Investigation of Fatigue Failure of Roll Shafts in a Tube Manufacturing Line

A failure analysis of steel shafts operating as roll components in a tube drawing machine was conducted. Visual inspection, optical microscopy, SEM fractography, and hardness testing were used as the principal analytical tools for the failure investigation. The findings showed that the failure mechanism is rotating bending fatigue under low stress–high stress concentration conditions. The primarily inadequate component design resulted in high stress concentration factors interacted with the soft annealed material used for the component and caused fatigue under the presence of fluctuating stresses.     

Pitting corrosion of triggering initial fractures of palm oil screw press machine shafts

Investigation was carried out following the frequent occurrences of shaft failures in a number of palm oil screw press machines in a Malaysia palm oil mill company. Visual inspection, chemical analysis on the shaft material, fatigue analyses by utilizing traditional method and microscopic examinations were performed to support the investigation. Overview on pitting corrosion problems is presented. Common locations of the failure are at around bottom edges of keyway and shoulder fillets of the shafts. The findings indicate that pitting corrosion is identified as the main root causes of the premature shaft failures. In turn, poor surface condition would significantly reduce the fatigue endurance limit of the shafts under torsional loading.     

Failure mode analysis of two crankshafts of a single cylinder diesel engine

This paper reports an investigation carried out on two damaged crankshafts of single cylinder diesel engines used in agricultural services for several purposes. Recurrent damages of these crankshafts type have happened after approximately 100 h in service. The root cause never was imputed to the manufacturer. The fatigue design and an accurate prediction of fatigue life are of primordial importance to insure the safety of these components and its reliability. This study firstly presents a short review on fatigue power shafts for supporting the failure mode analysis, which can lead to determine the root cause of failure. The material of these damaged crankshafts has the same chemical composition to others found where the same type of fracture occurred at least ten years ago. A finite element analysis was also carried out in order to find the critical zones where high stress concentrations are present. Results showed a clear failure by fatigue under low stress and high cyclic fatigue on crankpins.     

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.     

Failure of stainless digester shafts in a paper production plant

The stainless steel connecting shafts of digester discharge screws of a paper production plant failed within a relatively short period after the production start of the plant. To investigate the reasons for these failures, stress analysis and material characterization of the broken shafts were performed. The test program included tensile, impact and hardness tests and metallographical and fractographical investigations. Fractographical examination verified that crack growth due to fatigue would have not been a contributing damage mechanism. Existence of chromium carbides together with a martensitic structure in the welded regions between the shaft body and its blades had provided potential zones for crack initiation. Stress corrosion cracking (SCC) was judged as the main damage mechanism in the failure of the shafts. The high temperature steam containing aggressive chemical species caused SCC. Thus, the material selected for the DDS shaft is not proper with respect to resistance to the corrosive atmosphere in the digester housing.     

Failure analysis of gears,shafts and keys of centrifugal washers failed during life test

This work presents a failure analysis of a transmission gearbox used in a motor of a food centrifugal dryer tested with a life test procedure developed by Electrolux Professional. The test apparatus consisted in a prototype of the centrifugal dryer where some aluminum cylinders were installed on the drying basket in order to simulate the maximum loads, that in-service are transferred by the food processed in the dryer to the transmission system investigated in this work. This system is employed for the motion of the basket trough an electric motor. The aim of this test apparatus was to simulate the service conditions of the components in order to evaluate their mechanical resistance and to verify that the life of the appliance is consistent with the project specifications. Moreover, the life-test presented in this paper can be used to test new materials for this specific application.The gear and the shafts analyzed in this work are made of low-alloyed steel heat treated by induction quenching followed by tempering.Premature failures occurred during the life test are considered in this work. In particular, the components interested by failure are the gear's teeth or the keys used to transfer force from the shaft to the gear. The failure of these components was observed after about 3000 of ON-OFF cycles.The microstructure of the gears and shafts, that exhibited premature failure together with that of intact components, was investigated by optical microscopy. The chemical composition of these components was characterized by means of Rf-GDOES (Glow Discharge Optical Emission Spectroscopy). The mechanical properties of the components were investigated by Vickers micro-hardness tests.The experimental results obtained in this work indicate that the failure of the components could be related to the quality of the materials of the components. In particular, the life test used in this work proved to be an important tool to evaluate the risk of a possible reduction of the products life due to non-conformity with materials specifications.     

