TC17钛合金盘件的低周疲劳行为

研究了p锻TC17钛合金压气机盘件的应变控制低周疲劳性能及疲劳裂纹扩展途径.结果表明,当应变量△ε/2在0.5%～2.0%范围内,应变比R=-1和循环超过10次后,材料基本上表现为轻度的循环软化.疲劳裂纹萌生于试样表面.当疲劳裂纹与片状α或晶界α之间的夹角小于45°,裂纹沿片状α或晶界α的界面扩展;否则,疲劳裂纹将以穿过片状α或晶界α的方式增长.     

发动机用灰铸铁的低周疲劳行为

研究了发动机缸体用灰铸铁材料在室温、150℃和250℃下的低周疲劳行为。根据对拉伸应力-应变、循环应力-应变和应变-疲劳寿命数据的分析,给出了疲劳参数。结果表明:在高温下灰铸铁的弹性模量、强度降低,延伸率增大;循环应力响应表明,在较小的应变幅下经历初期循环硬化、循环软化、断裂,而在高温和较大应变幅下几乎没有硬化阶段,循环软化至断裂;其室温疲劳寿命最长,150℃最短,250℃居中。微观分析结果表明:疲劳裂纹萌生于片状石墨尖端、夹杂物及孔洞处,沿石墨扩展,夹杂物导致分支裂纹及裂纹偏转,延缓裂纹的扩展;灰铸铁的疲劳断裂方式为沿晶和准解理断裂的复合机制,存在扇形解理面和二次裂纹,解理台阶上观察到疲劳条带和韧窝。     

涡轮盘风冷过程数值模拟研究

采用商用CFD分析软件Fluent对涡轮盘固溶处理后的风冷过程进行了数值模拟研究,定量分析了盘件内温度、冷速等参数的分布情况.模拟结果显示,单风扇风冷过程中盘件沿径向和周向的温度分布较三风扇冷却方式均匀.两种形式风冷过程的风场结果表明,单风扇冷却时盘件表面的冷却速度较高.     

GH2132三齿二级涡轮盘榫齿裂纹分析

对GH2132三齿二级涡轮盘在使用过程中第一榫齿产生的裂纹进行了光学金相和扫描电镜分析。结果表明,该裂纹属于高周疲劳裂纹,疲劳源区无冶金缺陷及加工刀痕。对失效件的化学成分、力学性能以及显微组织进行了检测,其结果均符合技术条件要求。疲劳裂纹产生的原因,是由于二级涡轮盘与二级涡轮叶片榫齿配匹不均匀,在发动机工作时,由于热应力作用,两种材料的线膨胀系数不一样(GH2132合金线膨胀系数大,而GH4037合金线膨胀系数小),使之对盘的榫齿产生相当大的压应力,导致在榫齿配合面上产生了压陷,在交变载荷作用下,在离压陷边缘0．5mm处产生了疲劳裂纹。     

某型发动机I级涡轮盘的剩余寿命计算

对某典型飞行科目的载荷谱进行处理,得出对涡轮盘损伤影响较大的主次循环。根据三循环载荷谱,对该科目进行载荷等效转换,并分别对涡轮盘进行弹塑性分析,从而得到在不同循环载荷下的低循环疲劳损伤。进行蠕变分析得到蠕变损伤。通过对已完成的寿命损伤以及计划完成的寿命损伤计算,利用线性累加理论求得剩余寿命。     

涡轮盘榫槽综合测具的研究

涡轮盘是发动机重要承力构件,在转速高、温度高的环境下工作,涡轮盘具有较高的抗疲劳、抗高温氧化及抗燃气腐蚀能力。涡轮盘沿圆周均布一般在60-102个榫槽,叶片用枞树形榫头插入盘的枞树形槽内,检测榫槽的尺寸、位置度技术条件要求,保证叶片传递载荷分布均匀,提高发动机的性能稳定性。     

高压涡轮盘的热弹性应力分析

本文利用大型通用有限元程序ALGOR某型发动机的高压涡轮盘及其榫齿进行了三维热弹性应力分析,对如何处理轮盘和叶片之间的连接进行了研究,并在有限元计算中应用了边界元法,从而得到了盘及榫齿的热弹性应力分布,并已应用于实际的发动机结构设计中。     

某发动机二级涡轮叶片断裂失效分析

在叶片断口宏微观断裂特征观察的基础上,结合叶片的金相组织、力学性能、硬度以及化学成分等,对叶片断裂失效的原因进行了研究.结果表明,发动机二级涡轮叶片失效是由于其中一片涡轮叶片低周疲劳断裂所致.该叶片的低周疲劳断裂失效与源区附近的R槽中的微裂纹、Zr含量偏高、HRC偏高以及断裂处在高应力区等因素有关,且叶片经历了短时超温,其温度约在1050～1100℃之间.     

涡轮盘篦齿裂纹扩展的有限元数值模拟

为了详细考察篦齿裂纹的扩展规律,对篦齿裂纹从齿尖一直扩展到即将完全穿透篦齿环的过程进行了数值模拟.含篦齿裂纹的涡轮盘有限元模型采用子模型法建立,使用M积分计算裂纹前沿的应力强度因子;在确定篦齿裂纹前沿每一节点处的局部扩展方向及距离后,通过样条曲线拟合出新裂纹前沿,并依靠自适应网格划分实现裂纹区有限元网格的更新.数值模拟结果表明,篦齿根部过渡圆角顶部可以视为裂纹缓慢扩展阶段与快速扩展阶段的分界点,在此之前篦齿裂纹以穿透型裂纹的形态以较低的速度进行扩展,在此之后篦齿裂纹开始向表面裂纹进行转化,并且平均扩展速度大大增加,分界点前的裂纹扩展寿命是之后的数倍.此外,由数值模拟结果还可以发现,增大篦齿根部过渡圆角半径以及减小相邻篦齿的间距,均有助于延缓篦齿裂纹的扩展.     

