超高周疲劳的研究进展

论述了超高周疲劳研究的背景及意义,总结了近年来超高周疲劳的研究成果包括超高周疲劳的典型特征如S-N曲线、裂纹起源、起裂机理、影响超高周疲劳行为的因素等,介绍了超高周疲劳的常用实验手段,提出了今后超高周疲劳研究的课题。     

钛合金榫头微动疲劳试验研究现状与发展

综述了涡轮发动机钛合金叶片榫头微动疲劳失效的两种试验方法(轴向微动疲劳试验和榫型微动疲劳试验)的研究现状。轴向微动疲劳试验技术适用于微动疲劳失效机理的研究,应用于抗微动疲劳防护层试验验证的研究也较多;而榫型微动疲劳试验技术则多用于力学分析和模型建立等方面。榫头微动疲劳问题的研究还远未完善,应综合运用微动磨损、轴向微动疲劳和榫型微动疲劳等技术,并配合有限元分析手段,开展微动疲劳机理、多因素影响及防护层作用等方面的系统研究。     

轴承钢滚动接触疲劳研究进展

对轴承钢的滚动接触疲劳领域的研究重点、研究方法和研究进展进行了综合性的阐述。首先分析了滚动接触条件下材料内赫兹应力的分布以及轴承钢对循环应力的响应,解释了轴承钢发生次表面疲劳的根本原因;接着对轴承钢疲劳测试的方法进行了总结,分析了各种测试方法的优劣势;然后讨论了影响轴承钢滚动接触疲劳寿命的关键因素;最后,对轴承钢次表面诱发的滚动接触疲劳的两大表现形式,即疲劳裂纹生长和显微组织退化,进行了系统性阐释,介绍了重要的疲劳机理并提出了未来的重点研究方向。     

钢轨钢的滚动接触疲劳

钢轨钢的接触疲劳一直为铁路运输部门和研究机构所重视。轮－轨经过长时间滚动接触会导致轨面剥落,产生疲劳。本综述了钢轨钢的滚动接触疲劳特征及其原因,探讨了提高钢轨钢接触疲劳寿命的途径。     

金属热疲劳损伤的一种新判据

本文提出一种新的热疲劳损伤判据，用以评估金属材料的热疲劳性能，研究表明，Ｇｌｅｅｂｌｅ动态热、力学模拟试验机是研究热疲劳行为的有效手段；η－Ｎ曲线和ε－Ｎ曲线可以定量地反映金属材料裂纹萌生前的热疲劳损伤规律，预测金属材料的热疲劳寿命，利用Ｇｌｅｅｂｌｅ热模拟机研究了Ｒｅｎｅ４１高温合金的热疲劳行为。     

FGH95合金高低周复合疲劳行为

为了解高周振动应力对FGH95合金低周疲劳过程的影响,对FGH95合金进行高低周复合疲劳和低周疲劳试验。试验结果表明：在低周疲劳过程中叠加的高周振动明显降低了FGH95合金的低周疲劳寿命;且叠加的高周振动应力越大,FGH95合金的低周疲劳寿命降低程度越大。宏观和体视显微镜下分析的试样断口形貌显示：断口呈平坦区和倾斜区两大部分,表面粗糙,有明显的反光小平面。最后,着重用扫描电子显微镜（SEM）分析疲劳裂纹扩展不同阶段的形貌特征,并对不同试验条件下的相同裂纹扩展阶段的裂缝形貌特征进行比较。     

二次带状组织对低合金非调质钢疲劳性能的影响

采用应力比为0.1的轴向拉伸疲劳试验分别研究了低合金钢DG20Mn和35CrMo钢的疲劳性能与带状组织的关系.结果表明:带状组织对试验材料的轴向拉伸性能没有明显影响,对35CrMo钢的轴向拉伸疲劳性能影响较小,但严重减弱DG20Mn钢的轴向疲劳性能.带状组织对疲劳性能的影响主要是由于在高的疲劳拉应力下,带状组织引发疲劳微裂纹、微空洞等疲劳损伤,导致疲劳裂纹萌生及扩展模式发生变化,从而影响疲劳性能.      

