带有齿根裂纹故障的齿轮传动系统非线性动力学模型研究

在考虑齿面摩擦、时变啮合刚度、传递误差和质量偏心的情况下,利用集中质量法及牛顿定律建立了齿轮传动系统非线性振动微分方程.通过时变啮合刚度仿真了齿根裂纹故障,进而建立了具有齿根裂纹的非线性动力学故障模型.该模型在计算摩擦力时,考虑了载荷在啮合区的动态分配以及利用齿轮副的检验标准与公差值来确定齿轮副的传递误差.模型数值解的结果与故障特征的规律相符,为频谱机理的分析及故障特征的提取提供了有力的理论依据.     

双圆弧齿轮轮齿弯曲应力的研究

 用三维边界元法对GB12759—91双圆弧齿轮的轮齿弯曲应力进行了分析计算，并在此基础上得出齿根应力与法向载荷之间、齿腰应力与法向载荷之间、齿根应力与当量曲率半径之间及齿腰应力与当量曲率半径之间的关系曲线．研究表明，大螺旋角或小载荷时，齿腰应力大于齿根应力．因此，齿腰应力也是关键环节，需受到重视.     

Measuring fatigue cracks in fillet welded joints

Accurate measurement of short (<1 mm depth) elliptical fatigue cracks that grow from the toes of fillet welds has proved to be an obstacle to the application of fracture mechanics principles to welding fatigue. This paper reports a DC potential drop technique which allows continuous measurement of the depth of such elliptical cracks. A delicate compromise between sensitivity and accuracy, combined with superior electrical stability displayed by the measurement apparatus, has allowed detection of: 1 — crack growth less than 0.01 mm and; 2 — crack growth rates less than 10^?7 mm/cycle for cracks less than 1 mm deep.Preliminary results have indicated the relative importance of stress ratio, defect size and material variation on the growth of these short elliptical cracks. When the weld toe is subject to high stress ratios the phenomenon may be considered propagation dominated whereas low stress levels increase the influence of threshold and initiation mechanisms.     

Experimental and numerical investigation of fatigue crack growth in the cracked gear tooth

The numerical simulation was conducted to analyse the fatigue crack growth in gear with the finite element codes ansys (ANSYS, Inc. Canonsburg, Pennsylvania, USA.) and franc 3d (Fracture Analysis Consultants, Inc. Ithaca, New York, USA.), and the corresponding fatigue test was also carried out. During the simulation, the location of maximal stress induced by the external force was first determined by the code ansys , and then the obtained results were imported into the franc 3d to analyse the crack growth. The analysed results were input into the codes ansys and franc 3d again to compute the stress and the stress intensity factor in the following steps. After several rounds of analysis, the results of the fatigue crack propagation were obtained. The investigations show that the crack mode I is dominant during the crack growth and the stress intensity factor K_I raises with increase of crack growth length and a series of quarter‐elliptical cross sections of the ruptured gear tooth are obtained. The simulation results are in good accordance with experimental findings.     

Molecular dynamics simulation of crack initiation and propagation in bcc iron under load within spur gear tooth root

Spur gears are widely used in practice, and one of their typical failures is tooth breakage. In general, the tooth breakage occurs at tooth root, and the amount of crack growth during a meshing cycle is in atomistic scale. This work aims at identifying the mechanisms of crack initiation and propagation at tooth root by using molecular dynamics simulation. The results prove that there are phase transition regions and edge dislocations at crack tips. According to the distribution characteristic of the atomic potential, its concentration can be observed obviously by visualization software. In these concentration regions, microvoids come into being and expand gradually, which results in the subcrack initiation. Additionally, the microvoids and subcracks propagate along the high potential direction and then come together to accelerate the crack growth. Through carrying out a comparative simulation, the effects of heavy load at single meshing area on crack initiation and propagation are addressed.     

Experimental investigation of spur gear tooth mesh stiffness in the presence of crack using photoelasticity technique

Gear mesh stiffness plays a very important role in gear dynamics and it varies in the presence of gear fault such as crack. The measurement of stress intensity factor can lead to the determination of gear tooth mesh stiffness variation in the presence of crack in a spur gear system. In this paper, the technique of conventional photoelasticity has been revisited to explore the possibility of using it as a supplementary technique to experimentally measure the variation of gear mesh stiffness. An attempt has been made to calculate the variation of mesh stiffness for a pinion having a cracked tooth and a gear tooth with no crack of a spur gear pair. An analytical methodology based on elastic strain energy method in conjunction with total potential energy model has been adopted and implemented within the mesh stiffness calculations. To visualize the state of stress in a structure using finite element and other currently available methods, photoelasticity is considered to be one of the oldest and most developed experimental technique. An experimental methodology based on conventional photo-elasticity technique for computing stress intensity factor (SIF) for cracked spur gear tooth is presented for different single tooth contact position and crack length. The relation between contact position, crack length, crack configuration, SIF and the variation of total effective mesh stiffness have been quantified. Finally, a comparison has been made and the results obtained from finite element method (FEM) based on linear elastic fracture mechanics (LEFM), analytical method and proposed experimental method has been outlined.     