Torsion fatigue failure of bus drive shafts

The mystery surrounding high failure rates in the drive shafts of a large municipal transit agency's fleet of 40 newly acquired articulated buses is investigated. The drive shafts were fabricated from a low-carbon (0.45%) steel such as AISI 5046. An examination of the drive shafts on all 40 buses is conducted, and 6 different drive shaft designs are identified among the fleet, but all of the failures, 14 in all, are limited to just one of the identified designs. Microscopic examination of the fracture surface of one of the failed drive shafts under a scanning electron microscope is conducted to determine the failure mode. Evidence of high-cycle fatigue is found, and a finite-element analysis is conducted to compare the maximum stress of the design exhibiting failures with the most common of the other designs that exhibits no failures. A fatigue life prediction is performed to determine just how much longer the expected fatigue life of the surviving design is compared to the design that suffered the early failures.     

Crankshaft failure analysis of a motor vehicle

A case study of a crankshaft catastrophic failure of a motor vehicle and its failure analysis is presented. The crankshaft suffered a mechanical seizure on the crankpin no. 2 after 3 years in service. It was repaired and after 30,000 km the vehicle had a damage again, with a catastrophic failure on the same crankpin. A transversal macrograph of the crankpin revealed that the crankpin was rectified and filled with a metal alloy for the same nominal diameter. Two fatigue cracks growing to the center of the crankpin where the final fracture occurred. The symmetric semi-elliptical crack front profile confirms the effect of a pure mode I under alternating bending. The catastrophic failure was a consequence of the inadequate repairing by a non-authorized manufacturer.     

基于试验模态安全吊焊缝开裂原因分析

GQ70型轻油罐车上拉杆安全吊在车辆运行过程中经常发生焊缝开裂。安全吊不承受大载荷,可排除强度断裂原因。运用试验模态分析的方法,对关键部位安全吊进行锤击法模态试验,找出各个安全吊模态频率,并经过对比分析找出易裂部分安全吊焊缝开裂原因,提出改进建议。     

Failure of a swing pinion shaft of a dragline

The causes of failure of a swing pinion shaft of a coal handling dragline have been investigated in the present work. Along with the failed shaft, a small piece of material from the tooth of another shaft that rendered design life in service has also been analyzed. The chemical composition and general heat treatment of the shafts were as per recommendation. The microstructure of both the shafts was tempered bainite, which is usual for such pinion shafts. The mechanical properties met the requirement for such applications. The investigation included metallography, microscopy (SEM), hardness and fractography. Analysis revealed fatigue cracks initiated at a number of places along the length of the tooth, and grew to a considerable depth. Improper surface hardening of the pinion teeth is believed to have rendered the teeth susceptible to bending fatigue failure. Other factors like lubrication and impact loads in the tooth roots might have aggravated the failure.     

The effect of steady torsion on fatigue crack growth in shafts

Most of catastrophic mechanical failures in power rotor shafts occur under cyclic bending combined with steady torsion: Mode I (ΔK_I) combined with Mode III (K_III). An analysis of the influence of steady torsion loading on fatigue crack growth rates in shafts is presented for short as well as long cracks. Long cracks growth tests have been carried out on cylindrical specimens in DIN Ck45k steel for two types of testing: rotary or alternating bending combined with steady torsion in order to simulate real conditions on power rotor shafts. The growth and shape evolution of semi-elliptical surface cracks, starting from the cylindrical specimen surface, has been measured for several loading conditions and both testing types. Short crack growth tests have been carried out on specimens of the same material DIN Ck45k, under alternating bending combined with steady torsion. The short crack growth rates obtained are compared with long crack growth rates. Results have shown a significant reduction of the crack growth rates when a steady torsion Mode III is superimposed to cyclic Mode I. A 3D Finite Element analysis has also shown that Stress Intensity Factor values at the corner crack surface depend on the steady torsion value and the direction of the applied torque.     

