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.     

东风4A、4B型机车车轴的超声波探伤

中修时东风4A、4B型机车车轴疲劳裂纹的超声波探伤用三种方法:透声检查、小角度纵波探伤和斜探头横波探伤.介绍了它们在探伤时所出现的各种情况,并提出了改进建议.     

高速机车车辆车轴的疲劳设计

从提高高速机车车辆车轴的疲劳寿命出发,系统介绍了国外主要高速动车车轴的材质选择、强度计算、结构特点、表面处理、维修周期、检修内容以及超声波探伤技术的改进等问题,并通过对其结构参数、疲劳极限应力、表层残余应力及维修规程的分析,说明了这些车轴之所以具有高疲劳可靠性的原理。     

东风4、7型机车车轴使用寿命的探讨

指出东风4、7型机车车轴的疲劳裂纹集中发生在齿轮镶入部的喇叭口处,距轴端面630～680mm,并分析了疲劳裂纹产生的原因.提出对带裂纹的车轴在退轴后进行旋削处理,可在车轴镶入部尺寸限度允许的情况下继续使用,这样既能保证行车的安全,又延长了车轴的使用寿命.     

机车车轴多通道超声波探伤系统

简要介绍了机车车轴受力状况和目前采取的探伤手段。对机车车轴采用多通道超声波探伤系统进行了探讨。其结果对机车车轴,尤其是对空心轴结构的快速机车车轴探伤的效率、精度、可靠性具有一定的意义。     

小辅修机车车轴探伤中缺陷定量的影响因素分析及建议

针对小辅修机车车轴小角度纵波探伤中缺陷定量误差较大的现象,通过对影响车轴实物探伤中缺陷定量的几大因素进行分析,提出车轴探伤中如何准确对缺陷定量的方法和建议,保证了探伤的有效性。     

浅析对比试块与机车车轴的超声波探伤

车轴镶入部裂纹的位置是依据实物对比试块上人工模拟裂纹定位的,深浅是参照人工模拟裂纹的深度来判断的,透声灵敏度是根据TS-1试块的第10次底波为荧光屏满幅度的80%以及衰减的dB值来确定的,用于标定探伤灵敏度的为对比试块,因此对比试块应与被检车轴的材质相同。在调研中发现同类型的对比试块存在着差异,对此进行了探讨。     

车轴探伤方法的探讨

针对车轴探伤中几种常用的探伤方法,分别对其检测方式、不同的特点及它们的不足之处进行了分析研究,并提出了改进建议,以提高探伤质量.     

对DF4型机车车轴齿轮镶入部疲劳裂纹定量的探讨

1问题的提出齿轮镶入部的裂纹是威胁行车的最大隐患,在日常的检测中经常发现齿轮镶入部喇叭口根部有裂纹,但对疲劳裂纹定量的难度比较大。若是把超限的裂纹判小了,随着时间的推移,再加上外力的作用,将会导致行车事故的发生。2车轴齿轮镶入部疲劳裂纹的深度定量铁道部1998年12月     

DF型机车车轴镶入部超声波探伤波形分析

轮轴是机车走行部重要部件,从其镶入部产生裂纹的机理及表现形式入手,对超声波探伤中产生的各种波形进行分析,指出故障车轴的具体判别方法,对现场生产具有重要指导意义。     

Allowable defect sizes in a sour crude oil pipeline for corrosion fatigue conditions

A fracture mechanics treatment of corrosion fatigue crack growth rates is used to estimate corrosion fatigue life and allowable defect depths for specified lives of sour crude oil pipelines.The present study is based on a case history of a major Canadian crude oil pipeline that experienced five fatigue failures during its first 10 years of operation. Characteristic pressure fluctuation spectra have been derived from pump stations' pressure records. Fatigue crack growth rates for various crack configurations and orientations, and the effects of environment (crude oil with hydrogen sulphide content from zero to saturation) on these have been measured in the laboratory.Calculated fatigue lives have been verified by full-scale pipe tests pressurized with crude oil containing 100 ppm of hydrogen sulphide, using the characteristic pressure spectrum simulating operating conditions.     

Crack Propagation and Initiation Lives for Surface Pitting Due to Rolling/Sliding Contact

The stress intensity factors of a multiply kinked crack in a half-space are analyzed under rolling/sliding contact with frictional heat. On the basis of these analytical results, rolling contact propagation fatigue life is predicted numerically for the case of high carbon-chromium bearing steel. The initial crack is assumed to be inclined at the angle of maximum energy release rate, and the initial crack length can be determined by the threshold value criterion of the energy release rate. Applying the maximum energy release rate criterion to each kinked angle, the crack growth path can be described, and employing a mixed mode fatigue crack growth law, the associated propagation fatigue life can be predicted. Making use of the dislocation dipole accumulation model to the assumed initial crack, the crack initiation life also can be estimated. Combining the initiation life and the propagation life, the total rolling contact fatigue life for surface pitting can be predicted. The thermomechanical effects on these lives and induced surface pitting are considered.     