疲劳失效机理及热轧H型钢疲劳断口分析

介绍了疲劳断口类型、形貌及形成机理,并对热轧H型钢疲劳断口进行了分析,为今后型钢产品疲劳研究奠定基础。     

钢轨接触疲劳试验方法和几种组织的接触疲劳性能研究

本文阐述了利用MM-200磨损试验机,针对钢轨全长淬火新工艺研究,应用作者所研究的方法,进行了钢轨接触疲劳试验。提出了试样失效的条件、判断方法和评价钢轨接触疲劳性能的方法,最后提出了全长淬火钢轨接触疲劳性能所需要的组织保证。     

排气管挂钩失效分析

通过金相显微镜、扫描电镜和能谱等手段分析了某汽车排气管用挂钩疲劳断裂失效的原因。结果表明,排气管挂钩断裂位于焊接接头附近,腐蚀疲劳起源于挂钩表面的点蚀坑,点蚀由氯离子和吸氧腐蚀共同作用引起。排气管挂钩在使用过程中承受着交变应力的作用,裂纹由点蚀坑逐渐扩展直至穿透管壁。焊缝附近的断口处发现明显的疲劳辉纹、疲劳台阶、二次裂纹、晶间腐蚀以及一些腐蚀产物等,远离焊缝处只有典型的疲劳辉纹和光亮磨痕,整个疲劳断裂过程由腐蚀疲劳向机械疲劳逐渐转变,直至断裂。     

粉末冶金高强度烧结钢的疲劳特性

通过测定N-110烧结钢旋转弯曲疲劳下的S-N曲线、疲劳裂纹扩展速率da/dN以及疲劳门坎△K_th,对烧结材料的疲劳特性进行了探讨,初步阐明了孔隙的存在对各种疲劳性能的影响规律以及热处理状态与疲劳性能之间的关系。     

Statistical simulation of small fatigue crack nucleation and coalescence in a lamellar TiAl alloy

This article examines the possibility of fatigue failure as the result of fatigue crack nucleation and coalescence at stress ranges below the fatigue limit and the large crack threshold where fatigue cracks are expected not to grow. By representing the material as a two-dimensional array of beam elements, the nucleation of nonpropagating small cracks at various material locations is modeled via a statistical approach that considers fatigue crack nucleation by accumulation of damage at randomly distributed weak regions. Once nucleated, the fatigue cracks do not propagate but extend only by linking with fatigue cracks subsequently formed in the contiguous elements. Result of the computer simulation suggests that fatigue failure by crack nucleation and coalescence is feasible, but the cycles-to-coalescence is much longer than the cycles-to-initiation for the first crack. Implications of the results in fatigue life assessment based on the Kitagawa diagram are discussed for TiAl alloys.     

Gigacycle Fatigue Behavior of 1800 MPa Grade High Strength Spring Steel for Automobile Lightweight

Gigacycle fatigue behavior of 60Si2CrVA high strength spring steel was investigated by ultrasonic fatigue test machine. Fatigue fractography was observed by scanning electron microscopy （SEM）. Maximum inclusion sizes and fatigue strength in different volumes were estimated by statistics of extreme values （SEV） and generalized Pareto distribution （GPD） methods. The results showed that S N curves of 60Si2CrVA spring steels for two rolling processes were not horizontal asymptotes but a gradient in a regime of 109 cycles, and traditional fatigue limits were eliminated. Surface machined topography and inclusions in steel were major factors that led to elimination of fatigue limit for 60Si2CrVA spring steel. The SEV and GPD methods could effectively predict size of the maximum inclusion and fatigue strength in different volumes of 60Si2CrVA spring steel. Predicted fatigue strength was in accordance with experimental results by ultrasonic fatigue testing.     

High cycle fatigue behavior of DP980 steel and DP980 steel laser welded joints

For the study of the DP980 steel high cycle fatigue property, high fatigue tests of DP980 steel and DP980 steel laser welded joints were carried out with fatigue testing machine, the Basquin equation was concluded. Microstructures and fractures were analyzed by optical microscope and scanning electron microscope. The results show that DP980 steel laser welding joints have the weld concavity at the welding root and top, the quality of welded joints is medium. The fatigue limit of DP980 steel is 341MPa, the fatigue limit of DP980 steel laser welded joint is 148MPa, the fatigue limit decreases by 50% compared with the fatigue limit of the base metal. For DP980 steel, the crystal boundary of the ferrite/martensite is the main location of micro cracks initiation, the fatigue fracture of DP980 steel is the quasi cleavage fracture. For DP980 steel laser welding joints, the fatigue cracks initiation is located in the weld concavity, not in the heat affected zone, the fatigue fracture is cleavage fracture. DP980 steel and DP980 steel laser welding joints crack propagation is characterized by the obviously fatigue striations coupled with secondary cracks.     

