Failure analysis of Ti6Al4V gas turbine compressor blades

The failure mechanism of Ti6Al4V compressor blades of an industrial gas turbine was analysed by means of both experimental characterisations and numerical simulation techniques. Several premature failures were occurred in the high pressure section of the compressor due to the fracture of the blade roots. Metallurgical and mechanical properties of the blade alloy were evaluated. A 2D finite element model of the blade root was constructed and used to provide accurate estimates of stress field in the dovetail blade root and to determine the crack initiation in the dovetail.

The results showed no metallurgical and mechanical deviations for the blade materials from standards. SEM fractography showed different aspects of fretting fatigue including multiple crack initiation sites, fatigue beach marks, debris particles, and a high surface roughness in the edge of contact (EOC). The numerical model clearly showed the region of highest stress concentration at the front EOC of the blade root in the dovetail region, correlated closely with the experimentally characterised fatigue crack region. It was concluded that this failure has occurred due to the tight contact between the blade root and the disk in the dovetail region as well as low wear resistance of the blade root.     

Experimental crack propagation and failure analysis of the first stage compressor blade subjected to vibration

This paper presents results of experimental vibration tests of the helicopter turbo-engine compressor blades. The blades used in investigation were retired from maintenance under technical inspection of engine. Investigations were conducted for selected undamaged blades, without existence of preliminary cracks or corrosion pits. The blades during experiment were entered into transverse vibration. The crack propagation process was conducted in resonance condition. During the fatigue test, the growth of crack was monitored. In the second part of work, a nonlinear finite element method was utilized to determine the stress state of the blade during vibration. In this analysis a first mode of transverse vibration were considered. High maximum principal stress zone was found at the region of blade where the crack occurred.     

Fracture surface topography analysis (FRASTA)—Development, accomplishments, and future applications

In the late 1970s, Dr. George Irwin suggested to his colleagues at the University of Maryland that valuable information about a fracture event was recorded in fracture surface topography. Under his urging, Takao Kobayashi, an associate professor at the time, began quantifying and interpreting topographical features. Over the subsequent 30 years the procedures for quantifying and interpreting fracture surface topography grew continuously into an established technology that allows a fracture event to be reconstructed in microscopic detail. FRASTA (fracture surface topography analysis) has now been applied to achieve solutions to a wide variety of failure problems. This paper chronicles the historical development of FRASTA, recounts several notable achievements, and presents the plan for further development and future applications.     

冰箱压缩机阀片断裂失效分析

压缩机是冰箱的心脏,压缩机阀片的断裂失效可引起制冷系统严重故障。本文利用表面应力分析、金相组织和显微硬度分析、成分分析等方法,以及三维视频光学显微镜、扫描电子显微镜等,研究了阀片断裂的特征和机制。断口和裂纹分析表明,阀片失效是疲劳断裂机制,断口具有明显的疲劳扩展区和多处裂纹源。阀片的材质和组织正常。阀片表面的局部损伤容易引起断裂。塑料垫片和阀片形状设计对断裂失效有重要影响。在上述分析的基础上,提出了质量改进措施并取得了良好效果。     

RIK90-4型空压机增速器振动值高的分析与处理

介绍两套23500m3/h空分设备配套的进口大型空压机增速器振动值超高的现象及其分析、处理过程,通过重新加工小齿轮轴上的止推盘以及安装找正对中,排除了设备的重大隐患,避免事故的发生,保证供氧需求。     

Failure analysis of a cast steel railway wheel

The failure analysis of a broken railway pearlitic cast steel railway wheel, which was involved in a train derailment, has been investigated. The fractographic results near the fracture origin of the wheel have been compared to the regions of stable (fatigue) and unstable crack propagation of cast steel fracture toughness samples. The macro and microfractographic features of the broken wheel did not show any evidence of the occurrence of a fatigue mechanism, indicating that its fracture was caused by transgranular cleavage fracture, as a consequence of the train derailment.     

