Failure Analysis of Friction Weld (FRW) in Truck Axle Application

A section of a fractured spindle from an axle housing was metallurgically examined. The axle fractured at the friction weld (FRW) interface and was from a truck with only about 8,000 miles of service. SEM and metallographic examinations of the weld fracture revealed that a ferritic band existed at the weld interface. A significant amount of oxides and some micro-porosity was observed in the ferrite. The existence of this type of microstructure compromised the strength of the weld and resulted in the overload fracture of the axle. FRW is supposed to be a solid-state process; however, melting-solidification was evident in this case, as suggested by the band of oxides caused by liquid phase oxidation of the molten layer at the interface and micro-shrinkage porosity formed during solidification of the liquid film. Process conditions that resulted in high heat input and liquidizing of the weld interface before the upsetting stage of the friction welding process should be mitigated. This article was published in Materials Science & Technology 2007 Conference and Exhibition: Exploring Structure, Processing, and Applications Across Multiple Materials Systems (Detroit, MI), September 17–20, 2007, What We Can Learn from Failure Analysis Symposium, ASM International, Materials Park, OH, 2007.     

Critical Malfunction of Diving Equipment

Two identically constructed diving devices showed complete and uncontrolled release of breathing air at depth below 30 to 40 m. The failures occurred during separate dives. In one case a fatal accident resulted. Post-mission testing procedures for the diving equipment did not show any technical failure, but a subsequent failure analysis revealed a principal problem. The problem resulted from a minor modification and the use of a protective cover. These changes caused pressure equalization to be hindered and caused a temporary blocking of a bypass valve in the “valve-open” position. The blocking occurred at depths below 30 m. An uncontrolled and sudden complete loss of air supply followed. This malfunction could not be reproduced with the equipment by examination onshore, because it only occurred underwater during a dive and was the result of a sequence of events. Modification of the valve design solved the critical and dangerous problem.     

Crankshaft failure analysis of a boxer diesel motor

This paper reports a failure mode analysis of a boxer diesel engine crankshaft. Crankshafts are components which experiment severe and complex dynamic loadings due to rotating bending combined with torsion on main journals and alternating bending on crankpins. High level stresses appear on critical areas like web fillets, as well as the effect of centrifugal forces and vibrations. Since the fatigue fracture near the crankpin-web fillet regions is one of the primary failure mechanisms of automotive crankshafts, designers and researchers have done the best for improving its fatigue strength. The present failure has occurred at approximately 2000 manufactured engines, and after about 95,000 km in service. The aim of this work is to investigate the damage root cause and understand the mechanism which led to the catastrophic failure. Recommendations for improving the engine design are also presented.     

A View on the General Practice in Engineering Failure Analysis

Analysis of engineering failures is a complex process that requires information from personnel having expertise in many areas. From the information gathered, a failure analyst tries to discover what was fundamentally responsible for the failure. This fundamental cause is termed the “root cause” and helps in the determination of the sequence of events that led to the final failure. Root cause analysis also helps in finding solutions to the immediate problem and provides valuable guidelines as to what needs to be done to prevent recurrence of similar failures in future. However, experience suggests that most failure analyses fall short of this goal. A significant number of failure analysts incorrectly use the term “root cause” when what they really establish is the primary cause of failure or simple physical cause. This paper examines a few service failures to demonstrate that the term root cause is not adequately understood.     

Causes and effects of spacecraft failures

In a study conducted for the USAF Rome Air Development Center to improve reliability prediction for spacecraft approximately 2600 incident reports on 300 spacecraft (representing 100 programmes) that were launched between the early 1960s and January 1984 were analysed. The causes of the spacecraft failures and the severity of the observed effects are examined. The classification of causes is explained in detail and examples of each type of failure are provided. Differences in the relative frequency of certain causes between pre-1977 missions and later ones are analysed and some significant trends are identified. The association of spacecraft subsystems with the major causes of failure is investigated. Finally, the severity of the failure effects due to the identified cause categories is discussed. A significant finding is that a large fraction of the incidents is due to design and environmental causes rather than to random failures.     

