摩托车离合器主轴断裂失效分析及其机理

本文分析了摩托车离合器主轴用材、金相组织、显微硬度以及断口扫描电镜(SEM)宏观、微观形貌,结果表明,该摩托车离合器主轴断裂主要原因是轴颈突变截面尖角顶端曲率半径ρ值太小,形成很大的应力集中从而形成裂纹源,然后裂纹逐步扩展造成的。     

大型齿轮箱输出轴断裂失效分析

利用金相检查、SEM分析和X射线衍射物相分析等方法对材料为42CrMo的开裂大型齿轮箱输出轴进行失效分析,结果表明残余拉应力和位于中心的严重的冶金缺陷是输出轴失效的原因.     

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.     

A Case Study on Fatigue Failure of a Transmission Gearbox Input Shaft

In this paper, a root cause analysis of premature failure of a gearbox input shaft, manufactured of AISI 1045-H, was performed through standard procedures for failure analysis. Shaft failed on cross oil hole through a helical fracture and therefore did not meet bogie 100,000 cycles during the verification with 10 Hz frequency cyclic testing. The fracture in the oil hole implied evidence of fatigue (i.e., beach marks on the fracture surface were clearly visible). Prior to improving the fatigue life and suggesting required remedial actions, mechanism of failure has to be understood, especially the initiating point of cracking. To this end, chemical analysis, microstructural characterization, fractography, hardness measurements, and finite element simulation were used to assess the nature of fracture in detail. The fractography analysis showed that fatigue beach marks originate from transition zone of the case on the cross oil hole. This is possibly due to the fact that torsional strength in this area is lower than torsional fatigue strength which leads to fatigue crack initiation, crack growth, and final fracture. At the end of this paper, proper remedial actions have been proposed.     

某船用减速器螺栓断口的SEM分析

对某船用减速器断裂螺栓的断口形貌进行了SEM分析,同时结合螺栓的工况条件和受力情况,分析了其疲劳剪切断口形成的机理和过程,推断了引起螺栓断裂的原因,并提出了相应的解决措施,为整机的安全运行和优化结构设计提供了重要的参考依据。     

Failure Analysis of a Vehicle Engine Crankshaft

An investigation of a damaged crankshaft from a horizontal, six-cylinder, in-line diesel engine of a public bus was conducted after several failure cases were reported by the bus company. All crankshafts were made from forged and nitrided steel. Each crankshaft was sent for grinding, after a life of approximately 300,000 km of service, as requested by the engine manufacturer. After grinding and assembling in the engine, some crankshafts lasted barely 15,000 km before serious fractures took place. Few other crankshafts demonstrated higher lives. Several vital components were damaged as a result of crankshaft failures. It was then decided to send the crankshafts for laboratory investigation to determine the cause of failure. The depth of the nitrided layer near fracture locations in the crankshaft, particularly at the fillet region where cracks were initiated, was determined by scanning electron microscope (SEM) equipped with electron-dispersive X-ray analysis (EDAX). Microhardness gradient through the nitrided layer close to fracture, surface hardness, and macrohardness at the journals were all measured. Fractographic analysis indicated that fatigue was the dominant mechanism of failure of the crankshaft. The partial absence of the nitrided layer in the fillet region, due to over-grinding, caused a decrease in the fatigue strength which, in turn, led to crack initiation and propagation, and eventually premature fracture. Signs of crankshaft misalignment during installation were also suspected as a possible cause of failure. In order to prevent fillet fatigue failure, final grinding should be done carefully and the grinding amount must be controlled to avoid substantial removal of the nitrided layer. Crankshaft alignment during assembly and proper bearing selection should be done carefully.     

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 Water Pump Shaft

A number of shaft failures were encountered in water recirculation pumps of an industrial setup. The shafts were made of martensitic stainless steel. A detailed study was carried out to determine the cause of the pump shaft failures. In this connection, the analyses performed include chemical analysis, microstructural characterization, fractography, tensile, shear, and hardness measurement. The chemical composition of the shafts was as per standard, however, hardness was very low. It was concluded that the material was used without heat treatment, causing inferior properties (hardness, tensile, and shear). Experimental heat treatments were done to improve the properties of the shaft material.     

Failure Analysis of Mill Shaft Roll

A strip mill roll shaft failure was investigated. The investigation revealed that the fatigue strength of the shaft had been compromised by a combination of several factors that included: inadequate fillet radius size, the use of dissimilar filler materials to rebuild the shaft surface, the presence of slag inclusions at the weld/alloy interface, and machining defects on the shaft surface. Such failures have occurred repeatedly, and this paper presents a case study investigating the cause of the problem and discusses possible remedial measures to prevent similar occurrences.     

