Investigation on the failure of the gear shaft connected to extruder

In respect to the fracture of the gear shaft of an extruder, the torque on the shaft replaced the fractured one is measured under typical work conditions. The fatigue and material mechanics properties of the fractured shaft are obtained by tensile and fatigue test. Based on the analysis of cyclic fatigue load and the stress of gear shaft, the reason of the shaft fracture is discussed. The analysis indicates that when the extruder is running, high mean stress occurs in the gear shaft, the failure of the gear shaft was caused by fatigue and material strength degradation. Finally, suggestions are given to guide the future operating of the extruder to prevent the gear shaft from fracture.     

沙滩车倒车档轴断裂分析

采用化学分析、断口形貌分析和金相组织检验等方法,对沙滩车断裂的倒车档轴进行了分析。结果表明,倒车档轴断裂属多源旋转弯曲疲劳断裂,裂源处机加工精度不高,造成应力集中,是发生断裂的原因之一;而该倒车档轴由于渗碳淬火层深度不够,心部铁素体较多,导致其抗疲劳能力下降,因此热处理工艺不当也是发生断裂的另一重要原因。     

火电机组给水前置泵轴断裂原因分析

某火电厂4号机组B给水前置泵轴投运仅19h即发生断裂。经对断裂泵轴进行宏观分析、化学成分分析、常温力学性能测试、金相检验及断口扫描电镜分析,探讨并明确了泵轴断裂原因,同时提出了防范措施。结果表明：该给水前置泵轴断裂为疲劳断裂,在弯曲及扭转载荷作用下于变截面的应力集中部位的不连续及夹杂物处形成疲劳裂纹,同时大量夹杂物及沿晶分布的粗大a铁素体的存在严重降低了基体强度,使轴体所能承受的循环应力大大降低,即在较低的循环应力作用下疲劳裂纹不断扩展并最终断裂。     

飞机操纵系统链条销轴断裂分析

某型飞机操纵系统链条销轴在使用中断裂。采用化学成分分析、外观检查、断口分析和表面质量检验等方法对断裂销轴进行了分析,又对有裂纹的销轴与断裂销轴进行了对比分析。结果表明：销轴表面存在原始缺陷,加上链条链板在长期使用中的磨损使得链板间隙增大,导致销轴承受剪切力的同时又承受弯曲载荷,最终导致销轴发生疲劳断裂。     

Microstructural Investigation on Failure of Internal Drive Shaft

17-4 PH stainless steel is used as internal drive shaft material in liquid engine pumps. One of the drive shafts failed during operation. The shaft pieces were in contact for short duration after failure, which has resulted in abrasion of fractured surfaces. Samples from the location of failure were taken, and investigation of the failure was carried out using optical and scanning electron microscopy. The microstructural analysis of the material and fractographic analysis of the fractured surface show that the failure was caused by excessive torsion.     

汽车发动机曲轴断裂分析

某6缸发动机曲轴在运行8910km时,第六曲拐颈断裂。对断裂曲轴进行了断口观察、化学成分复验、基体硬度和显微组织检验。结果表明,曲轴的拐颈断裂为扭转疲劳断裂,断裂疲劳源位于油道孔与倒圆角曲面交接处,此处的切削加工刀痕及金属损伤形成应力集中且处于最大主应力面上,因而引发扭转疲劳断裂。     

Examination of the causes of a bucket wheel fracture in a bucket wheel excavator

A bucket wheel excavator failure occurred in a brown-coal mine. The failure was caused by a fractured shaft of the bucket wheel. An attempt to determine the causes of the bucket wheel shaft fracture has been made. To that end, the character of changing loads and their maximum amplitudes has been determined by performing measurements on the excavator. A discreet model of the shaft was built and a numerical simulation of the shaft operation using the FEM method was achieved. An analysis of the materials in the fracture area was also implemented. Macroscopic and microscopic images of the fracture area are provided. The shaft fracture was mainly caused by a non-metallic inclusion located below the surface of the shaft as a result of its being rolled. Moreover, it was discovered that the shaft had not been heat-treated.     