车用空调斜盘压缩机活塞断裂问题分析

双向斜盘式压缩机是汽车空调系统中广泛使用的一种压缩机。在研发新产品试制样机过程中，活塞中部台阶处经常断裂。针对这一问题，本文根据双向斜盘式压缩机活塞的结构与工作过程，分析活塞受力随转角的变化情况，并采用商用有限元软件对活塞进行应力分析。发现活塞中部台阶处承受交变应力，且应力集中现象明显，为此提出需要增大该处的过渡圆角。通过应力分析结果的对比以及试验验证，发现该法可以很好地解决活塞中部的断裂问题。     

Determination of the Failure Mode and the Rupture Pressure in a Mechanically Damaged Pipeline

The following case study outlines metallurgical, finite element, and fracture mechanics analyses conducted to determine the cause of a pipeline rupture that resulted from prior external damage. Metallurgical and fractographic analyses indicated that the rupture initiated from a shear crack caused by mechanical damage, and that the fracture mode was overload; no indication of progressive growth was observed. Stress and fracture mechanics analysis indicated that the pipe ruptured at a pressure below the maximum allowable operating pressure.

Fatigue life assessment for brake disc of railway vehicle

The brake disc of a railway should have stability. After long-term use, the brake disc may be seriously damaged by thermal fatigue cracks on the frictional surface. In this study, fatigue tests were carried out for a brake disc material (GC25). Furthermore, in order to determine the cause of the thermal fatigue cracks, contact pressure and thermal stress analyses were performed. From these results, the linear relation between temperature and stress variations was obtained, and the remaining life assessment of the brake disc of a railway vehicle was performed by using it.     

Brittle Fracture of a Lifting Stud During Assembly Operations

A lifting stud from a stator frame broke during assembly operations. The part was hot rolled from a 50 W grade low-carbon steel (according to the Canadian standard CSA G40.21-04), which is the equivalent of AISI 1022 grade. Complete metallurgical characterization of the material showed that the chemical and mechanical requirements of the aforementioned standard were met. Moreover, the tensile testing showed that the material had good ductility. Fractographic investigation, both at the macroscale and microscale levels, indicated that the lifting stud failed under bending overload, in a brittle mode. It was found that brittle behavior of the ductile material was caused by the sudden application of the load combined with triaxial stresses promoted by the threaded geometry.     

Numerical stress and crack initiation analysis of the compressor blades after foreign object damage subjected to high-cycle fatigue

This paper presents results of the complex stress and crack initiation analysis of the PZL-10 W turbo-engine compressor blade subjected to high cycle fatigue (HCF). A nonlinear finite element method was utilized to determine the stress state of the blade during the first mode of transverse vibration. In this analysis, the numerical models without defects and also with V-notches were defined. The quality of the numerical solution was checked by the convergence analysis. Obtained results were next used as an input data into crack initiation (ε–N) analyzes performed for the load time history equivalent to one cycle of the transverse vibration. In the fatigue analysis the different methods such as: Neuber elastic–plastic strain correction, linear damage summation and Palmgreen–Miner rule were utilized. As a result of ε–N analysis, the number of load cycles to the first fatigue crack appearing in the compressor blades was obtained. Moreover, the influence of the blade vibration amplitude on the number of cycles to the crack initiation was analyzed. Values of the fatigue properties of the blade material according to Baumel–Seeger and Muralidharan methods were calculated. The influence of both the notch radius and values of the UTS of the blade material on the fatigue behavior of the structure was also considered. In the last part of work, the finite element results were compared with the results of an experimental vibration HCF tests performed for the compressor blades.     

Structural analysis of tape-wrapped structures

The present study investigates the method of structural analysis and failure prediction of tape-wrapped structures that have been used in the conventional nozzle structures of rockets. Four-point bending test and its finite element analysis were performed to study how to model tape-wrapped structures and to investigate the failure characteristics of tape-wrapped structures. For dynamic characteristics, the natural frequencies of an inclined stacked plate and a tape-wrapped cylinder were measured and compared with the analytical characteristics.     

Fracture analysis of collapsed heavy-duty pulley in a long-distance continuous conveyors application

In this paper we present a case study of a heavy-duty pulley that failed after 2.1 × 10⁷ cycles. The pulley was installed as a take up on a continuous conveyor under a load of 350 kN transmitted by the counterweight tower. The failure was analyzed using (a) finite element analysis by Ansys, (b) field data analysis, and (c) fracture macro examination. The prior FEA analysis showed that the pulley was designed according to its field application and moreover when re-simulated, by applying higher loads, revealed high potential towards its safety factor. The field examination showed that the conveyor did not suffer any overload that would contribute to the pulley collapse. The macro failure analysis revealed stress discontinuities and fatigue symptoms such as beach marks and even chevron marks within the welding region. In the meantime the welding region did not show evidence of thermal affected zone (TAZ), which is the key to its mechanical strength. The case analysis showed that the pulley was designed in accordance with British Standard [British Standards Institution, BS 5400:1980. Steel, concrete and composite bridges: Part 10: code of practice for fatigue; 1980] but a welding failure generated unexpected stresses and weakness on the welding region which generated fatigue and the final fracture.     

