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排序方式: 共有1502条查询结果,搜索用时 324 毫秒
351.
为了研究TC11钛合金铣削加工过程中刀具磨损对加工表面质量的影响规律,设计了刀具磨损与铣削表面粗糙度、表面残余应力的试验。结果表明:TC11钛合金铣削加工过程中的刀具磨损可以分为:初期磨损、正常磨损、剧烈磨损三个阶段。当刀具处于"初期磨损"时,TC11铣削表面粗糙度随切削时间逐渐减小,铣削表面残余应力也呈减小趋势;当刀具处于"正常磨损"阶段时,铣削表面粗糙度和铣削表面残余应力都呈增加趋势,但增加的速度平稳;当刀具进入"剧烈磨损"阶段时,铣削表面粗糙度迅速增大,表面残余应力也较前两个阶段显著增加。另外,试验过程中的TC11铣削表面残余应力均表现为压应力。 相似文献
352.
离散式粗糙元诱导翼型边界层转捩的数值和实验研究 总被引:1,自引:0,他引:1
在Ma=0.6来流条件下,针对三维离散式圆柱粗糙元诱导NACA0012翼型边界层转捩问题开展了直接数值模拟(Direct numerical simulation,DNS)和油膜干涉风洞实验研究,分析了粗糙元诱导转捩的机理及粗糙元高度和相邻粗糙元间距对转捩位置的影响。结果表明,翼型表面粗糙元能够通过诱导出三维Λ涡和马蹄涡促进边界层转捩,达到转捩控制的效果。粗糙元高度和相邻粗糙元间距对边界层转捩有影响,且增加粗糙元高度和减小相邻粗糙元间距能够促进转捩。粗糙元高度对转捩的影响大于粗糙元间距,且对粗糙元后方区域影响大,对相邻粗糙元中间区域影响小。 相似文献
353.
为分析洛伦兹力磁轴承驱动磁悬浮控制敏感陀螺(MSCSG)转子偏转过程中的稳定性,针对现有双频Bode图稳定性判据方法仅适用于最小相位系统的不足,提出一种基于扩展双频Bode图的稳定性分析方法。根据洛伦兹力磁轴承工作原理建立了MSCSG转子偏转系统动力学模型;通过变量重构,将实系数双输入双输出系统等效变换为复系数单输入单输出系统;在分析Nyquist曲线与Bode图关联性的基础上,提出针对非最小相位系统的扩展双频Bode图稳定性判据,对不同转速下MSCSG转子系统稳定性进行预测,并通过转速根轨迹曲线预测转子系统的转速稳定区间。所提出的扩展双频Bode图稳定判据结果与时域仿真校验结果相一致,验证了本文所提出的稳定性分析方法的正确性和有效性。 相似文献
354.
355.
航天器表面介质材料易遭受表面充放电危害。利用30keV单能电子对几种不同的航天介质材料进行了表面充放电模拟试验,测量了不同电子通量辐照下的表面充电电位以及放电脉冲。试验结果表明,聚酰亚胺薄膜在接地处理不当时表面可充至千伏以上,易发生表面放电,且辐照强度越大,放电频率越高。表面镀铝的聚酰亚胺薄膜在不接地时,铝膜成为悬浮导体更加剧了放电的危害。而通过渗碳处理的聚酰亚胺薄膜,其良好的导电性能可有效抵御nA/cm~2量级电子的表面充电。聚四氟乙烯天线罩表面未进行防静电处理时,表面充电电位可达万伏量级,极易发生放电。 相似文献
356.
Hydrodynamic journal bearings are used to support the planetary gears in the transmission system of a Geared Turbo Fan engine, and they operate under severe working conditions, such as misalignment, high speed, and heavy load. Surface texture is regarded as an effective approach to improve mechanical properties under severe working conditions. However, the effects of surface texture on misaligned journal bearings under severe conditions have not been well studied. Therefore, a thermoelastohydrodynamic(TEHD) lubricating model with a textured and misaligned journal is presented in this study. Solid deformation, heat transfer between oil and the bearing, and heat convection between air and the bearing are considered in the model. The effects of cavitation and viscosity-temperature are also taken into account. The impacts of surface texture parameters and the misalignment angle on lubricating properties are investigated in the model. Results indicate that the bearing lubricating performance is greatly improved by optimal surface texture considering journal misalignment. The maximum oil film pressure and load-carrying capacity of a journal bearing increase with journal misalignment. Meanwhile, the oil film temperature increases sharply while considering misalignment. 相似文献
357.
Experimental study of effect of post processing on fracture toughness and fatigue crack growth performance of selective laser melting Ti-6Al-4V 总被引:1,自引:0,他引:1
For Ti-6Al-4V, a titanium alloy increasingly used in aerospace structure, selective laser melting (SLM) is an attractive additive manufacturing technology, which is attributed to its complex construction capability with high accuracy and good surface quality. In order to obtain qualified mechanical properties, SLM parameters and post processing should be tailored for diverse service conditions. Fracture toughness and fatigue crack growth (FCG) behavior are critical characteristics for damage tolerance evaluation of such metallic structures, and they are affected by post processing technologies significantly. The objective of this study is to obtain the fracture toughness and fatigue crack growth behavior of Ti-6Al-4V manufactured by SLM, and to evaluate the influence of post-SLM thermomechanical treatment and surface machining. Fracture toughness and FCG tests were performed for SLM Ti-6Al-4V in three types of post processing status: as-built, heat treated and hot isostatically pressed (HIPed), respectively. Specimens with as-built and machined surface were tested. The microstructure and fractography were analyzed as well in order to investigate the relevance among manufacture process, microstructure and mechanical properties. The results demonstrate that as-built SLM Ti-6Al-4V presents poor ductility and FCG behavior due to martensitic microstructure and residual stresses. Both heat treatment and hot isostatic pressing improve the plane-stress fracture toughness and FCG performance considerably, while surface machining shows slight effect. 相似文献
358.
The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields.However,the local load ing process forming limit is restricted by forming defects in the transitional region.In this work,the feasibility of controlling forming defects and improving the process forming limit by adjusting die parameters is explored through finite element (FE) simulation.It is found that the common cavum and folding defects in the transitional region are significantly influenced by the fillet radii of left rib and middle rib,respectively.The cavum and folding defects can be effectively controlled by increas ing the fillet radii of left rib and middle rib,respectively.The process forming limits considering forming defects in the transitional region are determined by the stepwise searching method under various die parameters.Moreover,the relationship between the process forming limit and die parameters is developed through the response surface methodology (RSM).The developed RSM models suggest that increasing the fillet radii of left and middle ribs is effective to improve the pro cess forming limit during local loading forming of rib-web components.The results will provide technical basis for the design of die parameters and the reduction amount,which is of great impor tance to control forming defects and improve the process forming limit in local loading forming of Ti-alloy large-scale rib-web components. 相似文献
359.
360.