HXD1机车牵引电机转轴组件断裂失效分析

HXD1型电力机车的牵引电机转轴和小齿轮轴采用圆锥过盈配合传动结构(下称转轴组件),使用中该组件出现了早期断裂失效.本文通过理化检测、断口和配合面宏/微观形貌观察等失效分析技术对失效组件进行了分析.结果表明,材料成分、组织和显微硬度正常,小齿轮轴和电机转轴的失效形式分别为高周疲劳断裂和微动疲劳断裂.造成组件失效的原因和过程是,小齿轮轴近齿端油槽-油孔交界线处有较大的结构应力集中,油槽底部周向加工刀痕造成附加应力集中,在应力集中和旋转弯曲疲劳载荷作用下油孔边两个应力集中点萌生了疲劳裂纹并扩展;随小齿轮轴裂纹的不断扩展转轴组件结构刚度减小,继而诱发了与小齿轮轴匹配的电机轴配合面的微动疲劳,电机轴疲劳裂纹萌生于微动区的边缘处;电机转轴先于小齿轮轴完全断裂.基于本文的分析结果提出了提高组件抗疲劳断裂的技术措施.     

高压燃油泵凸轮轴失效分析与改进

通过对凸轮轴失效的综合分析,揭示了其失效过程的微观机制是微动磨损疲劳,对系统的设计,装配结构及相关零件等方面进行了综合研究,指出油泵凸轮轴与传动齿轮间锥度配合设计上的缺陷,探讨了改进措施,取得了显著效果。     

接触应力对车轴钢旋转弯曲微动疲劳寿命的影响

研究LZ50车轴钢不同过盈配合接触应力水平对旋转弯曲微动疲劳寿命的影响。分别利用光学显微镜、扫描电子显微镜对过盈配合表面的微动损伤表面和断口进行分析。结果表明,随着过盈量的增加,LZ50车轴钢旋转弯曲微动疲劳寿命呈现先降低而后升高的非线性特征,这是多轴复杂应力、配合面的接触应力、微动摩擦应力以及微动磨损交互作用的结果。     

TC21钛合金微动磨损特性的研究

采用SRV磨损试验机研究了TC21钛合金与0Cr13Ni8Mo2Al不锈钢配副件的微动磨损特性;用正交实验法设计实验,系统研究了微动频率、法向载荷、微动振幅对钛合金磨损量的影响,测试了不同实验条件下摩擦系数与循环次数的关系。结果表明:微动振幅对磨损量的影响高度显著,法向载荷的影响显著,微动频率有影响但不显著;在微动过程中摩擦系数呈现出阶段性变化,同时变化幅度随着微动频率的增加逐渐减小。TC21微动磨损发生的初期,其磨损机制主要以磨粒磨损为主,随着微动的进行剥落磨损和粘着磨损的作用逐渐明显。     

基于有限元法的螺旋锥齿轮传动误差研究

在传统螺旋锥齿轮传动误差分析基础上引入惯量、材料阻尼因素、齿轮支撑系统,提出螺旋锥齿轮动传动误差分析方法。通过与传统静传动误差分析结果比较,该方法能更好描述螺旋锥齿轮在啮合过程中的振动、噪音等动态性能;分析材料阻尼对螺旋锥齿轮动传动误差影响,通过对不同阻尼情况下传动误差结果比较,获得阻尼变化对传动误差变化影响规律,对螺旋锥齿轮传动过程中振动与噪音控制具有重要指导意义。     

克林根贝尔格螺旋锥齿轮接触区修正

克林根贝尔格螺旋锥齿轮在工业上的应用极为广泛,尤其是在一些传动设备中,克林根贝尔格螺旋锥齿轮更是发挥了重要的作用。在克林根贝尔格螺旋锥齿轮的使用过程中其具有传动平稳、噪声低、振动小能够适应高速传动要求等的特点,能够承载较大的传动力矩和实现较大的传动比,是一种极为优良的传动部件。在克林根贝尔格螺旋锥齿轮的制造过程中需要对轮齿的接触区引起足够的重视,本文将在分析克林根贝尔格螺旋锥齿轮接触区特点及重要性的基础上对如何做好克林根贝尔格螺旋锥齿轮接触区的调整进行分析阐述。     

装甲铝合金显微硬度及微动磨损对其影响的研究

利用MH-6型显微硬度仪和MGW-01高频往复式微动磨损试验机进行7A52装甲铝合金的显微硬度测试和微动磨损试验，分析不同取向表面显微硬度及微动磨损试验对显微硬度的影响。结果表明不同取向表面显微硬度基本相同，试验范围内微动磨损表面显微硬度比基体表面显微硬度增加。     

