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。     

基于灵敏度分析的盘式开沟机性能分析及优化

为了解决某盘式开沟机工作时刀盘断裂的问题,采用响应面分析方法和灵敏度分析方法对开沟机进行性能分析及优化.首先,建立了开沟机仿真模型,利用有限元分析法对开沟机刀具进行动力学仿真,通过响应面分析得出了刀盘边缘应力集中是刀盘断裂的主要原因;其次,通过灵敏度分析得到了导致刀盘断裂的最大应力对各刀具受力的灵敏度,建立了基于不同刀...     

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.     

0Cr17Ni4Cu4Nb钢锻件延迟断裂失效分析

通过化学分析、力学性能检测、表面残余应力检测、金相检验和断口分析的方法,分析了0Cr17Ni4Cu4Nb钢锻件开裂的原因,结果显示,该锻件的开裂是由于回火不足引起的应力腐蚀开裂。     

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。     

Failure analysis of a slot-welded impeller of recycle hydrogen centrifugal compressor

A recently failed slot-welded impeller of recycle hydrogen centrifugal compressor has been investigated by material tests, theoretical calculation and numerical simulation, which focus on the environmental susceptibility of material, the corrosivity of environment and the characteristic components of the stress state. It is found that the matrix of FV520B precipitated hardening stainless steel used in the failed impeller did not match the optimal combination of strength, toughness and corrosion resistance, and large volumes of δ ferrite with banded appearance further increased the environmental susceptibility of material; the electrochemical corrosion environment came into being due to the presence of hydrogen sulfide and condensed water vapor in the recycle medium; the high hoop stress in the failed impeller was mainly caused by the shrink fit during manufacturing and the centrifugal force during operation. Based on these results, the failure of this slot-welded impeller can be mainly attributed to sulfide stress cracking (SSC), and hydrogen induced cracking (HIC) is found to accelerate SSC by breaking the continuity of material and hence increasing local stress. Additionally, the prevention and mitigation measures against failure have been discussed, which can provide some insight into improving the reliability of centrifugal compressor impeller.     

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.

Failure analysis of an aircraft engine cylinder head

The piston engine of the training aircraft malfunctioned during the flight due to the cracking of its cylinder head (CH), which is manufactured from an aluminum casting alloy. Based on the fractographic examination of the mating fracture surfaces, the characteristic ratchet and beach marks were observed indicating the occurrence of fatigue failure. The crack was initiated from multiple origins located on the inner flange fillet on the exhaust side of the CH. The metallography examination has shown that the fatigue was promoted from pre-existing material defect due to an elevated presence of shrinkage pores at the crack initiation zone and was most likely associated with the manufacturing process of casting. The finite element (FE) method, utilized to determine the stress state of the CH subjected to gas pressure, also confirmed that the crack origin was located at the most stress area.     

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.     

Fracture failure analysis of AISI 304L stainless steel shaft

Fracture failure analysis of an agitator shaft in a large vessel is investigated in the present work. This analysis methodology focused on fracture surface examination and finite element method (FEM) simulation using Abaqus software for stress analysis. The results show that the steel shaft failed due to inadequate fillet radius size and more importantly marking defects originated during machining on the shaft. In addition, after visual investigation of the fracture surface, it is concluded that fracture occurred due to torsional–bending fatigue during operation.     

Failure analysis of a diesel engine cylinder head based on finite element method

Macro fatigue cracks are expected to occur in valve bridges of cylinder head when engine is operating in normal working condition. In order to determine the causes of these failures, stress analysis is carried out using finite element method with a concern of temperature dependency of material properties. Mechanical and thermal properties of material tested at high temperatures are applied to the finite element analysis. Furthermore, temperatures of the cylinder head in actual working condition are measured to validate the simulation results of finite element analysis. After that, stress computation is performed and the regions of stress concentration on the flame deck surface are obtained. The analysis results of stress show that the regions of stress concentration are in agreement with the actual failure regions of the cylinder head. When analyzing the failures on the flame deck surface of a cylinder head by evaluating stress concentration, temperature’s effect on mechanical strength of material should not be ignored. The methodology of failure analysis proposed in this paper is time-saving and also relatively accurate and predictive in actual engineering practice.     

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.     

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。