高值电阻国际比对的方法研究

介绍了参加亚太实验室认可合作组织(APLAC)开展的高阻1 MΩ;10 MΩ实验间比对的方法,对一种用参考电压测量高阻的方法进行了描述,解决了其中的技术问题,对测量不确定度进行了分析,其结果为测量1MΩ的合成标准不确定度为3.10-6,测量10 MΩ的合成标准不确定度为5.10-6,APLAC公布的比对中期报告证明了该方法的可靠性。     

一种低位作业自动焊接方法--CO2焊与点焊在客车车身制造中的新运用

本文通过介绍一种客车顶盖蒙皮、顶骨架低位作业自动焊接方法,综合CO2气体保护焊和单面双点电阻焊,找出影响期焊接质量的原因及解决方法,以充分发挥其焊接变形小、焊接强度高、节能、高效的特点.     

磁转速表指针摆动的故障分析

就磁转速表活动系统的动态特性以及在附加交变力矩的作用下，指针摆动随转速变化的规律，从理论上进行了分析，并结合实际探讨了指针摆动的故障原因。     

磁悬浮框架飞轮磁轴承技术研究与发展现状

对磁悬浮框架飞轮(MSGFW)和高精度磁轴承研究现状及其未来发展进行了详细阐述。根据转子悬浮力类型，将磁悬浮框架飞轮分为磁阻力构型、洛伦兹力构型和混合力构型，并结合三种构型论述了国内外框架飞轮的发展过程。在此基础上，对球面磁阻力磁轴承和洛伦兹力磁轴承进行了详细介绍，并结合磁路图分析其工作原理，比较了同类磁轴承的优劣。展望了磁悬浮框架飞轮与高精度磁轴承的未来发展方向，指出高动态响应检控共位平动球面磁阻力磁轴承，标准磁悬浮动量球和磁悬浮控制敏感球是磁悬浮框架飞轮的研究重点。     

跨声速风洞斜孔壁非线性流动试验

为分析跨声速风洞斜孔壁近壁区域的流动特性，评估气流偏角-压力系数的非线性关联，在0.6 m跨超声速风洞中开展了基于七孔探针的流动特性测量试验。通过气流偏角和压力系数分布分析了斜孔壁流动的差阻特性，以及马赫数、模型升力对斜孔壁流动的影响，最后基于试验结果发展了计算斜孔壁特性参数的微分法，并与经验方法结果进行对比。结果表明，斜孔壁流动呈现出明显的差阻性和非线性，在负压差范围内，近壁流动仍以出流为主；高亚声速时，空风洞模型区孔壁流动特性趋于实壁；安装模型后，随着升力的增大，升力面对应的孔壁区域流动向入流发展，孔壁流动特性趋于开口边界。     

高精密小电阻测量方法及测量结果的不确定度评定

在高精密小电阻的测量过程中，由于接触电阻、测量线电阻及测量条件等都会对其测量结果产生不可忽视的影响，因此，选择合适的测量方法对提高测量结果的置信度尤为重要。本文着重介绍了用恒流源和数字电压表间接测量高精密小电阻的具体方法，对其测量结果的不确定度进行了分析与评定。     

化学气相反应法在C/C复合材料抗氧化处理中的应用

通过把硅蒸气渗入预制体孔隙与碳直接反应生成SiC的化学气相反应(CVR)方法,提高初始密度和预制体结构均不同的C／C复合材料的抗氧化能力,研究了C／C复合材料的密度变化与微观结构,并对其进行了氧化试验。结果表明,因CVR温度、C／C复合材料初始密度不同,抗氧化处理后的密度增加量有显著不同。针刺炭布C／C／SiC复合材料在马福炉中于1160℃经65min氧化后,其失重率仅2．6％,而密度为1．95g／cm^3的同结构C／C复合材料相在同条件下失重率高达32％。     

SiC/CVD SiC复合涂层的抗氧化及抗热震性能研究

为了提高C/SiC复合材料耐高温性能,采用泥浆浸渍裂解与真空化学气相沉积(CVD)在材料表面制备了SiC/CVD SiC复合涂层,通过XRD、SEM分析了涂层组成与结构;研究了复合涂层的高温抗氧化(700～1 500℃)和抗热震性能。结果表明,泥浆浸渍法制备的SiC涂层具有一定的封孔效果,可使材料开孔率下降,但高温抗氧化效果并不佳,1 200℃氧化10 min后材料弯曲强度保留率下降明显仅有86%。CVD SiC涂层结构致密,与SiC封孔涂层结合较好,在700～1 500℃具有较好的抗氧化效果,随着氧化温度的升高,氧化后涂层完好,表面O元素逐渐增加,材料失重率缓慢增加但不大于0.5%,且材料性能并未下降。涂层材料在1 200℃-10 min短时热震5次后材料弯曲强度保留率仍有95%以上,且未出现开裂、剥落等热震损伤。在1 200℃-30 min长时热震10次后,涂层材料基本被完全氧化,材料失去保护作用,弯曲强度下降至90%左右。     

A novel control method for turboshaft engine with variable rotor speed based on the Ngdot estimator through LQG/LTR and rotor predicted torque feedforward

In order to compensate for the disturbance of wide variation in rotor demanded torque on power turbine speed and realize the fast response control of turboshaft engine during variable rotor speed, a cascade PID control method based on the acceleration estimator of gas turbine speed (Ngdot) and rotor predicted torque feedforward is proposed. Firstly, a two-speed Dual Clutch Transmission (DCT) model is applied in the integrated rotor/turboshaft engine system to achieve variable rotor speed. Then, an online estimation method of Ngdot based on the Linear Quadratic Gaussian with Loop Transfer Recovery (LQG/LTR) is proposed for power turbine speed cascade control. Finally, according to the cascade PID controller based on Ngdot estimator, a rotor demanded torque predicted method based on the Min-batch Gradient Descent-Neural Network (MGD-NN) is put forward to compromise the influence of rotor torque interference. The simulation results show that compared with cascade PID controller based on Ngdot estimator and the one combined with collective pitch feedforward control, the novel control method proposed can reduce the overshoot of power turbine speed by more than 20%, which possesses faster response, superior dynamic effect and satisfactory robustness performance. The control method proposed can realize the fast response control of turboshaft engine with variable rotor speed better.     

Influence of pre-tension on ballistic impact performance of multi-layer Kevlar 49 woven fabrics for gas turbine engine containment systems

In this paper, ballistic impact tests on wrapped multi-layer Kevlar 49 woven fabric systems were carried out with a flat blade projectile to investigate the impact response during a fan blade out event. The influences of the number of Kevlar layers and pre-tension were discussed particularly. Test results were used to analyze failure modes and energy absorption characteristics of multi-ply Kevlar fabrics. Results show that there are two kinds of impact damage for fabrics: global deformation mainly involving stretching of yarns in the impact region and fabric wrinkle from both sides to the impact zone, and local damage characterized by yarn fracture, yarn pull-out, and yarn unraveling. The energy absorption capability of Kevlar 49 woven fabrics improves with the number of fabric layers. The energy absorbed by multi-layer fabrics increases slightly at the beginning and then decreases substantially with pre-tension. The work in this paper can provide guidance for designing light-weight multi-layer fabrics containment systems.