非线性超声理论在金属基复合材料结构应力检测中的应用

金属基复合材料结构是金属层与非金属层多层粘接而成的复合结构,非金属层的应力行为主要体现在粘接面上,利用应力一时延模型测量应力,非金属层的深层反射回波信号非常微弱,给各层信号的识别存在极大的困难,不能准确估计时间延迟.文中从非线性超声理论出发,提出运用非线性超声的二次谐波非线性系数进行非金属层应力检测,实验结果表明非线性系数可以表征应力.     

导弹发动机壳体粘接质量红外热波检测

发动机壳体粘接质量检测对确保整个导弹武器系统的安全可靠具有重要的意义。采用平底洞和预埋聚四氟乙烯薄膜层模拟各种类型壳体与绝热层的粘接缺陷,基于主动式脉冲加热的红外热波方法进行了检测研究,采用图像序列微分增强算法提高缺陷的检测能力,并与超声C扫检测结果进行了对比,实现了缺陷大小和深度的定量识别。结果表明:红外热波方法的检测速度远远快于超声C扫,其检测效率较高;该方法适用于复杂结构及任意形状的缺陷,便于实现在线检测,具有较强的工程应用价值。最后,给出了热波方法在导弹发动机壳体粘接质量检测中的适用范围及检测策略。     

连杆的运动及有限元分析

连杆是发动机曲柄连杆机构中重要的构件。其工作环境受力状况极其复杂,因而对连杆的要求极高。文中主要研究某型号发动机连杆的受力状况,并计算出其在工作工程中所受的惯性力及最大拉压应力。并建立连杆的模型,导入ANSYS中对连杆进行静应力有限元分析。分析得出连杆小头部分的变形最大、损伤最大、寿命最低。并对最大拉伸压缩工况下的最值数据进行对比,得出最大压缩工况对连杆的影响较大。为连杆机构的设计制造和优化提供重要的参考。     

奇异裂纹单元在固体导弹发动机药柱裂纹分析中的应用

为评估含裂纹的固体导弹发动机能否正常点火发射,利用奇异裂纹单元进行固体发动机药柱的裂纹分析.在发动机点火增压与轴向过载作用下,于发动机药柱危险截面的翼锥根部构建二维奇异裂纹单元,模拟裂纹扩展.随着裂纹的扩展,分别计算对应裂纹深度的应力强度因子,由此判断裂纹的稳定性.     

基于线性相位的弱信号调理电路的设计

针对应力波反射法应用于锚杆锚固质量检测时,二次反射信号很弱以及对反射信号的频率响应和时延特性要求高的特点,设计了一种具有线性相位的弱信号调理电路。该信号调理电路将压电式加速度传感器采集的声频应力波信号,进行隔直、交流放大和线性滤波处理,采用五阶贝塞尔有源低通滤波器,使通带内具有近似恒定的增益和群延,从而保证后续对信号相位信息处理更精确,该电路经实际应用,可以满足弱信号调理要求。     

随机载荷作用下某导弹挂架的疲劳寿命分析

对某导弹挂架在随机载荷作用下进行有限元动态仿真分析,基于随机谱分析基础,利用基于高斯分布和Miner线性累计损伤定律的三区间法对某导弹挂架进行了随机振动疲劳环境分析。分析得到:导弹挂架结构在飞机给定随机激励下的应力响应特征以及导弹挂架结构疲劳危险区域为耳片;根据材料疲劳特性,计算得到挂架结构空载及加载情况下的振动疲劳寿命系数,由寿命系数可知结构满足其寿命要求。     

用实验—有限元法确定圆环中残余应力的分布

1 简介为提高高压圆筒的承载能力和疲劳强度,常采用自增强处理工艺,使简体内壁产生残余压应力。残余应力的无损检测方法有X射线法、磁测法、超声法等。X射线法和磁测法只能测定试件表面一薄层材料的残余应力,超声法也只能测定简单应力状态的构件(如螺栓的轴向拉力),而对于象厚壁圆筒经自增强处理后的残余应力,用该法测定十分困难。残余应力的     

超声应力检测中的温度和应变影响分析

基于时延效应的超声应力测量，对温度以及微小应变都非常敏感，而当前各种测量技术对这两因素考虑不足，给应力的定量测量带来很大的误差。文章建立了应力测量的温度、形变与应力的关系模型，最后试验验证了分析的正确性，证明进行温度和应变影响修正的重要性。     

