基于稳健设计的FDM工艺参数优化(英文)

在一系列成形试验的基础上,分析了熔融沉积成形(Fused deposition modeling,FDM)工艺对制件精度影响因素,选择线宽补偿、挤出速度、填充速度和层厚4个工艺参数作为控制因子,采用稳健设计和多指标模糊综合评判的方法对FDM工艺参数进行优化。优化结果表明,4个工艺参数对制件精度影响程度不同,不仅每个参数本身需要优化,参数之间的相互匹配也必须满足一定关系,这样才能达到最佳组合,制造出较高精度的零件。     

加力燃烧室用气冷喷油杆结焦特性数值研究

为阐明实际工作环境参数下气冷喷油杆内燃油结焦速率与沉积厚度等特性,建立沿喷杆轴向的一维非稳态热-流-固耦合换热与燃油结焦计算模型,获得了喷杆壁面与燃油温度、结焦速率与相对结焦厚度等参数沿程分布。分析了燃油进口温度和质量流量对燃油结焦特性的影响,并与无气冷喷杆方案结果进行了对比。计算结果表明:燃油温度沿轴向逐渐升高,喷杆壁温在底端达到峰值。基准工况下气冷喷杆结焦速率和结焦厚度均沿轴向先升高后降低。结焦速率最大为26μg/(cm2·h),对应相对结焦沉积厚度0.6%。无气冷喷杆方案,在喷杆前端和底部各存在一结焦峰值区域。结焦速率峰值分别为398μg/(cm2·h)和807μg/(cm2·h),对应相对结焦沉积厚度8%和15%。固定燃油进口流量,随着燃油进口温度升高,结焦速率显著增大,喷杆内结焦总质量呈指数级增长趋势。固定燃油进口温度,进口流量越大,结焦速率略有增大,结焦总质量仅呈线性增长趋势。相较于无气冷喷杆,气冷喷杆可显著降低喷杆壁面与燃油温度,从而大幅抑制结焦生成。     

不同几何结构对燃油喷嘴热防护特性的影响

试验研究了不同管路结构对燃油结焦性能的影响,结果表明,在1 000 K、150 m/s来流条件和400 K、05 m/s燃油条件下,减小弯管角度和突扩管路的突扩尺寸可以降低结焦附着,且在对管路加热的初始阶段中,结焦量随时间增加会出现波动,在加热15 min时管壁结焦量达到最大,壁面上部分结焦的脱落使结焦量降低。随后,采用试验与数值模拟相结合的方法研究了喷嘴和喷嘴帽罩结构对热防护特性的影响。结果表明,主、副油路同心布置的喷嘴具有最好的热防护效果,在所试验工况下最高可降低湿壁温度近50%,甚至优于带空气隔热层的模型。而喷嘴帽罩对喷嘴出口油温的降低有限,但减小帽罩与喷嘴体的接触或在接触面处填充低热导率的材料仍是有效的改进措施,可降低出口油温约5 K。研究结果对喷嘴的热防护设计具有指导作用。     

Microstructure and mechanical properties of hybrid fabricated 1Cr12Ni2WMoVNb steel by laser melting deposition

 Laser melting deposition was carried out to deposit a 1Cr12Ni2WMoVNb steel bar on a wrought bar of same material. Room-temperature tensile properties of the hybrid fabricated 1Cr12Ni2WMoVNb steel sample were evaluated, and microstructure, fracture surface morphology, and hardness profile were analyzed by an optical microscope (OM), a scanning electron microscope (SEM), and a hardness tester. Results show that the hybrid fabricated 1Cr12Ni2WMoVNb steel sample consists of laser deposited zone, wrought substrate zone, and heat affected zone (HAZ) of the wrought substrate. The laser deposited zone has coarse columnar prior austenite grains and fine well-aligned dendritic structure, while the HAZ of the wrought substrate has equiaxed prior austenite grains which are notably finer than those in the wrought substrate zone. Besides, austenitic transformation mechanism of the HAZ of the wrought substrate is different from that of the laser deposited zone during the reheating period of the laser deposition, which determines the different prior austenite grain morphologies of the two zones. Microhardness values of both the laser deposited zone and the HAZ of the wrought substrate are higher than that of the wrought substrate zone. Tensile properties of the hybrid fabricated 1Cr12Ni2WMoVNb steel sample are comparable to those of the wrought bar, and fracture occurs in the wrought substrate zone during the tensile test.     

