TC18钛合金焊接接头力学性能试验研究

氩弧焊和电子束焊是钛合金加工中两类常见的工艺方法,对比研究两种工艺对焊接接头力学性能的影响对其在工程中的合理选用具有重要的参考价值。完成了TC18钛合金氩弧焊接头和电子束焊接头的静力拉伸及旋转弯曲疲劳试验,并根据试验结果对两类焊接接头的力学性能进行了对比分析,采用统计学方法给出了二者的中值疲劳寿命SN曲线及疲劳极限。研究结果表明：氩弧焊接头焊缝区内晶粒粗大,使得材料的力学性能明显劣化;电子柬焊接头具有更高的抗拉强度与更好的高周疲劳性能,更有利于工程应用。     

旋转对称结构零部件时变可靠性模型

分析了旋转对称结构零部件的失效特点以及对称单元数对零部件可靠性的影响,建立了能体现对称单元数的旋转对称结构零部件强度概率密度函数和累积分布函数.分别以随机载荷作用次数和时间为寿命度量指标,建立了随机载荷作用下能够全面体现载荷、强度、对称单元数、寿命指标等参数影响的旋转对称结构零部件时变可靠性模型与失效率计算模型.研究表明:在强度不退化的情况下,旋转对称结构零部件的可靠度也会随着寿命指标(载荷作用次数或时间)逐渐降低,失效率随寿命指标逐渐减小.对于具有相同对称单元的旋转对称结构零部件,随着对称单元数的增加,零部件可靠度会降低且失效率会增大.     

Phase Residual Estimations for PCVs of Spaceborne GPS Receiver Antenna and Their Impacts on Precise Orbit Determination of GRACE Satellites

In-flight phase center systematic errors of global positioning system(GPS) receiver antenna are the main restriction for improving the precision of precise orbit determination using dual-frequency GPS.Residual approach is one of the valid methods for in-flight calibration of GPS receiver antenna phase center variations(PCVs) from ground calibration.In this paper,followed by the correction model of spaceborne GPS receiver antenna phase center,ionosphere-free PCVs can be directly estimated by ionosphere-free carrier phase post-fit residuals of reduced dynamic orbit determination.By the data processing of gravity recovery and climate experiment(GRACE) satellites,the following conclusions are drawn.Firstly,the distributions of ionosphere-free carrier phase post-fit residuals from different periods have the similar systematic characteristics.Secondly,simulations show that the influence of phase residual estimations for ionosphere-free PCVs on orbit determination can reach the centimeter level.Finally,it is shown by in-flight data processing that phase residual estimations of current period could not only be used for the calibration for GPS receiver antenna phase center of foretime and current period,but also be used for the forecast of ionosphere-free PCVs in future period,and the accuracy of orbit determination can be well improved.     

Compressive properties of homemade carbon fiber composite laminates with delamination defect

Large numbers of aircraft composite structures were researched, and the distribution of delamination sizes and though thickness positions in the composite laminates were investigated. An experiment was conducted to probe into the effect of delamination sizes and through thickness positions on the compressive strengths of laminates with single embedded circular delamination with the most dangerous delamination sizes and positions defined from the distribution. A shell model was established for compressive strength prediction, and the virtual crack closure technique (VCCT) was employed for the strain energy release rate calculation. The finite element (FE) prediction was in good agreement with the experimental measurements, for the predicted compressive strengths stood within 10% error of experimental results. It was observed that the compressive strength was highly effected by the delamination size, while the though thickness position of delamination did not have significant effect on the compressive strength.      

预浸带的快速热压接技术及其搭接性能研究

为解决预浸带缠绕过程中手工搭接效率低的问题,针对原有缠绕设备,设计了一套预浸带自动快速热压接系统。首先分析了预浸带搭接面张力的重要性,并结合基体树脂的粘流特性,从热力学、动力学角度分析了影响搭接界面层搭接性能的主要因素,通过物理实验,分析了时间、温度及搭接长度对预浸带拉伸剪切强度的影响机制。据此,获得适于热压接系统的工艺参数;并对比手工缝接实验,说明该方案的优越性,对复合材料的自动化成型技术具有一定的指导意义。     

X-Cor夹层结构的平压性能

通过力学分析得到X-Cor夹层结构平压模量的解析式和计及泡沫对z-pin横向支撑的平压强度预测公式。分析X-Cor夹层结构平压模量的理论值与试验值误差,提出了结构屈曲和z-pin的长度差异引起的刚度折减的修正模型,修正后的夹层结构平压模量的理论值与试验值吻合。理论公式为X-Cor夹层结构的设计提供依据,进而为X-Cor夹层结构新材料在工程领域的应用奠定了基础。     

Effects of punch size,magnetic field,and magnetorheological elastomers medium on forming T-shaped thin-walled Inconel 718 tubes

This study aims at investigating the impact of using the Magnetorheological Elastomers(MREs) medium to improve the formability of T-shaped Inconel 718 tubes during the bulging process. Besides, the influence of the punch size and the intensity of the magnetic field on the branch height and wall thickness distribution of the T-shaped Inconel 718 tubes are also explored. The results showed that the parts formed by the punch with a length of 5 mm in the pressurization zone have better forming quali...     

浅谈A320系列主起落架外筒难加工点的加工方法

A320系列飞机主起落架外筒是形状不规则零部件,材料为超高强度钢,为难切削加工材料,一些孔径或者孔径的端面出现腐蚀后,需要镗削去除以满足CMM规定的修理要求。为解决此类难加工问题,本文设计了一种通用性强的T型非标BT-50铣刀,操作简单,成本效益高,大大提高了起落架维修能力。     

冷热循环对M40碳纤维/氰酸酯复合材料影响的试验研究

对M40碳纤维/氰酸酯复合材料进行了冷热循环试验,分别测试了经不同次数冷热循环后材料的质损率、弯曲强度和层剪强度,并通过扫描电镜对试样断口形貌进行了观察。结果表明:随着冷热循环次数的增加,样品有少量的质量损失;其剪切性能先增加后略有降低;碳纤维与树脂基体之间的界面结合状态良好。     

一种变信噪比条件下的恒虚警野值检测方法

野值检测又称异常值检测,是模式识别、机器智能和知识发现等领域经常面临的一个问题。当出现环境失配,数据信噪比（SNR）发生变化时,测试样本和训练样本所含噪声会有不同方差,以往的野值检测方法在虚警控制方面将会失效。针对这一问题,提出一种基于归一化残差（NR）的野值检测方法。该方法首先根据所需虚警概率和噪声方差变化情况确定野值检测门限,其次基于训练样本计算待考查模式的NR值,再比较NR值与检测门限的相对大小,从而判断待考查模式是否为野值。这一方法所依赖的检测门限对所需虚警率和噪声方差变化具有适应能力,因此可以在变信噪比条件下实现恒虚警（CFAR）野值检测。仿真实验验证了所提方法在虚警控制和野值检测方面的优越性能。