Ultrasonic vibration-assisted laser engineering net shaping of ZrO2-Al2O3 bulk parts: Effects on crack suppression,microstructure, and mechanical properties

Laser additive manufactured zirconia-alumina ceramic (ZrO₂-Al₂O₃) parts demonstrate severe problems resulting from cracking and inhomogeneous material dispersion. To reduce these problems, we propose a novel ultrasonic vibration-assisted laser engineered net shaping (LENS) process for fabrication of bulk ZrO₂-Al₂O₃ parts. Results showed that the initiation of cracks and the crack propagation were suppressed in the parts fabricated by LENS process with ultrasonic vibration. For the parts fabricated without ultrasonic vibration, the sizes of cracks decreased with the increase of laser power. Scanning electron microscope analyses proved that the introduction of ultrasonic vibration was beneficial for grain refinement and uniform material dispersion. Due to the suppressed cracking, refined grains, and homogenized material dispersion, the parts fabricated with ultrasonic vibration demonstrated better mechanical properties (including higher microhardness, higher wear resistance, and better compressive properties), compared with the parts fabricated without ultrasonic vibration.     

Optical and thermo-mechanical properties of fine-grained transparent yttria ceramics fabricated by hot-press sintering for infrared window applications

In this work, highly transparent yttria ceramics Φ?=?55?mm in size were fabricated by a hot-pressing method with 1 at.% ZrO₂ or 12 at.% La₂O₃ as a sintering additive. For a 4-mm-thick specimen doped with ZrO₂, the in-line transmittance reaches 71.1% at 400?nm and 80.9% at 1100?nm, and the transmittance of the La₂O₃-doped specimen is comparable to that of the ZrO₂-doped specimen. By means of the relatively low sintering temperature of 1600?°C, the present samples exhibited very fine microstructures (<2?μm), giving rise to excellent mechanical strength levels (～200?MPa). With regard to the 1 at.% ZrO₂-doped specimen, the combination of high strength and high thermal conductivity (～10 W/m?K) substantially improved parameters related to the thermal shock resistance. The results of this study indicate that the hot-pressed transparent yttria ceramic doped with 1 at.% ZrO₂ is optically, mechanically, and thermally suitable for high-temperature IR window applications.     

障板上矩形薄板在浅水环境中的振动及声辐射解析分析

通过推导得到浅水环境中矩形板声辐射阻抗矩阵的解析表达,进一步结合振动假设模态方法及辐射表面单元辐射器思想求解浅水环境中矩形板的振动响应,分析水深对矩形板模态附加质量的影响,给出矩形板模态附加质量随水深的变化情况,得到波导模态的激发对附加质量的影响,并通过对辐射抗矩阵的特征分析得到附加质量在板上分布的主要模式;进一步结合声辐射模态辐射效率,分析水深变化对矩形板振动响应峰值及远场声辐射的影响,分析结果表明:水深度变化对振动响应峰值及声辐射功率的影响与第1阶声辐射模态的辐射效率随深度的变化具有一致性。     

某轻型载货车储气罐支架振动断裂分析与优化

为了有效解决某轻型载货车储气罐支架的断裂故障,首先基于建立的储气罐支架有限元模型进行振动特性分析,分析结果表明其前三阶固有频率接均处于发动机激励频率范围之外,不会产生共振。其次测试各种道路的时域载荷,测试结果表明其中角度搓板路的激励频率与储气罐支架第一阶固有频率相接近,从而引起共振,不满足振动特性要求。然后对其进行振动强度分析,分析结果表明其应力水平不达标,其最大应力点与开裂处一致。再对其进行振动疲劳寿命预测分析,分析结果表明其疲劳寿命也不达标,其危险点也与失效位置相同。再采用集成平台对储气罐支架的结构进行优化设计,优化之后其模态频率、振动强度和振动疲劳均符合性能要求,并且其重量也有所减轻,总体优化效果较佳。最后整车试验结果表明优化之后储气罐支架的振动大幅度降低,并且没有发生失效。     