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.     

热泵干衣机仿真与优化

本文建立了热泵干衣机数学模型,包括稳态的热泵系统模型和动态的衣物干燥过程热质交换模型。利用模型仿真研究了各部件大小的匹配关系对单位能耗除湿量SMER和干燥时间的影响,并对重要的系统参数如循环风量、新风比例和制冷剂充注量进行了优化研究。将模型结果与实验结果进行了对比,干衣时间的误差小于3 min,耗电量的误差为-2.3%。结果表明,循环风量180 m~3/h、新风比例9%~10%时SMER最大;在冷凝温度限值之内,增加充注量有利于SMER的提高。研究结果可供热泵干衣机设计参考。     

Failure Analysis of Two Stainless Steel Based Components Used in an Oil Refinery

The petroleum industry has changed significantly over the past decades. For example, in Brazil, oil extraction under very deep sea water is growing very quickly. As a consequence, materials and components used for such applications must have properties required to withstand adverse conditions and ensure satisfactory performance and reliability in service. Nonetheless, components that normally fulfill these standard requirements can fail under severe service conditions such as high pressure and temperatures and high concentrations of H₂S and CO₂. Among the factors that can cause the premature failure in metallic components are the use of inadequate materials, the presence of defects that appeared during the production, and errors of project, assembly, or maintenance. Failure analysis allows the identification of causes and thus contributes to improvements in the operation and performance of similar equipment. In this work, light optical microscopy and scanning electron microscopy (SEM) were used to analyze the microstructure and fracture surface of two centrifugal pump shafts that failed during use in a Brazilian petroleum refinery. The results showed that one shaft, made of duplex stainless steel, failed by fatigue fracture, and the other, made of 316 austenitic stainless steel, experienced a similar fracture, which was promoted by the presence of nonmetallic inclusion particles.     

Failure analysis of the combat jet aircraft rudder shaft

This paper analyzes failure causes of the combat jet aircraft rudder shaft (RS) which occurred during the flight mission. A finite element method (FEM), utilized to determine the stress state of the RS subjected to hinge moment ultimate load, resulted in the high stress concentration sites around the rivet holes. The longitudinal crack was initiated from the corrosion pit in the zone of the rivet hole, where the fatigue beach marks were observed. The inner surface of the RS was heavily corroded. Moreover, pitting corrosion has destroyed approximately 50% of the wall thickness. Based on the presented results it was concluded that the failure of the RS had a character of fatigue combined with heavy corrosion. Therefore, it is recommended that the RS should be redesigned; the material changed into more corrosion resistant one and the maintenance procedure changed in order to avoid future similar failures.     

A methodology for risk-based inspection planning of oil and gas pipes based on fuzzy logic framework

In an efficient and effective pipe integrity management programme, maintenance engineers often use the risk-based inspection (RBI) and maintenance strategy. Unfortunately, the calculation of risk is a daunting task because in order to calculate the risk of failure, a maintenance engineer needs to predict the rate of growth of a defect, the effect of the defect on the integrity of the structure and the consequence of failure. Unfortunately precise calculation for either of these parts is quite difficult.Fuzzy logic is a mathematical tool suitable for handling imprecise information in the real world. The benefit of this approach lies in its ability to include personal experiences along with acceptable deterministic models in the calculation. The structure of the model also allows easy calibration of the model to suit a particular plant condition. This approach can thus help to reduce the dependence upon the precise data, allow modelling even when a phenomenon is incompletely understood, and reduce the difficulties arising due to the complex computation required by more traditional methods.This paper presents a proposed methodology, based on fuzzy logic framework, for the establishment of an RBI programme for pipes. The paper also presents in detail a section of the methodology that can be used for calculating the estimated rate of CO₂ corrosion in carbon steel pipes. In this technique the plant operating parameters (temperature, gas and liquid flow rates, total pressure, CO₂ partial pressure and pH) are taken as fuzzy variables and used to calculate the Predicted Rate of Corrosion. The inspected rate of corrosion and the efficiency of inspection are also considered as fuzzy variables and are used to calculate Trust in Inspection Results and Trust in Predicted Results. By combining all the modules an estimated rate of corrosion is calculated. This estimated rate of corrosion can then be used for developing the risk-based inspection programme.     