Thermospheric neutral density response to solar forcing

Recent measurements by the Solar EUV (Extreme Ultra Violet) Experiment (SEE) aboard the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics satellite (TIMED) provide solar EUV spectral irradiance with adequate spectral and temporal resolution, and thus the opportunity to use solar measurements directly in upper atmospheric general circulation models. Thermospheric neutral density is simulated with the NCAR Thermosphere–Ionosphere–Electrodynamic General Circulation Model (TIEGCM) using TIMED/SEE measurements and using the EUVAC solar proxy model. Neutral density is also calculated using the NRLMSISE-00 empirical model. These modeled densities are then compared to density measurements derived from satellite drag data. It is found that using measured solar irradiance in the general circulation model can improve density calculations compared to using the solar proxy model. It is also found that the general circulation model can improve upon the empirical model in simulating geomagnetic storm effects and the solar cycle variation of neutral density.     

Preliminary evidence for drizzle in the middle cloud layer of Venus

Vertical trajectory data from the VEGA 1 and 2 balloon flights in the atmosphere of Venus is re-analyzed. A previously employed helium leak rate profile invoked to entirely account for the decrease in equilibrium float altitude of VEGA 2 is questioned and deemed ad hoc. As an alternative, it is proposed that both VEGA 1 and 2 experienced in-flight mass increases due to the deposition of cloud particles onto their envelopes, as well as losing helium at a reduced rate consistent with the pre-flight prediction. Particle deposition rates are estimated and found to be compatible with this alternative scenario. Possible evidence for drizzle is also presented. Preliminary experiments to derive aerosol deposition rate on a flat plate and the maximum feasible liquid mass that may be accumulated on a near-spherical envelope are briefly described. Further experimental work is recommended to constrain the deposition efficiency values involved and the maximum feasible drizzle fluxes that could have been encountered by both VEGA 1 and 2.     

碳纤维表面CVD硅涂层对其性能的影响

 分析了碳纤维表面化学气相沉积Ｓｉ涂层的相结构,研究了Ｓｉ涂层对碳纤维抗氧化性能及强度的影响。结果表明：涂层中Ｓｉ元素呈非晶态分布；Ｓｉ涂层可提高碳纤维的抗氧化性能；氧化温度不同,Ｓｉ涂层碳纤维的氧化失重或增重规律也不相同。同时,Ｓｉ涂层降低了碳纤维拉伸强度,而适度空气氧化又可使Ｓｉ涂层碳纤维强度得到大幅度提高；Ｓｉ涂层碳纤维的强度随氧化温度、氧化时间的变化而改变。     

EBPVD法制备NiCrAlY/ZrO2-8Y2O3微层复合板的拉伸力学性能研究

采用电子束物理气相沉积(EBPVD)工艺制备了NiCrAlY／ZrO2—8Y2O3微层复合板，测试了该材料在不同温度下的拉伸力学性能，初步探讨了拉伸强度与延伸率随温度变化而变化的可能机理。结果表明：该材料的屈服极限、强度极限和最大延伸率均随温度的升高而降低，在室温时它是一种脆性材料而在高温时则是延性良好的塑性材料。     

MOCVD法制备一维氧化物阵列材料

介绍了一种新型的大气开放式金属有机物化学气相沉积(MOCVD)系统的结构及其新特点;以ZnO纳米棒阵列材料的制备为例,说明了大气开放式MOCVD法制备氧化物阵列材料的方法,并对氧化物阵列材料的制备过程进行了论述;扫描电镜研究发现这些取向生长的氧化物一维材料均垂直于基片沿某一方向生长,并且排列非常规整,具有无晶界、晶体缺陷少、体表面积小和具有特殊的尖端等特点;介绍了制备VO_x,FeO_x,TiO₂等一元金属氧化物和ZnAlO,ZnMgO等多元掺杂金属氧化物的一维阵列材料的方法.      

地面寿命试验中离子推力器表面的溅射沉积量计算

有效降低溅射沉积影响是离子推力器地面寿命试验需要解决的重要技术问题。文章建立了真空舱壁上溅射物沉积到离子推力器表面的计算模型。应用该模型计算了LIPS-200推力器在TS-7真空舱中进行寿命试验的背溅射沉积情况,对钛（Ti）材料和石墨（C）材料内衬,背溅射沉积量分别为0.79 μm/kh和0.20 μm/kh。对比美国NSTAR和NEXT离子推力器寿命试验中的背溅射沉积量测量数据,文章中的计算结果表明,LIPS-200推力器的表面沉积污染在可接受的范围。