基于传动误差检测法的早期齿轮磨损故障诊断

摘 要：针对齿轮系统在复杂结构复杂工况下早期故障难诊断的问题,借鉴精密机械中检测齿轮安装误差和加工误差的传动误差检测法,建立含故障的二级齿轮系统传动误差信号模型,分析中间轴齿轮早期单齿齿面磨损对齿轮系统传动误差的影响及特征规律。经齿轮传动系统实验台实测信号研究结果证明：传动误差信号信噪比高,能够有效识别复杂齿轮系统中齿轮早期磨损故障。     

Influence of different load models on gear crack path shapes and fatigue lives

A computational model for determination of the service life of gears with regard to bending fatigue at gear tooth root is presented. In conventional fatigue models of the gear tooth root, it is usual to approximate actual gear load with a pulsating force acting at the highest point of the single tooth contact. However, in actual gear operation, the magnitude as well as the position of the force changes as the gear rotates. A study to determine the effect of moving gear tooth load on the gear service life is performed. The fatigue process leading to tooth breakage is divided into crack‐initiation and crack‐propagation period. The critical plane damage model has been used to determine the number of stress cycles required for the fatigue crack initiation. The finite‐element method and linear elastic fracture mechanics theories are then used for the further simulation of the fatigue crack growth.     

球面渐开线齿形的螺旋锥齿轮NURBS设计

 为避免传统设计和加工的近似球面渐开线齿形螺旋锥齿轮存在的缺陷,提出了一种新型螺旋锥齿轮设计方案．从齿面精确组成和形状特征出发,将球面渐开线理论应用于齿面基本曲线的方程表达式求导中,实现了齿面曲线的分段参数化．然后,对组成齿面的各区域分别求取齿面离散点数据,并采用三次均匀B样条曲面方法进行初步的拟合与拼接．为了进一步提高齿面精度,借助NURBS方法对拼接后的齿面进行了统一的NURBS精确拟合,并给出了齿面统一参数化的优化方法．最后的算例表明了相关方法的精确性和可行性,为螺旋锥齿轮的数字化设计与NURBS加工提供了新的思路与途径．     

局部均值分解在齿轮故障诊断中的应用研究

局部均值分解(Local Mean Decomposition,简称LMD)作为一种新的自适应的时频分析方法,在故障诊断领域开始得到研究。本文利用仿真信号研究了LMD算法的特性,验证了LMD处理描述齿轮故障信号特征的多分量调幅调频信号的有效性;在此基础上将LMD综合应用于断齿、磨损和剥落三种齿轮故障诊断中,并与传统解调方法进行了对比。结果表明,LMD方法可以有效提取故障齿轮的故障特征,消除虚假成分的影响,从而提高了齿轮故障诊断的准确性     

齿根安全条件下多状态啮合齿轮传动系统安全-吸引盆侵蚀与分岔

轮齿折断是齿轮主要失效形式之一.以包含单双齿交替啮合、轮齿脱啮和齿背接触等的多状态啮合直齿圆柱齿轮传动系统为研究对象,计算齿根危险截面上的弯曲应力,以齿根许用弯曲应力为边界条件,建立防止轮齿折断的齿根安全条件.基于胞映射方法,用四阶Runge-Kutta法数值计算考察区域内随负载和齿侧间隙变化时系统的吸引盆及其演变过程...     

Dynamic analysis of a planetary gear failure caused by tooth pitting and cracking

Planetary gears are widely used in aeronautic and industrial applications that require compactness and high torque-to-weight ratios. Despite these advantages, the severe conditions under which such gears are typically used may lead to failure. Tooth pitting and cracking are frequently encountered failure modes. The defects are modeled and discussed for a planetary gear set. The influence of tooth defects on gear mesh stiffness is scrutinized. Healthy planetary gear dynamic response and the response of planetary gears containing tooth defects are compared in both the time and frequency domains and in the joint time-frequency domains by use of the Wigner-Ville distribution.     

Crack behavior in a high contact ratio spur gear tooth and its effect on mesh stiffness

The efficiency of high contact ratio (HCR) gearing can be achieved by proper selection of gear geometry for increased load capacity and smoother operation despite of their high sliding velocities. The prediction of variation in mesh stiffness of HCR gearing is critical as the average number of teeth being in contact is high at a given time as compared to conventional low contact ratio (LCR) gearing. In this paper, linear elastic fracture mechanics (LEFM) based finite element method is used to perform the crack propagation path studies of HCR spur gear having tooth root crack for two gear parameters viz. backup ratio and pressure angle. A total potential energy model has been adopted to analytically estimate the mesh stiffness variation. The results depict the mesh stiffness reduction in the presence of the crack. The percentage change in mesh stiffness with increasing crack length is an important parameter in fault diagnosis of geared transmission. Higher the percentage change in mesh stiffness, easier to detect the fault. Two gear parameters viz. back-up ratio and pressure angle has been studied and the effect of crack length on mesh stiffness have been outlined. With the increase of deterioration level gears having lower back-up ratio fault can be detected at an early stage, similarly, chances for early fault detection is more for gears having higher pressure angle.     

