喷雾共沉积石墨增强锌基复合材料的低频内耗

 在ZA27合金中添加50mg.g-1Si并采用喷雾共沉积技术制备了石墨颗粒体积分数分别为5%,10%,15%的锌基复合材料。采用多功能内耗仪对材料的低频内耗（1Hz,4Hz）行为进行了测量。结果发现,复合材料的内耗值大小与温度显着相关,较低温度时复合材料的内耗值低于喷雾沉积材料;随着温度的上升,40℃以后高于喷雾沉积材料;同时随石墨颗粒体积分数的增加,复合材料的内耗值逐步提高且不同频率条件下内耗相等时所对应的温度值线性上升。分析了石墨复合前后材料的主要内耗机制。     

对直升机增速齿轮传动中大齿轮齿根弯曲疲劳应力计算的研究

作者系统地研究了影响直升机增速齿轮传动中大齿轮齿根弯曲疲劳应力的诸因素,并推导出包括齿间滑动摩擦力在内的实际外载荷作用下大齿轮齿根弯曲疲劳应力计算公式。研究表明,齿间摩擦力对大齿根弯曲疲劳强度的影响不可忽视。     

电场影响铁磁流体摩擦系数的试验研究

通过试验研究了处于边界润滑状态下钢-钢摩擦副在铁磁流体及加有添加剂的铁磁流体中的摩擦特性,特别是在电场作用下摩擦系数的变化情况.在销-盘试验机上进行的试验表明:加有添加剂的铁磁流体在不同方向的直流电流作用下,其摩擦系数变化的幅度最大可达到23％.因此得到了一种在边界润滑状态下摩擦系数可控的新型润滑介质.这样就可能通过外加电场的手段实现摩擦系数的主动控制,达到减摩、节能的目的.      

TiAl金属间化合物与42CrMo"三体"摩擦焊接头的热机械处理

在对"三体"摩擦焊热机械处理(TMP)的作用原理进行理论分析的基础上,研究了接头的组织变化和动态再结晶规律,从而形成了以摩擦焊热力耦合与焊后热处理制度复合的TMP模式。     

高强度镶嵌自润滑材料的设计及摩擦实验

铜基镶嵌型自润滑轴承的承栽压强大约为50MPa,难以满足重型工程机械对自润滑轴承的要求。本项研究利用赫兹接触理论及摩擦的粘着理论,导出了摩擦因数随栽荷变化的定量关系,提出了以轴承钢代替传统镶嵌型复合材料的铜合金的设计方案,研制出新型轴承钢／聚四氟乙烯镶嵌型复合材料。摩擦实验结果表明,这种新型复合材料的承栽压强可达到90MPa,摩擦因数低于0．15,能够满足苛刻工况条件下工程机械对重栽自润滑轴承的要求。     

基于CMAC的伺服系统控制研究

针对高精度伺服系统中存在的非线性和各种不确定性因素,提出了基于小脑模型神经网络的复合控制方法,控制器由前馈控制器、比例微分控制器(PD)和小脑模型神经网络控制器(CMAC)构成,该方法在传统的PD+前馈控制方法上加入了CMAC神经网络算法的快速学习,精确逼近的优点,既保证了快速实时跟踪,又进一步提高了跟踪精度。实验结果证明,用CMAC控制方法后系统的跟踪精度比PD＋前馈控制方法提高近一个数量级,同时该方法对摩擦引起的波形畸变有很好的抑制作用,仿真和实验研究表明了该方法的可行性和有效性,并能满足实时性要求,对提高伺服系统的高精度动态跟踪性能有很好的工程参考价值。     

黏性对高压空气弹射装置内弹道性能的影响

针对高压空气弹射装置中,气体黏性流动造成的内耗散和沿程损失对内弹道性能的影响,结合高压下空气黏度公式,重点考虑低压室内的黏性流动,得到了未充分发展黏性流体在非定常状态下的能量损失计算方法。基于高压空气真实气体效应分析,建立了考虑气体摩擦的高压空气弹射内弹道数学模型,进行了数值求解。对比结果表明:气体摩擦效应对快速、瞬时过程造成的干扰量较小,对象宏观特性变化不大,低精度系统中可忽略不计。通过对结果的规律性进行探究,发现摩擦效应降低了有用功的转化率,减缓了气体膨胀速率,造成低压室压力的非均匀分布、高压室到低压室的质量流量波动和弹体初始时刻的碰撞。      

