底盘构件多轴随机载荷下高周疲劳准则研究

为探明汽车底盘构件在随机载荷下多轴高周疲劳准则的应用方法与寿命预测规律,以某品牌B级轿车为研究对象,通过采集试验场强化路轮心六分力信号,建立了整车多体动力学模型,应用虚拟迭代法获取转向节与其他零件连接点的载荷时间历程;建立转向节有限元模型,通过模态仿真与试验验证了有限元模型的准确性;提取了von Mises应力下寿命值最小节点的应力分量时间历程;研究了8种高周疲劳准则所基于的3种类型临界平面的计算方法,通过多轴循环计数提取临界面上正应力幅与剪应力幅,并计算不同准则对应的等效应力幅,总结幅值分布与寿命预测规律。研究结果表明,在幅值分布与寿命预测方面,Zhang-Yao准则的等效剪应力幅值整体偏大,预测寿命为1.09×105周次,较其他准则偏于保守;McDiarmid准则的大应力幅仅占3.4%,预测寿命为1.25×106周次,明显大于其他准则的预测寿命值,而改进的McDiarmid准则预测寿命值明显减小。在计算成本方面,von Mises准则无需提取临界面与多轴循环计数,应用最为便捷;Findley准则提取临界面过程需要计算所有平面的正应力与剪应力数据,故计算成本最高。     

LIFE PREDICTION APPROACH FOR RANDOM MULTIAXIAL FATIGUE

According to the concept of critical plane, a life prediction approach for random multiaxial fatigue is presented. First, the critical plane under the multiaxial random loading is determined based on the concept of the weight-averaged maximum shear strain direction. Then the shear and normal strain histories on the determined critical plane are calculated and taken as the subject of multiaxial load simplifying and multiaxial cycle counting. Furthermore, a multiaxial fatigue life prediction model including the parameters resulted from multiaxial cycle counting is presented and applied to calculating the fatigue damage generated from each cycle. Finally, the cumulative damage is added up using Miner's linear rule, and the fatigue prediction life is given. The experiments under multiaxial loading blocks are used for the verification of the proposed method. The prediction has a good correction with the experimental results.     

多轴变幅载荷下基于载荷支配模式的缺口件疲劳寿命预测方法

提出一种多轴变幅载荷下基于载荷支配模式的缺口件疲劳寿命预测方法。首先,通过循环计数方法确定多轴变幅载荷历程的计数循环(反复);其次,通过材料的循环应力应变关系和Neuber法推导出虚拟等效应变与真实等效应力之间的关系,并且分别将拉伸型和剪切型Shang-Wang多轴疲劳损伤参数替换虚拟等效应变幅来求解临界面上的真实等效应力幅;然后,通过真实等效应力幅和Neuber法则计算临界面上真实的拉压和剪切等效应变幅,并运用Manson-Coffin方程分别计算缺口部件的拉压和剪切疲劳寿命;最后,选择拉压和剪切疲劳损伤值中的较大值作为每个计数反复的疲劳损伤,并采用Miner法则进行疲劳损伤累积。缺口件多轴疲劳试验结果表明,采用基于载荷支配模式的缺口件疲劳寿命预测方法具有较高的预测准确度。     

一种随机多轴疲劳的寿命预测方法

叙述一种多轴随机载荷的疲劳寿命预测方法，该方法首先由多轴随机载荷的权值平均最大剪应变平面确定临界平面，然后以临界平面上剪应变和正应变历史为研究对象，进行多轴载荷压缩处理和多轴循环计数，得到剪应变和正应变的循环计数结果，最后给出多轴疲劳寿命估算模型，并用多轴程序载荷实验验证。     

Fretting fatigue crack initiation behavior using process volume approach and finite element analysis

