22MnB5超高强钢板热成形中的回弹机理分析

回弹是影响热冲压件形状精度的主要因素,为研究影响22MnB5超高强钢板热冲压成形中回弹的因素,在不同温度下对22MnB5高强钢板进行拉伸试验,考察了变形温度和应变速率对弹性应变和蠕变应变的影响,获得其热力学性能。通过等温度和非等试验考察了变形温度、热成形终了温度和压边对热成形后回弹的影响。采用有限元法对槽形件非等温热成形过程进行了数值模拟。从试验结果和模拟结果可知,热效应是引起回弹的主要因素,蠕变应变减少了热成形后的回弹量。蠕变应变和热效应是影响热成形中回弹的主要因素。     

二元机翼滑模变结构控制颤振主动抑制

颤振主动抑制(AFS,Active Flutter Suppression)是气动弹性综合研究的活跃分支,对飞行器设计具有重要意义.以带后缘控制面的二元机翼为对象,研究滑模控制(SMC,Sliding Mode Control)用于气动弹性AFS的可行性与机理.基于准定常气动力理论建立二元机翼气动弹性系统模型,设计SMC的滑模切换面及状态反馈控制切换函数,以实现受控对象AFS,从相空间状态轨线的角度,阐述SMC使闭环系统稳定的根源.此外,还对SMC的鲁棒性及延时效应做了分析与讨论.研究表明:该控制策略可用于AFS,在气动弹性主动控制方面具有应用前景.     

NiTiAl Intermetallic Alloys Strengthened by Mo Replacement

 NiTiAl based alloys have attracted attention as potential high temperature structural materials. Alloying is an effective way to improve their mechanical properties. The microstructures and mechanical properties of Ni₅₀Ti_44-xAl₆Mo_x (x = 0, 0.5, 1, 1.5, 3) alloys have been investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron mi-croscope (TEM) and compressive tests. It is found that Ni₅₀Ti_44-xAl₆Mo_x alloy is composed of NiTi (B2) and Ti₂Ni (FCC) phases when Mo content is no more than 1 at%. The effect of Mo solid solution hardening at room temperature has been indi-cated by the rise of yield strength and the fall of plasticity with increasing Mo content. For Ni₅₀Ti_42.5Al₆Mo_1.5 and Ni₅₀Ti₄₁Al₆Mo₃ alloys, a Mo solid solution appears and increases the yield strength by precipitation strengthening. The maxi-mum yield strength at 600 °C and elevated temperatures is presented in Ni₅₀Ti₄₃Al₆Mo₁ alloy not in alloys with a higher Mo content, which is possibly due to the softness of Mo-Ti-Ni solid solution phase.     

Detailed Design of a High Speed Switched Reluctance Starter/Generator for More/All Electric Aircraft

The basic concepts and advantages of more/all electric aircraft (M/AEA) are briefly addressed. The combined starter/generator (CS/G) system is introduced as a key technology to enable M/AEA. Some important performance requirements for CS/G system are obtained. Based on these requirements, a high speed switched reluctance machine (SRM) is designed to operate as a starter/generator. The entire design process is mainly divided into two stages: electromagnetic design and thermal design. In electromagnetic design stage, the electromagnetic structure and dimensions of the machine and the number of phase winding turns per pole are obtained; the topology and main technical details of the converter are briefly introduced as well. In thermal design stage, a liquid-cooling system is designed based on the thermal analysis of the machine. In the end, the performances of the designed SRM are basically verified by simulation. To get high performances, the exciting angles are optimized in two different operating modes respectively, and the optimized performances in the motoring mode are given as well.     

摆锤式冲击响应谱试验机的调试方法

文章对摆锤式冲击响应谱试验机的调试方法进行了实践总结。介绍了摆锤式冲击响应谱试验机的结构组成和工作原理。基于大量的调试试验和对调试结果的分析研究,总结了摆锤式冲击响应谱试验机的主要技术指标和冲击试验谱形的调试方法、调试规律等,为今后摆锤式冲击响应谱试验机的研究和应用提供一定的技术参考。     

基于DWT的汽油机爆震信号分析

为提高爆震检测精度,研究了离散小波变换在爆震信号分析中的应用.利用离散小波变换从汽油机的振动信号中提取出了轻微爆震特征,提出了一种根据离散小波变换特征域子带信号能量大小来评价爆震强度的指标,根据爆震发生时特征域子带信号能量阶跃变化的特性,提出了确定爆震阈值的方法,该方法经检验能准确判断发生爆震的临界值.研究成果为将小波变换应用于汽油机爆震的实时精确控制打下基础,可进一步通过点火提前控制使汽油机在轻微爆震区工作,汽油机的动力性、经济性都能够得到提高.     

Korean space food development: Ready-to-eat Kimchi, a traditional Korean fermented vegetable,sterilized with high-dose gamma irradiation

Addition of calcium lactate and vitamin C, a mild heating, deep-freezing, and gamma irradiation at 25 kGy were conducted to prepare Kimchi as a ready-to-eat space food. It was confirmed that the space food was sterilized by an irradiation at 25 kGy through incubation at 37 °C for 30 days. The hardness of the Space Kimchi (SK) was lower than the untreated Kimchi (CON), but higher than the irradiated Kimchi (IR). Also, this result was supported by the scanning electron microscopic observation. Sensory attributes of the SK were similar to CON, and maintained during preservation at 35 °C for 30 days. According to the Ames test, Kimchi sterilized with a high-dose irradiation exerted no mutagenic activity in the bacterial strains of Salmonella typhimurium. And, the SK was certificated for use in space flight conditions during 30 days by the Russian Institute of Biomedical Problems.     

导弹表面流动分离与后体减阻设计

采用基于压缩性修正的两方程K\|ω\|WD+模式数值求解雷诺平均的Navier\|Stokes方程组,数值模拟导弹跨、超声速流动(含底部),研究导弹后体多台阶、环向凹槽等典型分离流动的被动减阻措施对阻力缩减的影响。与分离导致阻力增加的传统观点不同,通过分析计算结果发现多台阶能有效降低摩阻及底部阻力;环向凹槽则有利于降低摩擦阻力,底阻减小不明显;组合外形未必能获得较基准外形更多的阻力缩减,欲获得更多的阻力缩减,仍须开展更深入细致的工作。
     

减压阀节流口流场仿真和分析

采用Fluent软件对火箭姿态控制系统减压阀环形节流口流场进行了数值仿真,得到了流场有关参数图形。减压阀节流口气体流场为非自由、紊动、冲击、壁面射流,气体在节流口达到音速,贴壁面高速射流出去后,相互撞击、压缩并撞击阀芯柱面产生激波,气流总压损失较大,建议采用等温过程进行特性计算。减压阀环形节流口后流场存在激波,总压并不守恒,目前通用的气流稳态流动力计算公式并不合适,应借助流场分析工具进行节流元件受力分析。