一种摩擦阻尼器在整体叶盘结构的应用

介绍了一种应用于整体叶盘结构的摩擦阻尼器，即在轮缘下方加工销孔，安装阻尼销.工作时，由于离心载荷的作用，阻尼销与轮缘相互摩擦，从而消耗振动能量.这种阻尼器被应用于两台发动机的涡轮整体叶盘减振方案中，试验结果显示:其减振效率差异较大.数值模拟分析证明，这种阻尼器的减振效率和振动能量在叶-盘间的传递有关.对于叶-盘强耦合振型，这种阻尼器可以获取较高的减振效率，叶片振动应力水平下降了约70%；但对于叶-盘弱耦合振型，叶片振动应力幅值没有明显下降趋势.      

Minimizing airfoil drag at low angles of attack with DBD-based turbulent drag reduction methods

Dielectric Barrier Discharge (DBD) based turbulent drag reduction methods are used to reduce the total drag on a NACA 0012 airfoil at low angels of attack. The interaction of DBD with turbulent boundary layer was investigated, based on which the drag reduction experiments were conducted. The results show that unidirectional steady discharge is more effective than oscillating discharge in terms of drag reduction, while steady impinging discharge fails to finish the mission (i.e. drag increase). In the best scenario, a maximum relative drag reduction as high as 64 % is achieved at the freestream velocity of 5 m/s, and a drag reduction of 13.7 % keeps existing at the freestream velocity of 20 m/s. For unidirectional discharge, the jet velocity ratio and the dimensionless actuator spacing are the two key parameters affecting the effectiveness. The drag reduction magnitude varies inversely with the dimensionless spacing, and a threshold value of the dimensionless actuator spacing of 540 (approximately five times of the low-speed streak spacing) exists, above which the drag increases. When the jet velocity ratio smaller than 0.05, marginal drag variation is observed. In contrast, when the jet velocity ratio larger than 0.05, the experimental data bifurcates, one into the drag increase zone and the other into the drag reduction zone, depending on the value of dimensionless actuator spacing. In both zones, the drag variation magnitude increases with the jet velocity ratio. The total drag reduction can be divided into the reduction in pressure drag and turbulent friction drag, as well as the increase in friction drag brought by transition promotion. The reduction in turbulent friction drag plays an important role in the total drag reduction.     

Mechanism of interconnected synchronized switch damping for vibration control of blades

The Synchronized Switch Damping (SSD) is regarded as a promising alternative to mitigate the vibration of thin-walled structures in aero-engines, especially for blades or bladed disks. The common manner is to shunt the switch circuit independently to a single piezoelectric structure. This paper is aimed at exploring a novel way of using the SSD, i.e., the SSD is interconnected between two piezoelectric structures or substructures. The damping mechanism, performance, and effective range of the interconnected SSD are studied numerically and experimentally. First, based on a dual cantilever beam finite element model, the time domain and frequency domain modeling and solving methods of the interconnected SSD are deduced and validated. Then, the influence of the amplitude and phase relationship on the damping effect of the interconnected SSD is numerically studied and compared with the shunted SSD. A self-sensing SSD control board is developed, and experimental studies are carried out. The results show that the interconnected SSD establishes an additional energy channel between the corresponding piezoelectric structures. When the amplitudes of the two cantilever beams are different, the interconnected SSD balances the vibration level of each beam. When the amplitudes of the two cantilever beams are the same, if the appropriate interconnection manner is selected according to the phase, the resonance peak can be reduced by more than 30%. When the vibration is in-phase/out-of-phase, the damping generated by the interconnected SSD in a cross/parallel manner is even more significant than the shunted SSD. Furthermore, this novel connection scheme reduces the number of SSD circuits in half. Finally, for engineering applications, we implement the proposed damping technology to the finite element model of a typical dummy bladed disk. A piezoelectric damping ratio of 13.7% is achieved when the amount of piezo material is only 10% of blade mass. Compared with traditional friction dampers, the major advancements of the interconnected SSD are: (A) it can reduce the vibration level of blades without friction interface; (B) the space constraint is overcome, i.e., the vibration energy is not necessarily dissipated independently in one sector or through physically adjacent blades, and instead, the dissipation and transfer of vibrational energy can be realized between any blade pair. If a specific gating circuit is adopted to adjust the interconnection manner of the SSD, vibration mitigation under variable working conditions with different engine orders will be expected; (C) designers do not need to worry about the annoying nonlinearities related to working conditions anymore.