多轴同步载荷的疲劳强化效能探讨

针对可靠性强化试验的RS(repetitive shock)机全轴随机振动环境3个主要特性之一的多轴同步加载特性开展其疲劳强化机理研究。本文首先归纳了多轴疲劳频域分析方法,然后在此基础上证明了多轴振动激励同步加载比单轴振动激励依次加载更能有效激发疲劳失效,从而揭示RS机全轴随机振动环境多轴同步加载特性的疲劳强化机理。     

基于最大切应变幅和修正SWT参数的多轴疲劳寿命预测模型

工程中的大多构件承受着复杂的载荷形式,将单轴疲劳模型应用到多轴载荷情况已不能满足工程精度的要求,多轴载荷下的疲劳寿命计算日益引起人们的重视。基于临界平面的思想,结合Fatemi-Socie(FS)模型和Smith-Watson-Topper(SWT)参数各自的优点,提出一种新的多轴疲劳寿命预测模型。该模型以最大切应变幅与最大切应变幅平面上修正SWT参数的和作为多轴疲劳损伤控制参量,此参量可以同时考虑非比例附加循环硬化和平均应力对材料多轴疲劳寿命的影响,能同时适用于比例和非比例加载下的多轴疲劳问题。采用纯钛Ti、BT9钛合金、304不锈钢、S45C钢和1045HR钢5种材料多轴疲劳试验数据对提出的模型进行评估和验证,对几种材料比例和非比例加载下的多轴疲劳寿命预测结果大都分布在试验结果的2倍分散带之内,结果表明提出的多轴疲劳寿命模型具有较高的预测精度。     

材料多轴疲劳破坏准则回顾

对多轴疲劳载荷作用下材料的疲劳破坏准则作了系统的回顾，按照用于描述材料疲劳破坏的参量，将多轴疲劳破坏准则划分为三类，应力准则、应变准则、能量准则。分别对这三种准则按多轴比例加载及多轴非比例加载两种情况进行阐述，并进行简单的评述。     

基于多轴载荷的汽车控制臂疲劳载荷块编制

目前大多数控制臂台架疲劳载荷为单向加载的块谱,忽略了载荷的多轴性。依据已测得的控制臂试验场道路载荷谱,通过多轴雨流投影方法分析了其载荷的多轴性,并以多轴雨流投影结果一致为目标,通过迭代方法求解获得其考虑载荷多轴性的载荷块谱。再通过疲劳计算方法对比了单轴与多轴载荷块在寿命预测的差异性,并与控制臂应变采集测试点的疲劳损伤对比,发现考虑多轴的载荷块具有更高的预测精度。载荷多轴性的载荷块编制方法可为汽车其他零件台架疲劳载荷块编制提供参考。     

金属多轴疲劳行为与寿命预测研究进展

多轴疲劳损伤行为和寿命预测研究关系着复杂加载条件下金属结构件的服役安全,一直受到科学和工程领域的重视.总结多轴低周和高周疲劳试验性能测试一般过程和疲劳行为研究,重点论述多轴非比例加载对低周疲劳和高周疲劳行为的影响,受加载路径,加载载荷和材料类型的影响,非比例加载对材料低周疲劳循环硬化行为和疲劳寿命的影响有差异,对低周疲劳和高周疲劳表现的疲劳行为的影响也有差别,作用机理不尽一致.单轴本构关系通过引入非比例度因子、修正循环强度系数或将多轴加载时的应变等效为单轴应变等方式可推广到多轴疲劳领域.基于应力、应变、能量、临界面和临界面应变能密度法的多轴疲劳寿命预测模型在文中做了综述,疲劳损伤参量中包含能量项的一些多轴疲劳寿命预测方法常被用于多轴低周和高周疲劳寿命预测.缺口件多轴疲劳寿命可采用多轴损伤参量结合局部应力应变法、应力梯度法、应力场强法及临界距离法等进行预测.     

多轴非比例加载下疲劳短裂纹扩展速率的探讨

为了揭示出多轴非比例加载下疲劳短裂纹扩展的规律,利用搜寻临界面的方法确定短裂纹的萌生与扩展的方向,在临界面上分析多轴非比例加载与单轴加载下疲劳短裂纹扩展律的相似性,应用载荷的等效原理,类比单轴加载的研究过程,并将力学参数加以修改,导出多轴非比例加载下疲劳短裂纹扩展速率的计算公式。     

