Failure Investigation of a Locomotive Turbocharger Main Shaft and Bearing Sleeve

A failure investigation was conducted on a locomotive turbocharger main shaft and a bearing sleeve which had been assembled with the main shaft. The fracture of the main shaft took place at a sharp edged groove between two journals with different cross-sectional areas. The dominant failure mechanism of the main shaft was low-cycle and rotation-bending fatigue. Wear failure occurred on the bearing sleeve through a mixed mode of abrasive and adhesive wear. Detailed metallurgical analysis indicated that the bearing sleeve and the journal surface assembled with the sleeve had been subjected to abnormally high temperatures which led to increased friction between the bearing sleeve and the bearing bush, the sleeve, and the journal surface. In addition, the abnormally high temperature softened the induction-hardening case on the journal surface and decreased the fatigue strength. Fatigue crack initiation occurred at the root fillet of the groove because of the stress concentration in that area.     

Failure Analysis of High-Speed Pinion Gear Shaft

The failure of a high-speed pinion gear shaft was investigated. The pinion gear was an integral part of a system used to compress the natural gas. It was a high-speed gear mounted on two roller bearings. An abnormal wear pattern was observed on the shaft surface, beneath the inner race of the bearing. The material from shaft was observed to be dislodged and stuck to the surface of the inner race. This transfer of material imparted an imbalance to the assembly, and abnormal sounds and fumes were observed two days before failure. The macrofeatures of the fracture surface resemble these of fatigue but electron microscopy showed brittle and mostly intergranular fracture. Fatigue features such as striations were not found on the fracture surfaces. Fatigue samples made from the same material and heat-treated to the same hardness were tested under uniaxial fatigue and the fracture features were compared with the original crack surface. The microfeatures of fracture surfaces were almost identical. The root cause of failure was determined to be fatigue, and cracks on the pinion shaft in the region beneath the inner bearing race lead to the transfer of material.     

Fracture and Wear Failure of a Locomotive Turbocharger-Bearing Sleeve

A failure investigation was conducted on a locomotive turbocharger-bearing sleeve. The failed bearing sleeve is made of 38CrMoAl steel and the external and internal surfaces are nitrided. The fracture took place at the transition fillet between the cylinder and the plate of the bearing sleeve. Multiple origin fatigue fracture was the dominant fracture mechanism. Serious wear took place on the external surface of the bearing sleeve. Metallurgical examination indicated that the depth of the nitrided layer on the surfaces of the bearing sleeve was generally below the acceptable limit set by the manufacturer. The thin nitrided layer on the external surface of cylinder was rapidly worn from the cylinder in service and the soft underlying matrix was exposed. At this point, the wear on the cylinder surface increased intensely and ultimately lead to increased friction between the external surface of the bearing sleeve and the bearing bush. Fatigue crack initiation occurred at the root fillet between the cylinder and the plate because of stress concentration in that area and the increased frictional forces. In addition, the insufficient nitrided layer depth in the fillet region facilitated propagation of fatigue crack. Appropriate nitriding process should be conducted on the bearing sleeve to obtain a sufficient hardening depth thus inhibiting surface wear and preventing fillet fatigue failure.     

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.     

TA1钛合金单搭自冲铆接头微动磨损机理

对TA1钛合金单搭自冲铆接头进行疲劳实验研究接头失效形式;用扫描电子显微镜和X射线能谱线扫描研究铆钉各部位微动磨损程度的差异和接头微动磨损机理;采用威布尔分布验证数据有效性.结果表明:接头疲劳失效形式主要为上板断裂,高周疲劳均为上板断裂,低周疲劳为上下板混合断裂;微动磨屑包含氧、钛、锌和锡元素,铆钉头部微动磨损程度高于铆钉腿部.微动磨损区出现严重脱层、微动磨屑堆积和微裂纹萌生等现象,随着微动磨损及剪切力共同作用导致接头断口部位出现大量微裂纹并逐步沿深度和宽度方向扩展为宏观裂纹,最终导致接头疲劳失效.     

