YLⅡ-10000K烟气轮机叶片断裂失效分析

烟气轮机叶片在使用中断裂,叶片断裂属于疲劳断裂,裂纹起始于榫齿的边缘和榫齿的根部.叶片在加工制造过程中工艺控制不严格,导致同盘叶片的金相组织差异较大.另一方面,由于叶片的加工精度等使叶片在运行过程中受力不一致,使叶片在应力集中部位产生疲劳断裂.     

喷丸强化在提高Ⅱ级涡轮盘第一榫齿高温疲劳强度方面的作用

一、前言 在使用中Ⅱ级涡轮盘第一榫齿转接圆根部经常发现裂纹,其中严重者曾引起过一等事故。历年来的试验研究业已确认,Ⅱ级盘第一榫齿裂纹属于机械疲劳裂纹。 提高航空零件疲劳强度有三种途径:即改进设计、正确选材与合理的加工工艺。当设计和选材确定之后,改进零部件的加工工艺也可以使疲劳强度获得一定程度的改善,喷丸强化工艺即是其中的一种。生产和使用实践业已表明,喷丸强化是提高零部件疲劳强度和抗应力腐蚀能力的一种行之有效的工艺。     

高温合金的裂纹扩展与强韧化

用直接流位法研究了高温合金涡轮材料的裂纹扩展速率，结果表明，高温合金涡轮盘材料的裂纹扩展速率快不完全取决于材料强度，更主要地取决于持久塑性，在考察高温合金涡轮盘材料的裂纹扩展时，不能仅以速率ｄａ／ｄｔ的绝对值来衡量，还应看裂纹扩展速率曲线的斜率是否锐减或曲线出现明显的拐点，以及曲线所对应的应力强度因子△Ｋ的范围。     

某型航空发动机篦齿盘裂纹的原位涡流检测

针对某型航空发动机篦齿盘上产生的裂纹缺陷,在不拆分发动机的前提下,提出采用涡流检测的方法对篦齿盘进行原位无损检测．设计完成了一套可用于篦齿盘裂纹原位检测的涡流无损检测系统．采用正交型锁相放大器对涡流检测信号进行处理,提高了信号检测精度同时达到了抑制干扰的作用．在标准检测试件和模拟试件上分别进行了试验,试验结果表明,该涡流检测系统可以实现航空发动机篦齿盘裂纹缺陷的原位检测,并且可以定性判断裂纹的深度．     

GH33A合金在蠕变-疲劳交互作用下的裂纹扩展特性

通过对 GH33A 合金在蠕变与疲劳复合加载条件下的系列试验,发现拉伸保时使蠕变与疲劳发生了交互作用,加快了疲劳裂纹扩展速率,加速裂纹早期进入失稳扩展,大大降低了疲劳寿命。GH33A 合金具有良好的抗蠕变裂纹扩展能力,但疲劳裂纹扩展阻力较低。由此讨论了拉伸保时对裂纹扩展的影响,并对在蠕变-疲劳交互作用下的裂纹扩展模型作了探讨。     

GH36和GH132高温合金低周疲劳特性的研究

本文研究了GH36与GH132两种高温合金的高温低周疲劳和热疲劳性能。通过对两种疲劳试验的测试,获得了一些有参考价值可供比较的数据,为发动机涡轮盘的选材与设计建立了一定的理论根据。对用J积分表达高温裂纹扩展速率也作了初步尝试,并确定出公式中的常数。     

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.     

某飞机GH1140排气导管裂纹分析

某飞机在进行检查时发现,其起动机GH1140高温合金排气导管内层加强筋处有一条裂纹,采用化学成分分析、金相检验、断口分析等方法对裂纹产生的原因进行了分析。结果表明:由于高温气体的冲刷作用使排气导管内表层晶界出现了贫铬,降低了合金的强度、持久性能和疲劳性能;排气导管开裂主要是由于其内表面曾被打磨,打磨处形成应力集中萌生裂纹源,在起动机内部反复热应力和机械振动等作用下,以及表面氧化物的进一步促进作用下发生的热疲劳开裂。     

高炉煤气透平动叶片裂纹分析

在对高炉煤气余压透平发电机转子动叶片进行表面渗透探伤时,发现Ⅰ级动叶片组中有6片叶片的叶榫部有裂纹.为探明裂纹的形成原因,对叶榫裂纹进行了化学成分、高、低倍组织及断口的宏、微观分析.分析结果表明,叶榫第一齿根裂纹属于疲劳裂纹.疲劳裂纹形成的原因主要与齿根底部过渡圆弧类似于直角、圆弧底部的加工条痕比较粗糙、显微组织粗大不均匀、铁素体条带分布不合理以及楔块装配面接触不良等因素有关.     

高温合金低压涡轮盘机械加工技术研究

以GH4169低压涡轮盘为载体,研究、确定高温合金低压涡轮盘型面的加工工艺以及合理的加工路线。针对高温合金材料难加工的特点进行切削加工试验,摸索该材料的加工特性,确定最佳加工工艺路线、切削参数,研究最适合的刀具材料,不但满足零件尺寸精度,表面粗糙度和技术要求,而且要有效的延长刀具的使用寿命。进行分析高温合金材料车加工变形规律,并提出控制加工变形的有效措施;还进行研究、确定高温合金低压涡轮盘榫槽拉削加工工艺研究试验。     

Analysis of fracture failure of fir-tree serrations of stage II turbine disks

This paper presents an analysis of fracture failure of fir-tree serrations in stage II turbine disks in a certain type of engine. On the basis of statistical analysis, basic fracture features and fracture mechanisms of stage II turbine disk serrations have been summarized. The reasons for the serration fracture failure are: (a) the first order bending resonance k=5 in the turbine blade occurring at the speed of 9700 rpm; (b) the unreasonable design of the five-serration structure, which causes each serration to bear non-uniform stresses; (c) the disk being made of the alloy GH2036 having a low fatigue resistance; (d) the high intergranular corrosion sensitivity of GH2036. Finally, measures, i.e. the change of the five-serration structure into a three-serration structure and the replacement of GH2036 with GH2132, have been given to prevent the fracture failures, and the application has indicated that these measures are effective.     

