叶片多源疲劳断裂分析

用金相，电镜，能谱仪等手段对叶片多源疲劳断裂进行了分析，结果表明，Ｃｒ的分布不匀易萌生疲劳裂纹，从而导致叶片的腐蚀疲劳断裂，提出了改进措施。     

伺服机构涡轮泵转子叶片断裂失效分析

某伺服液压源涡轮泵转子在测试过程中转子叶片发生断裂,通过对失效转子的观察、测试与分析认为:转子叶片的断裂性质为疲劳断裂,断裂原因是在叶片根部存在疲劳裂纹,疲劳裂纹在动静载荷作用下失稳扩展而发生疲劳断裂.分析认为转子叶片发生疲劳破坏与其组织在锻造成型工艺过程中存在工艺缺陷,导致材料疲劳寿命下降有关.     

高压涡轮导向叶片裂纹分析

对某发动机高压涡轮导向叶裂纹的性质和产生原因进行了分析。结果表明，导向器叶片裂纹的性质属典型的热疲劳断裂失效，引起该发动机导向叶片热疲劳断裂失效的主要原因是试验温度偏高，温度场分布不均，排气边冷却效果不良也是影响叶片开裂的因素。     

汽轮机末级叶片断裂原因分析

某机组低压末级叶片在运行过程中发生断裂。采用化学成分分析、力学性能检测和显微组织检验及用X射线法分析叶片的残余应力等方法对断裂叶片进行了分析。结果表明：疲劳裂纹起源于一个机械缺口,裂纹源在交变应力和残余应力的共同作用下不断扩展,导致叶片疲劳断裂。     

某发动机压气机三级转子叶片断裂原因

某发动机压气机三级转子叶片发生断裂,采用宏观观察、化学成分分析、扫描电镜和能谱分析、金相检验、硬度测试等方法,并结合叶片振动模态分析,对其断裂原因进行分析。结果表明：叶片的断裂性质为疲劳断裂,疲劳起源于叶片叶盆面距离进气边约0.8 mm的腐蚀坑处;腐蚀坑降低了叶片的抗疲劳能力,是叶片发生疲劳断裂的主要原因;叶片在工作转速范围内存在11阶共振,引起叶片疲劳裂纹的萌生和扩展。     

某发动机Ⅱ级涡轮叶片排气边裂纹分析

对WP13F发动机Ⅱ级涡轮叶片排气边裂纹、断裂进行了汇总分析。该叶片裂纹、断裂都属于以低周疲劳为主的高、低周复合疲劳失效模式；在疲劳起始区均存在一个黑色粗糙区(月牙形多晶区)；断口上存在的大量粗大初生碳化物降低了材料的断裂韧性，加速了疲劳裂纹的扩展。     

LC9CGS3铝合金光滑与缺口疲劳试样在不同载荷条件下的断裂行为

用ＳＥＭ电镜观察分析了ＬＣ９ＣＧＳ３铝合金在不同载荷下光滑与缺口疲劳试样的断裂行为。结果表明：两种试样的疲劳裂纹均为两阶段扩方式，而且疲劳裂纹Ⅰ阶段扩民菜区面积随应降低而增大。     

高速离心式压缩机叶片断裂失效分析

某高速离心式压缩机叶片在运行过程中发生断裂。通过对叶片断口及冲蚀表面进行宏观观察、材料化学成分分析、力学性能测试、断口扫描电镜观察、能谱分析和显微组织分析,找出了叶片的断裂失效原因。结果表明:压缩机叶片断裂主要是由于级间冷却器流体布局设计不合理,致使叶片在运行时不断受到冷却器管束铝翅片微粒高频脉动的冲刷磨损作用,在局部叶片迎风表面形成垢层,产生了高周疲劳载荷,使位于其对称位置的叶片在相对薄弱的顶部萌生裂纹并逐渐扩展,最终导致叶片高周疲劳断裂失效;另叶片材料冲击韧度低加速了疲劳裂纹的扩展。     