Vibration signal modeling of a planetary gear set for tooth crack detection

In a planetary gearbox, there are multiple vibration sources, and the transmission path of vibration signals changes due to the rotation of the carrier. This study aims to model the vibration signals of a planetary gearbox and investigate the vibration properties in the healthy condition and in the cracked tooth condition. A dynamic model is developed to simulate the vibration source signals. A modified Hamming function is proposed to represent the effect of the transmission path. By incorporating the effect of multiple vibration sources and the effect of transmission path, resultant vibration signals of a planetary gearbox are obtained. Through analyzing the resultant vibration signals, some vibration properties of a planetary gearbox are revealed and the fault symptoms of sun gear tooth crack are identified and located. Finally, the proposed approach is experimentally verified.     

基于特征处理的MVU算法在齿轮故障诊断中的应用

针对不同故障类别齿轮的故障信息难以有效获取、齿面多类故障难以准确聚类的问题,提出一种基于特征处理的最大方差展开(Maximum Variance Unfolding,MVU)维数简约的齿轮故障诊断模型。首先对获取的振动信号进行最小熵反卷积(Minimum Entropy Deconvolution,MED)预处理,将高低频段进行分离并筛除不确定信号,并在多域上提取信息熵作为特征指标;而后,利用样本点分布矩阵筛选高效表征特征指标并构建高维特征空间,并利用改进的MVU算法对其进行维数简约,获取低维的真实子空间;最后,将其输入到超球多类支持向量机中进行超球构造与分类识别。通过实验数据的分析对比验证模型的有效性。     

Experimental and numerical evaluations on the effects of adhesive fillet,overlap length and unbonded area in adhesive‐bonded joints

To realize robust structural design, the effects of the adhesive fillet, overlap length and unbonded area in adhesive‐bonded joints need to be fully understood and incorporated into a fatigue life estimation method. In the present work, both static and fatigue experiments are performed on six types of adhesive‐bonded joints to illuminate these effects systematically. A straightforward total fatigue life evaluation method is proposed to address these effects. A statistical crack initiation model is established based on the fatigue data of bulk adhesive specimens. Growth life is calculated using the interfacial crack model and mixed mode crack growth method. Good correlation is observed between the calculated and experimental fatigue lives. Furthermore, the effects of the adhesive fillet, overlap length and unbonded area are analysed based on both calculated and experimental results. Results indicate that adhesive fillet postpones crack initiation by reducing local strain level, both overlap length and unbonded area change the growth life by length. Besides, overlap length promotes the fraction of mode II strain energy release rate in total, reducing crack growth rates and extending growth life.     

Investigation of crack propagation scatter in a gear tooth’s root

This paper describes the problem of determining crack initiation location and its influence on crack propagation in a gear tooth’s root. Three different load positions on the gear tooth’s flank were considered for this investigation of crack initiation and propagation. A special test device was used for the single tooth test. It can be concluded from the measurements that a crack can be initiated at very different locations in a tooth’s root and then propagate along its own paths. A numerical investigation into a crack initiation’s position and its influences on its propagation were carried out within the framework of linear fracture mechanics. The influence of a tooth’s load position, the geometry of the tooth’s root, and the influence of non-parallel load distribution on the tooth’s flank were considered when investigating the crack initiation’s position. Results show that linear fracture mechanics can be used for determining crack propagation, if better initial conditions for crack initiation are considered.     

Fracture analysis of fisheye failures in the tooth root fillet of high-strength gears made out of ultra-clean gear steels

Forschung im Ingenieurwesen - In shot-peened components, failures can be caused by a&nbsp;crack initiation below the surface at a&nbsp;non-metallic inclusion in the steel matrix. This...     

基于双模齿轮的大排量齿轮泵的流场可视化仿真研究

 研究双模组合齿形齿轮泵的流量、压力特性.通过将不同模数的齿轮叠加组合,设计双模数齿形的主、从动齿轮,以增加齿轮啮合过程中的容积变化量,提高齿轮泵的排量,利用Fluent 对齿轮泵内液压流场进行了仿真,得出齿轮泵在启动和稳定工作状态下流场压力分布云图、速度分布云图和速度矢量图,并据此分析了齿轮泵流场的流态.结果表明:同体积下双模齿轮泵的输出流量是普通齿轮泵的16～33倍,该齿轮泵中大齿将流场分成不同压力区,且大齿两侧流体压力差较大,齿顶间隙处液体流动速度较大,说明齿轮泵径向泄漏较为严重,在泵的入口处存在涡流现象,会产生压力冲击,影响齿面的使用寿命．     

双圆弧弧齿锥齿轮齿根应力沿齿长分布的研究

 用有限元方法，对双圆弧弧齿锥齿轮沿齿长方向齿根应力进行了计算． 通过应力计算结果的分析，得出了凸、凹两齿侧应力沿齿长的分布规律．计算结果表明，对凹齿侧，最大应力发生在靠近小端处；对凸齿侧，最大应力发生在靠近齿长中点大端处．