Erosion–corrosion of heat exchanger tubes

The shell and tube heat exchanger failed before 5 years of operation. The failure was caused by pits on the tube outside surface developing until its perforation. Inside the Cu-DHP tubes in soft temper a cooling agent circulated to cool down industrial water at the shell side from 16 to 4 °C. The cooled water was hard, rich in chloride ions with relatively low sulphate ions concentration and pH ranging from 4 to 7. The leaking tubes were subject to standard metallographic examination, hardness measurement, scanning electron microscopy and X-ray energy dispersion analysis. It was found that the tube damage was caused by erosion–corrosion induced by two factors: disturbed flow of water containing suspended solid particles and chemical composition of water rich in chlorides that resulted in loss of stability of protective cuprous oxide layer.     

Effect of ZrSiO4 on the Friction Performance of Automotive Brake Friction Materials

Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested. Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy （SEM）, and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820℃. Density of the final samples decreased with increasing the amount of reinforcing elements （ZrSiO4） before pre-sintering. However after sintering, there is no change in density of the samples including reinforcing elements （ZrSiO4）. With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed. However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0. 5% reinforced ZrSiO4. The SEM images of the sample indicated that while bronze-based break lining material without ZrSiO4 showed abrasive wear behaviour, increasing the amount of ZrSiO4 resulted a change in abrasive to adhesive wear mechanism. All samples exhibited friction-wear values, which were within the values shown in SAE-J661 standard. With increasing the amount of reinforcing ZrSiO4, wear resistance of the samples was increased. However samples reinforced with 5% and 6% ZrSiO4 showed the best results.     

塑胶场所有害气体成分分析方法的探究

在介绍塑胶场地材料和工艺的基础上,从主要来源、产生危害和环境限值等方面对塑胶场所存在的主要有害气体成分进行了讨论,指出了主要污染物不同于室内空气中的污染物成分.针对塑胶场所有害气体成分的采样和检测方法进行了综述,总结了污染物测定的研究进展和发展趋势,提出了建立有效测定塑胶场所有害气体成分分析方法的理论思想、基本要求和技术性支持,最后,对塑胶场所有害气体成分分析方法的发展趋势进行了展望,为标准的制定提供借鉴和参考.     

塑胶跑道中有害物质成分分析

采用顶空-气相色谱法(HS-GC)对塑胶跑道中甲苯二异氰酸酯(TDI)、苯及苯系物(甲苯、乙苯、邻二甲苯、间二甲苯、对二甲苯)的含量进行了分析,对色谱条件和顶空进样的条件进行了优化,该方法的回收率为95.3%~101.8%。实验结果表明,该方法操作简单,重现性好,灵敏度高。     

Sliding Friction of Al-Cu-Fe-B Quasicrystals

Dry sliding friction between the Al_59Cu_25.5Fe_12.5B_3 quasicrystals (QCs)/coating of the diamond-like carbon (DLC) was carried out by self-made tribometer under different conditions. The influences of four parameters (temperature, sliding velocity, applied load, atmosphere) on friction and wear of quasicrystal surface were studied. Microstructure of quasicrystal, morphology of worn surface, and wear debris were observed by scanning electron microscopy (SEM). The results showed that for QCs, the friction coefficient and roughness of worn surface were influenced by the parameters, especially greatly by the temperature. With rise of the applied load and sliding velocity, the friction coefficient decreased. The dominant wear mechanism at 350℃ was delamination for QCs. The cracks formed on the worn surface during the friction. Moreover, phase transformation was not observed on worn surface of QCs at 350℃. All the results are discussed and explained.     