Experimental investigation of fatigue behaviour for welded joint with mechanical heterogeneity

Because of material and mechanical heterogeneity in welded joints, experimental studies of low-cycle fatigue (LCF) life and fatigue crack initiation behaviour were performed on weld metal, heat-affected zone (HAZ) and base metal of 16 MnR pressure vessel steel. A fatigue damage test was carried out by introducing a new damage variable. The fatigue damage evolution laws in each zone of a welded joint were obtained. A circular-notched compact tension specimen was designed and the whole process of fatigue damage, crack initiation and crack growth in each zone was investigated. The effect of mechanical heterogeneity in welded joints on the fatigue damage behaviour and fatigue crack initiation life was also investigated. The experimental and theoretical results indicate that the fatigue behaviour is markedly different in three zones of welded joints; there is a trend toward reduction in the fatigue life of HAZ as compared with the base metal. The weld metal does not have the same fatigue behaviour as confirmed by LCF life and crack growth rate. This study leads to the conclusion that fairly accurate estimates of fatigue life for welded joints should include the whole process of fatigue damage evolution and fatigue crack initiation as well as crack growth. Furthermore, a local experimental method should be carried out for weld metal, HAZ and base metal, respectively. Finally, the local fatigue failure criterion based on the weakest chain model has been presented.     

内燃机受热部件热疲劳模拟试验台的研究与开发

通过对内燃机受热部件热负荷、热应力和热疲劳损伤的分析,提出以试验的形式模拟受热部件的实际工作状况,实现对受热部件热疲劳强度、热疲劳寿命和可靠性的试验研究.为此,研究了受热部件热疲劳模拟试验台的组成和发展现状,分析了模拟试验台冷却系统、控制系统、温度检测系统、裂纹检测系统、应力应变检测系统和火焰检测系统的研究方法,对以后的研究具有一定的参考价值.     

Fatigue crack initiation and propagation in austenitic stainless steels for light water reactors

The determination of fatigue life of components containing defects usually takes into account crack propagation only. In a real situation, a number of cycles are often required to reach fatigue crack initiation and predictive evaluation of fatigue crack initiation phases of real defects in austenitic stainless steel welded joints are presented. Fatigue crack growth rates in wrought and cast austenitic stainless steels and associated welds are also presented. Effects of various mechanical parameters (R ratio and variable amplitude loading) of a PWR environment and of metallurgical factors (δ ferrite content and ageing in cast austenitic stainless steels) are discussed.     

Modelling crack growth for creep and fatigue loading

Estimates of creep crack growth in engineering components under steady load conditions are usually based on the application of fracture mechanics concepts. In particular the creep parameter C* has become widely used together with creep crack growth data obtained from laboratory tests. There are now a number of practical methods to utilise experimental data. For high temperature components, which are subjected to cyclic (fatigue) as well as creep loading, the estimation of the fracture mechanics parameters becomes much more difficult, and consequently the extent to which the growth of pre-existing cracks grow by creep and fatigue is difficult to quantify. In this paper the response of Type 316L stainless steel is examined. This material progressively strain hardens under reversed cyclic loading, and the creep behaviour also changes. Using uniaxial fatigue and creep results, fracture parameter maps are developed to establish the appropriate regimes for creep-fatigue crack growth. Using the maps a model is developed which can predict the combined effect of fatigue and creep on crack growth. The implications of the model are discussed in relation to the limitations of obtaining results from laboratory tests at short times, and the assessment of practical engineering components.     

Fatigue crack propagation behavior of fuel cell membranes after chemical degradation

The durability of fuel cells is significantly impaired by chemical and mechanical degradations of perfluorosulfonic-acid membranes. However, how the mechanical degradation, especially the fatigue crack propagation behavior, is impacted by chemical degradation is not clear. In this paper, the fatigue crack propagation behavior of Nafion 212 and Nafion XL composite membranes after chemical degradation are investigated. The fluoride release rates of Nafion 212 and Nafion XL membrane are 0.335 and 0.095 μmol cm⁻² h⁻¹, respectively. Likewise, the fatigue crack propagation rate of Nafion 212 membrane is also larger, which is attributed to two fatigue crack propagation mechanisms induced by chemical degradation, including bubble collapsing and pore interconnecting. By contrast, the fatigue crack propagation mechanism of Nafion XL membrane is not significantly changed where chemical degradation only accelerates crack growth in exterior surface layers. These findings provide new insights into the failure mechanisms under combined chemical and mechanical degradations.     

Exploring the role of reinforcement in controlling fatigue crack propagation behavior of perfluorosulfonic-acid membranes

Reinforced composite membranes in polymer-electrolyte fuel cells (PEFCs) are attracting more and more attention due to their simultaneously superior durability and high performance. Despite its improved durability during accelerated stress testing, the underlying mechanism of reinforcement in improving mechanical durability, particularly the crack propagation resistance, has not well been investigated. In this paper, we report the fatigue crack propagation behaviors of reinforced Nafion XL membrane and unreinforced Nafion 212 membrane. It is found that the fatigue crack growth rate of Nafion 212 membrane depends on stress ratios, and that of Nafion XL membrane depends on initial crack length and membrane orientation. In addition, the microstructure changes of reinforced Nafion XL membrane are examined through microscopy studies where two distinct features are observed: crack propagation in outer ionomer layers and interfacial delamination. These two features well explain the distinct fatigue crack propagation behavior of Nafion XL membrane, such as slow and almost constant fatigue crack propagation rate. The findings reported here are not only beneficial for understanding fatigue crack propagation mechanism of reinforced composite membrane but also helpful for designing and optimizing composite ion-conductive membranes.     

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.     

Fatigue failure criteria for thick-walled cylindrical pressure vessels

The fatigue failure of simple thick-walled cylinders under repeated internal pressure is considered with a view to establishing general criteria for failure which can be of use in design. The factors controlling the endurance limit and the limited life range are considered separately, utilising current thinking on the fatigue process. It is found that the fatigue behaviour of cylinders can be adequately predicted from conventional material fatigue data when the complexities of the elastic-plastic stress-strain state in a pressurised cylinder are taken into account. The importance of pressurising medium in assisting crack development is noted.