激光熔覆MoNbTaVW难熔高熵合金涂层微动磨损性能

研究了采用激光熔覆技术制备的MoNbTaVW难熔高熵合金涂层在不同载荷(10N、20N、30N)、不同微动磨损幅值(50μm、150μm、250μm)、不同循环次数(5 000、10 000、15 000)下的微动磨损性能及微动磨损机制。结果表明:所制备的MoNbTaVW难熔高熵合金涂层由Fe₇Ta₃型HCP固溶体相、FCC固溶体相及(Fe,Ni)基体相组成,其中FCC相为未熔的高熵合金粉末。根据正交实验极差分析可知,微动磨损幅值对磨损体积的影响最大,微动磨损载荷对磨损体积的影响次之,微动磨损循环次数对磨损体积的影响最小,其中MoNbTaVW难熔高熵合金涂层在15 000次、20N、250μm微动磨损条件下的磨损体积达到最大值;微动磨损载荷对摩擦系数的影响最大,微动磨损幅值对摩擦系数的影响次之,微动磨损循环次数对摩擦系数的影响最小,其中MoN bTaVW难熔高熵合金涂层在10 000次、30 N、150μm微动磨损条件下的摩擦系数达到最大值。MoNbTaVW难熔高熵合金涂层的微动磨损机制主要为氧化磨损和黏着磨损,磨损产生的磨损碎片主要为Ta、...     

某机尾桨轴颈叉耳耳环断裂分析

对某机尾浆轴颈叉耳耳环提前破坏原因进行了全面的检查分析。结果表明：叉耳耳环提前破断是由于耳孔与销子配合不当,而产生滑动磨损（微动）引起疲劳断裂,其磨损特征也不是单一的,而是粘着磨损、磨粒磨损和接触疲劳磨损的复合磨损方式。     

PMMA转动微动摩擦学行为的研究

在新型转动微动试验机上,进行了 PMMA与GCr15钢球(40mm直径)在转动角位移幅值为0.25～ 2.5°和法向载荷为100N的转动微动试验.在摩擦动力学行为研究的基础上,结合磨痕的微观分析,研究了其转动微动磨损机理.结果表明:随转动角位移幅值的增加,PMMA的转动微动会依次呈现三个区域,即部分滑移区、混合区和完全滑移区;相比部分滑移区和完全滑移区,混合区的摩擦系数明显较高;部分滑移区摩擦系数保持在较低水平且损伤轻微,微动的相对运动由弹性变形协调.在混合区和滑移区PMMA的转动微动磨损机制为伴随黏性流动的颗粒剥落和磨粒磨损.研究发现在混合区和滑移区的磨斑中央产生因黏性流动造成的损伤累积所致的材料隆起.     

Analysis of a shrink-fit failure on a gear hub/shaft assembly

The paper presents results and conclusions arising from an investigation into a shrink-fit failure on a gear hub/shaft assembly. The work formed one element of a full failure investigation and set out specifically to determine whether or not fretting or micro-slipping was the cause of failure. The basic rationale of the study was to start with assumed operating conditions and progressively refine the model in order to accurately take account of the true operating conditions. This approach permitted conclusions to be drawn after every simulation concerning the propensity to slip along the gear hub/shaft interface. Two modelling techniques were used in parallel: a novel analytical approach and a finite element study. Results from the two approaches were consistent and in relatively good agreement. The principal conclusion made was that the observed slip and subsequent fretting damage could only have occurred as a result of another, principal, failure mechanism which was responsible for increasing the internal diameter of the gear hub.     

Failure analysis of a final drive transmission in off-road vehicles

This paper presents a case study in failure analysis of a final drive transmission in an off-road vehicle. The failure involved a satellite gear mounting shaft that departed from the differential assembly as a result of fracturing of a retaining pin. An investigation of the mechanical condition of various transmission components, consisting primarily of visual (macroscopic) inspection, geometrical investigation and analysis of mechanical loads, led to the assignment of two principal causes of failure. Firstly, it was established that the retaining pins installed in the assembly were shorter than required, allowing them to shift in their guide holes and assume a single-shear position. Secondly, in this position they were loaded to failure in shear by abnormally high frictional forces acting at the shaft/satellite interface. These loads were attributed to severe usage and handling of the vehicle. The scope of this case study is broadened to include a review of failure incidents, that followed in additional transmissions containing short retaining pins. An account of actions taken to address the problem from a maintenance and reliability viewpoint is also included, as are further recommendations made to the operator.     

