在役超高压反应管的疲劳强度及裂纹扩展寿命的研究

本文根据带内外壁人工缺口高压聚乙烯反应管的内压疲劳试验结果,分析了适用于厚壁管的应力强度因子表达式,研究了残余应力衰减对反应管疲劳裂纹扩展寿命的影响。研究结果表明:厚壁管的疲劳裂纹扩展计算应采用Newman—Raju公式(对外壁裂纹还应进行适当修正);自增强残余应力的作用主要在提高裂纹萌生寿命,而对在役反应管的裂纹扩展寿命影响不大;反应管的裂纹扩展寿命较短,所以应尽量避免内外壁产生裂纹。     

泵阀箱材质自增强与疲劳强度研究

以内壁带“Ｖ”型缺口的厚壁圆环为对象,对两种高压泵阀箱常用钢４３ＣｒＮｉ２ＭｏＶａ、４２ＣｒＭｏＡ在自增强处理前后的疲劳寿命进行了理论分析与实验研究。首先用弹塑性有限元法计算了自增强后所形成的残余应力,发现自增强处理后在缺口根部所形成的残余应力有一最大值,有明显的残余应集中现象。     

喷砂工艺对双金属带锯条锯切性能和疲劳寿命的影响

用快速高压喷砂和慢速低压喷砂两种喷砂工艺对双金属带锯条进行处理,通过锯切GCr15和空转疲劳测试,分别对比两种工艺处理后带锯条的锯切寿命和疲劳寿命。通过影像测量仪和扫描电镜观察带锯条锯刃和锯条体表面形貌,通过X射线衍射检测带锯条锯条体表面的残余应力。结果表明:与快速高压喷砂相比,慢速低压喷砂能够优化锯齿齿尖形貌,减少锯切过程中的崩刃,从而提高带锯条的锯切性能;同时还能增加锯条体表面残余压应力,并使表面形貌均匀,从而提高带锯条的疲劳寿命。     

压裂泵阀箱自增强技术仿真研究

基于弹塑性自增强理论,对压裂泵阀箱进行了弹塑性有限元非线性研究,探讨了自增强技术和机械加工精度对阀箱疲劳寿命的影响。分析了不同自增强压力下的阀箱应力,确定了阀箱内腔相贯线处最佳自增强压力为420.6 MPa。对自增强前后阀箱的疲劳寿命进行预测结果表明:阀箱疲劳薄弱区位于内腔相贯线处,自增强后疲劳薄弱区向壁间转移,偏离了疲劳危险区域,阀箱内壁表面材料得到有效保护。自增强技术使阀箱应力峰值降低了30.61%,最低疲劳寿命提高了6.97倍。自增强技术与提高阀箱内腔表面加工精度的方法相比,前者对延长阀箱疲劳寿命效果更佳。     

柴油机连杆疲劳失效的影响因素分析

运用有限元方法与疲劳寿命预测理论,对柴油机连杆在疲劳耐久性试验条件下的三维应力分布和疲劳寿命进行了数值模拟。通过对比连杆疲劳试验与寿命预估结果,结合连杆疲劳断口的微观分析,表明残余压应力使疲劳裂纹源的位置向连杆次表层推移,对高强度连杆的疲劳寿命具有重要影响。     

新型传动滚筒疲劳寿命分析

在ANSYS中对新型传动滚筒进行瞬态动力学分析,得到多种工况下该传动滚筒的最大等效应力云图、最大主应力时间历程。应用n Code Glyph Works的雨流分析模块对传动滚筒时间历程曲线进行雨流计数,并对载荷谱外推和叠加。基于疲劳寿命预测的相关理论,采用Stress Life模块分析其疲劳寿命和疲劳敏感性,得到传动滚筒损伤直方图以及在过载和残余应力影响下传动滚筒最小疲劳寿命曲线图。研究结果表明,该传动滚筒力学性能良好,传动滚筒的最小疲劳寿命约为783天,满足使用要求。过载和残余应力均对传动滚筒的疲劳寿命具有明显影响。     