Automated multiple failure FMEA

Failure mode and effects analysis (FMEA) is typically performed by a team of engineers working together. In general, they will only consider single point failures in a system. Consideration of all possible combinations of failures is impractical for all but the simplest example systems. Even if the task of producing the FMEA report for the full multiple failure scenario were automated, it would still be impractical for the engineers to read, understand and act on all of the results.This paper shows how approximate failure rates for components can be used to select the most likely combinations of failures for automated investigation using simulation. The important information can be automatically identified from the resulting report, making it practical for engineers to study and act on the results. The strategy described in the paper has been applied to a range of electrical subsystems, and the results have confirmed that the strategy described here works well for realistically complex systems.     

纳米流体在摩擦领域中的应用

为了寻找更好的润滑剂使机械零件的磨损最小化,人们尝试把纳米材料加入到基础润滑油里形成的纳米流体,与传统的润滑油相比,该流体具有更好的减摩抗磨性能。文中介绍了纳米流体的制备方法,包括单步法及两步法,并评价了各自的优缺点;详细论述了多种纳米颗粒添加剂对基础润滑油摩擦学性能的影响;指出了纳米流体后续研究中需要注意的一些问题。     

Failure of a Freeze Dryer Slot Door

Freeze-drying is utilized in the biopharmaceutical industry to give higher stability, broader temperature tolerance, and longer shelf-life to formulations that are unstable in aqueous solution (Green and Perry, Perry’s Chemical Engineers’ Handbook, 1997). Freeze-drying equipment consists of a drying chamber, condensers, a cooling system, and a vacuum system. The drying chamber is where the product is placed to undergo the lyophilization process. The chamber has two access points: a maintenance door, located in a mechanical room, and a slot door, located in a sterile clean room. The maintenance door permits entry into the chamber. The slot door facilitates tray loading and unloading from the clean room using an automatic tray handling system. At 9:26 AM on March 2, 2008, a freeze-dryer failed during the steam-in-place (SIP) cycle. As a result of the failure, the slot door was plastically deformed. Several items in the proximity of the slot door sustained damage. Fortunately, no personnel were inside the clean room when the event occurred; there were no injuries or loss of life. The impact to production was severe. The event removed the freeze dryer from service for approximately 2 months, reducing bulk powder production capacity by 33% during the time it was down. The failure occurred because the slot door was not closed properly when the SIP cycle began. Instead of being completely restrained, it was allowed to become simply-supported, seriously compromising its pressure-containing ability.     

Failure Analysis of Horizontal Hinge Pin Components from an Army Cargo Helicopter

A horizontal hinge pin (HHP) assembly from an Army cargo helicopter was examined to determine the root cause of ring and roller fracture and spalling. Chemical analyses, metallography and hardness testing indicated that the rings and rollers conformed to the material requirements of the governing drawing. Metallography and visual and scanning electron microscopy indicated the failure likely initiated in the lag ring due to rolling contact fatigue (RCF) because of high service loads. Evidence of subsurface crack initiation was observed. This article was originally published as “Failure Analysis of a Ring and Rollers from an Army Cargo Helicopter Rotary Wing Head Lag Horizontal Hinge Pin” in 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. 249–259, and is reprinted with permission.     

Microstructure and Mechanical Properties in Dissimilar Butt Friction Stir Welding of Severely Plastic Deformed Aluminum AA 1050 and Commercially Pure Copper Sheets

In this study,AA 1050 aluminum alloy and commercially pure copper in annealed and severely plastic deformed conditions were used.The technique used for imposing the severe strain to the sheets was constrained groove pressing（CGP） process.The annealed and severely plastic deformed sheets were subjected to friction stir welding（FSW） at different rotation and traverse speeds.Cu was placed in advancing side.Constant offset of approximately 1 mm was used toward Al side for all welds.A range of welding parameters which can lead to acceptable welds with appropriate mechanical properties was found.For the FSWed CGPed samples,it was observed that the welding heat input caused grain growth and decrease in hardness value at Al side of the stir zone.It was found that,generally the weakest parts of weld joints of annealed and CGPed samples were Al base metal and stir zone,respectively.Further investigations showed that several forms of intermetallic compounds were produced.