C/SiC复合材料在典型模拟环境下高温拉伸性能研究

以先驱体浸渍裂解（PIP）工艺制备的C/SiC复合材料为对象，研究了C/SiC复合材料在典型模拟环境下的高温拉伸性能，首次获得了约3 000 s时间不同变状态条件下材料的高温拉伸性能数据，探讨了不同条件下C/SiC复合材料高温承载行为及其变化规律。研究结果表明，C/SiC复合材料经历约3 000 s复杂阶梯热环境后拉伸强度仍保持60%左右；经历大温度梯度热震后，C/SiC复合材料的高温拉伸性能保持率反而提高，最高保持率超过80%；热震温差越大，热震后保温时间越长，对材料的高温拉伸性能保持和提高越有利。     

Ironing effect on surface integrity and fatigue behavior during ultrasonic peening drilling of Ti-6Al-4V

Imposing compressive residual stress field around a fastening hole serves as a universal method to enhance the hole fatigue strength in the aircraft assembly filed. Ultrasonic Peening Drilling (UPD) is a recently proposed hybrid hole making process, which can achieve an integration of strengthening and precision-machining with a one-shot-drilling operation. Due to the ironing effect of tool flank surface, UPD introduces large compressive residual stress filed in hole subsurface. In order to reveal the strengthening mechanism of UPD, the influence of ultrasonic vibration and tool dynamic relief angle on ironing coverage rate and its corresponding effect on surface integrity in UPD were analyzed. The experiments were conducted to verify the influence of ironing effect on surface integrity and fatigue behavior of Ti-6Al-4V hole in UPD. The results indicate that the specimen features smaller surface roughness, higher micro-hardness, plastic deformation degree and circumferential compress residual stress under higher ironing coverage rate. The fatigue life increases with the raise of ironing coverage rate, and the fatigue source site in UPD shifts from surface to subsurface comparing with that without vibration assistance. The results demonstrates that a better strengthening effect can be obtained by reasonably controlling the ironing coverage rate in UPD.     

Multi–physical-field characteristics modeling and structure optimization for kW-level ultra-high-speed PM motors with integrated support system

In the aerospace industry, the low-mass ultra-high-speed flywheel system play a critical role. In this paper, a kW-level Ultra-High Speed Permanent Magnet Synchronous Motor (UHSPMSM) as the core component of flywheel system is proposed and analyzed with consideration of multiple physical fields, including electromagnetic characteristics, mechanical strength and rotor dynamics. The integrated support structure is put forward to improve rotation accuracy and operation stability of the UHSPMSM. Further, influence of the integrated support structure on critical speed is explored, and the key parameters such as support position and support stiffness are designed. Moreover, the rotor strength is analyzed by analytical model developed of rotor stress that can deal with multiple boundary types. Material and thickness of the sleeve are optimized, and range of interference value is accurately limited based on four extreme operating conditions. The 3-D Finite Element Model (FEM) is used to validate the strength characteristics and stress distribution of rotor. A 1.5 kW-150000 r/min UHSPMSM with integrated support system is manufactured and tested. The feasibility of UHSPMSM proposed and the accuracy of analysis method are verified through electromagnetic, temperature rise and vibration characteristics test. The machine prototype realizes the load operation at rated speed and the multi-physical-field characteristics achieve the design specification.     

低密度镁锂合金性能强化与精密成形技术

针对轻质高强和近成形复杂结构的技术要求，提出一种基于低密度镁锂合金薄壁筒形件的等温超塑性双向挤压近净成形方法，研究了铸态成形性能、铸态和轧制态在不同温度下的力学性能变化规律。研究结果表明，铸态下延伸率约12%，抗拉强度约145 MPa，轧制态下延伸率变化不大，但抗拉强度提升到180 MPa以上。采用本论文方法镁锂合金的延伸率和抗拉强度显著提高，分别达到21%和216 MPa，表明高温大变形过程中，实现了晶粒细化，大量增强相弥散在晶粒内部，起到性能强化作用，成功实现其性能强化和复杂结构件的精密成形。     

2524与7150铝合金激光焊T型接头的组织与性能

介绍了2524与7150铝合金激光焊T型接头优化的工艺参数,并研究了T型接头在优化工艺下的显微组织与力学性能,进行金相分析、显微硬度测试与接头拉伸试验。结果表明:优化工艺下焊缝没有裂纹、气孔,金相组织晶粒细小、致密,焊缝区域的硬度最低;T型接头x方向的拉伸强度达到384 MPa,z方向的拉伸强度为236 MPa。     

2219 铝合金单、双道焊接头性能分析

通过对比2219 铝合金单道氩弧焊和氦弧打底+氩弧盖面双道焊接头的常温及液氮温度拉伸性
能、显微硬度分布、单向拉伸过程的数字散斑测量(DIC)结果,发现在常、低温条件下双道焊接头的拉伸强度和
延伸率均比单道焊接头高10% ~20%,单道焊接头焊缝及热影响区内材料的显微硬度值相比母材的降低程度
比双道焊接头更为显著,其主要原因是单道焊接头的一次性热输入大于双道焊,材料受热影响更严重,焊漏高
度及形状的可控性更差。     

碳纤维表面状态对C/C复合材料性能影响的研究

用两种经高温处理的碳纤维织物,以酚醛树脂作为基体先驱体,制备了二维C／C复合材料。通过扫描电镜（SEM）,X－射线光电子能谱（XPS）研究了两种碳纤维（TCF和JCF）的表面状态,测试了C／C复合材料（TCC和JCC）的层间剪切强度,拉伸性能,SEM观察表明,TCF及JCF表面都有沟槽,但TCF横断面呈腰子形非圆形,XPS分析表明TCF表面含氧官能团数量多,力学测试结果为：TCC层间剪切强度（ILSS）高于JCC,达到16．1MPa;TCC拉伸强度,模量均高于JCC,而JCC断裂延伸率达1．1％,是TCC的3倍,拉伸断口SEM分析表明,TCC断口平整,无纤维拔出,呈脆断,JCC断口有纤维拨出,是纤维控制的多层基体断裂。     

Through-thickness heterogeneity in creep properties of friction stir welding 7B50-T7451 aluminum alloy thick plate joint: Experiments and modeling

Through-thickness heterogeneity in creep properties of 7B50-T7451 aluminum alloy Friction Stir Welding(FSW) joints was investigated. Creep tests for three slices of the FSW joint were conducted at the temperature of 150–200 °C and applied stress of 60–225 MPa. The theta projection method was used to predict creep curves and minimum creep rate. The results show that the minimum creep rate increases and creep rupture life decreases with the increase of creep temperature and applied stress. Creep p...     

空间级硅橡胶胶黏剂粘结界面改性分析

针对空间级硅橡胶与聚酰亚胺的粘结界面呈现低表面能、粘结可靠性差的现状，利用有机硅烷的润湿和键结作用对界面进行预处理，改善其粘结强度。通过FTIR、¹H-NMR和GC-MS分析，有机硅烷的主要成分中对粘结性能影响较大的是正硅酸丁酯和丙基三甲基硅氧烷，采用两种偶联剂对聚合物表面进行预处理，在聚合物间不同均相结构层通过硅烷相互扩散和互穿网络形成的分子桥可实现致密交联。力学试验表明，经有机硅烷对待粘结界面表面预处理，粘结构件的剪切强度值可达0.65 MPa；选择适当的有机硅烷作为附着力促进剂，利用其有机官能团、成膜性和交联性可提高粘结构件的可靠性。