曲轴扭转疲劳断裂分析

发动机曲轴在进行扭转疲劳试验过程中出现非正常疲劳裂纹,裂纹未从应力最集中的油孔处起源,造成曲轴扭转疲劳强度达不到设计要求。分析认为造成曲轴非正常扭转断裂的原因是油孔内壁存在加工沟槽,通过钻完油孔后采用旋转锉打磨,提高了曲轴的扭转疲劳强度。     

大型柴油机曲轴断裂失效分析

对失效件进行了宏观分析、化学成分分析、表面硬度分析、力学性能分析、金相分析和开裂断面电子形貌分析后,认为该曲轴断裂性质为疲劳断裂。材质不均匀、硬度不均匀以及严重的组织疏松、组织偏析和非金属夹杂物导致曲轴于应力集中最为严重的曲拐与扇板过渡“R”部位产生了裂纹源,发生疲劳断裂,导致曲轴失效。     

超临界机组再热热段疏水管内壁裂纹原因分析

通过现场勘察以及材料成分分析、力学性能试验、扫描电镜及能谱分析等技术,对某超临界机组材质为SA-335P91的再热热段管道疏水管(材质为SA-335P91)内壁裂纹产生原因进行分析,结论是由于机组运行状况不稳定、疏水管结构布置不合理导致材料热疲劳而产生裂纹,并提出了相应的解决方案和预防措施,以确保机组安全运行。     

某柴油机试验台连杆断裂失效分析及改进

某柴油机轴瓦实验台连杆发生断裂,通过断口形貌分析及化学成分、力学性能、夹杂物等材料检测分析判断其为疲劳断裂.通过受力分析确定危险截面,并通过有限元方法研究连杆的应力分布.结果表明连杆小头在平行于接合面且靠近内壁处开设的螺纹孔引发的应力集中是造成本次连杆断裂的根本原因.据此对连杆结构进行了改进,实施了取消螺纹孔等改进方案...     

热电厂叶片断裂事故分析

对叶片裂纹、断裂进行了分析,该叶片材质为2Cr13钢,叶片的成分、组织、性能均符合标准要求,断口的宏观和微观分析表明,叶片的断裂起源于叶片机械加工遗留的刀痕、磕碰形成的缺口和尖锐的圆孔边缘,工艺缺陷降低了叶片的使用寿命。裂纹源在交变应力作用下不断扩展,导致叶片发生疲劳断裂。     

超临界350MW机组给水泵汽轮机第5级动叶片断裂原因调查分析

对某电厂超临界350MW机组给水泵汽轮机第5级动叶片进行了故障现场调查、断裂叶片的材质检验和断口分析、叶片离心应力和叶轮叶片系统振动特性的有限元计算分析及断裂原因分析.结果表明,叶片的断口性质为高周疲劳断裂,裂纹起源于叶片出汽侧的腐蚀坑,叶片材料与断裂无关;叶片断裂的原因为机组给水泵汽轮机存在超负荷运行的情况,致使给水...     

GH2132三齿二级涡轮盘榫齿裂纹分析

对GH2132三齿二级涡轮盘在外场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，该裂纹属于高周疲劳裂纹，疲劳源区无发现冶金缺陷及加工刀痕。对故障件的材质的化学成分、性能以及晶粒完整性进行了测试其结果材质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，这样，在榫齿配合面上就产生了压陷，在交变载荷作用下，在离压陷边缘0．5mm处产生了疲劳裂纹和断裂。     

内燃机曲轴疲劳断裂失效特征及原因探析

曲轴是内燃机的核心零件之一,受力复杂,服役环境恶劣,在多种因素的影响下常常发生早期疲劳断裂。在总结曲轴工程实际应用及试验中发生早期疲劳断裂情况的基础上,介绍了曲轴疲劳断裂特征,分析了引起曲轴疲劳断裂的因素;认为曲轴的早期疲劳失效涉及从材料、结构、加工、受力、服役环境等多个方面,并简述了曲轴疲劳断裂失效分析的手段及对断裂失效分析人员的要求。     

