Advances in fabrication of ceramic corundum abrasives based on sol–gel process

Corundum abrasives with good chemical stability can be fabricated into various free abrasives and bonded abrasive tools that are widely used in the precision machining of various parts. However, these abrasives cannot satisfy the machining requirements of difficult-to-machine materials with high hardness, high strength, and strong wearing resistance. Although superhard abrasives can machine the above-mentioned materials, their dressing and manufacturing costs are high. By contrast, ceramic corundum abrasives fabricated by sol–gel method is a cost-effective product between conventional and superhard abrasives. Ceramic corundum abrasives exhibit self-sharpening and high toughness. In this review, the optimization methods of ceramic corundum abrasive properties are introduced from three aspects: precursor synthesis, particle shaping, and sintering. Firstly, the functional mechanism of seeds and additives on the microstructural and mechanical properties of abrasives is analyzed. Specifically, seeds can reduce the phase transition temperature and improve fracture toughness. The grain size and uniformly dense structure can be controlled by applying an appropriate amount of multicomponent additives. Then, the urgent need of engineering application and machinability of special shape ceramic corundum abrasives is reviewed, and three methods of abrasive shaping are summarized. The micromold replication technique is highly advanced and can be used to prepare functional abrasives. Additionally, the influence of a new sintering method, namely, two-step sintering technique, on the microstructural and mechanical performance of ceramic corundum abrasives is summarized. Finally, the challenge and developmental trend of the optimization of ceramic corundum abrasives are prospected.     

波音737-800飞机起飞性能随襟翼放出量的变化特点

波音737飞机与其他民用机型的一个不同之处是前缘缝翼在起飞时可以使用开缝状态。分析了波音737-800飞机下列四个起飞性能参数与襟翼放出量的关系:场地长度限制的最大起飞重量;爬升梯度限制的最大起飞重量;障碍物限制的最大起飞重量;起飞决断速度。结果显示这四个参数在襟翼放出量为10时出现异常,原因是前缘缝翼状态发生了变化。在襟翼放出量由5增大到10的过程中,前缘缝翼由不开缝的放出状态变成开缝的完全放出状态,降低了升力系数。     

Controller development of photo bioreactor for closed-loop regulation of O2 production based on ANN model reference control and computer simulation

When Bioregenerative Life Support System (BLSS) is used for long-term deep space exploration in the future, it is possible to perform closed-loop control on growth of microalgae to effectively regulate O₂ production process in emergencies. However, designing controller of microalgae cultivating device (MCD) by means of traditional methods is very difficult or even impossible due to its highly nonlinearity and large operation scope. In our research, the Artificial Neural Network Model Reference Control (ANN-MRC) method was therefore utilized for model identification and controller design for O₂ production process of a specific MCD prototype—photo bioreactor (PBR), based on actual experiment and computer simulation. The results demonstrated that the ANN-MRC servo controller could robustly and self-adaptively control and regulate the light intensity of PBR to make O₂ concentrations in vent pipe be in line with step reference concentrations with prescribed dynamic response performance.     

可靠性设计优化的球空间设计法

可靠性设计优化（RBDO）在航空航天等领域已经被广泛应用，具有显著提高可靠性的效果；然而它包含两个迭代循环-总体优化循环和可靠性分析循环，双循环求解方法效率低下甚至难以承受。本文提出一种可以提高可靠性设计优化求解效率的方法-球空间设计法，该方法可以方便地表达搜索区域，最大可能失效点可以从极值点处精确获取；同时，该方法可以将总体优化以及可靠性分析同步进行。本文所提出的球空间法的有效性将通过2个算例进行测试，测试结果表明该方法不仅精度与同类方法持平，求解效率有明显提升，它将会对提高航空航天装备如卫星、火箭、飞行器等产品的可靠性提供更为有效的方法和技术支持。     

纤维金属层板的开发和应用现状

随着我国航空航天领域器械的飞速发展,对该领域中结构件所用材料的综合性能及轻量化提出了新的要求。在过去几十年里,大型客机的市场需求不断扩大,刺激了新型材料的兴起,使材料向着高性能,轻质量发展。纤维金属层板是由铝合金与纤维预浸料交替铺层固化而成的层间混杂复合材料。纤维金属层板结合了金属与复合材料的优良特性,具有密度小、损伤容限优良、抗冲击和疲劳性能,越来越受到航天航空和轨道交通领域的关注。目前用于商业生产的金属纤维层压板(FMLs)多以基于芳纶纤维(ARALL)与基于高强玻璃纤维(GLARE)的层板为主。概括了纤维金属层板的制备前表面处理工艺,对其弯曲测试、拉伸测试、冲击测试和疲劳测试等力学性能的测试方法进行综述,同时对未来新型纤维金属层板的开发进行探究,为纤维金属层板的开发提供参考信息。     