大型超静定回转窑支承系统疲劳强度与轴线偏差关系研究

回转窑运行中由于轴线偏移,支承载荷分配严重不均,托轮轴疲劳断裂现象频繁。本文通过对回转窑托轮轴进行力学分析,导出托轮轴危险截面等效应力幅的计算方法;结合现场实例分析表明,托轮轴疲劳强度主要受对应载荷的影响,等效应力幅与所受载荷成良好的线性关系;从而根据支承系统载荷分配与运行轴线偏差的关系,得到支承系统疲劳强度与轴线偏差的线性关系式,对关系式进一步分析,得出一些有益的结论。     

Corrosion induced fatigue failure of railway wheels

Two AAR class B rolled wheels for locomotives failed after about two years of service. The fracture surfaces of the failed railway wheels were examined. The examination showed that there were corrosion pits on the back plate surface of the failed wheels. All of the fracture originated from corrosion pits at the wheel plate surface and fatigue propagated to a length and then expanded rapidly by cleavage. Fatigue specimens cut from the wheel plate were corroded with different time duration in an artificial corrosion environment to simulate the corrosion states of the wheels. The fatigue properties of the un-corroded specimens and the specimens corroded with different times were tested in air. Finite element method (FEM) and Sines' criterion were used to evaluate the safety of the wheels. The results showed that the wheel plates without corrosion pits exhibited an excellent resistance to failure. The corrosion pits could promote the initiation of fatigue cracks and drastically lower the fatigue limits of corroded specimens. The real root cause of the failure of the subject wheels was due to the corrosion pits at the wheel plate surfaces. A critical depth of the corrosion pit on the wheel plate 300 μm was recommended. Protection of the wheel plate was important to ensure the safety of wheels and the rust prevention oil was recommended to be applied on the wheel plate regularly.     

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.     

Failure analysis of an automobile differential pinion shaft

Differential is used to decrease the speed and to provide moment increase for transmitting the movement coming from the engine to the wheels by turning it according to the suitable angle in vehicles and to provide that inner and outer wheels turn differently. Pinion gear and shaft at the entrance are manufactured as a single part whereas they are in different forms according to automobile types. Mirror gear which will work with this gear should become familiar before the assembly. In case of any breakdown, they should be changed as a pair. Generally, in these systems there are wear damages in gears. The gear inspected in this study has damage as a form of shaft fracture.

In this study, failure analysis of the differential pinion shaft is carried out. Mechanical characteristics of the material are obtained first. Then, the microstructure and chemical compositions are determined. Some fractographic studies are carried out to asses the fatigue and fracture conditions.     

Life prediction for rolling contact fatigue crack initiation of kiln wheels

This paper investigates the rolling contact fatigue life of kiln wheels with respect to the axis line deflection related with the applied supporting loads on wheels. Fatigue crack initiation criterions for elastic shakedown, plastic shakedown, and ratcheting material responses are applied to assess wheels responses with two sets of axial line deflection, one is measured in field and the other is optimal adjustment for the measured axial line deflection. The finite element simulations are performed by using the Bilinear material mode for nonlinear and kinematic hardening within ANSYS 11.0. By comparing life prediction from different criterions, it is showned that the low-cycle fatigue is the predominated failure. Results from different axial line deflection indicate that the optimum adjustment can greatly enhance the whole life of the supporting structure, that is useful for kiln adjustment and maintenance.     

Analysis of a J69-T-25 engine turbine blade fracture

The fracture of a turbojet engine turbine blade was investigated. Visual and surface examination showed that the turbine blade had initially cracked by a fatigue mechanism over a period of time and then failed by overload at the last moment. The fatigue crack initiated on a surface damaged by rubbing. Also the cracked turbine blade was severly damaged by hot gas flow and discolored. This heat damage made the gamma prime phase in the matrix (Ni-base superalloy) coarsen and lowered the fatigue strength of the base material assisting to the premature fatigue fracture. The decrease of the strength of the material due to degradation of gamma prime phase was verified by hardness measurements. The possible relevance of other parts attached to the engine shaft to the fracture was reviewed. From this review it is inferred that the root cause of cracking and excessive heat damage might be attributed to eccentricity of the shaft resulting from various reasons—shaft misalignment, uneven wear of bearing elements and mismatch in clearance, etc. However this is an assumption that should be verified by positive supporting evidence from condition monitoring of engines.     