黄台发电厂7#机末级叶片断口分析

对黄台发电厂７＃机末级叶片断口进行了分析。认为,在该叶片进汽侧靠近头部的硬质合金堆焊层中,由于成分偏析,夹杂等原因产生微小裂纹,并在运行中产生应力腐蚀或腐蚀疲劳裂纹并扩展,最终导致叶片断裂。     

空气压缩机叶片断裂失效分析

采用扫描电子显微镜、能谱分析仪和金相显微镜对空气压缩机叶片的宏微观形貌、断口表面成分、金相组织及硬度进行了观察和分析。结果表明:断裂叶片的硬度低于其他叶片,导致其抗高周疲劳性能下降,在近表面夹杂物处萌生疲劳裂纹,最终发生断裂。     

Ti60钛合金中富钕稀土相颗粒对叶片室温振动疲劳性能的影响

采用振动疲劳实验及SEM断口分析等方法,研究了含稀土元素Nd的Ti60高温钛合金稀土相颗粒对叶片振动疲劳裂纹萌生的影响.结果表明:叶片振动疲劳寿命与稀土相颗粒的尺寸和分布位置具有密切关系.稀土相颗粒尺寸越大,对叶片振动疲劳裂纹的萌生作用也越大,疲劳寿命降低;外露于或镶嵌于叶片表面的稀土相颗粒明显促进了叶片振动疲劳裂纹的萌生.     

镍基单晶合金涡轮叶片开裂原因

某发动机高压涡轮叶片为镍基单晶合金叶片,在室温下进行振动疲劳试验后发现叶片开裂,通过宏观观察、金相检验和扫描电镜分析等方法对叶片开裂的原因进行了分析.结果表明:进气边叶根和榫头伸根的开裂形式均为疲劳开裂;进气边叶根气膜孔内壁存在多处小缺口及榫头伸根亚表面存在疏松缺陷,这些缺陷部位容易形成裂纹源,促进了裂纹的萌生,裂纹扩...     

Stochastic fatigue damage assessment of metro switch blade

Stochastic fatigue damage of a metro switch blade is studied with a combination of explicit finite element model (FEM), multiaxial fatigue criterion, and statistical analysis. The explicit FEM is used to reproduce dynamic procedure and to provide detailed stress/strain state variation. A multiaxial fatigue criterion proposed recently is extended to 3D conditions for fatigue prediction. The influence of stochastic impact position is considered by statistical analysis. After analysis, the formation of the serious unstable crack (continuous bites) on the switch blade can be revealed. From the perspective of service life, increasing traction coefficient and decreasing friction coefficient between wheel flange and switch blade gauge surface are beneficial but not significant. However, a speed increase from 36 to 54 km/h can lead to 40% reduction in service life. This work enhances the cognition of damage mechanism on switch blade and provides theoretical foundation for service life design and maintenance operation.     

Gas turbine disk-blade attachment crack

Evaluation of a gas turbine disk revealed a crack in the blade attachment area. The subsequent effort to understand the origin of this crack led to a series of analyses that included computing the stresses on the attachment, characterization of fatigue crack growth, and a model for fretting fatigue crack growth. These elements were brought together to simulate the conditions that led to the cracking. It is concluded that the crack was probably caused by fretting fatigue induced by the stresses related to normal takeoff and landing cycles and exacerbated by aircraft maneuvers, and that short periods of blade resonance may have contributed to the cracking. If material had not been removed from the attachment surface of the disk by service-induced wear, it is likely more cracks would have been found.     