残余应力对齿轮弯曲疲劳的量化影响研究

随着风电、高铁、掘进等高端装备对齿轮功率密度、服役寿命等要求的提高,齿轮的弯曲疲劳问题日益显著。为提升齿轮弯曲疲劳性能,通过渗碳热处理、喷丸强化等工艺为齿轮引入较高的残余压应力已逐渐成为工业界的标配。为揭示残余应力对齿轮弯曲疲劳性能的量化影响,在最大主应变寿命预测准则中引入残余应力影响项,通过弯曲疲劳试验确定最优残余应力影响系数,进而采用新的试验数据验证模型的准确性。基于工程应用出发,引入修正应力的概念统一不同残余应力状态下的齿轮弯曲应力-寿命(S-N)曲线,研究结果显示,最大主应变准则中,残余应力影响系数取值为0.15时,可实现较高的寿命预测精度,而修正的S-N曲线中,最佳残余应力影响系数为0.25。研究成果可用于工程实际中齿轮弯曲疲劳快速评估。     

立磨减速机弧齿锥齿轮副动态疲劳性能研究

建立磨减速机输入弧齿锥齿轮副的三维接触有限元模型,借助LS-DYNA软件对锥齿轮副柔性体动力学进行仿真分析,得到锥齿轮副的瞬态接触力,以此为疲劳寿命分析的载荷谱,结合静载作用下的应力结果和锥齿轮副材料S-N曲线,在FE-SAFE中采用最大主应力算法对锥齿轮副进行疲劳寿命分析,并研究了应力集中系数、载荷和残余应力对锥齿轮副疲劳寿命的影响规律。研究结果表明,锥齿轮副寿命随应力集中系数和载荷的增加而减小,疲劳寿命对载荷较敏感;残余拉应力使锥齿轮副的疲劳寿命降低,而残余压应力使锥齿轮副的疲劳寿命提高。     

2024-T351铝合金喷丸残余应力松弛模型研究

喷丸引入的残余压应力场可以有效地提高构件的疲劳性能,但残余压应力会随着循环周期而发生松弛,进而降低残余压应力对疲劳性能的增益效果,因此深入研究残余应力松弛规律,有助于更加准确的掌握其对疲劳性能的影响.为了系统性地研究残余应力松弛规律,以2024-T351铝合金标准试件为研究对象,综合考虑应力幅、载荷条件和喷丸引起冷作硬化程度的改变对残余应力的影响,根据理论构建残余应力松弛模型.通过拉伸疲劳试验,基于全寿命试验数据和阶段性试验数据对松弛模型进行验证,证明了模型的有效性.     

基于应变硬化模型的复合自增强圆筒的应力分析

自增强是通过提高压力容器的残余应力来增强他们的承载能力和疲劳寿命。自增强复合圆筒可以承受比一个具有相同尺寸的单层圆筒更高的压力。引入了应变硬化模型,对自增强复合圆筒的残余应力进行了分析,并对其分布进行了预测。研究表明:复合圆筒内壁的切向残余应力和应力幅随着超应变度的增大而增大。缩套是提高压缩残余应力的一个非常有效的方法。     

Elastic-plastic stress analysis and fatigue lifetime prediction of cross-bores in autofrettaged pressure vessels

Elastic-plastic stress analysis has been performed to evaluate the fatigue life of an autofrettaged pressure vessel containing cross-bores subjected to pulsating internal pressure of 200 MPa. Finite element analyses were used to calculate the residual and operating stress distributions of the pressure vessel due to the autofrettage process and pulsating internal pressure, respectively. Theoretical stress concentration factors of 3.06, 2.58, and 2.64 were obtained at the cross-bore of the pressure vessel due to internal pressure, 50%, and 100% autofrettage loadings, respectively. Local stresses and local strains determined from the elastic-plastic finite element analysis were employed to calculate the failure location and fatigue life of the pressure vessel with radial cross-bores, incorporating the low-cycle fatigue properties of the pressure vessel steel and fatigue damage parameters. Increase in the amount of overstrain by autofrettage process moved the crack initiation location from the inner radius toward a mid-wall, and extended the crack initiation life, Predicted fatigue life of the fully autofrettaged pressure vessel with cross-bores increased about 50%, compared to the unautofrettaged pressure vessel. At the autofrettage level higher than 50%, the failure location and fatigue life of the pressure vessel were not significantly influenced by the autofrettage level.     