Failure Investigation of an Aircraft Crankshaft Gear Connection

Improper assembly of an aircraft crankshaft can have serious consequences. If an adequate joint clamping force is not applied to the connection between the crankshaft and crankshaft gear during assembly, relative motion in the system could create flexural loads on connection components, and cause damage such as cyclic fatigue cracking, shear overstress fracture, and plastic deformation. Many factors can contribute to insufficient joint clamping, including poor joint seating, the presence of a foreign object on the faying surface, and failure to apply proper torque during assembly. This paper reviews a case involving a crankshaft gear connection, which separated while the subject aircraft was in flight, causing the engine to fail and the aircraft to crash. To determine the root cause of the failure, a metallurgical analysis was performed.     

Fretting fatigue of a shrink-fit pin subjected to rotating bending: Experiments and simulations

Fretting fatigue initiation was studied for a shrink-fit pin at rotating bending. Eight assemblies with four different grips were manufactured from soft normalized steel and tested at loads well below bending endurance. All pins displayed rust-red fretting oxides deep into the contact and black oxidised fretting scars with fretting fatigue cracks at the rim. The slip evolution was simulated in a three-dimensional FE model including assembly, bending and sufficiently many rotations to reach a steady-state. The extension of cyclic slip agreed with the black oxidised scar. Deeper into the contact a monotonic slip developed to the positions with rust-red oxides. Asymmetric slip and traction on the interface sides together with a slight twist of the pin in the hub and the slip development process, illustrated that a three-dimensional analysis was required for the interface. Both the stress amplitude and the Findley multi-axial criterion predicted fretting fatigue of the pin although the rotating bend stress was well below the endurance limit.     

Investigations on fretting fatigue in aircraft engine compressor blade

An investigation of several cracked blade tangs in the military aircraft engine compressor was conducted to identify the root cause of the failure. These cracks were found during the scheduled maintenance with fluorescent penetration inspection. The engine compressor blade made of Ti–6Al–4V is attached to compressor rotor by means of inserting retaining pin through rotor and blade tang. By analyzing the fracture surface of the failed blade tang, it is found that the crack in the blade tang was initiated by fretting fatigue and propagated under low cycle fatigue. Stress analysis of the blade using a non-linear finite element method is coincident with the results of fractography. The clearance between retaining pin and tang hole caused small amplitude of sliding motion leading to fretting wear during engine operation. Consequently, the damaged area due to fretting wear acts as a stress raiser inside tang hole and contributes to accelerate fretting fatigue.     

Multiaxial fretting fatigue testing and prediction for splined couplings

This paper presents a combined experimental and computational methodology for fretting fatigue life prediction of aeroengine splined couplings under combined loading cycles involving cyclic torque and axial load, as well as rotating bending and fluctuating torque. The experimental method is based on the concept of a simplified representative test, which mimics the multiaxial fretting conditions between spline teeth via biaxial loading of specially-designed bridge pads and a fatigue specimen. The numerical method is based on a three-dimensional finite element model of the test rig assembly, including frictional contact effects, along with a multiaxial, critical-plane fatigue parameter for crack nucleation followed by crack growth prediction in the Paris regime using El Haddad small crack correction. The prediction methodology is shown to successfully capture the effect of the key fretting fatigue stress, which mimics the spline rotating bending moment, on total fatigue life.     

Early stage crack propagation in fretting fatigue

A stress model of the fretting fatigue damage mechanism is developed on the basis of microscopic observations of the fatigue failure process in fretting. According to the model the state of stress in the element in the region of fretting pads defines the fatigue strength of the fretting assembly. Areas where the first fatigue crack initiates and the direction of its early stage propagation can be well explained by the elastic strain energy in the specimen near the fretting pads. The main fatigue crack initiates in the cyclically loaded member from the edge of the fretting pad, grows at the beginning and then stops, becoming a non-propagating crack, when the member is loaded below the fretting fatigue limit.     

考虑齿距累积误差的人字齿轮系统动态特性分析

基于Timoshenko梁理论和有限单元法,引入时变啮合刚度和综合啮合误差,建立了人字齿轮系统动力学模型,研究了齿距累积误差对人字齿轮系统动态特性的影响。研究表明:齿距累积误差使动态传递误差出现显著的轴频成分和调制边频带。当负载扭矩较小时,边频成分大于啮合频率及其倍频成分,随着负载扭矩的增加,啮合频率及其倍频成分逐渐增强。当齿距累积误差相位不同时,人字齿轮系统将出现明显的轴向窜动现象。同时,齿距累积误差相位差对系统振动影响显著,通过调整相位差可以显著降低系统振动。研究结果可为人字齿轮系统低噪声设计加工与装配提供理论依据。