This study investigates crack initiation behavior by incorporating fretting fatigue process volume. Three critical plane based fretting fatigue crack initiation parameters are characterized by computing their averaged values over the process volume and then comparing with their counterparts obtained from the localized approach. Two approaches are used: first one involves the computation of parameter at several points over a rectangular region and then its average, and second approach computes the average state of stress/strain over a radial region from which the averaged parameter is calculated. Both approaches require pre-determination of a critical location at or around which the process volume needs to be placed. Effects of size and location of process volume on the averaged value of parameters are studied in detail. Two radii of cylindrical pad are analyzed to investigate the effect of severity of stress gradient on process volume approach. Effects of finite element mesh refinement are also investigated. Averaged value of parameter decreases with the increase of process volume size. This decrease is higher when the process volume is located in the region that is away from the contact zone. Further, a parameter based on normal stress on the critical plane shows more dependence on the size of process volume than that based on shear stress or on a combination of both shear and normal stresses. Orientation of crack initiation changes within a range that is well within the scatter band of experimental observations as the process volume size increases. Averaged value of parameter for a pad with higher stress gradient has a larger reduction with the increase of process volume size than that with a lower stress gradient. Process volume size has less effect on the averaged value of parameter with coarser finite element mesh. Finally, the localized approach provides a conservative value of fretting fatigue crack initiation parameter compared to its counterpart based on the process volume.     

A Critique of Rolling Contact Fatigue Criteria for Bearing Rings with Hoop Stresses

Tensile residual and interference fit stresses not treated in classical bearing formulations are known to reduce bearing rolling contact fatigue (RCF) life. Recent modifications of such theory to account for these stresses have simply included them in the computation of a single yield stress type criterion—either maximum shear or equivalent stress. An alternative modification is proposed and demonstrated for fatigue crack initiation that recognizes the primary influence of the maximum range of shear stress but includes the effect of normal stress on the critical planes, as in other successful bulk fatigue criteria for multiaxial nonproportional stress cycle fatigue.     

基于临界面法的缺口件多轴疲劳寿命预测

基于多轴损伤临界面原理，根据多轴疲劳损伤和裂纹萌生与扩展的特点，在所建立的统一型多轴疲劳损伤模型的基础上，进一步推广应用到缺口件的多轴疲劳寿命预测中，经多轴疲劳试验验证表明，所建立的多轴疲劳损伤模型可以较好地预测比例与非比例加载下缺口件的多轴疲劳寿命。     

多轴随机载荷下断裂平面的确定方法

在分析材料平面切应变特性的基础上,提出权值平均最大切应变平面的概念,给出多轴随机载荷下断裂平面的确定方法。该方法中,以材料损伤为权值函数,平均最大切应变峰值点对应的平面方向。通过多轴比例、非比例加载试验验证权值平均最大切应变平面与疲劳裂纹萌生平面的相关性。     

基于临界面理论的多轴等效应变疲劳寿命预估模型

针对等效应变模型未考虑非比例附加强化影响这一不足,将最大剪切应变幅所在平面定义为临界面,引入剪切平面上的最大正应力、正应变变程以及相位差作为损伤参量来反映非比例加载条件下的附加强化效应,该损伤参量还考虑了临界面上的最大正应力和正应变变程对材料裂纹萌生和扩展的影响。采用16MnR、GH4169、S460N、45钢和Pure Ti五种薄壁圆管试件来验证模型的正确性和有效性,并与三种经典模型进行对比分析,结果表明,新模型的预估能力要优于其他三种模型,且寿命预测结果较为精确。     

基于剪切形式的多轴疲劳寿命预测模型

在多轴损伤临界面的基础上,结合多轴疲劳损伤和裂纹萌生与扩展的特点,提出了一种剪切形式的多轴疲劳损伤参量,该参量不含有材料常数,进而建立了一种新的多轴疲劳寿命预测模型,经多轴疲劳试验验证表明,所建立的寿命预测模型可同时适用于多轴比例与非比例循环加载。     

