Study on Thermal Deformation Behavior and Properties of Vacuum Hot-press Sintered W(50)/Cu-Al_2O_3 Composite

In this work, the tungsten particulate reinforced Al2O3 dispersion strengthened copper base composites were successfully fabricated by using a vacuum hot-press sintering method. With the test temperature varying from 650 to 950 ℃ and the strain rate varying from 0.01 to 5 s-1, the W(50)/Cu-Al2O3 composites were isothermally compressed on a Gleeble-1500D thermal simulator. The true stress-strain curves of the W(50)/Cu-Al2O3 under different test conditions were obtained. The dynamic recrystallization of the W...     

Kernel TIF method for effective material removal control in rotating pitch tool-based optical figuring

While opticians have used pitch tools for superb surface finishing, their poor controllability in material removal and associated lengthy tooling overhead have been well known in optics fabrication communities. We report a new computational technique called kernel tool influence function (KTIF) that can bring higher predictability to pitch tool-based material removal. The term ??kernel?? is defined as the ratio of experimental to simulated removal depth, therefore transforming the material removal coefficient of Preston??s equation to a removal scaling function at each point on the tool surface. This approach offers a unique inherent control feature incorporating ??real-life shop floor effects associated with pitch tool polishing variables?? into the tool influence functions without the need for theoretical expressions for the effects of individual variables on material removal behavior. Using a modified Draper-type polishing machine and a rotating pitch tool, we first generated kernel TIFs with zero stroke and used them for simulation and trial experiments of extended TIFs with variable tool strokes. The results show that the root mean square (rms) TIF profile differences between the prediction and experiments are in the range of 11 to 29?nm for conventional TIF and 7 to 15?nm for the KTIF. We then generated conventional TIF and KTIF database sets and applied them to surface figuring simulations. The results confirm that the kernel TIF has superior performance to the conventional TIF in controlling the material removal for correction of the chosen surface error.     

Prediction of formation enthalpies for Al2X-type intermetallics using back-propagation neural network

A back-propagation artificial neural network (ANN) was established to predict the formation enthalpies of Al₂X-type intermetallics as a function of some physical parameters. These physical parameters include the electronegativity difference, the electron density difference, the atomic size difference, and the electron–atom ratio (e/a). The values calculated by the ANN method agree with experiments well to typically within 10%, indicating that the well-trained back-propagation (BP) neural network is feasible, and can precisely predict the formation enthalpies of Al₂X-type intermetallics. The method comparison based on the predicted formation enthalpies suggests that our ANN method is superior to Miedema's model. Some trends of formation enthalpies for Al₂X-type intermetallics were also observed from the ANN.     

Improved model and 3D simulation of densification process for iron powder

A new model for describing the compaction process of iron powder was proposed based on the continuum hypothesis and elliptical yield criterion. To simulate the densification behaviour, the constitutive model was implemented in Marc computer program. For the relationship between load and displacement, different models were compared and the influence of the parameters in the constitutive equations was determined by means of simulation and experiments. The density distribution of a balancer was measured and simulated. The results show that the parameter η adopted plays a modification role for the load-displacement curve, and compared with other models the present model fits better with the experimental data in the later stage of the compaction process mainly due to the different parameters A and B. The friction on the contact surface contributes to the inhomogeneous density distribution under large deformation of the workpiece. The comparison between the simulation and experimental data indicates that this model can be used to predict the powder compact process precisely and effectively.     

泡沫玻璃在房屋建筑中的应用及其施工质量控制

本文主要介绍了一种新型的、可用于节能窗玻璃或是建筑维护结构的保温隔热材料——泡沫玻璃,对其主要物理性能、分类、应用技术特点进行了简要分析,并对其在房屋建筑工程应用中的施工准备和施工过程的质量控制进行阐述,以供参考。     

华东电网CPS考核标准运行分析

介绍了华东电网目前频率质量控制的现状和考核标准,结合实际运行数据分析了现行考核标准CPS在实际运行中所表现出的约束效力和其有待改进之处,由分析结果提出了对考核标准的改进方法和今后电网的频率质量控制手段.     

直线电机的H∞迭代学习控制设计

直线电机的诸多非线性与不确定性因素是影响其控制精度的主要原因.文中基于H∞理论和迭代学习控制思想,设计应用于直线电机运动系统的迭代学习控制器,利用鲁棒控制实现系统镇定和克服各种不重复干扰和不确定性的影响,利用迭代学习控制提高系统的跟踪性能并克服重复性干扰的影响.仿真实验结果表明,采用H∞迭代学习控制器的直线电机运动系统的跟踪性与抗扰性均明显改善.基于H∞的迭代学习控制能够提高直线电机运动系统的控制性能.     

基于MATLAB的交流永磁同步电机解耦控制研究

介绍了一种采用现代控制理论对交流永磁同步电机的直交轴耦合分量进行解耦的有效方法,该法通过加入状态反馈矩阵使电机的电磁力矩得到独立控制,MATLAB仿真结果证明了该方法的有效性。     

船舶舵减摇的H∞控制设计

针对舵减摇控制系统的特点,提出了一种H∞设计方案.忽略了艏摇特性和横摇特性之间的耦合作用,分析了舵减摇控制系统.采用H∞混合灵敏度的设计方法,从基本的性能要求和鲁棒稳定性要求出发,阐述了舵减摇控制系统H∞设计中权函数的选择依据和确定过程.对所设计的H∞控制器进行了降阶处理,分析了利用积分作用进行相位补偿的设计原理.仿真结果表明,所设计的舵减摇控制系统在相应的频带内具有指定的性能,而且满足鲁棒稳定性要求.对H∞设计结果的详细验证和分析表明H∞设计是一种定量设计,所有的设计要求和指标都可以定量地给出设计结果.