Filter Debris Analysis for Aircraft Engine and Gearbox Health Management

Oil filters capture a tremendous amount of tribology information about the operation of a machine. Removal and analysis of the filter debris has proved to be an effective tool for engine health management by determining wear modes and observing failure progression providing long lead times for maintenance remediation. The process of manual debris removal and analysis in a laboratory, however, is tedious. An automated filter debris analysis system provides a repeatable process for at-line or laboratory use. The filters are automatically cleaned; the particles are counted and sized utilizing a quantitative oil debris sensor; and the debris is deposited on a patch for automatic analysis by an integral energy dispersive X-ray fluorescence spectrometer. The XRF analysis procedure provides metallurgical analysis and an expert determination of engine condition. The system has been successfully applied to two operational aircraft fleets, the Canadian Forces S-61 Sea King helicopter fleet and the US Navy EA-6B Prowler aircraft fleet. In both applications, significant benefits have been realized. Reprinted with permission from Integration of Machinery Failure Prevention Technologies into Systems Health Management, Proceedings of the 61st Meeting of the Society for Machinery Failure Prevention Technology, Society for Machinery Failure Prevention Technology, 2007, pp. 239–245.     

Failure Analysis of a Diesel Engine Connecting Rod

A failure investigation has been conducted on a diesel engine connecting rod. The fracture occurred at the small head of the connecting rod. Visual and scanning electron microscopy observations show that a lot of axial grooves appear on the internal surface close to the fracture and the fatigue cracks initiated from the axial grooves. Fractography indicates that the multiple-origin fatigue fracture is the dominant failure mechanism. The machining or assembling process was responsible for the formation of the axial grooves.     

汽车变速箱输出轴断裂失效分析

针对某汽车变速箱输出轴断裂失效问题,运用失效分析方法,开展了宏观痕迹分析、断口分析、化学成分分析、金相检验,硬度测试及氢含量测定。结果表明:汽车变速箱输出轴断裂为延迟断裂,输出轴尾部螺纹处表面渗碳层较高硬度的回火马氏体组织为延迟断裂提供"必要条件",这与螺纹处局部处理工艺的控制不合理相关;一定的外加静拉应力、自身残余应力和氢含量为延迟断裂的"充分条件"。最后提出了改进与预防措施。     

Failure Analysis of Al 356-T6 Clutch Lever

A permanent mold cast Al 356-T6 aluminum clutch pedal lever is investigated to determine the mode of failure. The part is investigated using visual inspection, metallography, scanning electron microscopy, energy dispersive spectroscopy, and hardness (HRB) testing. The part is found to have casting defects ranging from extreme porosity to intergranular fusion voids causing brittle fracture of clutch lever.     

Failure Analysis of a Truck Diesel Engine Crankshaft Made from Spheroidal Cast Iron

A diesel engine crankshaft fractured in service after 13,656 km of operation. The fracture took place on the sixth, the fifth, and the fourth crankpins and the fracture surfaces have a 45° inclination with respect to the axial of crankshaft. The cracks of the sixth and the fifth crankpin are across the oil hole and a complete fracture took place at the sixth crankpin which bore the maximum torque load. On the fourth crankpin, crack is only through the thin wall side of oil hole. The results indicate that fatigue fracture is the dominant failure mechanism of the crankshaft. It was observed that the fatigue cracks in the crankpins initiated at machining dents present on the wall of oil hole. The appearance of the machining dents on the wall of oil hole suggests improper machining and these dents supplied the stress concentration site that was mainly responsible for the fatigue fracture of crankshaft.     

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.     

发动机启动发电机弹性轴断裂分析

通过硬度检验、断口分析和金相检验等方法,确认断裂的发动机启动发电机弹性轴为扭转疲劳断裂失效,弹性轴锥体和衬套间配合松动导致的反复冲击是其断裂失效的关键因素,键槽设计的深度较大和加工质量粗糙进一步增大了转角处的应力水平,促进了裂纹萌生。     

Fatigue Failure of a Drive Shaft

The drive shaft in the propulsion system of a boat broke, while the vessel was sailing along the Western Canadian coast. This part was made from a low-alloy steel grade 4340 quenched and tempered. Fractographic investigation at macro scale revealed that the shaft failed under low rotating-bending variable stress. Fatigue propagation occurred on about 95% of the total cross section of the shaft, under both low-cycle and high-cycle fatigue mechanisms. It was found that the fillet radius present at the fracture’s origin was smaller than the one provisioned by design. This situation has raised the stress level at this location higher than the one taken into consideration at the moment of the design calculations and caused the initiation of the cracking. Moreover, although the shaft has been quenched and tempered, its actual hardness did not have the optimal value for long-life fatigue strength.