超声检测表面残余应力的研究与发展

叙述了超声检测残余应力的特点，阐述了研究现状和应用领域，对超声检测残余应力的关键技术进行了分析，指出超声检测残余应力的发展方向和广阔的应用前景，为进一步开展研究提供一定依据和指导。     

奇异裂纹单元在固体导弹发动机药柱裂纹分析中的应用

为评估含裂纹的固体导弹发动机能否正常点火发射，利用奇异裂纹单元进行固体发动机药柱的裂纹分析。在发动机点火增压与轴向过载作用下，于发动机药柱危险截面的翼锥根部构建二维奇异裂纹单元，模拟裂纹扩展。随着裂纹的扩展，分别计算对应裂纹深度的应力强度因子，由此判断裂纹的稳定性。     

非线性超声在金属基复合材料结构界面粘接强度评价中的应用

针对常规超声波难以对金属基复合材料结构的界面质量进行评价的问题,设计了非线性超声检测系统,利用超声波在界面上传播时微小缺陷与其相互作用产生的非线性响应信号,通过计算回波信号的超声非线性系数,就可以进行金属基复合材料结构界面弱粘接缺陷的检测,进而评价界面的粘接质量.实验结果表明超声非线性系数与界面的粘接强度之间存在一定的关系,因此,非线性超声检测方法有望用于金属基复合材料结构的无损评价.     

基于汽车驱动桥壳再制造的堆焊可靠性研究

为了研究汽车驱动桥壳表面损伤后的堆焊修复层能否满足再制造的要求,选用H13CrMoA和ER50-6焊丝并采用亚激光瞬间熔工艺,在汽车驱动桥壳片表面制备不同厚度的堆焊层。利用金属磁记忆检测仪和扫描电镜分析堆焊试样的应力分布和断面组织特征,同时测试堆焊试样的硬度并进行渗透、磁粉和X射线三种无损检测。结果表明：ER50-6堆焊试样的堆焊层与母材硬度相近,母材热影响区未发生局部软化,堆焊层与母材结合良好,不存在焊接缺陷和应力集中区,应力分布不均匀程度低于H13CrMoA堆焊试样。
     

导弹转运车软管的优化设计

将波纹管和网套作为整体的软管作为研究对象,利用有限元分析软件ANSYS平台提供的二次编程语言APDL,建立了导弹转运车金属软管的参数化有限元模型,在此模型基础上,以提高金属软管的使用寿命为目标,对模型的重要参数-过渡波下降高度和波数进行了优化设计,使最高应力下降30％,从而提高了软管的使用寿命,得到了较为合理的金属软管有限元模型,为导弹的安全转运提供了必要的保障;为金属软管的生产设计工作提供了可靠的理论依据和有价值意义的参考.     

Microcontroller based system for electrical breakdown time delay measurement in gas-filled devices

This paper presents realization of a digital embedded system for measuring electrical breakdown time delay. The proposed system consists of three major parts: dc voltage supply, analog subsystem, and a digital subsystem. Any dc power source with the range from 100 to 1000 V can be used in this application. The analog subsystem should provide fast and accurate voltage switching on the testing device as well as transform the signals that represent the voltage pulse on the device and the device breakdown into the form suitable for detection by a digital subsystem. The insulated gate bipolar transistor IRG4PH40KD driven by TC429 MOSFET driver is used for high voltage switching on the device. The aim of a digital subsystem is to detect the signals from the analog subsystem and to measure the elapsed time between their occurrences. Moreover, the digital subsystem controls various parameters that influence time delay and provides fast data storage for a large number of measured data. For this propose, we used the PIC18F4550 microcontroller with a full-speed compatible universal serial bus (USB) engine. Operation of this system is verified on different commercial and custom made gas devices with different structure and breakdown mechanisms. The electrical breakdown time delay measurements have been carried out as a function of several parameters, which dominantly influence electrical breakdown time delay. The obtained results have been verified using statistical methods, and they show good agreement with the theory. The proposed system shows good repeatability, sensitivity, and stability for measuring the electrical breakdown time delay.     