风力发电机组齿轮箱弹性支撑橡胶疲劳寿命分析

针对风力发电机组齿轮箱弹性支撑疲劳寿命预测问题,将数值仿真技术应用到了橡胶疲劳分析中。使用橡胶模型参数建立了轴瓦弹性支撑有限元模型,进行了静刚度试验,通过对比发现了仿真结果与试验结果比较符合;选定疲劳损伤模型,进行了橡胶材料的疲劳寿命测试,拟合了模型参数;在风电机组设计载荷下,开展了齿轮箱弹性支撑橡胶的疲劳损伤分析,提出了多轴变载工况下橡胶疲劳分析方法,将疲劳载荷时序加载转换成位移时序加载,计算了时序疲劳载荷损伤和等效疲劳损伤,得到了弹性支撑在不同部位疲劳损伤分布情况。研究结果表明:时序疲劳载荷相对等效疲劳载荷对橡胶的疲劳损伤更大,实际疲劳校核应按时序疲劳载荷进行。     

45钢非线性多轴疲劳累积损伤律研究

对45号中碳钢薄壁圆管试件进行了拉-扭复合双轴加载的多种比例及非比例路径下的常幅疲劳寿命试验以及多种组合两级变路径的多轴累积疲劳试验。应用所得试验数据对现有的常用疲劳损伤累积模型进行验证,基于Manson损伤曲线累积模型添加载荷路径变换因子,提出了一个适用于多轴非比例加载的非线性疲劳损伤累积模型,并对模型进行了验证,数据点基本控制在2倍误差带之内,得到令人满意的预测结果。     

单轴向与多轴向随机载荷下星载单机的疲劳损伤研究

基于随机振动频域理论,采用“3σ法则”和等效应力-应变的疲劳分析方法,对比研究单轴、多轴载荷下某星载单机的疲劳损伤,评估两种试验方案的等效性。结果表明：该单机对z向激励敏感,z向随机载荷造成的疲劳损伤远大于x、y向载荷;多轴向随机载荷作用下单机的最大等效应力、疲劳损伤累积均大于单轴向随机载荷作用;3个正交轴下的单轴依次振动替代多轴随机振动试验的等效方案为欠试验方案,需要从定量角度优化试验方案。     

多轴疲劳研究

介绍多轴疲劳研究的几个主要问题。（１）非比较加载引起的附加循环化。（２）最大剪切平面与自由表面相对取向对疲劳寿命的影响。（３）零部件承受多轴疲劳载荷时寿命的估算。本文就目前所采用的单参数双参数疲劳寿命估算准则进行了评述。     

Vibration fatigue analysis and multi-axial effect in testing of aerospace structures

The work reported in this paper compared the fatigue damage accumulated under uni-axial loading (a procedure promoted by the vibration testing standards) to that induced by multi-axial loading. The comparison was performed for a helicopter structural element (the flare dispenser bracket of the self-defensive system's Chaff), which is exposed to the particular combination of wide-band random with sinusoidal vibrations, which is characteristic to the helicopter dynamic environment. The evaluation of the fatigue damage induced by these loads requires the calculation or measurement of the structure's dynamic response in terms of stresses or strains, and the application of the appropriate methodology to this response. In this work, dynamic response was calculated in the frequency domain based on the relations between the power spectral density matrixes of the excitations to that of the responses for a linear system. The transfer matrix that relates the excitation to the responses was evaluated numerically. The power spectral densities of the responses evaluated at different locations on the structure were used in the determination of the responses’ statistics (the counting of the loading cycles), which, combined with an appropriate physics of failure model (fatigue model), enabled the evaluation of the accumulated fatigue damage. The uni-axial-induced fatigue was evaluated from vibration tests of the kind promoted by military standards (it is assumed that axis-by-axis loading is cumulatively equal to multi-axial loading), and compared to that evaluated by analysis for the multi-axial loading. Also a numerical comparison of the effects of the two kinds of loading was performed. The results showed that the error of uni-axial testing varied for a wide range of parameters. The work led to the conclusion that simultaneous multi-axis vibration testing can improve significantly the laboratory's vibration simulation realism.     

多轴载荷作用下减振器耐久性试验载荷谱编制

传统的减振器耐久性试验只考虑减振器的垂向载荷,对于水平力的加载没有统一的标准,导致试验结果不准确,针对该问题,结合实测用户道路载荷,提出了一种考虑多轴载荷作用的载荷谱编制方法。为了分析某型轿车出现减振器失效漏油的原因,采用低频信号叠加高频信号的方式构建载荷谱,运用半功率带宽法和最大线速度原理确定低频及高频信号,并进行了垂向力及水平力同时加载的减振器台架耐久性试验。试验结果表明,在水平力作用下减振器寿命受到较大影响,且失效里程与调查结果基本吻合,由此说明所编制的耐久性试验载荷谱能够较为准确地复现减振器的实际工作情况,可为减振器的设计和改进提供技术支持。     