新的多轴非比例加载低周疲劳寿命估算公式

利用对 3 16L不锈钢多轴非比例加载低周疲劳的试验结果 ,对现有的多轴低周疲劳寿命估算方法进行讨论 ;基于 3 16L不锈钢非比例加载低周疲劳的微观机理 ,选择最大剪应变以及应变路径的非比例度作为损伤参量 ,建立基于临界面方法的新的非比例加载低周疲劳寿命估算公式 ;利用新的非比例加载低周疲劳寿命估算公式对寿命的预测结果表明 ,新的寿命估算公式对剪切型破坏的 3 16L与 3 16LN不锈钢及拉伸型破坏的 3 0 4不锈钢非比例加载低周疲劳寿命预测精度比现有的临界面方法高     

考虑附加强化效应及平均应变的多轴疲劳寿命预估

考虑多轴加载条件下裂纹萌生和扩展的物理意义,将Miner理论与临界面法相结合提出了一种多轴等效线性疲劳寿命预估模型;将循环屈服应力与静态屈服应力的比值用来反映材料的循环强化能力,并定义了附加强化因子,考虑相位差及载荷条件对非比例附加强化效应的影响,对非对称加载下的平均应变进行了修正;利用等效应变预估模型、最大剪切应变幅模型及所提模型对5种材料的光滑及缺口试样多轴疲劳寿命进行了预估,并将预估结果与试验结果进行了对比分析,结果表明：比例加载时,3种模型都能获得较好的效果;非比例加载时,所提模型的预估效果要优于其他两种模型的预估效果。同时也验证了所提出的附加强化因子能够反映相位差及材料特性对附加强化效应的影响。     

高温比例与非比例加载下多轴疲劳寿命预测

针对拉扭多轴疲劳加载情况,分析最大剪切平面上的应变特性。利用临界损伤平面原理确定不同加载参数下的临界损伤平面,在此基础上提出一种基于单轴疲劳材料常数和高温蠕变特性的高温多轴疲劳寿命预测模型。利用高温合金材料GH4169薄壁管疲劳试样在控制应变拉扭循环加载下的试验数据,对所提出的寿命模型进行验证。结果表明,在高温低周拉扭循环加载下,所提出的高温疲劳寿命预测模型可以较好地预测高温疲劳寿命。     

非比例载荷下304不锈钢低周疲劳寿命预测

在拉扭疲劳试验机上完成了一系列非比例加载下对304不锈钢的低周疲劳试验,对目前常用的几种多轴疲劳寿命预测模型进行了分析比较。结果表明,以单轴疲劳寿命分析方法为基础的等效应变法,不能预测多轴非比例加载下的低周疲劳寿命,以临界面法为基础的Socie剪切模型对非比例加载下304不锈钢材料的疲劳寿命预测较好。     

椭圆方程式的多轴疲劳寿命预测模型

建立一种椭圆方程式的多轴常幅疲劳寿命预测模型,该模型采用临界平面概念,以临界平面上的最大切应变幅和法向应变程作为基本参数,并引入最大等效应力来考虑非比例循环附加硬化的影响。对该模型的理论分析表明,在单轴拉伸及单轴扭转应力状态下该模型能退化为常规的疲劳应变寿命模型,具有很好的兼容性。采用现有的304不锈钢和S45C钢材料的多轴疲劳试验数据对该模型及其他几种经典的多轴疲劳寿命模型进行寿命预测分散带及标准差的对比,结果显示该疲劳寿命预测模型的寿命分散带和标准差最小。分析表明,所建立的疲劳寿命预测模型可同时适用于多轴比例与非比例循环加载,且具有较小的寿命分散带和标准差,预测精度高,材料适用范围较广,计算方便可行。     

基于临界距离-临界平面方法预测DZ125缺口低循环疲劳寿命

考虑到镍基定向凝固合金滑移相关的塑性流动和裂纹萌生机制,视其面心立方晶体结构中可能开动的滑移系为临界平面并以最大分切应变范围(∆γmax)为损伤参数,分别采用热点法和临界距离理论(Theory of critical distance,TCD)对DZ125的低循环疲劳寿命进行分析和预测。研究结果表明,基于热点法的临界平面法其寿命预测偏保守,且应力集中程度越大其保守程度越明显;运用TCD时发现,缺口试件的临界距离不仅同材料、失效寿命以及应力比有关,同应力集中程度亦相关。如果以尖锐缺口试件为校准试样或采用平均思想处理临界距离,其寿命分散带均大于10倍。而假定临界距离同应力集中程度相关时获得的寿命预测分散带缩小为2倍。     