A residual stress analysis program using a Matlab GUI on an autofrettaged compound cylinder

A program for the residual stress analysis of an autofrettaged compound cylinder is designed using a Matlab graphical user interface (GUI) and program design technique. The high-pressure vessels are autofrettaged in order to increase their operating pressure and fatigue life. An autofrettage process causes plastic expansion of the inner section of the cylinder, adding residual compressive stress to the bore after relaxation. Such a compound cylinder is produced via a shrink-fit procedure that incorporates a monobloc tube that has previously undergone autofrettage. This paper presents a simple and visual tool to calculate the residual stress and describe the distribution of residual stress for both the elastic-perfectly plastic model and the strain-hardening model.     

等离子喷涂NiCrBSi涂层接触疲劳过程中残余应力变化规律研究

采用超声速等离子喷涂技术在45钢基体上制备NiCrBSi合金涂层,涂层整体结构致密,含有少量微缺陷。使用球盘式接触疲劳试验机在接触应力为1.86 GPa,转速为1 500 r/min的条件下对涂层试样进行接触疲劳试验,得到涂层的接触疲劳寿命为9.0×105周次;同时建立Weibull失效概率图,通过该图可以直观地得到在同一工作条件下,涂层任意循环次数的失效概率。测量涂层不同疲劳阶段的残余应力,结果表明:一旦进行接触疲劳试验,其残余应力形式由拉应力迅速转化为压应力,在整个疲劳过程的前半段,应力增强较为缓慢,在疲劳过程的后半段,应力值迅速增大,疲劳过程的中期成为了应力变化的转折点。根据这一规律,可以有效地判定涂层处于疲劳过程的哪个阶段,从而为预防涂层的突然失效提供了一种新的手段。     

A study on integrated design for improving fatigue life of common rail pipe considering stress concentration at complex shape

Common rail pipe in a clean diesel vehicle plays a key role in supplying fuel from a rail to an injector of each cylinder connecting engine under a repeated internal pressure. For satisfying EU emission standards, fuel injection pressure is increased to be over 200 MPa, and it causes stress concentration at the outer surface of neck part with discontinuity and complexity of shape of the pipe. For preventing folding defects and for improving a fatigue life, integrated design of a heading process and an autofrettage process are required because the methods for reducing the stress concentration by using changing design, material and adding heat treatments cause considerable effects on performance and price of the pipe. In this study, the heading process for checking folding defects of pipe head is performed by FEA, and an autofrettage process is designed for improving a fatigue life by considering the stress concentration at the complex and discontinuous shape. The optimal autofrettage pressure is required not only to relieve the stress concentration but also to be not beyond the allowable internal pressure for the process safety. The allowable internal pressure for the autofrettage process is determined by using theoretical analysis and FEA, and the stress distributions through the autofrettage process are obtained by using the commercial software, ANSYS-Workbench. On the basis of the FEA results, the autofrettage pressure is optimized, and SEM (scanning electron microscope) and fatigue tests were performed for prototypes to validate analysis of the integrated process design (Heading process and the autofrettage process).     