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.     

阀片机械颤振对制冷吸气充量的影响

本文通过制冷压缩机的气阀阀板运动的数学模拟过程计算和与之相对应的实验结果对比分析表明 ;阀板的开度 (挠度 )、厚度及预弯量等技术结构参数的大小会引发气阀的机械颤振。这种机械颤振会严重地影响压缩机吸气过程的充量甚至阀片失效。为此 ,本文对阀片的厚度和预弯量进行优化选择计算并给出优化计算结果。本文的阀片运动数学模拟的设计程序可提供给有关企业使用。     

Failure analysis of cast-on-strap in lead-acid battery subjected to vibration

Lead-acid batteries (LAB) are widely used in transportation sector for starting, lighting and ignition application. The possibility of vibration mode of failure occurs in this application due to wear and tear of the road. These vibration causes fatigue failure, particularly between the cast on strap and pillar post leading to loss of electrical connection. In this paper vibration test is conducted on a 12 V/75 Ah AGM Valve Regulated Lead-Acid Battery (VRLAB) used for above mentioned application in India. The test is carried out using Electrodynamic Vibration System model SD-10-240/GT500M/DA-10. The shaker is performed with a sinusoidal excitation, with an acceleration of 2.143G and a fixed frequency of 16.7 Hz. The peak to peak displacement is 4 mm. The deformation and crack propagation features on the surface and cross sectional area of pillar post and strap in both positive and negative group are observed with Scanning Electron Microscope (SEM). The material is yielded due to improper fusion between pillar post and strap which could not stand the vibration force. During vibration this region is vulnerable for fatigue failure.     

Failure analysis of the draft tube connecting bolts of a Francis-type hydroelectric power plant

In this paper, the failure of the bolts that fasten the draft tube of a 95-MW Francis turbine is presented. The fracture of the bolts is especially frequent when the machine operates at partial load. Fracture surface analysis and stress measurements under several power levels were done. Stress was also measured, while pressure relief in the spiral case was performed. Finally, stress measurements were conducted while pressured air was injected at the stay vanes and the machine was operating at partial load. With the strain measured, stress on the bolts was calculated.The fracture surface analysis showed that fatigue is the failure mechanism. Stress measurements revealed that strong vibration and broad stress variation is present when the machine operates at powers below 80 MW. Air injection effectively decreases vibration and stress fluctuation, but pressure relief in the spiral case did not show any beneficial effect.     

3MSGE-25/15型离心空压机振动原因分析与处理

介绍3MSGE-25/15型离心空压机因停电而非正常停机后设备损坏,虽多次检修但因振动值高而不能正常运转的故障。通过综合分析现场的具体情况及相关数据,并在齿轮专业制造厂对空压机的相关部件进行检测后,终于找到了设备损坏和振动值超高的原因,采取相应措施后空压机运转正常。     

基于复特征值分析的某盘式制动器制动尖叫问题改进

以某车型出现2 000 Hz制动尖叫问题的盘式制动器为研究对象,建立制动器的有限元模型.通过试验模态对有限元模型进行修正,应用复特征值分析技术,获取系统的复特征值和振型,并通过ODS测试确认与制动尖叫频率对应的不稳定模态.然后针对此不稳定模态,通过相关性分析量化制动器零件对系统不稳定模态的贡献,采用优化具有最大贡献量的...     

Fatigue life prediction and failure analysis of a gas turbine disc using the finite-element method

A numerical prediction of the life of a gas turbine model disc by means of the finite‐element technique is presented and the solution is compared with an experimental rim‐spinning test. The finite‐element method was used to obtain the K solution for a disc with two types of cracks, both at the notch root of the blade insert and located in the corner and in the centre. A crack aspect ratio of (a/c) = 1 was assumed. The fracture mechanics parameters J‐integral and K were used in the assessment, which were computed with linear elastic and elastic–plastic material behaviour. Using a crack propagation program with appropriate fatigue‐creep crack growth‐rate data, previously obtained in specimens for the nickel‐based superalloy IN718 at 600 °C, fatigue life predictions were made. The predicted life results were checked against experimental data obtained in real model discs. The numerical method, based on experimental fatigue data obtained in small laboratory specimens, shows great potential for development, and may be able to reduce the enormous costs involved in the testing of model and full‐size components.