基于P-ε-N曲线整体推断的涡轮盘寿命可靠性分析

疲劳寿命符合对数正态分布,并且对数寿命的标准差随弹性应变幅和塑性应变幅的减小而增大。采用基于异方差回归分析的整体推断方法在现有低循环疲劳试验数据的基础上,得到了航空发动机涡轮盘材料GH4133在温度250℃下的P-ε-N曲线;利用P--εN曲线对某涡轮盘进行低循环疲劳寿命可靠性分析,得到置信度0.95,可靠度0.998 7的轮盘寿命为1 866次循环,合683飞行小时,与涡轮盘疲劳试验分析得到的技术寿命接近。整体推断得到的P-ε-N曲线精度较高,利用P-ε-N曲线进行轮盘寿命可靠性设计分析具有计算简便、节约试验成本的优点。     

Simulation software for the spiral trajectory of our Moon

At 4.56 Ga, the accretion of the slowly rotating Solar Nebula led to the formation of Sun and its Planets in the plane of disc of accretion. Moon was formed by accretion from a circumterrestrial disk of debris generated by the glancing angle impact of the young Earth by a Mars size planetary embryo at about 4.5 Ga at a distance of 15,000 km. The Moon since then has migrated to the present position of 384,400 km from the center of the Earth. In course of this outward migration it has slowed down the spin rate of Earth and caused the lengthening of diurnal day length from 5 h initially to 24 h presently. The basic mechanics of Earth–Moon System has been worked out and theoretical determination of lengthening of day curve is carried out. This theoretical lengthening of day curve is compared with the observed lengthening of day curve based on paleobotanical evidences, ancient tidalites and Australian Banded Iron Formation. There is a remarkable correspondence between the two curves except for intermittent deviations due to geographical and geophysical factors. Based on the theoretical curve of lengthening of day, an empirical formula for the lunar orbital radius expansion is determined. Based on this empirical formula, simulation software is developed that gives the correct evolution of the semi-major axis (a) of our Moon for any time span from the inception to the time chosen under study. For mathematical simplicity the system is considered to be a two body rotating system throughout its evolutionary history of 4.5 Gyrs. This simulation draws the Moon’s spiral trajectory from its inception to any subsequent epoch. The terminal epoch is an input to the simulation software to arrive at the spiral trajectory of the Moon from the inception to the given epoch. The basic mechanics of Earth–Moon System and this simulation can be generalized to lay the foundation of simulation software for any Planet–Satellite pair or any Sun-Planet pair in our Solar System or Star-Planet pair in any Extra-Solar System. The basic dynamics has been found to be valid for Star–Planet pair also. So this Simulation Methodology can as well be applied to study the migratory evolution of Gas Giants also.     

高精度反射面板的形面调节新技术

提出了一种基于形面多点调节的紧缩场反射器面板精密柔性成形新技术,对面板形面调节机理进行了分析,提出了确定调节点位置、数量、调节量的形面调节核心技术,借助数值模拟方法确定了矩形面板调节点位置、数量,在实验基础上建立了调节量计算方法.设计、开发了面板形面调节实验平台;针对具有不同初始形面误差的面板进行了形面调节可行性数值模拟分析及实验验证.结果表明,利用所提出的调节技术和开发的形面调节实验平台能够实现双夹层金属蜂窝面板形面的有效调节,获得很高的形面精度.该项技术可以在现行成形技术的基础上进一步提高形面精度,可明显提高面板制造成品率,解决大尺寸高精度面板和较大曲率面板的制造难题,并能改善面板的使用及维护性能,延长紧缩场的使用寿命.     

基于关联探测的新型测距方法研究

设计了一种基于关联探测的新型测距方法,将关联探测应用到测距领域,通过分析时间关联符合计数,寻找最大符合计数所对应的延时,完成了实验室条件下短距离计算的实验验证,此外还设计了强度关联代替时间关联,寻找最大对比度所对应的位置信息,同样进行了功能验证,这为将来基于关联探测原理的新型测距仪的设计提供了理论依据和实验基础.     