基于混沌理论的弧形闸门支臂振动特性

为了研究弧形闸门支臂的振动问题,采用混沌理论对时间序列进行处理,确定延迟时间τ、嵌入维数m进行相空间重构,并计算时间序列的混沌特征值,进而研究弧形闸门在启闭过程中振动的复杂性。以某水电站弧形闸门支臂振动为研究对象,根据支臂振动加速度原型观测资料,分析不同开度的振动情况,发现启门振动的复杂程度高于闭门工况,小开度的振动复杂程度更高,且支臂振动的复杂程度为与面板连接位置最大,与闸墩连接位置最小,中间位置介于前两者之间。为弧形闸门短期振动预测提供了支持。     

严重突出煤层穿层钻孔“钻冲筛运”一体化瓦斯治理技术研究与应用

鹤煤公司八矿地质构造复杂、断层褶曲发育,尤其井田深部断层多,并且煤层透气性低且松软,打钻塌孔、喷孔严重,瓦斯抽放效果不好,给煤炭开采和瓦斯综合治理带来了困难。针对鹤煤公司八矿穿层钻孔瓦斯治理技术措施进行井下现场探索与研究,通过在3205底抽巷经过多次技术方案论证、实践,摸索出一套钻冲筛运一体化整套技术流程,并分析高压水力冲孔瓦斯涌出特征、有效影响半径。通过采用高压水力冲孔、振动筛选、转载装运,提高了水力冲孔效果和效率,改善了工作环境。     

一种振动矢量测量及调整的方法

针对消失模生产中振实设备的振动过程不满足工艺要求的情况下会产生的问题,详细阐述了基于消失模振实、紧实过程的测量方法和评价方法,通过使用该种方法可以得出振动矢量和振幅,进而对振实紧实设备和振动紧实工艺进行调整和优化,杜绝干砂振动紧实过程中的各种问题,保证铸件质量。可以普遍应用在干砂振实设备研发、校检、定期维护等各个过程,可以有效提升设备的工艺符合性,减少模样及铸件不合格品的产生。     

基于NI-PXIe的矿用通风机滚动轴承振动信号采集系统设计

针对矿用通风机滚动轴承振动信号部件采集需求,设计了一种基于LabVIEW软件以及NI-PXIe硬件的振动信号采集系统。系统硬件部分由PXIe1082机箱以及PXIe4492数据采集卡组成。以LabVIEW为开发软件完成了系统软件部分的设计。利用该系统进行了轴承振动信号采集试验,试验结果表明,系统能够稳定、高效地对轴承振动信号进行采集,具有一定的实用价值。     

Experimental research on the MRR of ultrasonic vibration aided electric discharge milling of ceramic materials using deionized water as processing medium

Abstract

Electric Discharge Milling Machining (EDMM) simplifies the electrode manufacturing process and reduces the cost. However, the introducing of new parameters, such as the three-dimensional motion and the electrode rotation speed, results in a periodic change of control state that can reduce the control performance and processing efficiency. In this work, ultrasonic vibration of tool electrode was used to improve the processing efficiency of ceramic materials. The effect of ultrasonic vibration on the EDMM process was analyzed by comparing the experimental findings. The results have shown that the ultrasonic vibration can improve the material removal rate, and a treble processing efficiency was achieved. The effect of processing parameters on the material removal rate, such as the open voltage, the peak current, the pulse during time and the pulse off time, was analyzed. When aided with the ultrasonic vibration, the best processing efficiency was achieved at 220?V for the open voltage, 10?A for the peak current and 15?μs for both the pulse during time and pulse off time.     

基于Romax行星齿轮传动振动特性仿真分析

以某行星齿轮传动为研究对象,分析行星齿轮传动原理;建立行星齿轮三维模型,导入仿真软件Romax对行星齿轮传动模态、固定内齿圈振动加速度、振动速度等振动特性进行仿真分析。仿真结果表明:行星齿轮传动不同阶数下的振动频率、振型和振动总位移不同;行星齿轮传动固定内齿圈的振动加速度、振动速度都呈现在某一均值波动的情况。该研究为避免行星齿轮传动发生共振、减小振动噪声及增加疲劳寿命提供理论依据。