无针搅拌摩擦点焊技术研究现状分析

无针搅拌摩擦焊可以在一定厚度范围内实现铝合金薄壁结构的可靠连接,从而在铝合金汽车带筋壁板结构的连接和装配中具有应用前景,同时可以扩展到飞机机身带筋蒙皮、隔离框板结构、机翼以及运载火箭的整流罩等壁板结构。现有的研究成果主要以工艺试     

冲压发动机针刺C/SiC喷管的烧蚀行为研究

为探索C/SiC喷管在固液冲压发动机上应用的可行性以及固液冲压发动机工作环境下的烧蚀行为,对冲压发动机针刺C/SiC复合材料喷管进行了研究.研究结果表明:针刺C/SiC复合材料喷管能够适应冲压发动机富氧、长时间的工作环境;C/SiC复合材料喷管入口段和扩张段存在轻微的氧化,喉部以热化学烧蚀为主,收敛段以热化学烧蚀和热机械侵蚀为主;收敛段为整个喷管的薄弱环节,应根据不同的工作条件和烧蚀机理,对C/SiC喷管的厚度进行分别设计.     

考虑组织因素的航空维修差错产生机理分析

为有效防范航空维修差错的发生,从组织因素角度对航空维修差错产生机理进行分析,在对组织因素影响维修差错作用关系分析的基础上,建立了组织因素导致维修差错的成因机理分析模型,从差错产生的潜伏阶段、发生阶段、纠正或扩展阶段和致灾阶段4个阶段对差错产生的演化过程进行了分析,进一步构建了组织层面的维修差错防控体系,为维修差错的系统...     

Deformation Behavior of Mg-8 wt%Li Alloy under High-speed Impact

Deformation behavior of the Mg-8 wt%Li alloy at high strain rate was studied by means of the Split Hopkinson Pressure Bar （with strain rate of 10^3 s^-1）. It is found that shear localization proves to be the main damage mode for the alloy during dynamic loading. Strain and strain rate arc the two necessary parameters affecting the occurrence of deformation and shear bands. Deformation bands begin to form when the strain and strain rate reach 0.20 and 1 900 s^-1 respectively and will develop gradually with the strain rate increasing. Besides, deformation bands will transform into shear bands when the strain and strain rate reach above 0.25 and 3 500 s^-1 separately.     

网络非法外联监控系统技术探析

内网中的拨号外联行为是一个重大的安全隐患，网络非法外联监控系统可以全面、实时地监控整个单住网络内部的拨号行为。本文介绍了两种主流架构的网络非法外联监控系统，即双机架构与C／S架构，并进行了深入的对比分析，阐述了实际的部署实施策略。     

TC21合金的高温变形行为

采用等温压缩试验法,研究了TC21钛合金在温度范围为900～1100℃和应变速率为0.01～50s-1范围内的高温变形行为,建立了合金热变形的本构方程。结果表明,TC21合金在较高温度条件下,变形机制为动态回复,在较低温度下,变形机制为晶界滑移。其转折温度在相变点附近,在此温度上下,变形激活能不同,两相区变形激活能为330.57kJ/mol,β区变形激活能为176.49kJ/mol。     

Calculation of high-temperature insulation parameters and heat transfer behaviors of multilayer insulation by inverse problems method

In the present paper, a numerical model combining radiation and conduction for porous materials is developed based on the finite volume method. The model can be used to investigate high-temperature thermal insulations which are widely used in metallic thermal protection systems on reusable launch vehicles and high-temperature fuel cells. The effective thermal conductivities（ECTs） which are measured experimentally can hardly be used separately to analyze the heat transfer behaviors of conduction and radiation for high-temperature insulation. By fitting the effective thermal conductivities with experimental data, the equivalent radiation transmittance, absorptivity and reflectivity, as well as a linear function to describe the relationship between temperature and conductivity can be estimated by an inverse problems method. The deviation between the calculated and measured effective thermal conductivities is less than 4%. Using the material parameters so obtained for conduction and radiation, the heat transfer process in multilayer thermal insulation（MTI） is calculated and the deviation between the calculated and the measured transient temperatures at a certain depth in the multilayer thermal insulation is less than 6.5%.     

热变形参数对镁合金力学性能及微观组织的影响

基于热模拟机GLEEBLE1500,以AZ31为研究对象进行热压缩实验,获得材料的应力-应变曲线。用金相显微镜对不同温度及应变速率下的金相进行观察分析,并对比分析热压缩前后的微观组织。同时分析了不同温度及应变速率下材料的力学行为,其行为属于典型的动态再结晶型。当热压缩温度为350℃和400℃时,材料强度随应变速率增大而增大,且加工硬化也增大。当应变速率为0.01和0.1/s时,随着变形温度的升高,材料的应力逐渐降低。在不同温度下,应变速率为0.01/s时的应力比应变速率为0.1/s时的应力要低。     

置氢Ti-6Al-4V合金超塑变形行为

研究了置氢Ti-6Al-4V合金的超塑变形行为.结果表明,氢可以增强动态回复和动态再结晶效应,使真应力-真应变曲线表现出相对稳定的流变应力;置入适量的氢可以使峰值流变应力降低58%,从流变应力的角度出发,相当于使应变速率提高几倍或使超塑变形温度降低约50℃;随氢含量的增加,延伸率呈下降趋势,超塑拉伸断口由延性断口转变为脆性断口.     

离子聚合物胶体的电化学-力学耦合模型及数值方法

离子聚合物胶体中充满着液体,并能吸附电荷,在外部化学场或电场的激励下,能产生巨大的膨胀.由于这些特性,离子聚合物可以作为电化学 - 力学驱动器.本文采用电化学 - 力学多场耦合数学模型,并应用有限元法进行了数值计算.计算结果表明该模型能很好地模拟离子聚合物在电场作用下的离子重分布和胶体的膨胀与收缩行为,同时能计算胶体中离子浓度.