轻合金自冲铆微动磨损及疲劳性能研究

选择4组轻合金自冲铆进行疲劳实验,用扫描电子显微镜和能谱仪对其断口进行微动磨损机理分析,并系统地研究了接头疲劳寿命和失效形式的影响因素。结果表明,下板与钉腿区的微动磨损是导致下板沿纽扣断裂和铆钉断裂的主要原因,两板间的微动磨损是导致上板靠钉头断裂的主要原因;微动磨屑主要成分为金属板材氧化物,并对微动磨损起缓冲作用。增加板厚可提高接头疲劳寿命,且疲劳载荷较大时寿命提高更为显著;增加板强可提高接头疲劳寿命,且寿命提高程度受疲劳载荷影响较小。增加板厚使失效形式从上板断裂变为下板断裂,增加板强使失效形式从板材断裂变为铆钉断裂。     

Failure Analysis of a Locomotive Engine Oil Pump Shaft

In this study, the fracture of a locomotive engine oil pump shaft is investigated. According to the reports, all oil pump shafts of this type fail in short periods of time due to the fracture at a location on the shaft which is in contact with a pinion. Stress analysis showed that the shaft bears torsion and cyclic bending stresses in the fracture site. The fracture surface observations revealed that the cracks are generated from the surface, and fatigue fracture occurs due to the cyclic bending stresses. According to the laboratorial analysis, the shaft is a surface-hardened low alloy steel. The lack of suitable pre-heat treatment and surface hardening and the roughness created by the slippage between the shaft and the pinion are concluded to be responsible for the failure of the oil pump shaft.     

Failure Investigation of Spline-Shaft of an Under Slung Crane

Investigation of the causes of premature failure of a spline-shaft used in the hoist gear box assembly of an under slung crane has been presented. The investigation consisted of visual inspection, chemical analysis, characterization of microstructures by optical and scanning electron microscopes, energy dispersive spectroscopy (EDS), and hardness measurement. Visual observation of the fracture surface of the shaft revealed multiple cracks all of which initiated at the sharp corners of the spline. Fractography of the shaft showed striations confirming fatigue. The chemical composition of the shaft was found to be close to EN-24 grade of hardened and tempered steel which is specified as per IS 5517. Microstructural examination showed branched-out cracks and few of them were associated with oxide layer or scale which was confirmed by EDS analysis. Since the shaft was not exposed to high temperature in service, formation of scale along the crack suggested that it was pre-existing in the component. Base matrix of the shaft revealed bainitic microstructure. Hardness values were found to be lower than that obtained for EN-24 grade in hardened and tempered condition. Analyses of the results suggest that the component suffered from fatigue under reversed torsional loading, which initiated at pre-existing cracks in the component.     

Fatigue crack growth simulation in a first stage of compressor blade

A first-stage rotary compressor blade of a Model GE-F6 gas turbine failed due to vibration in early March 2008. Initial investigations showed that pitting on the pressure side of the blade caused micro cracks, leading to larger cracks due to high cycle fatigue. To assess this failure, a series of experimental, numerical, and analytical analyses were conducted. Fractography of the fractured surface of the blade indicated that two semi-elliptical cracks incorporated and formed a single crack. In this study, static and dynamic stress analyses were performed in Abaqus software. Moreover, fracture mechanics criterion was accomplished to simulate fatigue crack growth. This was carried out using a fracture analysis code for 3-dimensional problems (Franc3D) in two states. Firstly, stress intensity factors (SIFs) for one semi-elliptical surface crack and then SIFs for two semi-elliptical surface cracks were taken into account. Finally, the Paris and Forman–Newman–De Koning models were used to predict fatigue life. Since stress level and crack shape in both conditions are the same and the SIF at the crack tip reaches the fracture toughness of the blade, SIFs results indicate that insertion of a second crack has no effect on the final SIF, however, the second crack facilitates the process of reaching the critical length. So, fatigue life in two-crack condition is less than in the one-crack state.     