基于弧长参数的开边自由曲面构件上纤维均匀覆盖(英文)

This article uses arc-length parameters for path planning to carry out robotic fibre placement （RFP） over open-contoured structures This allows representing the initial path and offset points using an identical mathematical equation and computation by more simple arithmetic. With the help of classical differential geometry, the calculation of fiber-placing paths may be reduced to solution of initial-value problems of first-order ordinary differential equations in the parametric domain （parametrically defined mould surface） or in 3D space （an implicitly defined mould surface）, thereby significantly improving on the existing methods. Compared with the conventional methods, the proposed method, besides its computational simplicity, has a better error control mechanism in computing the initial path and offset points. Numerical experiments are also carried out to demonstrate the feasibility of the new method in composite forming processes and also its potential application in computer numerical control （CNC） machining, surface trim, and other industrial practices.     

飞机蒙皮拉伸成形加载轨迹设计及优化

加载轨迹是决定飞机蒙皮拉伸成形质量的关键因素.首先对双曲度单凸蒙皮变形最大截面采用应变控制方法,通过解析分析公式推导设计拉形加载轨迹范围;然后将各加载参数转化为拉形设备中夹钳和工作台运动参数,并作为设计变量;最后采用最优化理论与算法和有限元数值模拟相结合的方法,以减小卸载回弹提高贴模度为研究目标,以单元最大主应变和厚度减薄率为约束条件建立最优化数学模型,采用序列二次规划的优化方法确定最合理的拉形加载轨迹;对优化结果进行实验验证,实验结果和优化结果相吻合.分析表明加载轨迹优化后,成形零件的贴模度、应变分布与厚度的均匀程度均有明显提高.      

航天器空间碎片超高速撞击防护的若干问题

空间碎片对航天器的超高速撞击损伤已受到国内外的普遍重视,如何使在轨航天器对空间碎片进行有效防护是航天器长寿命、高可靠安全运行的重要保障。文章概述了空间碎片环境现状、空间碎片超高速撞击危害以及国内外空间碎片防护的研究现状和趋势。重点介绍了航天器常用的Whipple防护结构及其各种衍生结构的防护性能和弹道极限方程（BLE）,评述了这些防护结构防护性能的优缺点。     

复杂异形截面薄壁环形件动模液压成形研究

 液压成形技术是成形薄壁零件的一种有效的解决方法。针对具有异形截面结构的某型发动机高温合金薄壁环形件,提出了液压成形结合动模轴向加载的复合成形方法,依据塑性力学方法和增量理论对成形过程进行了应力应变特征分析,并建立了有限元模型。基于有限元模拟和工艺试验,研究了筒坯成形区高度和型腔液压加载路径等关键工艺参数对零件成形结果的影响,探讨了成形过程中壁厚过度减薄、材料堆积"折叠"、形状不对称等失效形式,提出了优化的工艺参数。结果表明,提出的工艺方法可实现复杂异形截面薄壁环形件的整体精确成形,采用优化的筒坯成形区高度和液压加载路径可获得壁厚分布均匀、成形质量较好的零件。     

钛合金筋板类构件局部加载成形有限元仿真分析中的摩擦及其影响

局部加载等温成形为大型钛合金筋板类构件省力、高性能成形制造提供了有效的途径。然而其成形过程复杂,材料参数、几何参数、工艺参数高度耦合作用,精确预测困难。有限元仿真为此类复杂成形问题的分析和优化提供了有力的工具。而摩擦模型和摩擦条件是数值模拟的重要边界条件之一,影响到预测结果的精度及可靠性。本文着重分析了库伦摩擦模型、剪切摩擦模型、库伦-剪切摩擦模型、库伦-粘着摩擦模型以及摩擦大小对筋板类构件局部加载成形仿真分析结果的影响。研究结果表明:剪切摩擦模型适用于局部加载成形过程的建模仿真;确定精确的摩擦条件可降低载荷预测误差15%以上;主动调控局部区域摩擦条件可改善局部加载成形过程的充填、减少缺陷。     

LY12蠕变时效成形机制及回弹规律研究

研究了LY12的蠕变时效成形过程中第二相的析出演变特征,从微观角度分析了蠕变时效成形的强化机制。修正蠕变本构方程并开发为ABAQUS/CREEP,模拟研究了时效时间、时效温度和预弯半径对回弹规律的影响,建立了回弹函数。验证结果表明,回弹函数的计算准确率较高。