热电联产汽轮机调节级叶片断裂的分析与改进

热电联产用汽轮机运行中轴承振动突然升高，发生材质为1Cr11MoV的调节级叶片断裂事故。通过断口微观结构、化学成分、金相检验以及运行工况等分析原因，结果表明：裂纹源位于叶根承载面与叶根颈部交接倒角处，裂纹源区和扩展区占整个断口面积的80%以上，断口形貌呈高周疲劳断裂特征；机组运行中存在的进汽参数大范围高频波动以及少数超温超压，产生的交替动应力造成了叶片疲劳损伤；从稳定运行参数和叶根加工装配方面提出了改进措施，更换调节级叶片后机组恢复正常运行。     

大功率发动机曲轴疲劳断裂研究

公司开发的大功率发动机曲轴在进行疲劳试验过程中,主轴颈及连杆轴颈圆角处出现裂纹并断裂。我们通过搜集大量的工艺参数及检测结果对曲轴疲劳断裂的机理进行了全面分析,得出了曲轴断裂的原因,并依据分析原因,制定了整改方案,解决了曲轴疲劳断裂的问题。     

印度工程用P91热压三通冷校开裂原因分析

某热压三通P91用水压机进行冷校时开裂成两半,在断口上有一处裂纹缺陷,我们在裂纹缺陷处取纵向试样进行了化学成分、力学性能和金相组织的测定,找出了造成P91三通冷校开裂的主要原因,另外采用冷校工艺也不合理。     

The application of fracture mechanics to boiler drum/nozzle joints

Recent treatments of post yield fracture mechanics and fatigue crack growth laws are applied to a situation typical of a boiler drum/nozzle joint. Critical defect sizes are calculated for boiler plate material and the weld metals. It is shown that these defect sizes are less than those obtained using linear elastic fracture mechanics (LEFM), and that the amount of crack growth is larger than previously obtained.     

Fatigue crack growth in multi-pass butt-welded joints of mild steel

Fatigue crack growth rate properties obtained by testing multi-pass butt-welded joints in the through-the-thickness direction are presented along with a characterization of the mild steel base material. Edge-notched four-point-bending specimens are used to investigate R-ratio, specimen geometry and post-weld heat-treatment effects on fatigue crack growth rates. The pervasive influence of residual stresses on welded joint fatigue testing using the fracture mechanics approach is also discussed. For these multi-pass joints, conservative fatigue crack growth rates are obtained with post-weld heat-treated specimens.     

Stress intensity factors for a pipe-plate welded joint

A major component of any linear elastic fracture mechanics model for fatigue crack growth is the calculation of the crack tip stress intensity factor. This is particularly difficult for welded joints due to the complex geometry. While some data are available for cracks in welded T-plate joints, there is relatively little data available for larger cracks in more complex tubular joints. Such cracks are of significant interest since the most practical application of fracture mechanics models is the prediction of remaining life for cracks discovered in service.

A pipe-plate joint has been developed as a simplified model of tubular joint geometries for fatigue studies. Two such specimens have been tested in air, with detailed monitoring of crack growth behaviour using potential drop techniques. These data were used to obtain crack growth rate data from which estimates of stress intensity factors were made. Separately, finite element analyses for various discrete crack configurations were performed. The results of these analyses are presented and discussed, with particular emphasis on the accuracy of the results and the implications for fracture mechanics modelling.     

