基于统计分析WC-15Ni添加对NiCrBSi涂层接触疲劳寿命的影响

离散性是涂层接触疲劳寿命分布的显著特点,难以采用某一确定的寿命值来描述涂层的接触疲劳寿命。因此采用统计分析方法来处理离散的接触疲劳寿命数据并揭示WC-15Ni添加对NiCrBSi涂层接触疲劳寿命的影响尤为重要。该文采用等离子喷涂技术制备NiCrBSi涂层和NiCrBSi/WC-15Ni复合涂层,并在不同接触应力水平下考察这两种涂层的滚动接触疲劳寿命。采用统计分析的方法(正态性W检验、t检验、方差分析、回归分析等)研究WC-15Ni添加对NiCrBSi涂层接触疲劳寿命的影响。结果表明:这两种涂层接触疲劳寿命都服从正态分布;在较高的接触应力水平下,两种涂层的接触疲劳寿命分布相当,但是复合涂层的接触疲劳寿命分布更加集中;在较低的接触应力水平下,复合涂层的接触疲劳寿命要显著高于NiCrBSi涂层,并且寿命分布也更加离散;方差分析结果表明两种涂层承受的接触应力对其接触疲劳寿命都具有显著影响,但接触应力对复合涂层的寿命影响更为显著;回归分析表明两种涂层的接触疲劳均值寿命与接触应力具有高度的线性相关性,但复合涂层的接触疲劳均值寿命随着接触应力的增加而降低的程度更为显著。     

基于统计分析的等离子喷涂层接触疲劳寿命和失效模式

在不同应力水平下考察等离子喷涂镍基合金涂层的滚动接触疲劳寿命和失效模式。以R-3.1.1软件为平台,采用统计分析方法(方差分析、回归分析、判别分析等)对其进行分析和讨论。结果表明:涂层的滚动接触疲劳寿命呈正态分布;随着接触应力的增加,涂层的均值寿命和方差都减小,并且疲劳寿命的分布更加集中;方差分析表明,接触应力对涂层的滚动接触疲劳寿命有显著性影响,且寿命均值与接触应力具有高度的线性相关性;建立了涂层失效模式的判别准则,当指定接触应力和疲劳寿命时可以预测涂层的失效模式,且预测正确率在65%以上;疲劳寿命对失效模式的累积贡献率明显高于接触应力对失效模式的累积贡献率,因此疲劳寿命是决定涂层失效模式的主要因素。     

微缺陷对热喷涂涂层接触疲劳性能的影响

采用超音速等离子喷涂设备在45号钢基体上制备了三种含有不同微缺陷的NiCrBSi合金涂层。使用球盘式接触疲劳实验机对涂层的接触疲劳性能进行了测试,建立了Weibull失效概率图;使用扫描电子显微镜对涂层的微观结构和失效形貌进行了表征;比较了三种涂层的接触疲劳寿命及涂层的主要疲劳失效模式。结果表明,涂层内的微缺陷主要由微孔隙和微裂纹构成,涂层接触疲劳寿命的长短与这些微缺陷含量的多少成反比,涂层的孔隙率为2.5%,1.3%和2.1%,对应的接触疲劳寿命分别为7.77×105,8.99×105,7.81×105周次。同时,涂层微缺陷含量较少时涂层的失效模式主要以剥落失效为主;涂层微缺陷含量较多、结合强度较差时主要以分层失效为主;涂层内存在较大的孔隙可致使涂层的提早失效,同时涂层表面磨损失效的概率增加。     