AMT执行机构多轴道路模拟试验台设计

提出了一种基于远程参数控制(RPC)的电控机械式自动变速器(AMT)执行机构多轴道路模拟试验台,重点对试验台装夹部分和运动学进行了设计和分析。结合AMT在实车上的安装情况,设计了一套夹具装置,并在动力学仿真软件ADAMS中建立了试验台运动学和动力学仿真模型,通过仿真分析,解决了运动干涉问题,优化了试验台运动范围。结合RPC技术,可以在所设计的多轴试验台上复现AMT执行机构的实际行驶道路载荷谱,从而在室内对AMT执行机构疲劳可靠性进行评价和考核。     

Estimates of the creep rupture lives of structures subjected to cyclic loading

Constitutive relationships are discussed for materials which undergo creep rupture due to cyclic loading. Relationships are proposed which describe the strain rates in terms of the current stress and a single state variable. An approximate method is derived which enables a lower bound on the rupture life to be obtained for kinematically determinate structures subjected to cyclic load and isothermal conditions. The bound on the rupture life is expressed in terms of the energy dissipation rates within the structure corresponding to stationary-state creep. The effect of multi-axial stress creep-rupture upon the structural performance is examined and bounds are derived for materials which obey maximum tension and octahedral shear stress criteria. For both multi-axial stress rupture laws and structures subjected to cyclic and reverse load conditions formulae are derived which express the lower bound rupture life in terms of the behaviour of a steady-load uni-axial creep rupture test. Results of experiments which have been carried out on copper and aluminium beams are presented for cyclic and reverse load conditions. For both rupture laws the experimental rupture times are closely predicted by the representative rupture stresses and uni-axial data.     

阶梯式半挂车车架疲劳寿命预测

根据某阶梯式半挂车车架的结构特点,建立了其有限元模型,通过分析得到车架静态应力分布;基于半挂车多体动力学模型,以H级路面的路面载荷作为边界条件进行动力学分析得到车架载荷谱。以上述分析数据为依据,综合考虑影响半挂车车架疲劳特性的主要因素,采用多轴临界面法Brown-Miller疲劳损伤平均应力修正模型预测了半挂车车架的多轴疲劳寿命,得到其疲劳薄弱部分,为结构和工艺优化提供参考。     

Multi-axial creep rupture of a model structure using a two parameter material model

A simplified, two parameter creep curve model is developed, which represents primary-secondary-tertiary creep behaviour. The two parameters are related via the secondary strain respectively to: the sum of secondary and primary strains; and, the sum of secondary and tertiary strains. Techniques are described for fitting the model to laboratory data; and, for the determination of the parameters which characterize primary-secondary and secondary-tertiary creep. The single state variable theory used to describe tertiary creep is compared with mechanisms based models and shown to closely predict the effect of stress-state on rupture strain. A two bar plane strain model component subjected to steady load is studied and used to determine the effect on the component lifetime of primary creep; and, of the multi-axial creep rupture criterion. The representative rupture stress is found to be weakly dependent on primary creep and strongly dependent on the multi-axial rupture criterion of the material.     

基于灰色理论镍基单晶合金多轴非比例加载低周疲劳研究

基于灰色理论研究DD3镍基单晶合金高温多轴非比例加载低周疲劳特性,对等效应变范围、温度、应变路径角、拉/扭载荷相位角和轴向应变比等影响疲劳寿命的因素进行灰色关联度分析,并引入损伤参量Q表征非对称循环特性和拉/扭多轴效应,以参量Q、等效应变范围Δεe和Mises等效应力范围Δσe构造疲劳损伤参量,建立低周疲劳寿命GM(1, N)预测模型。结果表明,各影响因素与多轴低周疲劳寿命的关联度等级依次为等效应变范围、温度和应变路径角为一级,拉/扭载荷相位角为二级,轴向应变比为三级;680 ℃和850 ℃温度下的GM(1, N)疲劳寿命模型的预测寿命与试验寿命的绝对关联度分别为0.97、0.86,平均相对误差分别为4.9%、6.0%;两种温度的试验数据几乎分别落在1.93、2.13倍偏差分布带内。     

多轴非比例低周疲劳寿命估算方法的研究

利用临界面法、有限元法和实验分析方法对多轴加载条件下低周疲劳寿命估算问题进行了研究。确定了试件在单轴加载、双轴比例加载、双轴非比例加载、三轴比例加载和三轴非比例加载条件下，6种疲劳损伤参量的最大值及临界面位置。在此基础上，估算了试件在不同加载条件下的疲劳寿命，并对损伤模型进行评估。     

多轴压缩机逆向设计方法研究

阐述了多轴压缩机相对于一般压缩机所具有的优点及其主要结构特征,对多轴压缩机半开式叶轮的数据采集方法、三维模型重建进行了详细分析,并介绍了多轴压缩机齿轮箱和蜗壳的逆向设计过程与注意事项,论述了多轴压缩机逆向设计技术所存在的问题,进一步说明逆向工程技术是满足市场需求、促进新产品研发以及加快先进透平机械设备国产化步伐的重要手段。