基于弹塑性理论的燃机转子寿命分析

深圳南天电厂用于联合循环的13E2型燃气轮机出现压气机转子裂纹事故,为准确预测同类机组的疲劳寿命,基于弹塑性理论,考虑温度场与离心力对燃机压气机转子疲劳寿命的影响,建立该型燃气轮机压气机转子的有限元热-固耦合数值仿真模型。基于低周疲劳理论,计算该燃气轮机压气机转子的疲劳寿命寿命为5333次,该燃气轮机压气机转子在电厂的实际疲劳寿命为4435次,计算误差在20%以内。利用该方法可以较准确地估算燃气轮机转子的寿命。     

FGH95粉末盘剩余循环寿命的裂纹源制作及测定

应用电火花加工技术,制作出宽度为０．０５ｍｍ±０．０２５ｍｍ,深度为０．２５ｍｍ±０．０１３ｍｍ,长度为１ｍｍ±０．０５ｍｍ的裂纹源,预制出长度为１．５０ｍｍ±０．１３ｍｍ的疲劳裂纹,然后对剩余循环寿命进行了测定。     

A unified approach for high and low cycle fatigue based on shakedown concepts

ABSTRACT The purpose of this paper is to present a unified analysis to both high and low cycle fatigue based on shakedown theories and dissipated energy. The discussion starts with a presentation of the fatigue phenomena at different scales (microscopic, mesoscopic and macroscopic) and of the main shakedown theorems. A review of the Dang Van high cycle fatigue criterion shows that this criterion is essentially based on the hypothesis of elastic shakedown and can therefore be expressed as a bounded cumulated dissipated energy. In the low cycle fatigue regime, recent results by Skelton and Charkaluk et al. show that we can speak of a plastic shakedown at both mesoscopic and macroscopic scale and of a cumulated energy bounded by the failure energy. The ideas are also justified by infrared thermography tests permitting a direct determination of the fatigue limit.     

GC4超高强度钢在腐蚀介质中的低周疲劳性能试验研究

对ＧＣ４超高强度钢在腐蚀环境下的低周疲劳寿命进行了试验研究，得出了在不同腐蚀环境下的低周疲劳寿命变化规律，为确定飞机腐蚀疲劳寿命提供了重要依据。     

Comparative analysis of three thermal fatigue experiments

This paper presents an analysis of the ability of different criteria to predict fatigue crack initiation under thermal loading. More precisely the predictions of the number of cycles to crack initiation are compared with experimental results obtained using five different fatigue criteria in three types of thermal fatigue tests (namely the FAT3D, JRC and SPLASH test campaigns). This analysis has revealed that:

• ? The conventional criteria based on equivalent strain variation substantially overestimate the lifespan of a structure subjected to thermal loading.
• ? A criterion making account for loading multiaxiality is required to estimate thermal fatigue life.

Three of the criteria studied give satisfactory results: the Zamrik criterion, the Park and Nelson criterion and a criterion taking hydrostatic pressure into consideration proposed by Amiable et al. The latter should be preferred for the accuracy of its results and the Zamrik criterion for its simplicity.     

Low‐cycle fatigue/high‐cycle fatigue interactions in notched Ti‐6Al‐4V*

Combined low‐cycle fatigue/high‐cycle fatigue (LCF/HCF) loadings were investigated for smooth and circumferentially V‐notched cylindrical Ti–6Al–4V fatigue specimens. Smooth specimens were first cycled under LCF loading conditions for a fraction of the previously established fatigue life. The HCF 10⁷ cycle fatigue limit stress after LCF cycling was established using a step loading technique. Specimens with two notch sizes, both having elastic stress concentration factors of K_t = 2.7, were cycled under LCF loading conditions at a nominal stress ratio of R = 0.1. The subsequent 10⁶ cycle HCF fatigue limit stress at both R = 0.1 and 0.8 was determined. The combined loading LCF/HCF fatigue limit stresses for all specimens were compared to the baseline HCF fatigue limit stresses. After LCF cycling and prior to HCF cycling, the notched specimens were heat tinted, and final fracture surfaces examined for cracks formed during the initial LCF loading. Fatigue test results indicate that the LCF loading, applied for 75% of total LCF life for the smooth specimens and 25% for the notched specimens, resulted in only small reductions in the subsequent HCF fatigue limit stress. Under certain loading conditions, plasticity‐induced stress redistribution at the notch root during LCF cycling appears responsible for an observed increase in HCF fatigue limit stress, in terms of net section stress.     

三维应力状态下高温低周疲劳寿命分析

通过带缺口的圆柱形ＬＤ８铝合金度样的高温低周疲劳试验,并应用ＴＭＦ程序,进行了轴对称问题的循环应力应变计算,探讨了应用当量应变范围评价三维低周疲劳特性,研究结果表明,三维应力状态下,当量应变范围可以作为三维高温低周疲劳的有效力学参量。