单钉机械连接孔边应力及失效分析

采用非线性Gap单元建立了复合材料层合板单钉连接有限元分析模型,并对五种不同铺层比例的层合板进行了计算,同时,还运用Hoffman失效判据对层合板进行了失效分析.根据计算结果分析了铺层比例对孔边应力分布、钉孔接触力分布和孔边失效系数的影响,得出最优铺层比例方案,其结论对复合材料层合板单钉机械连接设计具有一定的工程参考价值.     

涡轮叶片前缘对冲孔排气膜冷却特性的数值研究

对涡轮叶片前缘对冲孔排和错位对冲孔排的气膜冷却特性进行了数值研究,分别在吹风比为05、10、15、20的工况下,分析了模型表面气膜冷却效率和表面传热系数的分布规律,对比了不同气膜孔排结构和孔间距对下游气膜冷却效率和传热系数的影响。结果表明:相比于传统同向倾斜孔排结构,对冲孔排结构并没有减弱气膜的冷却特性,反而在靠近端壁处比传统同向倾斜孔排更易于加工;两种孔排下的气膜冷却效率均随着吹风比的增大而减小,而传热系数值均随着吹风比的增大而增大;在孔排近下游范围内,随着孔间距的增大,气膜冷却效率逐渐减小且在小吹风比下更加明显,传热系数值随着孔间距的增大逐渐减小且在大吹风比下更加明显。      

搅拌摩擦焊匙孔修复技术研究现状

搅拌摩擦焊虽是一种环保高效的固态连接方法,但在收焊处遗留的匙孔却难以避免,往往需要对匙孔进行修复.本文综述了搅拌摩擦焊匙孔修复技术国内外研究现状,指出了匙孔修复对采用搅拌摩擦焊结构的重要性,为实际生产过程中搅拌摩擦焊缝匙孔修复提供参考.     

涡轮叶片先进气膜冷却与相关激光打孔技术进展

航空发动机涡轮叶片依赖于高温基体、热障陶瓷涂层和气膜冷却技术实现高的工作温度,进而实现高的燃油效率和推重比.介绍了气膜冷却技术的演化趋势,并通过猫耳异型孔与直圆孔的仿真对比,指出复杂异型气膜孔的重要性.进一步论述了单步加工异型孔的必要性和工艺方案,指出为解决单晶叶片异型孔加工难题,超短脉冲激光加工虽然成为研究热点,但水助激光加工更应该引起重视.     

Console形气膜孔改善冷却效率的数值研究

运用剪应力输运湍流模型对Console形孔的气膜冷却结构,在不同吹风比下的气膜冷却效率的分布进行了数值研究;并在保持冷气入口相同开孔率的条件下,将其与圆形和缝形气膜孔的冷却效率进行比较.结果表明:随着吹风比的增加,Console形气膜孔的冷却效率也在增加;在相同吹风比条件下,Console形孔的冷却效率较圆形孔高,较缝形孔低;但在小吹风比时,基本与缝形孔的冷却效率相当.      

含孔复合材料层合板孔边应力集中的近似计算

针对含圆孔有限大复合材料层板的应力集中间题,提出一种计算孔边应力分布及应力集中系数的方法:先利用经典层板理论,将复合材料层合板化归为各向异性板;再将各向异性板等效转换为一偏轴拉伸的单向纤维层板;最后利用含圆孔偏轴单向板的孔边应力计算公式来分析一般铺层层合板孔边应力集中情况.根据所推导的含孔有限宽度复合材料层合板应力集中系数的表达式,分析讨论了板宽/孔径比、铺层比例、铺层方式、材料性能参数等因素对孔边应力集中的影响.     

TC11钛合金盘不同显微组织的疲劳-蠕变特性

3种显微组织的TC11合金盘疲劳-蠕变交互作用试验的结果表明,循环应力σ_(max)在560～660MPa范围内,双态组织具有最好的疲劳-蠕变性能,网篮组织次之,等轴组织最差;其它应力范围,网篮组织寿命远高于等轴组织,也高于双态组织。SEM观察发现,3种组织裂纹源区和扩展早期均具有明显的解理特征,且解理平面的形成与裂尖塑性应变累积和高温氧化效应有关。随着裂纹扩展,解理迹象逐减,疲劳条纹和蠕变空洞骤增,交互作用明显增强。     

High energy radiation from the direction of the galactic black hole Sgr A

X-ray observations indicate that the Galactic black hole Sgr A^∗ is inactive now, however, we suggest that Sgr A^∗ can become active when a captured star is tidally disrupted and matter is accreted into the black hole. Consequently the Galactic black hole could be a powerful source of relativistic protons with a characteristic energy ∼10⁵² erg per capture. The diffuse GeV and TeV γ-rays emitted in the direction of the Galactic Center (GC) are the direct consequences of p–p collisions of such relativistic protons ejected by very recent capture events occurred ?10⁵ yr ago. On the other hand, the extended electron-positron annihilation line emission observed from GC is a phenomenon related to a large population of thermalized positrons, which are produced, cooled down and accumulated through hundreds of past capture events during a period of ∼10⁷ yr. In addition to explaining GeV, TeV and 511 keV annihilation emissions we also estimate the photon flux of several MeV resulting from in-flight annihilation process.     

Theoretical study of flow ripple for an aviation axial-piston pump with damping holes in the valve plate

Based on the structure of a certain type of aviation axial-piston pump＇s valve plate which adopts a pre-pressurization fluid path （consisting a damping hole, a buffer chamber, and an orifice） to reduce flow ripple, a single-piston model of the aviation axial-piston pump is presented. This sin- gle-piston model comprehensively considers fluid compressibility, orifice restriction effect, fluid resistance in the capillary tube, and the leakage flow. Besides, the instantaneous discharge areas used in the single-piston model have been calculated in detail. Based on the single-piston model, a multi-piston pump model has been established according to the simple hydraulic circuit. The sin- gle- and multi-piston pump models have been realized by the S-function in Matlab/Simulink. The developed multi-piston pump model has been validated by being compared with the numerical result by computational fluid dynamic （CFD）. The effects of the pre-pressurization fluid path on the flow ripple and the instantaneous pressure in the piston chamber have been studied and opti- mized design recommendations for the aviation axial-piston pump have been given out.