Hydrogen enhanced fatigue in full scale metallic vessel tests – Results from the MATHRYCE project

This study investigates the fatigue life of CrMo pressure vessels for hydrogen storage by hydraulic and hydrogen pressure cycle tests. Two different sized cylinders have been tested; 35 L inner volume and 28 MPa working pressure (WP) and 198 L volume and 41 MPa WP. On the inner surface of the cylinders U-shaped notches of different depths were machined by electro discharge machining technique. The initial notch sizes were designed based on a two stage fatigue predictive model based on fracture mechanics to develop through wall cracks in the deepest notches after about 50,000 hydraulic cycles together with crack propagation of the intermediate notches and crack initiation in the smallest. The cylinders were cycled between the nominal pressure of 2 MPa and the WP until leak before break (LBB). Strain gauges were placed at the external surface of the cylinders in correspondence of the internally machined notches. On the notches which developed through wall, the strain showed a progressive decrease followed by an increase of the hoop strain during the final stage of crack propagation until LBB failure. Hydrogen effect was clearly identified by the reduction in the number of cycles to failure comparing tests in hydrogen and in oil. Subsequent failure analysis at the end of each test revealed a typical trans-granular fatigue crack surface morphology (with fatigue striations) for tests in oil, while quasi cleavage and intergranular fracture appearance were found for hydrogen tests.     

Computational simulation of fatigue crack growth and demonstration of leak before break criterion

A thick plate with a semi-elliptical surface crack subjected to remote tension and tension fatigue loading is considered for the analysis. In the present study the material is assumed to have variable fracture toughness in the surface and thickness directions. Material with isotropic fracture toughness is also considered. The developed three dimensional finite element code which has the capability to handle singularity and evaluate fracture parameter based on force method is used to characterise the fatigue crack growth. Parametric study involving various initial crack sizes is carried out and Foreman’s equation is used to predict the crack growth. Various regions viz. break, leak before break are obtained.     

增压锅炉耐火砖衬结构的断裂失效分析

针对增压锅炉炉膛耐火砖衬出现横向裂纹的现象,综合考虑耐火砖所承受的热冲击、高温烟气冲刷及机械载荷的复杂工作环境,对局部砖衬结构进行了三维仿真建模,采用有限元方法进行瞬态温度场和应力场计算。结果分析表明：耐火砖衬结构的断裂失效主要是由于增压锅炉快速升、降温过程引起的拉压应力反复作用所致的疲劳损伤,停炉降温过程中的拉应力是引起断裂失效的直接原因。     

Calculation of stress intensity factors for semielliptical cracks in a thick-wall cylinder

Weight functions for the surface and the deepest point of an internal semielliptical crack in a thick-wall cylinder were derived from a general weight function and two reference stress intensity factors. For several linear and nonlinear crack face stress fields, the weight functions were validated against finite element data. Stress intensity factors were also calculated for the Lamé through the thickness stress distribution induced by internal pressure. The weight functions appear to be particularly suitable for fatigue and fracture analysis of surface semielliptical cracks in complex stress fields. All stress intensity factor expressions given in the paper are valid for cylinders with an inner radius to wall thickness ratio, R_i/t = 4.     

DF4D型机车在役车轴超声波探伤方法探讨

分析了DF4D型机车在役车轴疲劳裂纹产生的原因,介绍了车轴疲劳断裂过程。根据疲劳裂纹的特点确定了探伤条件,通过选择正确的探头角度、制作实物试块而明确提出了超声波探伤方法,并介绍了车轴疲劳裂纹波形特点和疲劳裂纹定量的影响因素。     

An analysis of crack extension by corrosion fatigue in a crude oil pipeline

Corrosion fatigue subcritical crack extension was found to be the most likely cause of four service failures in an 864-mm (34 in) diameter and 7·14-mm (0·281 in) wall thickness crude-oil pipeline. The results of examination of the failures are summarised and a fracture mechanics analysis of corrosion fatigue crack extension in the pipeline, from initial defect to critical size, is presented. The analysis is based on fatigue crack growth rate data measured in crude oil, saturated with H₂S, and an operational pressure fluctuation spectrum in the pipeline, acquired from the pressure records at pump station discharges. The additional effects of frequency of shutdowns and hydrostatic pressure tests are considered. The fatigue crack growth lives are calculated for various depths of initial defects.