DP980钢及DP980钢激光焊接接头的高周疲劳性能

摘要：为了研究DP980钢的高周疲劳性能,采用疲劳试验机对DP980钢和DP980钢激光焊接接头进行高周疲劳试验,得到Basquin方程,并利用光学金相显微镜和扫描电镜进行组织和断口分析。结果表明：DP980钢激光焊接接头的焊缝根部和顶部出现形状凹陷,焊接接头的质量为中等。DP980钢疲劳极限为341MPa,DP980钢激光焊接接头的疲劳极限为148MPa,激光焊接接头的疲劳极限较母材的疲劳极限降低约50%。对于DP980钢而言,铁素体/马氏体晶界是裂纹萌生的主要位置,疲劳断口为准解理断口。对于DP980钢激光焊接接头而言,疲劳裂纹源位于焊缝凹陷处,而非热影响区及母材,疲劳断口为解理断口。DP980钢和DP980钢激光焊接接头的疲劳裂纹扩展区均有明显的疲劳条带,并伴随有二次裂纹。     

不同渗碳层深度下重载齿轮钢的疲劳性能

 国家工程研究中心, 北京100081;3. 中国钢研科技集团有限公司科技质量部, 北京 100081)     

Fatigue crack formation and propagation behavior of 30Cr3WVE bearing steel

The fatigue characteristics of a high cleanliness bearing steel(30Cr3WVE)produced by double vacuum melting and the effect of non- metallic inclusions on fatigue properties were studied by mechanical analysis and SEM analysis of microstructure and fatigue fracture morphology.The results show that the 30Cr3WVE bearing steel achieves excellent mechanical properties after being quenched at 870?? and tempered at 550??, and its ultimate rotating bending fatigue strength reaches 732MPa.Through observing SEM results of fatigue fracture,the fatigue crack originates from the surface defects and internalnon- metallic inclusions. Surface defects are caused by the abscission of non- metallic inclusions and machining marks. The internal non- metallic inclusions are mainly oxides of Al, Mg, Si and Ca. The influence of inclusions on the ultimate bending fatigue strength of 30Cr3WVE bearing steel is closely related to its size and distance to the surface. The model of influence of the size and distribution of inclusions on the rotating bending fatigue strength of 30Cr3WVE bearing steel is constructed. The rotational bending fatigue strength of the steel can be improved remarkably by controlling the size and quantity of inclusions.     

奥氏体-贝氏体球墨铸铁中石墨与基体界面的疲劳强度

采用系统分析的方法，通过3点弯曲疲劳实验，跟踪监测了奥氏体-贝氏体球墨铸铁试样的疲劳损伤过程。实验结果表明，奥氏体-贝氏体球墨铸铁中石墨球与基体组织界面有一定的疲劳强度；在不同的疲劳载荷作用下，该处疲劳开裂的时间和程度存在差异，并对疲劳裂纹的萌生和扩展有不同的影响。     

2 000 MPa高强度钢的超高周疲劳破坏行为

通过USF-2000超声波疲劳试验机研究了500 kg真空感应炉+电渣重熔冶炼的2000 MPa高强度钢(%:0.45C、2.0Si、0.9Cr、0.001S、0.005P、0.026Al、0.001 5O、0.002 8N)在共振频率20 kHz、载荷比R=-1,共振间隙150 ms时的超高周疲劳破坏行为。结果发现,疲劳裂纹大部分起源于钢中非金属夹杂物(夹杂平均尺寸12.3μm),钢的疲劳强度和寿命随夹杂物增大而降低;内部夹杂物引起的疲劳破坏往往呈鱼眼型;随疲劳断口裂纹源夹杂物处应力场强度因子ΔK_inc的减小,钢的疲劳寿命N_f增加。     

100Cr6轴承钢的超高周疲劳性能研究

采用旋转弯曲疲劳、SEM+EDS、面扫描等方法,研究了试验用100Cr6轴承钢的高周及超高周疲劳性能,以及传统疲劳极限附近的失效概率分布,并统计了夹杂物的成分、尺寸等信息。结果表明试验钢100Cr6的传统疲劳极限为967 MPa,在其之下的960 MPa应力幅值条件下,部分试样通过107循环周次后仍出现疲劳断裂失效,非无限寿命。在传统疲劳极限附近,相比于正态分布,疲劳寿命数据更符合二参数威布尔分布。相比于金相检验和面扫描,疲劳+EDS方法更能发现尺寸较大且为刚性的D类和Ds类夹杂物。