Autofrettage of thick-walled pipe bends

The bending of a thick-walled cylinder to a given radius involves an elastic–plastic deformation that results in a residual, axial stress distribution. The latter alternates from maximum tension to maximum compression between top and bottom halves of the cross-section. The residual stress levels depend upon the depth of plastic penetration and may be determined as a closed solution when they arise from a bending moment applied to either a non-hardening or linearly-hardening material. When the bent pipe receives an autofrettage treatment without an intermediate heat treatment, this produces a further residual, triaxial stress state. The interaction between the residual states from bending and autofrettage has an important effect upon the net axial stress and the equivalent stress. It is shown that large plastic penetrations arising from bending and autofrettage can residually stress the section beyond its yield point: in tension and in compression across both its halves. With the unloading from each process, a Bauschinger effect reduces the yield point to assist with the onset of reversed plasticity. The latter is far less beneficial than when unloading is elastic. It is shown how a nonlinear kinematic hardening model can be employed to avoid unloading plasticity at the inner and outer diameters. The consequence of interacting residual stresses is that axial stress can play as important a role as hoop stress when designing for safe service loadings. In general, an enhanced residual stress state is beneficial when compressive but detrimental when tensile. Pre-compression is often employed in practice to reduce tensile stress arising from internal pressure, axial force and self-weight. Here, the compressive residuals arising from an autofrettage treatment have long been exploited to enhance the fatigue life of process piping and weaponry.     

滚动轴承疲劳寿命的影响因素

对影响滚动轴承疲劳寿命的各种因素进行了综述，包括各种疲劳诱导应力(最大切应力、最大动态切应力、Von Mises应力和八面切应力)，切向力、残余应力和环向应力疲劳极限应力、表面粗糙度、弹流润滑、表面处理、润滑油中污染颗粒、温度、速度、不失效寿命和钢材纯净度(氧含量)的影响，为轴承寿命的准确预测提供参考。     

在役自增强反应管残余应力衰减规律及影响

采用Sachs内孔逐层镗削应力释放法测试AISI4333M4在役自增强反应管残余应力。结果显示,在役反应管经过17年的运行使用后,周向残余应力衰减了18．0％。分析表明,在长期的交变压力和高温作用下,在役反应管的应力松弛随管壁厚度呈V字形变化,弹塑性界面沿半径外扩,疲劳强度减小,这为在役反应管安全评估提供了参考。     

焊接残余应力对桥壳疲劳寿命的影响研究

桥壳作为驱动桥的核心零部件,其疲劳寿命对驱动桥乃至整车安全性有决定性的影响,对于制造过程中使用焊接工艺的桥壳,焊接残余应力的影响不容忽略。以某商用车驱动桥桥壳为研究对象,在获得其焊接残余应力分布的基础上,分析焊接残余应力对桥壳在静态载荷和动态循环载荷工况下应力应变响应的影响。使用应变-寿命分析方法对桥壳在弯曲疲劳试验工况下的寿命进行预测,并与台架试验结果进行对比,结果表明考虑焊接残余应力时,疲劳寿命次数和破坏位置的预测结果与试验结果吻合较好,验证桥壳疲劳寿命预测模型的准确性。与不考虑焊接残余应力的模型相比,焊接残余应力导致桥壳疲劳寿命次数降低,且失效位置不同,说明了疲劳寿命预测时考虑焊接残余应力的必要性。本文方法可推广应用于含有焊接残余应力的结构疲劳寿命预测,为结构优化设计提供指导。     

高强螺纹滚压工艺的有限元模拟及试验研究

对高强螺纹进行滚压处理可有效提高螺纹结构的抗疲劳性能。为深入研究螺纹滚压工艺规律,以提高螺纹紧固件的抗疲劳性能,建立螺纹滚压工艺三维有限元模型,并基于该模型研究了滚轮参数对滚压后残余应力的影响规律,最终采用疲劳试验验证了该方法的有效性。结果表明:滚轮型面夹角、直径、型面圆弧半径等参数对滚压后引入的残余应力分布具有很大影响。滚轮型面夹角越小,滚压后引入的残余压应力层越深;较小的滚轮直径有利于引入较大的残余压应力和残余应力层深;较大的圆弧半径可获得较高的表面残余压应力和最大残余压应力,同时在一定范围内导致残余应力层深减小。疲劳试验结果表明,采用未经优化的滚轮强化后,螺纹疲劳寿命提高1.6倍,而采用经优化设计的滚压轮强化后,螺纹疲劳寿命提高4倍。该结果证实了基于有限元分析的滚轮优化方法的有效性。