶皱、划痕,提出旋转超声辅助磁力研磨加工技术对玉石表面进行光整加工的方法.对比了普通研磨和旋转超声辅助磁力研磨加工后玉石表面质量,分析了超声波频率、磁性研磨头直径和主轴转速对加工质量的影响效果.试验结果表明:当主轴转速1500r/min、研磨头直径为30mm,采用19 kHz高频振动频率对玉石表面研磨30min时,玉石表面研磨的表面粗糙度及表面形貌效果最好,玉石表面粗糙度从0.89μm降至0.13μm,有效的提高了玉石表面质量.