进料泵传动轴断裂分析

采用显微组织分析、扫描电镜分析和拉伸试验等方法对进料泵传动轴的断裂进行了失效分析。结果表明,泵轴断裂属疲劳失效,轴中段键槽处在制造过程中存在淬火裂纹是导致疲劳断裂的主要原因。     

Fatigue Failure of 321 Stainless Steel Superheater Tubes from a Thermal Incinerator

Several boiler superheater tubes showed circumferential cracking at weld seams after 2 years in noncontinuous service (several shutdowns). On-site inspection revealed that several tubes were cracked and leaked; while many others were cracked, however, the severity was less pronounced. Two types of superheater tubes samples were collected: one with butt-welded tubes and the other with fillet-welded sleeve. The latter was found to be out of the boiler fireplace, and the sleeve was used as tubing support to the boiler shell. Detailed investigation showed that the butt-welded tubes contained circumferential fatigue cracks that initiated from the internal surface. The cracks initiated in the heat-affected zone and propagated as a result of tube vibration. The variations in the tube internal diameter and tube wall thickness are expected to play a role in tube fatigue failure. On the other hand, tubes with fillet-weld sleeve showed circumferential cracking as a result of fatigue crack initiation from weld defects on the tube external surface. The high vibration during several unscheduled shutdowns in addition to several other factors such as variations in tube inside diameter, wall thickness, and weld defects resulted in the initiation and propagation of fatigue cracks and premature failure. White deposits, similar to those observed when boiler tubes failed by caustic exposure, were seen in the vicinity of the tube cracks. Therefore, it was difficult to confirm whether the boiler tubes failed because of the fatigue cracks or because of the caustic salts (pH control chemical).     

FATIGUE STRENGTH AND FRACTURE MECHANISMS OF CERAMIC- SPRAYED STEEL IN AIR AND A CORROSIVE ENVIRONMENT

Abstract— In order to investigate the fatigue strength and fracture mechanism of ceramic-sprayed steel, rotary bending fatigue tests were conducted at room temperature in air and 3% NaCl solution using specimens of a medium carbon steel (S45C) with sprayed coating layers of Ni-5% A1 (under-coating) and chromia (top-coating). The results obtained are discussed based on observations of fatigue cracks and experimental data on specimens subjected to individual treatments during the ceramic spraying process. It was found that at a very early stage of fatigue life, cracks were initiated at the interface between under- and top-coating layers, and grew rapidly into the ceramic-sprayed layer. However, these cracks did not propagate continuously into the substrate, and the final failure was led by the growth of a crack newly initiated at the surface of the substrate steel. Thus, the fatigue strength of the ceramic-sprayed steel in air could be evaluated due to the property of the substrate. The corrosion fatigue strength of ceramic- sprayed steel was improved when compared to that of the substrate steel. However, the coating layer contained many pores, through which NaCl solution was supplied from the specimen surface to the substrate. Corrosion pits were formed at the interface between the under-coating and the substrate. Subsequently, cracks initiated from the pits and grew into the substrate. Tests were also conducted on specimens whose pores were closed by a shielding treatment. In this case, NaCl solution was supplied to the substrate by cracks initiated in the top-coating layer. The shielding treatment was effective at low stress levels where fatigue life was more than 10⁷ cycles, while it had little effect on improving corrosion fatigue strength at higher stress levels because of the many cracks initiated in the top-coating layer.     

Failure Analysis of Gearbox and Clutch Shaft from a Marine Engine

This article presents metallurgical failure analysis of a gearbox shaft and a clutch shaft from a marine engine. The gearbox shaft was made of low alloy steel, and the clutch shafts were components made of carbon steel. Fracture surface examination revealed circumferential ratchet marks with the presence of inward progressive beach marks suggesting rotary-bending fatigue failure in the case of gearbox shaft. The star-shaped pattern on the clutch shaft fracture surface suggested that the failure was due to torsional overloading which might have initiated at corrosion pits visible around the fracture surface. The gearbox shaft experienced rotational bending stresses which induced fatigue failure because the fatigue strength of the alloy was too low. The fatigue failure of the gearbox shaft led to the torsional failure of the corroded clutch shaft. The sudden, high level failure load on the clutch shaft occurred when the gear box shaft failed.