航空GH2036合金硬度热处理优化及疲劳性能DIC分析

为探究热处理工艺参数对GH2036合金硬度及疲劳性能的影响,基于四因素三水平正交热处理实验,对GH2036铁基高温合金的硬度性能进行优化,并分析热处理后的显微组织;同时利用疲劳实验与DIC(digital image correlation)非接触全场应变测量相结合的方法,利用Y方向应变-疲劳寿命比的云图,直观地分析热处理后GH2036合金疲劳失效过程。结果表明:固溶温度对合金硬度性能的影响最大,其次是固溶时间、时效时间、时效温度,极差分析所得的最优热处理工艺为960℃/60 min+水冷+560℃/2 h;正交试验中最高显微维氏硬度(HV305.34)较未处理试样(HV260.41)提高17.3%;热处理后金相组织基体为奥氏体,增强相为第二相碳化物,显微硬度值随着奥氏体中的第二相碳化物含量的增加而升高;热处理后平均疲劳寿命(942372次循环)较未处理试样(450800次循环)提高109%,疲劳性能明显优化。     

锰系和锌系磷化对滚动轴承疲劳寿命的影响

对于一些大型低速重载的轴承,如轧机、风电大型轴承,极易产生擦伤,导致轴承的使用寿命缩短,目前有采用表面磷化处理来防止轴承擦伤,但在磷化处理对轴承疲劳寿命影响方面的研究较少。本文从表面涂层技术出发,通过对磷化工艺的研究,对滚子分别进行Mn系、Mn系去氢以及Zn系磷化处理,通过疲劳寿命试验机对各种磷化工艺下滚子的疲劳寿命进行评价,分析比较三种磷化处理对滚子接触疲劳寿命的影响。结果表明,与磷化前的滚子相比,Zn系磷化滚子的疲劳寿命显著提高,其次是Mn系去氢滚子,而Mn系滚子的疲劳寿命和磷化前滚子的寿命相差不大。     

基于统计学方法的热喷涂层滚动接触疲劳寿命研究现状

热喷涂层是对可再制造零件进行修复,并恢复其性能的一种重要手段。通过热喷涂技术获取的再制造零件,其表面接触疲劳主要表现为热喷涂层的滚动接触疲劳问题。目前,依据统计学方法常被用于热喷涂层滚动接触疲劳寿命研究的模型主要有:Weibull模型、疲劳曲线模型、理论预测模型和回归分析模型。从统计学理论及应用的角度出发,总结了各种方法研究和应用现状,对基于统计学方法提高热喷涂层滚动接触疲劳寿命预测的精确度和可靠性进行了展望。     

复合材料孔板疲劳寿命环境影响的试验研究

为研究环境因素对T300/QY8911疲劳性能的影响,开展了T300/QY8911含中心孔层压板疲劳试验.试验中分别采用无紫外无涂层试件、紫外无涂层试件、紫外有涂层试件测试其拉-拉疲劳寿命,并通过对试验结果的方差分析研究了有无涂层、紫外辐射及湿度等环境因素对T300/QY8911复合材料孔板拉-拉疲劳寿命影响的显著性.研究表明:无涂层、300MJ/m2紫外照射量时,湿度对试件疲劳寿命影响高度显著;干燥、无涂层时,有无紫外照射对试件疲劳寿命影响高度显著;湿润、600MJ/m2紫外照射量时,有无涂层对试件寿命影响显著.     

滚动接触条件下铁基涂层的疲劳磨损寿命实验研究

利用超音速等离子喷涂技术在45钢表面制备了铁基合金涂层,利用球盘式疲劳磨损实验机评价了铁基涂层在两种载荷条件下的疲劳磨损性能,利用两参数Weibull分布表征了涂层的疲劳寿命,采用扫描电子显微镜(SEM)分析了涂层的微观结构和失效形貌,利用有限元方法研究了涂层内部应力分布.实验结果表明,载荷条件可以显著地影响涂层的寿命和失效形貌,高载下涂层的寿命明显降低;随着载荷的增加,主要失效形式由表面磨损失效转换成剥层失效,其中表面磨损是由于粗糙接触引起,而剥层则与应力分布机制有关.     

热处理对镍钛合金丝材弯曲疲劳性能的影响

研究了热处理工艺对５０．６ａｔ％Ｎｉ－Ｔｉ合金丝材弯曲疲劳性能的影响。结果表明：该丝材经过固溶和时效后具有不同的弯曲疲劳寿命，其中固溶处理温度为１０２３Ｋ并且时效温度６７３Ｋ时，具有最高寿命；抗拉强度随热处理工艺的改变呈同样变化趋势。     

热处理工艺对支撑辊用钢疲劳剥落形式的影响

采用JPM-1型接触疲劳磨损试验机，对450℃、530℃两个回火温度下支撑辊用Cr5钢的线接触滚动疲劳寿命进行了测定；通过扫描电子显微镜（SEM）、X射线（X—ray）和显微组织观察的方法研究了两种热处理工艺下试验用钢的疲劳剥落形式，并对剥落形式及剥落机理进行了初步探讨。结果表明：450℃回火得到硬度为HRC51的试样失效形式主要为棘齿裂纹和深层剥落，疲劳寿命为1．5～3×10^6；530℃回火得到硬度为HRC45的试样失效形式主要为浅层剥落，疲劳寿命为0．5～2×10^5。     

几种常用的金属材料疲劳极限试验方法

金属疲劳试验用于测定金属材料的许用疲劳应力,绘制材料的疲劳曲线,进而在交变应力下测定金属材料的疲劳极限。疲劳研究的试验方法有很多,该文根据有关国家标准和现有文献资料对一些常用疲劳试验方法进行了综述,包括单点疲劳试验法、升降法疲劳试验、高频振动疲劳试验法、超声波法疲劳试验、红外热像技术疲劳试验方法,并对每种疲劳试验方法的试验目的、适用条件、试验试样、所需仪器、具体步骤和数据处理进行了介绍。     

A review of multiaxial fatigue of weldments: experimental results, design code and critical plane approaches

A survey of biaxial (bending or tension and torsion) constant amplitude fatigue of welded connections is presented. Re-analysis of 233 experimental results from eight different studies has been performed based on hot spot stresses and three potential damage parameters: maximum principal stress range; maximum shear stress range; and a modified critical plane model for welds. Of the three methods, the critical plane model was most successful in resolving the data to a single S – N line. The design curve for all toe failures based on the critical plane model was FAT 97 with a slope of 3. By excluding butt welds and including only fillet welds that failed at the weld toe, the design curve was increased to FAT 114 with a slope of 3. However, observed scatter was 70–100% larger than that observed in uniaxial loaded specimens analysed using the hot spot approach.     

Fatigue damage of medium carbon steel under sequential application of axial and torsional loading

Fatigue tests were conducted on S45C steel under fully reversed strain control conditions with axial/torsional ( at ) and torsional/axial ( ta ) loading sequences. The linear damage value (n₁/N₁+n₂/N₂) was found to depend on the sequence of loading mode ( at or ta ), sequence of strain amplitude (low/high or high/low) and life fraction spent in the first loading. In general, at loading yields larger damage values than ta loading and the low–high sequence of equivalent strain leads to larger damage values than the high–low sequence. The material exhibits cyclic softening under axial cyclic strain. Cyclic hardening occurs in the torsion part of ta loading, which elevates the axial stress in the subsequent loading, causing more damage than in pure axial fatigue at the same strain amplitude. Fatigue life is predicted based on the linear damage rule, the double linear damage rule, the damage curve approach and the plastic work model of Morrow. Results show that overly conservative lives are obtained by these models for at loading while overestimation of life is more likely for ta loading. A modified damage curve method is proposed to account for the load sequence effect, for which predicted lives are found to lie in the factor‐2 scatter band from experimental lives.     

On the estimation of the material fatigue properties required to perform the multiaxial fatigue assessment

To accurately perform the fatigue assessment of engineering components subjected to in‐service multiaxial fatigue loading, the adopted design criterion must properly be calibrated, the used information usually being the fatigue strength under both pure uniaxial and pure torsional fatigue loading. Because of the complex fatigue response of metallic materials to multiaxial loading paths, the only reliable way to generate the necessary pieces of calibration information is by running appropriate experiments. Unfortunately, because of a lack of both time and resources, very often, structural engineers are requested to perform the multiaxial fatigue assessment by guessing the necessary fatigue properties. In this complex scenario, initially, the available empirical rules suitable for estimating fatigue strength under both pure axial and pure torsional fatigue loading are reviewed in detail. Subsequently, several experimental results taken from the literature and generated by testing metallic materials under a variety of proportional and non‐proportional multiaxial loading paths are used to investigate the way such empirical rules affect the accuracy in estimating fatigue strength, the damage extent being evaluated according to the modified Wöhler curve method. Such a systematic validation exercise allowed us to prove that under proportional loading (with both zero and non‐zero mean stresses), an adequate margin of safety can be reached even when the necessary calibration information is directly estimated from the material ultimate tensile strength. On the contrary, in the presence of non‐proportional loading, the use of the empirical rules reviewed in the present paper can result, under particular circumstances, in a non‐conservative fatigue design.     

An apparatus for quantitative fretting testing

The design and construction of an apparatus for performing quantitative fretting fatigue experiments is described. The device allows accurate measurement and control of normal contact force, tangential contact force, relative displacement between contacting surfaces and bulk fretting loads, as well as measurement of average friction coefficients. Its design is simple, and includes interchangeable fretting contact pads, allowing the use of various pad geometries without major adjustment. The device incorporates many points of adjustment for alignment and compliance, making it a robust frame for a wide variety of fretting fatigue conditions involving different materials. The capabilities of this device are also verified by results of fretting fatigue experiments conducted on a 7075-T6 aluminium alloy.     

Micromechanisms of fatigue crack growth in aluminium alloys

The fatigue crack growth characteristics of high-strength aluminium alloys are discussed in terms of behaviour during mechanical testing and fracture surface appearance. For a wide range of crack growth rates, the crack extends both by the formation of ductile striations and by the coalescence of micro-voids. Dimples are observed at stress intensities very much less than the plane strain fracture toughness, and this is explained in terms of the probability of inclusions lying close to the crack tip. The striation formation process is described as a combination of environmentally-enhanced cleavage processes and plastic blunting of the crack tip.     

金属材料疲劳试验与数据处理方法

疲劳是金属材料机械构件常见的一种失效形式,疲劳试验方法与数据处理方法一直是研究学者们关注的热点。该文从疲劳寿命和规定寿命下的疲劳强度两个方面介绍了疲劳试验和数据处理方法的主要研究成果,并说明了几种典型的疲劳寿命试验方法与疲劳寿命概率分布参数的统计方法,以及规定寿命下的疲劳强度试验方法与规定寿命下的疲劳强度概率分布参数的统计方法;并通过算例,对比了不同方法之间的差异。     

玻璃陶瓷疲劳断裂的宏观规律研究

对K2O-MgO－AlO3-B2O3-SiO2-F多元系统的可切削微晶玻璃的疲劳行为进行了研究。结果表明：材料在静载荷、动载荷、循环载荷作用下的应力腐蚀指数n分别为69.54、35．2、18.18。应力腐蚀指数n的大小强烈依赖于加载方式，并能作为材料抵抗裂纹扩展的某种抗力指标，循环载荷和动载荷对材料造成了附加损伤，致使在相同应力水平下材料寿命明显下降。     

飞机典型机械紧固连接件腐蚀疲劳性能的试验研究EI

本文研究了飞机机械紧固连接件在腐蚀环境下的疲劳性能。试验结果表明，腐蚀环境在大多数情况下降低紧固件的疲劳寿命，其中盐雾环境对双剪密封铆接件的疲劳寿命的影响最为严重。给出了机械紧固件在不同状态下的细节疲劳额定值（ＤＦＲ）和可靠性寿命（Ｎ＿（９５／９５））。