Failure study of connecting shafts of a plug screw feeder in a paper production plant

The connecting shafts of two plug screw feeder units of a paper production plant failed within a relatively short period after the production start of the plant. To investigate the reasons for these failures, material characterizations of the broken shafts were performed. The program included tensile, impact and hardness tests and metallographical and fractographical investigations. Fracture surfaces of the failed shafts were studied using light and electron microscopy. Obvious striations and beach marks could be observed by fractographic examination. The fracture features observed on the fracture surfaces reveal that (a) the shafts had experienced fatigue crack growth before the final failure; (b) the crack growth initiated from a sharp undercut at the threaded part of the shaft; (c) the fatigue driving forces have combined torsional and bending loading, having torsional as the governing load.     

Research of rail traction shafts and axles fractures towards impact of service conditions and fatigue damage accumulation

Traction shafts and axles of railway vehicles are designed to be safe and reliable in normal service conditions. Accidental and unpredictable conditions including bad exploitation (rail tracks, maintenance and extreme long service life) make the probability of shaft and axle fracture realistic. This article contains the experience and analysis of the traction shafts and axles fractures and fracture processes. Research also shows service conditions with results presented in the form of service stress spectrums. Besides normal service conditions, the results also include unpredictable phenomenon such as natural torsion vibrations of the shaft and wheels caused by stick–slip processes at the moment of the set in motion of a full-loaded train or at the moment of braking. These vibrations create an extremely high level of torque which is the main cause of cracks initialization. The next part of the article contains the results of the traction shafts and axles endurance research. The results of testing are transformed using the results of calculation by the FE method and by statistical estimation of the failure probability distribution. The main part refers to the interaction (impact) of service stress probability and failure (endurance) probability, which leads to the traction shaft (axle) reliability definition. Using the established model, locomotive traction shaft reliability is calculated and analyzed. The final part of the article contains suggestions for the traction shafts (axles) failure prevention.     

Reliability-based design of automotive transmission systems

A reliability-based approach is presented for the design of three-speed automotive transmission systems. The design of an automotive transmission system involves the design of the gear train, shafts (input, connecting, and output), bearings, keys, and splines. The gear train is idealized as a weakest-link kinematic chain, and the design is conducted with respect to failure due to bending and surface wear. The shafts are designed with respect to fatigue failure due to bending and torsion. The design of bearings (cylindrical roller bearings), keys, and splines are based on the maximum allowable stress in the components. The failure of the system is assumed to correspond to zero output power from the transmission system based on a series-parallel model. The reliability-based design is conducted for a specified value of the reliability of the system. The structural and kinematic designs of the transmission system (i.e. the gear train) are assumed to be known. The design parameters such as power transmitted, gear face widths, dimensions of roller bearing, length of splines, length of keys, and material properties are considered as random variables. The reliability-based design results are compared with those obtained by a deterministic design procedure. The effects of variation of design parameters, such as the reliability of the system and coefficient of variation of the input speed are also studied. In addition, a comparison of the designs obtained with different distributions of the random variables is also made and conclusions drawn.     

坦克扭力轴表面缺陷对疲劳寿命的影响

为探求坦克扭力轴过早产生疲劳断裂的原因,应用弹性有限元方法模拟了坦克扭力轴表面各种形状、尺寸的凹坑处产生的应力集中现象,结合坦克在某一训练科目下的载荷谱,使用疲劳分析软件计算了具有不同形状和尺寸缺陷的扭力轴的疲劳寿命(存活率为99%).结果表明:一旦扭力轴表面出现了凹坑,尤其是出现了狭长的裂纹状凹坑时,其疲劳寿命会急剧下降;当出现狭长的裂纹状凹坑时,将其扩展成等径凹坑(不增大凹坑深度),可使凹坑对扭力轴疲劳寿命的影响降至最低.     