Optimised design of mandrels after fatigue failure

The drive shaft of a steel mandrel used in the production of glass-fibre-reinforced composite cylinders had failed in service. A fractographic analysis revealed that the shaft had failed by rotation-bending fatigue in the welded region where the shaft was attached to the flange. Subsequent non-destructive testing (NDT) of the remaining mandrels still in service showed that approximately half of these were cracked in the same region. It was only a question of time before these mandrels failed too, posing a severe safety hazard and resulting in production down-time.Fatigue life calculations showed that even with material properties within specification and flawlessly executed welds, the stresses in the welds were above the fatigue limit and failure during operation was to be expected. Thus, the design of the shafts had to be modified to reduce the operational stresses below the fatigue limit.The operational loads were measured by means of strain gauges during a full production cycle, including the loading and unloading of the mandrel, and the revolutions about its own axis during winding. The data showed that peak stresses due to dynamic shock loads of up to 1.3 times the quasi-static stress needed to be taken into account.Optimisation of the design was complicated by the highly constrained space within the machine. However, by moving the weld out of the most highly stressed region and increasing the fillet radius, the local stresses could be sufficiently reduced, as was verified by FEM and analytical stress assessment.The new weld was not trivial to produce and several iterations of weld trials were required to achieve a sound weld. Since some imperfections are permitted in a standard quality weld and must be expected for this type of weld, it had be shown by fracture mechanics that the new design remains crack-free throughout its service life and that inspections are not necessary to guarantee safety.     

Fretting fatigue fracture of the supporting shaft in a rotary kiln

The fracture failure of the supporting shaft in a rotary kiln was analyzed to determine the failure mechanism. The rotary kiln was used to heating and mixing nickel ores and was supported by four group riding wheels with two wheels in each group. One of the supporting shafts was found fractured after it was used for about two years. The fracture was located at the interface between the supporting shaft and the sleeve. This location was 100–120 mm far from the transition arc of the supporting shaft where high stress concentration usually occur. A failure analysis was carried out, using characterization techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and so on. Obvious fatigue propagation zone caused by multi-initial cracks were observed at the circle edge of the fracture surface. Adhesive wear and some circumferential cracks were found on the outside surface of the supporting shaft. It was considered that fatigue due to the fretting wear between the shaft and sleeve was the most probable mechanism.     

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.     

电厂外供泵轴断裂原因分析

某外供泵在运行期间其泵轴发生断裂。通过宏观和微观检验、化学成分分析以及硬度测试等方法对泵轴断裂的原因进行了分析。结果表明:该轴的热处理没有达到要求,使各项强度指标显著降低,加上在应力集中部位键槽根部产生了疲劳裂纹,并进一步扩展,最终导致泵轴断裂。     

Fracture failure analysis of AISI 304L stainless steel shaft

Fracture failure analysis of an agitator shaft in a large vessel is investigated in the present work. This analysis methodology focused on fracture surface examination and finite element method (FEM) simulation using Abaqus software for stress analysis. The results show that the steel shaft failed due to inadequate fillet radius size and more importantly marking defects originated during machining on the shaft. In addition, after visual investigation of the fracture surface, it is concluded that fracture occurred due to torsional–bending fatigue during operation.     

风机齿轮箱齿轮失效分析

某发电厂的风力发电机在运行中齿轮箱出现故障,经现场检查发现在风机某一级传动齿轮中有一个齿轮出现断齿现象,断裂部位在轮齿的中间腰部位置.为了判断风机齿轮箱的断裂性质及原因,对风机齿轮箱断齿残片进行了宏微观观察,对断齿残片基体及断口源区进行了能谱分析,测定了断齿表面残余应力,还对齿轮进行了断口定量分析.结果表明,风机齿轮箱齿轮轮齿失效性质为弯曲疲劳断裂.可基本排除齿轮设计、材质、使用维护方面的异常,齿轮断裂原因在于断裂部位存在夹渣缺陷.     

SF6断路器开关夹叉断裂原因分析

采用宏、微观断口分析、硬度测试、受力分析和工艺分析等方法对某SF6断路器开关夹叉断裂原因进行了分析。结果表明：由于制造过程中热处理工艺不当,夹叉材料没有获得设计要求的调质组织,导致材料性能达不到要求。在较大的冲击性拉应力反复作用下发生脆性断裂。     

Fracture Failure Analysis of a 30CrMnSiA Steel Shaft

A shaft suddenly suffered fracture during the test of loading in three directions. The shaft was made from 30CrMnSiA steel. The failure cause was analyzed by visual, stereo, and scanning electron microscopic observations of appearance and fracture surface of the shaft, micro-area composition inspection, metallographic examination, and measurement of the hydrogen content. The results showed that the failure mechanism of the shaft was fatigue fracture resulting from hydrogen-induced intergranular microcracks. The hydrogen-induced cracks were mainly caused by abnormal pickling during production of the shaft.     

