Fatigue behavior of direct laser deposited Ti-6.5Al-2Zr-1Mo-1V titanium alloy and its life distribution model

The present work aims to investigate the fatigue behavior of Direct Laser Deposition (DLD) Ti-6.5Al-2Zr-1Mo-1V titanium alloy under constant amplitude stress. 22 pieces of DLD Ti-6.5Al-2Zr-1Mo-1V titanium alloy standard cylinder specimens were tested under a stress level of 800?MPa with a stress ratio of 0.06. Fatigue fractography and fatigue life data were obtained. Through the fracture surface analysis, the specimens were divided into two categories in accordance with the location of crack initiation and defect types. Comparison of fatigue life and behavior between two specimen types was given, which was followed by a discussion about the impact of defect type, size and position on the fatigue life of the specimen. The fatigue test results also show a large variation of fatigue life. To illustrate the statistical characteristics of the fatigue life, probabilistic analysis was performed, and a novel bimodal lognormal model was established. The model has a good fit with the experimental data and can reduce the scatter of the fatigue life significantly.     

Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金绝热剪切和局部流动行为

在THERMECMASTOR-Z型热模拟机上对Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金在变形温度780～1 080 ℃,应变速率0.001～70.000 s^-1条件下的流动应力变化规律进行了研究,分析了变形工艺参数对Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金绝热剪切和局部流动行为的影响,并采用基于动态材料模型的功率耗散图分析了Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金易发生绝热剪切和局部流动的热力参数范围。结果表明:在所研究的热变形条件下,当温度较高、应变速率较低时,变形呈稳态流动特征,当温度较低、应变速率较高时,变形呈流动软化特征。通过功率耗散图分析及微观组织观察可知,在α+β两相区变形,应变速率高于0.100 s^-1时,功率耗散系数多数小于0.16,变形多处于流变失稳区域,其变形机制主要为绝热剪切和局部流动。     

TC11钛合金焊接接头低周疲劳分形损伤演化研究

基于损伤力学和分形理论,在金属材料疲劳断口的形貌特征具有统计自相似性的基础上建立了表征焊接接头断口损伤的面分形损伤演化模型.利用TC11合金低周疲劳试验后所得到的断口测得其面分维数,结合试验数据拟合获得该材料损伤演化方程参数;从而建立了TC11合金焊接接头三级载荷下的疲劳损伤演化方程;同时将该模型与基于断口表面裂纹扩展的线分形损伤演化模型加以比较.      

Ti-6Al-2Zr-1M0-1V合金的热变形行为

在Gleeble-1500热模拟机上对Ti-6A1-2Zr-1Mo-1V钛合金铸态材料进行了恒温和恒应变速率下的热压缩变形实验，温度范围是700～1000℃，应变速率范围是5×10     

Tool Life and Surface Integrity in High-speed Milling of Titanium Alloy TA15 with PCD/PCBN Tools

Titanium alloys are widely used in aeronautics that demand a good combination of high strength, good corrosion resistance and low mass. The mechanical properties lead to challenges in machining operations such as high process temperature as well as rapidly increasing tool wear. The conventional tool materials are not able to maintain their hardness and other mechanical properties at higher cutting temperatures encountered in high speed machining. In this work, the new material tools, which are polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN) tools, are used in high-speed milling of Ti-6.5Al-2Zr-1Mo-1V (TA15) alloy. The performance and wear mechanism of the tools are investigated. Compared to PCBN tool, PCD tool has a much longer tool life, especially at higher cutting speeds. Analyses based on the SEM and EDX suggest that attrition, adhesion and diffusion are the main wear mechanisms of PCD and PCBN tools in high-speed milling of TA15. Oxidation wear is also observed at PCBN tool/workpiece interface. Roughness, defects, micro-hardness and microstructure of the machined surface are investigated. The recorded surface roughness values with PCD/PCBN tools are bellow 0.3 μm at initial and steady cutting stage. Micro-hardness analysis shows that the machined surface hardening depth with PCD and PCBN tools is small. There is no evidence of sub-surface defects with PCD and PCBN tools. It is concluded that for TA15 alloy, high-speed milling can be carried out with PCD/PCBN tools.     

Electrochemical behavior of Ti-6.5Al-2Zr-1Mo-1V alloy under rotating condition with periodically fluctuating current density

Titanium alloy plays a crucial role in the electrochemical field due to its excellent corrosion resistance. The passivation and dissolution behaviors of Ti-6.5Al-2Zr-1Mo-1V（TA15） alloy in Na Cl solution were studied by simulating the electrochemical machining process in a rotating condition, which made the anode in a state with alternating high and low current density. Electron probe micro analysis, ultra-depth microscope, scanning electron microscope, and X-ray photoelectron spectrometer were u...     

超声振动载荷下合金的疲劳寿命性能研究

 应用超声共振试验技术研究了三种工程常用合金(Ｕｄｉｍｅｔ５００,１７４ＰＨ和Ｔｉ－６Ａｌ－４Ｖ)在超声振动载荷(ｆ＝２０ｋＨｚ,Ｒ＝－１)下的疲劳寿命性能,并与常规疲劳载荷(ｆ＝２０－５０Ｈｚ,Ｒ＝－１)下材料的有关性能做了对比分析。研究结果表明,材料的超声疲劳寿命性能与其动态振动特性、机械响应以及载荷体制有关。     

用自助加权范数法评估三参数威布尔分布可靠性最优置信区间

提出自助加权范数法,以评估三参数威布尔分布可靠性的最优置信区间.基于可靠性经验值与理论值的差异,通过6个最小加权范数准则,构建出威布尔分布的最优参数信息向量.对最优参数信息向量进行自助再抽样,获得生成参数信息向量,用于模拟参数的概率密度函数.在给定置信水平下,求解出参数的估计真值及其置信区间,并据此建立可靠性的估计真值函数及其最优置信区间函数.滚动轴承性能寿命案例、直升机部件失效案例与某试件疲劳寿命案例的研究表明:使用自助加权范数法,估计真值函数与可靠性经验值相一致,最优置信区间函数能描述试验结果的真实状态.      

激光沉积Ti-6Al-2Zr-Mo-V钛合金高周疲劳性能

 疲劳失效是钛合金工业应用中最重要的失效方式,疲劳强度是钛合金应用的关键性指标。为了研究激光沉积Ti-6Al-2Zr-Mo-V钛合金的疲劳性能和行为,在625 MPa到900 MPa不同应力水平下进行了室温高周疲劳(HCF)测试(应力比R=0.1,加载频率f=120~130 Hz),完成了疲劳断口表面分析。研究了气孔存在及分布对激光沉积Ti-6Al-2Zr-Mo-V钛合金疲劳性能的影响。激光沉积钛合金具有细小α/β片层组织。分析结果显示,虽然疲劳源区有气孔存在,激光沉积Ti-6Al-2Zr-Mo-V钛合金仍然具有优异的疲劳性能。取向丰富细小的α/β片层组织能有效减小疲劳源区滑移长度。分析结果还表明,应力水平对疲劳行为有一定影响。     

扩散连接界面缺陷对Ti-6Al-4V合金力学性能的影响

研究了φ4mm与φ2mm的扩散连接界面缺陷对Ti-6Al-4V合金力学性能的影响。当拉伸载荷方向与缺陷平面平行时,材料的强度与塑性与无缺陷材料相当,这是由于此类缺陷对样品受力截面的面积几乎没有影响。含有φ4mm缺陷试样的拉压疲劳寿命展现出很大的分散性,界面缺陷并未成为裂纹萌生的唯一位置。从表面起裂的样品均处于高寿命区域,而绝大部分从缺陷处起裂的样品均落于低寿命区域。有限元分析表明,当缺陷位于中心位置时其引起的应力集中较小,应力分布梯度较小;缺陷位于边缘位置时,应力集中效应增大。     

预腐蚀对疲劳寿命分布特性及参数影响的初步研究

预腐蚀是影响飞机结构安全性和经济性的重要因素.为研究预腐蚀对疲劳寿命的影响,进行30CrMnSiNi2A和LC4CS试件加速预腐蚀不同时间后的成组随机谱下的疲劳试验,采用概率回归方法对预腐蚀疲劳寿命分布特性进行检验,表明可采用对数正态分布和双参数威布尔分布描述疲劳寿命分布特性.然后对不同预腐蚀时间后的疲劳寿命分布参数进行估计,当假设疲劳寿命服从对数正态分布时,在工程常用的时间范围内,对数寿命标准差与预腐蚀时间无关;当假设疲劳寿命服从双参数威布尔分布时,可以认为斜率与预腐蚀时间无关.     

服从威布尔分布的小子样疲劳寿命分散系数及其应用

威布尔分布是一种具有良好拟合特性的疲劳寿命分布模型。本文假设小子样疲劳试验寿命服从双参数威布尔分布．基于顺序统计量理论，给出了对应于最小和最大寿命的分散系数计算公式。作为应用算例，采用本文计算公式评估了某风扇轮盘的安全寿命。结果表明：应用本文计算公式得到的分散系数与文献[2]吻合良好，分散系数对形状参数的变化比较敏感：由本文疲劳寿命分散系数计算公式得到的安全寿命偏保守。     

两类可靠性指标之间的关系研究

从可靠性寿命的定义出发,在一定的假设前提下,导出了双参数中威布尔分布的斜率参量α和对数正态分布子样标准差σ之间的关系;进而得到建立在对数正态分布基础上的疲劳寿命N_(90/99.9)和建立在双参数威布尔分布基础上的疲劳寿命N_(95/95)之间的关系;计算结果表明上述两类可靠性指标是一致的。     

某直升机主减速器传动系统的寿命与可靠性计算方法

通过对直升机典型任务剖面原始载荷数据谱进行统计处理,经三维有限元分析将所编系统载荷谱转化为齿轮应力谱;结合Goodman公式及材料P-S-N曲线(给定存活率下的疲劳寿命曲线)算出该系统各齿轮在各级载荷下的疲劳寿命,利用统计软件Minitab对寿命数据进行分析,得出齿轮的接触疲劳寿命服从两参数威布尔分布,根据威布尔分布的...     

疲劳强度概率分布的统计推断

 本文就疲劳强度概率分布问题从统计角度出发,利用统计推断方法处理。通过三组较大子样的疲劳试验数据的统计分析,得出与在假定一定的疲劳寿命概率分布下由数学分析方法推导出的理论概率分布完全不同的结论。该法中疲劳强度概率分布与疲劳寿命分布没有直接关系。     

Estimation method for random sonic fatigue life of thin-walled structure of a combustor liner based on stress probability distribution

As to the sonic fatigue problem of an aero-engine combustor liner structure under the random acoustic loadings,an effective method for predicting the fatigue life of a structure under random loadings was studied.Firstly,the probability distribution of Von Mises stress of thin-walled structure under random loadings was studied,analysis suggested that probability density function of Von Mises stress process accord approximately with two-parameter Weibull distribution.The formula for calculating Weibull parameters were given.Based on the Miner linear theory,the method for predicting the random sonic fatigue life based on the stress probability density was developed,and the model for fatigue life prediction was constructed.As an example,an aero-engine combustor liner structure was considered.The power spectrum density(PSD) of the vibrational stress response was calculated by using the coupled FEM/BEM(finite element method/boundary element method) model,the fatigue life was estimated by using the constructed model.And considering the influence of the wide frequency band,the calculated results were modified.Comparetive analysis shows that the estimated results of sonic fatigue of the combustor liner structure by using Weibull distribution of Von Mises stress are more conservative than using Dirlik distribution to some extend.The results show that the methods presented in this paper are practical for the random fatigue life analysis of the aeronautical thin-walled structures.     

小样本无失效寿命试验数据的轴承可靠性评估

针对小样本无失效寿命试验数据可靠性问题提出了评估模型。模型采用Bayes理论构造服从原始样本的抽样函数,结合Bootstrap法生成大量服从抽样函数的随机数作为增广样本,再通过最佳线性不变估计法分析原始样本及增广样本得到Weibull分布双参数估计值作为可靠性评估结果。通过Monte-Carlo法仿真生成服从Weibull分布的随机数,分别采用该模型、配分布曲线法及现有Bayes理论对此随机数做评估,对比发现:该模型得到的参数估计较现有Bayes理论和配分布曲线法更接近Weibull双参数真值,且形状参数和尺度参数估计值的相对误差均低于10%,验证了模型分析小样本无失效数据进行可靠性评估的可行性。借助文献实例对模型进行分析,对比得出模型能得到较现有Bayes理论和配分布曲线法更符合工程实际的评估结果;模型在小样本情况下的双侧可靠度置信区间长度低于现有Bayes理论和配分布曲线法,有效提高了小样本无失效数据可靠性评估精度。      

卫星推力器可靠性评估和寿命预测

提出一种卫星推力器无失效数据可靠性分析方法,该方法能够在高置信水平下给出卫星推力器可靠度和使用寿命的置信下限。同时还建立了卫星推力器强检验和弱检验方法,前者适用于对首次采用的卫星推力器的验收,而后者适用于对已长期使用的卫星推力器的例行的批抽样检验。文中对卫星推力器寿命遵循Weibull分布和对数正态分布的情况分别进行了详细讨论。      

双峰应力谱密度雨流幅值分布

为了在频域内解决双峰应力谱密度下的结构疲劳寿命估算问题,提出了双峰应力谱的雨流幅值分布模型,并给出了参数估算方法。假设雨流幅值分布为两个双参数Weibull分布的组合,权重系数反映了两个谱密度峰值对雨流幅值分布的贡献;雨流幅值分布模型中的参数均是随机过程谱参数的函数。数值模拟结果表明：两个Weibull分布的组合能够很好地描述双峰应力谱的雨流幅值分布,模型中的参数能够根据双峰应力谱密度的谱参数计算得出。     

民用航空发动机引气系统部件寿命建模

针对飞机维修工作中发动机引气系统故障率较高问题,以寿命数据分析为基础,运用威布尔分布模型定量评估航空发动机部件可靠性,建立了民用航空发动机引气系统部件可靠性寿命模型。以V2500发动机引气系统为例,收集了该系统的可靠性数据,分析了部件的非计划拆换情况。在数据计算过程中采用3参数威布尔分布模型对引气系统部件的寿命数据进行拟合。假设检验结果表明,在对部件进行寿命可靠性分析时,运用威布尔分布建立的数学模型符合客观规律,且能够取得良好的拟合效果。依据计算出的部件可靠性特征量对部件的可靠性状况进行定量评估,结果表明:在评估复杂机械电子系统的可靠性时,威布尔分布模型具有较大应用价值。