缺陷可检修型半灌浆套筒连接拉伸性能试验研究

为解决灌浆套筒的施工质量检测和修补的难题,提出了一种缺陷可检修型半灌浆套筒(defect detectable and repairable half grouted sleeve,DDRHGS)。为了验证DDRHGS连接接头的拉伸性能和修补功能的可靠性,综合考虑有无灌浆缺陷、灌浆缺陷率、是否修补、修补材料种类、钢筋直径等因素影响,设计制作了26组78个连接接头试件,开展了单向拉伸加载试验。结果表明:无灌浆缺陷连接接头试件的拉伸性能可满足相关规范要求;灌浆缺陷率对连接接头试件的拉伸性能影响最为显著,较高的缺陷率会导致钢筋滑移破坏,试件的承载能力和变形能力无法满足相关规范要求;新型套筒灌浆缺陷修补功能整体可靠,48个试件的破坏模式、承载能力和变形能力与无缺陷试件基本相当,同等级灌浆料和植筋胶作为修补材料均可保证其修补质量。     

Failure of two overhead crane shafts

The failure analysis of two overhead crane shafts is presented: the failure of an overhead crane drive shaft and the failure of an overhead crane gearbox shaft, due to rotating-bending fatigue. The fracture of the overhead crane drive shaft originated in small radius fillet between two different diameters of the shaft. A new shaft was made with a larger-size fillet, resulting in reduced stress concentration in this region. The failure of the overhead crane gearbox shaft originated at the intersection of two stress raisers, at the change in shaft diameter and in the keyway corner. A new shaft was made with a larger-size fillet and a larger size radius of the keyways corner to minimize stress concentration in this section. In both cases the installed couplings were replaced by gear couplings in order to allow parallel and angular misalignment as well as to avoid additional load due to misalignment. The analysis shows that the fatigue life can be significantly increased with a simple change in the structural details.     

轴坯校直断裂分析

材料为3Cr13钢的轴坯在进行机械校直时，有30%的轴坯发生了横向断裂。经分析，轴坯的化学成分符合技术条件要求。经宏、微观检验，发现轴坯的外表面有数条裂纹；其显微组织为位向明显的回火索氏体，裂纹表面有轻微的氧化脱碳；轴坯断口为萘状断口，其微观断裂途径为沿晶断裂。通过对断裂轴坯表面裂纹的分析，认为轴坯表面裂纹分为两类：一类裂纹是由于轴坯原材料表面有较深的纵向划伤缺陷，热处理时沿缺陷处进一步扩展形成的；另一类裂纹是轴坯在淬火加热过程中由于温度偏高而形成的过热裂纹。因此，淬火加热时的过热导致轴坯在淬火冷却时形成表面裂纹，这样在轴坯机械校直时表面裂纹又诱发轴坯发生断裂。     

The effect of helicoidal cracks on the behaviour of rotating shafts

Fatigue cracks can develop in rotating shafts: their propagation is mainly in planes perpendicular to the axis of rotation, but also slant or helicoidal cracks could appear in industrial machine shafts. In this paper the static elastic behaviour of a shaft affected by a slightly helicoidal crack has been analysed by means of 3D finite element non-linear models, calculating deflections in different load conditions. Differences with respect to shafts affected by planar cracks of same depth and extension are emphasized. In order to simulate the dynamic behaviour of rotating shafts, a simplified model of the elastic behaviour of the cracked shaft has been developed, validated and substituted to the cumbersome 3D model. This model has then been introduced in the model of a power plant turbogroup shaft line in order to analyse its behaviour. The results show the additional vibrations caused by the crack which could be measured in different operating conditions of the group.     

Failure modes and effective strength of two-phase materials determined by means of numerical limit analysis

Summary In the most general case, composites composed of two materials, exhibiting a matrix-inclusion morphology, can be described by three phases: the matrix phase, the inclusion phase, and the interface between the inclusion and the matrix. In order to relate effective material properties to the matrix-inclusion behavior and the morphology, i.e., to the arrangement of the inclusions within the matrix phase, analytical and/or numerical schemes may be employed. Regarding effective strength properties, averaging schemes used, e.g., for upscaling elastic and viscoelastic properties are not able to capture the localized mode of material failure and do not provide information about the failure modes within the material. In this paper, the application of limit analysis to two-phase materials subjected to uniaxial/biaxial loading is proposed, giving access to the respective material strength and the corresponding failure modes. Based on a discretized form of limit analysis, different strength properties are assigned to the matrix, the inclusion, and the interface. The solution of the underlying optimization problem arising from the respective upper- and lower-bound formulation is based on second-order-cone-programming (SOCP). The presented upscaling scheme is used to illustrate the finer-scale origin of frequently observed failure and degradation scenaria in matrix-inclusion materials, highlighting the effect of strength properties, morphology, and interface degradation on the effective strength of the composite material. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday