基于声发射衰减特性的故障行星轮定位研究

行星齿轮箱是风力机传动装置的重要组成部分,行星轮在低速重载、既自转又公转的复杂环境下容易诱发故障,其故障诊断特别是故障行星轮定位一直是研究重点和难点。建立了行星轮齿轮箱实验装置,模拟了行星轮故障,并利用声发射信号进行故障行星轮定位。实验研究了声发射信号在齿轮内部、齿轮与齿轮之间的传播特性,利用信号的幅值衰减特性简化了故障定位模型。利用信号幅度随信号传播距离增加而呈指数衰减的关系,建立了故障源定位方程组,从而获得故障齿的啮合位置,进一步确定故障行星轮的位置。实验结果表明:利用声发射信号的幅值衰减特性能够较为精确的确定故障行星轮的位置。     

声发射检测技术用于滚动轴承故障诊断的研究综述

声发射是材料受力变形产生弹性波的现象,故障滚动轴承在运转过程中会产生声发射.从几个方面综合阐述了国内外轴承故障声发射检测技术的研究和发展现状,即轴承故障声发射信号的产生机理,故障声发射信号的传播衰减特性,声发射信号的参数分析法和波形分析法对故障特征的描述,轴承故障声发射源的定位问题,根据信号特征进行故障模式识别以及声发射检测和振动检测的比较问题.通过分析总结出滚动轴承声发射检测技术下一步的研究方向,并指出滚动轴承故障的声发射检测是振动检测的有力补充工具,特别是在轴承低转速和故障早期的检测中更能发挥作用.     

金属材料声发射信号传播的声阻抗特性研究

金属材料声发射信号的传播特性是研究声发射技术的重要基础,声阻抗是表征金属材料动态特性的重要物理量,用声阻抗研究声发射信号传播特性,将有助于声发射信号在损伤检测中的应用。在综述金属材料声阻抗实测估计研究的基础上,提出了估计金属材料声发射信号声阻抗的方法,探讨了金属材料在经受荷载并卸载后以断铅声发射信号估计其声阻抗的方法。数值模拟和实验数据分析表明,通过断铅声发射可以估计材料经受荷载的声阻抗变化,金属材料声发射信号声阻抗估计值可以较好的表征声发射信号的传播特性,甚至还可能对材料经受荷载情况进行声阻抗成像,可能成为材料内部损伤检测的新方向。     

石油高压管汇声发射特性的研究

为了解决石油高压管汇常规无损检测费时费力的现状,提高检测准确性,从实验入手,根据声发射技术原理,分析出声发射源产生的声发射信号在石油高压管汇的的传播特性,给出检测中排除噪声的方法,通过破坏实验研究分析出石油高压管汇缺陷扩展的声发射信号参数特征,并给出石油高压管汇声发射检测的最佳布点方式.实验表明,声发射技术应用到石油高压管汇检测准确度高、效率高,为其他声发射信号传播衰减小、传播特性好的石油设备的声发射检测提供参考.     

强背景噪声下微弱声发射信号提取及处理研究现状

针对故障诊断领域声发射信号因工作环境及采集设备自身影响常受强背景噪声干扰导致混叠失真问题,对故障诊断中声发射信号特性及处理流程、强背景噪声下声发射信号降噪方法(小波分析,ICA,EMD)、声发射信号特征提取及故障识别等国内外研究现状进行综述;分析总结声发射信号在降噪、特征提取及故障识别研究中存在的不足,探讨解决方法,展望声发射信号处理技术发展。     

一类弱非线性波浪数值模型及其适用性分析

研究了一类含弱非线性的改进型Boussinesq水波方程,在非交错网格下,利用有限差分法建立了混合四阶Adams-Bashforth-Moulton的预报校正格式的波浪数值模型。在数值模型中,关于空间一阶导数差分格式采用四阶精度、二阶导数差分格式采用二阶精度。针对波浪的一维、二维传播变形问题进行了数值计算,并通过与相关实验结果对比分析考察了该数值模型的适用性。     

基于标准声源的有限水域试验场声传播特性试验研究

舰艇噪声控制实验中,为保证模型和实艇的声学相似性,增大模型比例是关键,实际上,大比例舰艇模型的声学实验很难在消声水池中进行,因此,天然有限水域试验场成为首选。在有限水域试验场中进行大型复杂结构的水下声振试验,声信号测量和数据处理至关重要。天然有限水域边界条件未知,水文环境及声传播特性复杂,仿真难度高,增加了水声信号的处理难度。基于标准声源试验研究某有限水域试验场的声传播特性,实质上是把水下辐射声压级测量值归一到距标准声源单位距离处的声压级,采用AcTUP软件对试验场的沉积层声学特性和水位选取原则进行探究,并基于射线声学理论对声压级试验值和理论值的偏差进行非相干分析,从而得到试验场基本声学参数对声传播特性的影响规律。     

基于近场波束形成法的声发射源定位研究

引入近场波束形成法处理声发射信号,研究在小区域布置少量传感器来实现声发射源定位的新方法.首先,利用板波理论进行声发射信号传播特性研究,对比了板中声发射信号与空气中声波传播的差异性,分析了波束形成法应用于声发射源定位的问题.并在板上进行断铅实验,验证了近场波束形成法进行声发射源定位的有效性.最后,在旋转机械碰摩模拟实验台上进行了碰摩实验,利用波束形成法进行碰摩声发射源定位,所提出的方法能有效地定位旋转机械初始碰摩位置.所得结果可为声发射源定位提供一种新途径.     

基于声发射和长短时记忆神经网络的端对端燃气高压调压器故障诊断

在燃气输配系统中燃气调压器处于关键位置,及时有效地诊断其故障类型具有重要意义。文章提出了一种基于声发射信号和长短时记忆神经网络的端到端故障诊断方法,直接利用时域声发射信号对调压器的运行状态进行诊断。首先,设计一个二阶巴特沃斯高通滤波器对采集的声发射信号进行预处理;其次,利用长短时记忆网络（LongShort Term Memory networks,LSTMs）的记忆特性,构建长短时记忆网络端到端（e2e-LSTM）故障诊断模型。实验结果表明,该模型根据输入的高压调压站采集的声发射信号,能够以端到端模式一次性地诊断五种高压调压器故障。     

声二极管中声传播模型研究

提出一种数值计算模型以描述声子晶体和包膜气泡群构成的声二极管中声传播。声子晶体中的声传播基于有限差分的方法数值求解,而微气泡中的非线性声传播采用非线性声波方程耦合微气泡振动方程求解。数值模拟的结果与已报道的实验结果相符合,证明了数值模型的有效性。在此基础上进一步讨论了包膜气泡参数改变对声二极管整流比的影响。     

The effect of helicoidal cracks on the behaviour of rotating shafts

Fatigue cracks can develop in rotating shafts: their propagation is mainly in planes perpendicular to the axis of rotation, but also slant or helicoidal cracks could appear in industrial machine shafts. In this paper the static elastic behaviour of a shaft affected by a slightly helicoidal crack has been analysed by means of 3D finite element non-linear models, calculating deflections in different load conditions. Differences with respect to shafts affected by planar cracks of same depth and extension are emphasized. In order to simulate the dynamic behaviour of rotating shafts, a simplified model of the elastic behaviour of the cracked shaft has been developed, validated and substituted to the cumbersome 3D model. This model has then been introduced in the model of a power plant turbogroup shaft line in order to analyse its behaviour. The results show the additional vibrations caused by the crack which could be measured in different operating conditions of the group.     

Torsion response of a cracked stainless steel shaft

Pump shafts used for power generation are susceptible to fatigue cracking while often in near-continuous operation. Technology based on torsional vibration is under development for condition-based assessment of shaft health. The focus of this paper is on the relationship between a crack, which propagated due to bending loads, and the torsional stiffness of the shaft. An analytical method to determine the compliance associated with a crack has been implemented for a semi-elliptical surface crack. A 3-D finite element model of a shaft section with a crack has also been used to predict the effect of a crack on stiffness. Fatigue cracks were seeded in shafts on a three-point bend apparatus. A benchtop test rig was constructed to evaluate the torsional natural frequencies of a cracked shaft system. Quasistatic torsional stiffness tests indicated that crack closure has an effect on the results. A torsional finite element model of the benchtop test rig indicates that the first torsional natural frequency is reduced by the propagation of a crack. The reduction in torsional stiffness of the shaft inferred from the natural frequency results is in reasonable agreement with the quasistatic results and the model predictions.     

HXD1机车小齿轮轴断裂失效应力分析

HX_D1机车牵引电机小齿轮轴的两个疲劳源位于齿轮轴大端油槽-油孔交界处,相对于油槽谷底直径平面呈反对称分布,且不在油槽谷底.为深入研究应力在疲劳裂纹源萌生位置和裂纹萌生过程中的作用,本文基于有限元法建立了HX_D1机车牵引电机转轴组件有限元细节应力分析模型,分析了在齿轮副啮合力作用下小齿轮轴的细节应力及分布状态.计算结果表明:小齿轮轴大端油孔两侧的两个应力集中点关于油槽谷底直径平面呈现反对称分布,这与裂纹源的实际位置吻合;从小齿轮轴锥端向齿端观察,油孔左侧应力集中点第一主应力值较右侧大(约26 MPa),这一区别导致左侧首先萌生疲劳裂纹的概率增大,该分析结果与失效小齿轮轴失效样本统计分析结果吻合.计算结果证实,油槽-油孔交界处呈反对称分布的应力集中在小齿轮轴的疲劳裂纹萌生过程中起决定性作用,建议采用表面机械强化的方法在两个疲劳危险点引入适当的残余压应力,以改善小齿轮轴的抗疲劳性能.     

Condition Monitoring of Slow‐Speed Shafts and Bearings with Acoustic Emission

Abstract: For various rotating machinery applications, condition monitoring using high‐frequency Acoustic emission (AE) technology has remained a subject of intense study since the late 1960s. This paper demonstrates the results of an investigation for detecting and monitoring natural crack initiation and propagation in slow‐speed rotating machinery with the AE technology. In addition to highlighting previous work published by the authors [ 1 - 3 ] on condition monitoring of slow‐speed rotating machinery, this paper presents experimental results on accelerated bearing fatigue under starved lubricating conditions. For these investigations, purpose‐built test rigs were employed for generating natural degradation on both a bearing and a shaft. It is concluded that crack initiation and propagation on slow‐speed bearings and shafts can be detected with the AE technology.     

坦克扭力轴表面缺陷对疲劳寿命的影响

为探求坦克扭力轴过早产生疲劳断裂的原因,应用弹性有限元方法模拟了坦克扭力轴表面各种形状、尺寸的凹坑处产生的应力集中现象,结合坦克在某一训练科目下的载荷谱,使用疲劳分析软件计算了具有不同形状和尺寸缺陷的扭力轴的疲劳寿命(存活率为99%).结果表明:一旦扭力轴表面出现了凹坑,尤其是出现了狭长的裂纹状凹坑时,其疲劳寿命会急剧下降;当出现狭长的裂纹状凹坑时,将其扩展成等径凹坑(不增大凹坑深度),可使凹坑对扭力轴疲劳寿命的影响降至最低.     

Detecting natural crack initiation and growth in slow speed shafts with the Acoustic Emission technology

This paper presents results of an experimental investigation to assess the potential of the Acoustic Emission (AE) technology for detecting natural cracks in operational slow speed shafts. A special purpose built test rig was employed for generating natural degradation on a shaft. It was concluded that AE technology successfully detected natural cracks induced on slow speed shafts.     

The influence of roller burnishing on the fatigue crack propagation in notched round bars—Experimental observations under three-point bending

Roller burnishing involves a local plastic deformation on the surface that permits the fatigue strength of structures to be increased. Crack propagation is delayed by the introduction of compressive residual stresses. In this way, the process is particularly useful in the presence of stress concentrators, for example in the fillets of crankshafts or in notched shafts. Crack propagation in round bars has been widely investigated, experimentally and numerically. However, the aim of the present work is to study roller burnished notched shafts (whose groove approaches the fillets of crankshafts) loaded in three‐point bending. Experimentally, a sequence of destructive interrupted tests has been performed to obtain the crack kinetics and shapes during fatigue life. Thus, the beneficial influence of roller burnishing has been confirmed on both crack initiation and propagation. Some cracks were even stopped by compressive residual stresses. Otherwise, the crack shape observed was very original : cracks propagated first at the edge of the coupon and then, into the depth of the shaft. Multicracking and crack closure have been pointed out and appear to be of great importance.     

Measurement of shaft diameters by machine vision

A machine vision method for accurately measuring the diameters of cylindrical shafts is presented. Perspective projection and the geometrical features of cylindrical shafts are modeled in order to enable accurate measurement of shaft diameters. Some of the model parameters are determined using a shaft of known diameter. The camera model itself includes radial and tangential distortions terms. Experiments were used to measure the accuracy of the proposed method and the effect of the position of the camera relative to the shaft, as well as other factors.     

Load distribution in the axial direction in a spline coupling

A finite element model has been made of a spline coupling between a shaft and a sleeve. The stress concentration factor is calculated and compared to analytical calculations. An analytical model for the load distribution in the axial direction and the torque transfer between shaft and sleeve is presented and compared to finite element results. Methods to uniform the load distribution and thereby decrease the stress concentration factor are tested with the analytical model. The induction hardened shafts with splines are fatigue tested and the lives are presented. The residual stress on the shaft surface is measured. The analytical model shows that the best way uniform the load is to vary the thickness of the spline tooth in the axial direction. Different shapes and sizes of the tooth thickness variation are also investigated. It is probably possible to extend the fatigue life at least two times for this spline, by uniforming the load distribution.     

Linearization of dynamic equations of flexible mechanisms—a finite element approach

A finite element based method is presented for evaluation of linearized dynamic equations of flexible mechanisms about a nominal trajectory. The coefficient matrices of the linearized equations of motion are evaluated as explicit analytical expressions involving mixed sets of generalized co-ordinates of the mechanism with rigid links and deformation mode co-ordinates that characterize deformation of flexible link elements. This task is accomplished by employing the general framework of the geometric transfer function formalism. The proposed method is general in nature and can be applied to spatial mechanisms and manipulators having revolute and prismatic joints. The method also permits investigation of the dynamics of flexible rotors and spinning shafts. Application of the theory is illustrated through a detailed model development of a four-bar mechanism and the analysis of bending vibrations of two single link mechanisms in which the link is considered as a rotating flexible arm or as an unsymmetrical rotating shaft, respectively. The algorithm for the calculation of the matrix coefficients is directly emenable to numerical computation and has been incorporated into the linearization module of the computer program SPACAR¹.