基于粒子群优化算法的永磁电机热网络参数识别

监测永磁电机的永磁体温度对于保证电机的使用寿命至关重要,因为过高的温度会产生永磁体不可逆失磁现象。提出了一种基于粒子群优化算法的永磁电机热网络参数识别方法,实现用热网络监测永磁体的温度。该方法首先建立永磁电机的热网络模型,利用粒子群优化算法结合电机温升试验所得温度数据对热网络模型的主要热力参数进行识别；然后利用该热网络模型进行在线温度识别,识别过程能够快速收敛,具备良好的辨识精度；最后,通过对比仿真识别温度和电机温升试验数据,验证了该方法的准确性。     

Thermo-mechanical properties of RTM-made carbon fibre/polyimide composite attaching collar under transient heating

This study focuses on the thermo-mechanical properties of Carbon Fibre/Polyimide Composite (CFPC) attaching collars under transient heating. The CFPC attaching collars were fabricated by a high-temperature resin transfer moulding process, and their thermo-mechanical properties under the conditions of simultaneous transient heating and bending load were investigated. The results show that the attaching collar tends to fail at 118% of the limit load. The failure mode includes the fracture of the connecting screws, local extrusion damage of the hole edges, and slight ablation damage at the outer plies. And there is no observable residual deformation in the composite attaching collar. Furthermore, considering that the material properties vary with temperature, a progressive damage model based on the sequential thermo-mechanical coupling method was established to study the failure mechanism of the attaching collar. Finally, the damage factor of the CFPC was calculated to assess the safety status of the attaching collar. The results show that the primary damage modes of the composite attaching collar are intralaminar failure, which mainly occurs at the heat insulation layer and the hole edges, and these slightly affect the structural bearing capacity. A good correlation between the experiment and FEA is obtained. The test methods and analysis models proposed contribute to the safety assessment of composite structures under transient heating.     

种子叶片自旋下落过程涡系的PIV实验研究

本文利用粒子图像测速技术研究种子叶片自由旋转下落过程中不同涡系的相互作用机理。以典型枫树种子叶片为研究对象,通过对比不同叶片长度、叶面厚度、叶面宽度、下落锥角、自旋角速度、下落速度和下落初始角度等参数对过渡期和稳定期的影响,分析了诱发叶片自旋的外形特征和空间特性。结合特征参数分析,对叶片自旋稳定期开展了PIV流场测量实验,解析了无干扰下种子叶片下落过程中涡系的产生和演化机理。实验结果表明:稳定期气流在叶尖正面位置产生前缘涡（沿展向呈圆锥状结构）,后缘位置产生反方向的后缘涡;两个涡发生相互耦合运动,前缘涡的强度大于后缘涡,从而导致叶面产生锥角。在前缘和叶尖前方观测到较高的速度向上的区域,而在后缘和叶根附近则出现较高的速度向下的区域,从而对种子产生向上的升力,使叶片实现自旋稳定下落。通过枫叶种子自由下落的无干扰PIV测量,初步获得了贴近叶片表面前缘涡的运动性状,验证了后缘涡的存在,结论对单翼型旋转叶片的设计有一定指导意义。     

变体翼梢小翼的减阻机理数值模拟

总结了对翼梢小翼减阻效果影响最大的几何参数,在此基础上采用数值模拟方法研究了这些几何参数的最佳变化范围,为变体翼梢小翼设计提供理论依据.并从气动性能、气动载荷分布和翼尖涡的角度探讨了变体翼梢小翼相对传统翼梢小翼的优缺点.结果表明:在飞机的起飞阶段,变体翼梢小翼的减阻效率比传统翼梢小翼高2.2%,同时将翼尖涡强度降低了15%,有利于提高飞机的燃油效率和机场空域安全;但也会增大机翼的翼根弯矩,因此必须权衡变体翼梢小翼带来的气动收益与结构强度不利因素.