Measurement of Attenuation of Ultrasonic Propagating through the Thin Layer Media with Time Delay Spectrum

The ultrasonic attenuation coefficient is one of the most important acoustic parameters to character the performance of a thin layer media, but it can not be measured due to mutual superposition of multiple reflected waves at the same interface in ultrasonic testing. Ultrasonic pulse echo and lamb wave to evaluate the thin layer media can not obtain attenuation coefficient at present. In this paper, analytical method was used to study the acoustics characteristic of thin layer media with the ultrasonic echo testing. Meanwhile, the process of ultrasonic attenuation measurement was presented. Simulation and experimental investigation is focused on a thin layer of rubber. Attenuation coefficient was introduced and evaluation mathematics model was established by the two echoes cross-correlation with and without the thin layer media based on the time delay spectrum. It involved the parameters related to the acoustic properties of the thin layer media. Through calculating the sound velocity and acoustic impedance with the evaluation model, it can deduce the relation between the attenuation coefficient and the frequency. Through analyzing the simulation results, it indicated that the attenuation coefficients were invariable with the varying of the frequency. However, the attenuation coefficients increased with the frequency increasing by ultrasonic testing the thin layer of rubber. The reason was that the attenuation factor was not taken into account during the simulation. This method overcomes shortcomings that the traditional ultrasonic testing can not evaluate the thin layer media whose thickness is less than motivation wavelength. It is a new solution to study the attenuation characteristic and on-line nondestructive evaluation in the thin layer media.     

Dynamic response of the temperature and stress fields in an I.C. engine piston

A numerical method is presented for calculating the dynamic response of temperature and thermal stress fields in I.C. engine parts. This method can be used for prevention of thermal failures in I.C. engines, such as thermal shock due to transient changes in load conditions, failure due to excessive thermal stresses, or deformations and metal fatigue. The program calculates the thermodynamic cycle, temperature and stress fields. A marine application was considered in this work and the change in b.m.e.p. and speed of the engine followed the propeller law. The results indicate that a sudden, even small change in power output above the nominal power may cause seizure of the piston due to excessive thermal expansion.     

国外弹道式导弹方位瞄准技术及其发展

弹道式导弹发展趋势向着固体火箭发动机、全机动发射方式、制导技术先进、命中精度高、飞行时间短、体积小、机动性强、反应速度快、突防能力强等方面发展,因此,与之相关导弹的瞄准技术也得到相应发展.导弹的方位瞄准直接影响导弹横向命中精度,得到了各国的重视和发展.本文介绍了国外铁路机动、地下发射井和潜艇发射导弹三种典型的瞄准系统,论述了导弹瞄准技术的发展.     

神经网络在参数估计中的应用

将神经网络用于线性连续不变系统（包括一种带时延的线性系统）参数估计中。线性系统分别用状态方程及传递函数来表示,给出了相应的神经网络结构及学习算法。     

微机化的多通道超声螺栓应力仪

本文介绍了一种新型的由微机控制及显示的超声应力仪的工作原理,该仪器可同时测定２４根螺栓应力,文章提出了声时差法测预紧应力,并推导了声时差同轴向应力以及三阶弹性常数的关系。采用声时差法多探头同时测量同一法兰上的各螺栓的预紧应力,可以克服偶合误差,可免测三阶弹性常数及温度等,使测量过程简便且严谨高。程序在Ｗｉｎｄｏｗｓ下设计,操作简便,应力能以多种图形方式显示。实验结果表明应力你于２５０ＭＰａ,夹紧距     

Effect of delay time on part strength in selective laser sintering

Selective laser sintering (SLS) is one of the most popular layered manufacturing processes used for making functional prototypes of polymers and metals. It is a powder-based process in which layers of powder are spread and laser is used to sinter selected areas of preheated powder. In the present work, experimental investigations have been made to understand effect of delay time on SLS prototypes. Delay time is the time difference for laser exposure between any two adjacent points on successive scanning lines on a layer. Tensile specimens of polyamide material as per the ASTM standard are fabricated on SLS machine keeping delay time range constant for the entire specimen. Specimens are fabricated for different ranges of delay time and tested on universal testing machine for tensile strength. An optimum value of delay time range is obtained experimentally. As delay time depends on part build orientation, an algorithm has been developed and implemented to find out optimum part build orientation for improving tensile strength. The obtained results from developed code are validated experimentally for tensile specimen. Case study for a typical 3D part is also presented to demonstrate the capabilities of developed algorithm.