离心叶轮叶片裂纹产生原因分析

某发动机离心叶轮叶片的排气边多处出现裂纹,通过理化检验和定量分析对裂纹产生原因进行了分析,并估算了叶片的裂纹扩展寿命及其占总寿命的百分比。结果表明:该裂纹为高低周复合疲劳裂纹,叶片在异常振动等大应力作用下产生了疲劳开裂。     

Acoustic emission detection of fatigue cracks in wind turbine blades based on blind deconvolution separation

The occurrence and expansion of fatigue cracks in large wind turbine blades may lead to catastrophic blade failure. Each fatigue phase of a material has been associated with a typical set of acoustic emission (AE) signal frequency components, providing a logical base for establishing a clear connection between AE signals and the fatigue condition of a material. The relevance of efforts to relate recorded AE signals to a material's mechanical behaviour relies heavily on accurate AE signal processing. The main objective of the present study is to establish a direct correlation between the fatigue condition of a material and recorded AE signals. We introduce the blind deconvolution separation (BDS) approach because the result of AE monitoring is usually a convoluted mixture of signals from multiple sources. The method is implemented on data acquired from a fatigue test rig employing a wind turbine blade with an artificial transverse crack seeded in the surface at the base of the blade. Two different sets of fatigue loading were conducted. The convoluted signals are collected from the AE acquisition system, and the weak crack feature is extracted and analysed based on the BDS algorithm. The study reveals that the application of BDS‐based AE signal analysis is an appropriate approach for distinguishing and interpreting the different fatigue damage states of a wind turbine blade. The novel methodology proposed for fatigue crack identification will allow for improved predictive maintenance strategies for the glass‐epoxy blades of wind turbines. The experimental results clearly demonstrate that the AE signals generated by a fatigue crack on a wind turbine blade can be synchronously separated and identified. Characterizing and assessing fatigue conditions by AE monitoring based on BDS can prevent catastrophic failure and the development of secondary defects, as well as reduce unscheduled downtime and costs. The possibility of using AE monitoring to assess the fatigue condition of fibre composite blades is also considered.     

Investigations on fretting fatigue in aircraft engine compressor blade

An investigation of several cracked blade tangs in the military aircraft engine compressor was conducted to identify the root cause of the failure. These cracks were found during the scheduled maintenance with fluorescent penetration inspection. The engine compressor blade made of Ti–6Al–4V is attached to compressor rotor by means of inserting retaining pin through rotor and blade tang. By analyzing the fracture surface of the failed blade tang, it is found that the crack in the blade tang was initiated by fretting fatigue and propagated under low cycle fatigue. Stress analysis of the blade using a non-linear finite element method is coincident with the results of fractography. The clearance between retaining pin and tang hole caused small amplitude of sliding motion leading to fretting wear during engine operation. Consequently, the damaged area due to fretting wear acts as a stress raiser inside tang hole and contributes to accelerate fretting fatigue.     

Assessment of the crack resistance of multiple-seated lock joints of gas turbine blades

We present results of assessing the crack resistance of three-seat lock joint of gas turbine blade under low-cycle fatigue and creep conditions of material in the presence of a hypothetical crack. The stress intensity factor is calculated by the finite element method. __________ Translated from Problemy Prochnosti, No. 5, pp. 89–95, September–October, 2008.     

Evaluation of corrosion fatigue crack propagation life at low-pressure steam turbine rotor groove

The corrosion fatigue crack propagation life of Christmas-tree type rotor groove with three hooks is studied. Each corner of the hook can be a candidate for crack initiation site therefore the condition where cracks initiate and propagate simultaneously at several hook corners must be considered. When a blade is inserted in the rotor groove, narrow gap is introduced unavoidably between the rotor groove and the blade root. The effect of this narrow gap on the crack behavior must also be considered. A procedure was presented to assess the crack initiation and propagation behavior under such a condition. Using the procedure, crack initiation and propagation behavior was evaluated for several gap conditions. It was revealed that the gap condition had little effect on the relation between crack depth at the third hook corner and life consumption ratio (ratio of loading cycle to final failure life). A corrosion fatigue test was performed using a rotor groove model specimen, and the results were compared with the evaluation results.