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.     

断口定量分析在评估构件疲劳寿命中的应用

通过断口疲劳条带反推寿命的理论基础,采用断口定量分析方法,在断口上测量裂纹长度α与裂纹扩展速率ｄａ／ｄＮ,运用Ｐａｒｉｓ公式推导出裂纹扩展速率曲线方程,计算出疲劳裂纹扩展寿命。此方法已应用于涡轮盘疲劳断口和３０ＣｒＮｉＭｏＡ试验断口。     

Failure Analysis and Repair of a Catastrophically Damaged Gas Turbine Compressor Disk Using SEM Technique and CFD Analysis

During a major overhaul of an 85?MW gas turbine unit in Iran-Rey power plant, 39 cracks were detected with different lengths and locations on the compressor disk of stage 11. All of the cracks initiated from the dovetail regions. Preliminary visual inspections and further micro-fractography using the scanning electron microscope demonstrated that the fretting fatigue phenomenon was the main cause of failure. Four repair methods were suggested to restart the unit. The first one was to remove all of the cracks from the disk by machining, or the so-called blending. The second, third, and fourth ways were to remove the entire rotor blades of stage 11, to remove the entire rotor and stator blades of the stage 11 simultaneously, and to remove those rotor blades of stage 11 corresponding to the damaged dovetails, respectively. Although the first way of solution was initially carried out on the damaged disk, the first author offered that restarting the unit with the blended disk is not reliable enough because of the presence of a large number of repair points on the disk. Using the numerical investigations based on the computational fluid dynamics, it was found that only the second suggestion (i.e., removing the entire rotor blades of the stage 11) might be applicable. Ultimately, the entire stage 11 rotor blades were removed from the blended disk, and the gas turbine unit was successfully restarted without encountering abnormal operation. Although the performed process resulted in approximately 20% output power loss compared with the unit's power before the blades' removal, the unit was quickly restored to be ready to restart, and the electric power could be generated during the period of peak consumption.     

AlSi10Mg(Cu)铸铝合金的热疲劳裂纹萌生及早期扩展行为

微观观察AlSi10Mg(Cu)铸铝合金在热疲劳裂纹的萌生和早期扩展过程,重点研究共晶硅粒子对热疲劳裂纹行为的影响。结果表明:热疲劳裂纹萌生于脱粘共晶硅粒子与铝基体间的开裂界面,原因是共晶硅粒子与铝基体的热膨胀系数不同,引起热循环过程中两相热应变不协调,从而在两相界面处产生循环应力而引起疲劳破坏。热疲劳裂纹的扩展在长度和宽度上同时进行,具有良好塑性的铝枝晶对疲劳裂纹的扩展起阻碍作用。对热疲劳过程中共晶硅粒子周围应力场的模拟分析进一步解释了实验现象。     

分动箱齿轮断裂原因

某分动箱的20CrMnTi钢齿轮在工作过程中发生断裂.采用宏观分析、微观分析、化学成分分析、硬度测试、硬化层深度测量、非金属夹杂物分析、金相检验等方法对齿轮的断裂原因进行了分析.结果表明:齿面上残留的加工刀痕导致应力集中,在周期载荷的作用下,疲劳裂纹源首先在残留的加工刀痕较深处形成,随后裂纹逐渐扩展,最终齿轮发生疲劳断...     

任意分布参数的涡轮盘裂纹扩展寿命可靠性分析

讨论了某型涡轮盘随机参数服从任意分布时的可靠性问题.在基本随机参数前四阶矩已知的情况下,以Pairs-Erdogan裂纹扩展模型为基础,应用随机摄动理论和Edgeworth 级数技术,采用疲劳寿命模型对某型涡轮盘随机参数服从任意分布时的可靠性进行分析,建立了涡轮盘疲劳寿命可靠性分析模型,并求得了涡轮盘裂纹扩展寿命的可靠度.模型计算结果与Monte-Carlo仿真结果非常接近,文章提出的方法对涡轮盘可靠性设计具有一定的参考价值.     

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.     

变速箱六档齿轮断裂分析及解决措施

对频繁出现轮齿早期断裂的变速箱六档齿轮进行了分析。通过对齿轮断裂特征、显微组织、硬度等方面的综合分析,确定了其断裂形式为低应力高周疲劳断裂。由裂纹扩展过程判断齿轮轮辐设计强度不足是导致其大批量早期疲劳失效的根本原因。据此通过改进齿形、油孔等设计措施,降低齿根部的设计应力水平,解决了这一问题。     

微量镁和锆对GH4133B合金缺口持久及低周疲劳性能影响EI

研究了微量镁和锆对ＧＨ４１３３Ｂ合金涡轮盘高温缺口持久性能及使用性能下的高温低循环疲劳性能的影响。采用光学金相、透射电镜和扫描电镜等进行了显微组织和断口分析。结果表明：镁和锆的微合金化改善了合金的晶界状态，对晶界碳化物起细化、分散和球化作用，使晶内和晶界强度及塑性得到很好的匹配。提高了合金的持久强度和塑性，消除缺口敏感性，同时提高了合金的高温低循环疲劳寿命。