Failure Analysis of Spline Shaft in Beco Lathe

The failure of Heavy Duty Facing Lathe has been systematically investigated using fractographic, metallographic, and analytical stress analysis methods. Failure occurred during machining of a large flange, the tool post had a collision with jaw of the rotating chuck and the spline shaft inside headstock was broken into two pieces. A detailed analysis of the fracture surfaces revealed partial damage of the surfaces due to their rubbing in operation and cleavage fracture in the remaining part of the surfaces. The stress analysis indicates that sudden reversing of the spindle had resulted in the stresses exceeding the fatigue limit of the shaft material. These stresses led to the formation of microcracks at the circlip groove. The collision accelerated the sudden failure of shaft. This failure analysis has led to identification of root cause and its elimination with corrective measures undertaken.     

压缩机连杆断裂失效分析

某炼油厂焦化装置富气压缩机连杆发生断裂。采用化学成分分析、金相检验、力学性能测试和断口分析等方法对断裂连杆进行了分析。结果表明,在交变栽荷的作用下,连杆的小头孔内应力集中处产生微裂纹并成为裂纹源,然后发生裂纹扩展,最终导致连杆小头处发生疲劳断裂。     

热处理不当导致风机主轴扭断

风机主轴在使用过程中，突然扭断造成停车。该轴断口齐平，具有明显的扭断特征。应用光学和电子显微镜，从断口的宏观和微观特征、金相组织及力学性能等方面，对风机主轴失效原因进行了分析。结果表明，热处理不当引起表层脱碳和组织粗大，是导致主轴扭断的内在原因；同时轴颈部位应力集中加速了断裂过程。     

Analysis of the fatigue failure of a mountain bike front shock

We present an analysis of a mountain bike front shock failure. The failure of the 1-year-old shock occurred catastrophically as the bike was ridden off of a 1-m drop. The failure was the result of fast fracture through both shock tubes at the location where the tubes were press fit into the shock upper crown. Examination of the fracture surfaces of the tubes revealed regions of fatigue crack growth that nearly penetrated the entire thickness of both tubes. An estimate of the forces during use, coupled with stress analysis, revealed three stresses near the fracture site—axial compression, bending, and hoop stresses. During operation, the axial compressive stress is negligible while the hoop and bending stresses are significant. Based on fracture mechanics, and an estimate of the bending stress from a 1-m drop, it is confirmed that the fatigue cracks present on the fracture surface were large enough to induce fast fracture. Prior to the existence of the fatigue cracks, the stresses were magnified locally near the fracture site by a significant stress concentration caused by the sharp transition from the shock tube to the crown. The fatigue cracks initiated at a circumferential location in the tube commensurate with high tensile bending stress and the stiffest region of the crown (highest stress concentration). Based on the evidence, the most probable cause of the bike shock fatigue failure was the shock design, which facilitated high local stresses during use.     

Fracture analysis of wind turbine main shaft

Shaft fracture at an early stage of operation is a common problem for a certain type of wind turbine. To determine the cause of shaft failure a series of experimental tests were conducted to evaluate the chemical composition and mechanical properties. A detail analysis involving macroscopic feature and microstructure analysis of the material of the shaft was also performed to have an in depth knowledge of the cause of fracture. The experimental tests and analysis results show that there are no significant differences in the material property of the main shaft when comparing it with the Standard, EN10083-3:2006. The results show that stress concentration on the shaft surface close to the critical section of the shaft due to rubbing of the annular ring and coupled with high stress concentration caused by the change of inner diameter of the main shaft are the main reasons that result in fracture of the main shaft. In addition, inhomogeneity of the main shaft micro-structure also accelerates up the fracture process of the main shaft. In addition, the theoretical calculation of equivalent stress at the end of the shaft was performed, which demonstrate that cracks can easily occur under the action of impact loads. The contribution of this paper is to provide a reference in fracture analysis of similar main shaft of wind turbines.