Effects of compressive stresses on torsional fatigue

Rolling contact fatigue (RCF) is the dominant failure mode in properly installed and maintained ball and roller element bearings. Lundberg and Palmgren in their seminal publication indicated that this failure is due to the alternating component of shear stress. Thus, torsional fatigue experiments have been used to predict the RCF behavior of bearing materials. In non-conformal contacts, due to Hertzian pressure the contact experiences large compressive stresses. Hence, it is critical to take into account the effect of these large compressive stresses in torsional fatigue to better simulate RCF conditions. This paper presents an investigation of torsional fatigue of bearing steels, while the effects of combined compressive stress and its relevance to material behavior in rolling contact fatigue is examined. An MTS test rig was used to investigate the fatigue life of several bearing steels and their failure mechanisms were evaluated through fractography. Then the effects of compressive stresses on torsional fatigue were investigated. A set of custom designed clamp fixtures were designed, developed and used to apply Hertzian pressures of up to 2.5 GPa on the torsion specimens. The experimental results indicate that at high cycle fatigue, a combination of shear and biaxial compression, by application of Hertzian contact, is more detrimental to fatigue life than shear alone; however, as expected it has little to negligible effects in the low cycle fatigue regime. Also the failure mode changes such that fracture planes form a cup and cone pair with multiple internal cracks as opposed to helical planes observed in pure torsion which are formed by a single crack. A 3D finite element model (using ABAQUS) was developed to investigate the fatigue damage accumulation, crack initiation, and propagation in the material. The topology of steel microstructure is modeled employing a randomly generated Voronoi tessellation wherein each Voronoi cell represents a material grain and the boundaries between the cells are assumed to represent the weak plane in the steel matrix. Continuum damage mechanics (CDM) was used to model material degradation during the fatigue process. A comprehensive damage evolution equation is developed to account for the effect of mean stress on fatigue. The model predicts the fatigue lives and crack patterns successfully both in presence and absence of compressive stresses.     

考虑平均剪应力效应的纯扭疲劳强度预测

针对高周疲劳损伤局部化,基于连续介质损伤力学,将临界域均布全寿命内禀损伤耗散作为等寿命条件,导出考虑平均剪应力效应的纯扭疲劳强度预测模型。新建预测模型揭示了纯扭疲劳强度与材料属性和平均剪应力的关联性,给出了该课题学术争议的合理解释。利用常见的三种不同金属材料的叠加平均剪应力纯扭疲劳实验数据,对比论证了新建预测模型与现有预测模型的差异。预测结果表明,新建预测模型预测精度明显优于现有模型。     

MW级风机塔筒门框焊缝的强度分析

运用有限元分析软件ANSYS建立某MW级风力发电机塔筒门框的有限元模型,分析了其在极限载荷下的静强度; 同时采用热点应力法对门框焊缝进行疲劳分析,基于临界面理论计算热点应力,并利用雨流计数法和Palmgren-Miner线性累积损伤理论计算了门框焊缝的疲劳损伤,结果表明,门框焊缝的极限强度和疲劳强度均满足使用要求。     

周向磁巴克豪森噪声分布及平面应力测量

磁巴克豪森噪声对应力非常敏感,是一种操作便捷、检测灵敏度高、重复性好的原位无损应力测量技术,在残余应力测定、零部件应力集中区评价、结构承载应力评估中有广阔的应用前景。工程中铁磁性材料表面平面应力测量时最大主应力及其方向测量是一项亟待解决的难题,提出了一种基于周向磁巴克豪森噪声分布的平面应力测量方法,建立了求解平面应力张量的模型,实现了测量点任意方向的正应力和剪应力解调。实验验证了该方法的有效性,测量结果表明,当主应力大于50 MPa时,实测的最大主应力方向偏差为10°,最大正应力偏差为5 MPa,最大剪应力偏差为6 MPa,具有较高的测量准确度。