超声冲击对高速列车转向架焊接接头超高周疲劳性能及失效机理的影响研究

With increasing the railway speed, there are more and more serious railway transportation accidents which caused by the fatigue cracking of bogie structure. It is a frontier project to avoid the fatigue damage of welded bogie structure and ensure its safe operation. The research object is the welded joint of SMA490BW steel which is used for manufacturing high-speed train bogie.The aim is to increase the ultra high cycle fatigue properties of welded joint of train bogie. The welded joint will be treated by using ultrasonic impact method. The plastic deformation mechanism and grain refining mechanism on the treated surface of welded joint will be researched by using SEM and TEM.The ultra haigh cycle fatigue S-N curves of treated and original joint will be determined by mearns of different fatigue test methods.The effect law of the effect of loading frequency on the welded joint of ultra high cycle fatigue properties will be researched. The differences of ultra high cycle fatigue properties and fatigue failue mechanism between original and treated welded joints will be deeply researched. The effect law of the effect of ultrasonic impact on the ultra high cycle fatigue properties and fatigue failure mechanism of welded joint will be revealed. The effect extent and law of grain refining, the changing of residual stress and stress concentration caused by ultrasonic impact on the ultra high cycle fatigue life will be explored. The effect law and quantitative relationship of inclusions and/or welding defects type and size on the ultra high cycle fatigue life will be determined. The theory evidences will be provided for increasing the fatigue life and operational reliability of welded joint of high-speed train bogie.

随着我国铁路提速战略的实施，转向架焊接构架疲劳开裂现象明显增加，防止转向架焊接构架疲劳破坏的发生，保证其安全运行是工程上急需解决的前沿课题。本项目以高速列车转向架用SMA490BW钢焊接接头为研究对象，以提高转向架焊接接头超高周疲劳寿命为目标。采用超声冲击方法对焊接接头进行冲击处理，借助SEM、TEM等手段研究接头超声冲击表面塑性变形机制及晶粒细化机制；通过不同疲劳试验方法获取原焊态和冲击态接头超高周疲劳的S-N曲线，研究加载频率对接头超高周疲劳寿命的影响规律；研究冲击态与原焊态接头超高周疲劳性能及失效机理的区别，揭示超声冲击对接头超高周疲劳性能及失效机理的影响规律；探索超声冲击引起的接头晶粒细化、残余应力与应力集中变化对接头超高周疲劳寿命的影响程度和规律；确定夹杂物/焊接缺陷类型、尺寸对接头超高周疲劳寿命的影响规律和量化关系，为提高高速列车转向架焊接接头疲劳寿命和运行可靠性提供理论依据。

随着我国铁路提速战略的实施，转向架焊接构架疲劳开裂现象明显增加，防止转向架焊接构架疲劳破坏的发生，保证其安全运行是工程上急需解决的前沿课题。本项目以高速列车转向架用SMA490BW钢焊接接头为研究对象，以提高转向架焊接接头超高周疲劳寿命为目标，以揭示冲击表面纳米化机理及超声冲击对转向架焊接接头超高周疲劳性能影响规律、失效机理为目的，在以下几方面进行重点研究：.为达到超高周疲劳试样与试验机谐振，对接头超高周疲劳试样的形状及尺寸进行了设计。采用有限元法对接头的应力集中系数进行了计算；对接头超声冲击表面微观组织进行了表征并就冲击表面塑性变形及晶粒细化机制进行了探究；对接头的超高周疲劳性能进行了研究，在1×108 循环周次下，冲击态对接接头的超高周疲劳强度为195MPa，与焊态接头的141MPa相比提高了38.3%。十字接头的条件疲劳极限值为100MPa；冲击态接头的条件疲劳极限为125MPa，疲劳极限提高了25%。无论是焊态还是冲击态，对接接头的条件疲劳极限值都明显高于十字接头，说明接头形式对条件疲劳极限值有较大影响。接头表面的晶粒细化过程主要依靠位错增殖、湮灭、重排等，进而形成位错墙与位错缠结，随着应变量的增加演变成小角度亚晶界；亚晶界处继续发生高密度位错的增殖和湮灭，小角度亚晶界演变成大角度亚晶界，形成晶粒细小的亚晶结构。随着变形量继续增加，演变成晶界清晰、随机取向的等轴状纳米晶组织。试验机频率对超高周疲劳性能的影响较小。超声冲击能够使部分接头的疲劳裂纹从焊趾表面萌生转为内部萌生。超声冲击使接头应力集中系数明显降低，表面组织细化，残余应力由拉伸变为压缩，三种因素的贡献率分别为59%，28%和13%。研究成果对为提高高速列车转向架焊接接头的疲劳寿命和运行可靠性提供理论和技术依据。.经过4年的研究，圆满完成了申报书中的研究内容。发表“Effect of ultrasonic impact treatment on the ultra high cycle fatigue properties of SMA490BW steel welded joints”等学术论文30篇（其中SCI检索3篇、EI检索12篇、ISTP检索2篇）。申请发明专利3项，获批实用新型专利3项，培养研究生6名，青年教师3名，目前正在撰写专著一本。