高强钛合金的微动损伤与疲劳

本文对高强钛合金Ti-10V-2Fe-3Al在不同温度下的微动损伤和疲劳特性进行了研究。试验结果表明:在常温下,微动疲劳强度较非微动疲劳强度下降57％。疲劳损伤的主要机制是疲劳 脱层,它是由作用在材料表层的交变切应力引起的,它将导致疲劳裂纹的萌生和早期断裂,疲劳裂纹扩展方向可根据接触应力分析得到解释。在较高试验温度下,微动损伤程度减弱。     

抗微动磨损钢丝绳

起重机械正向高速度、高扬程、高负载方向发展,对钢丝绳耐疲劳性能要求逐渐提高。微动磨损和微动疲劳是钢丝绳失效的主要原因之一。对制绳用钢丝进行表面处理,提高表面的耐磨性和降低摩擦系数是提高钢丝绳抗微动磨损能力的有效手段。制绳钢丝经锰系耐磨磷化处理,可以提高表面耐磨损、抗腐蚀性能,改善钢丝表面携带润滑剂的能力,从而有效抑制微动磨损和微动疲劳的发生,延长钢丝绳使用寿命。     

钛合金微动磨损的研究进展

钛合金耐磨性能较差,对微动磨损十分敏感,使其应用和发展受到了一定的限制。为此,总结了钛合金微动磨损性能的影响因素,综述了钛合金抗微动损伤方法的研究进展。目前,关于钛合金微动磨损的研究主要存在两方面的局限性：(1)对于钛合金微动磨损的研究大多是在单一影响因素及稳定参数下进行的;(2)缺乏关于钛合金在特殊工况下微动磨损的研究。因此,未来对于钛合金微动磨损的研究应多结合工业应用中微动磨损的失效实例,加强多因素、变参数以及特殊工况下的微动磨损研究;在掌握微动磨损失效机理的基础上,根据钛合金的特性,探索新型表面处理技术,进一步改善钛合金微动磨损失效问题。     

S45C-A电机转轴疲劳试验断裂原因分析及其应对措施

某S45C-A电机转轴在进行疲劳试验的过程中发生断裂。通过宏观形貌分析、金相显微组织分析、化学成分分析及扫描电镜微观形貌分析等方法,对发生断裂的转轴试样进行了失效原因分析。分析结果表明:转轴断裂是由表面擦伤引起的疲劳断裂,表面擦伤属于零件表面微动磨损的一种。预防零件表面微动磨损,首先要对零件连接部位加强紧配合,使之不出现微振,其次是在零件连接部位填充润滑油等隔离接触表面。     

微动磨损对机械的危害及预防措施

在机械装备中,由于环境的影响和工况条件的复杂多变性,在接触面上很容易出现微动磨损造成接触表面的微动损伤。为此,主要介绍了机械中两固体接触面上因出现周期性小振幅震动造成损伤的微动磨损的特征;揭示了微动磨损机理是同时涉及到粘着、磨料、氧化和疲劳4种基本磨损机理的一种特殊磨损形式,通过实例论证了微动磨损对机械零件的危害以及通过结构改进设计、材料的选择和表面强化工艺等措施预防和减少微动磨损,提高机械运行的可靠性。     

热喷涂技术在抗微动损伤中的应用

微动损伤普遍存在于紧密配合部件中,是造成零部件失效的主要祸患之一。采用热喷涂技术,在配合件接触面喷涂抗微动损伤涂层,能有效地降低微动损伤,具有抗损伤效果好、经济效益显著等特点,得到了较广泛的研究与应用。     

二次带状组织对低合金非调质钢疲劳性能的影响

采用应力比为0.1的轴向拉伸疲劳试验分别研究了低合金钢DG20Mn和35CrMo钢的疲劳性能与带状组织的关系.结果表明:带状组织对试验材料的轴向拉伸性能没有明显影响,对35CrMo钢的轴向拉伸疲劳性能影响较小,但严重减弱DG20Mn钢的轴向疲劳性能.带状组织对疲劳性能的影响主要是由于在高的疲劳拉应力下,带状组织引发疲劳微裂纹、微空洞等疲劳损伤,导致疲劳裂纹萌生及扩展模式发生变化,从而影响疲劳性能.     

工件疲劳强度试验裂纹分析

为研究微动疲劳产生机阻,太原重工轨道交通设备有限公司使用全尺寸疲劳测试的方式,再现了微动磨损裂纹,并通过宏观观察、扫描电镜分析、显微组织检查、低倍分析、拉伸试验,对工件疲劳强度试验后出现的轮座部位的裂纹的性质和形成原因进行了分析。结果表明,工件断裂为疲劳断裂。断裂原因是工件表面由于微动磨损,导致微动疲劳产生接触疲劳裂纹。以接触疲劳裂纹为源,引发严重应力集中型疲劳断裂。     

Q345B H型钢高应变低周疲劳断口分析

介绍了典型的拉-压疲劳失效的形成机理、宏观形貌以及微观形貌,并对Q345B H型钢高应变低周疲劳断口进行了分析,为今后进行相关疲劳研究奠定基础。     

Q235钢结构材料的超低周疲劳性能

对钢结构材料 Q235钢的超低周疲劳性能进行了研究。采用横向应变控制方法,保持频率1 Hz 恒定,在岛津电液伺服疲劳试验机上开展了试验钢的超低周疲劳试验。获得了循环应力响应特征曲线等实验数据,并在此基础上分别建立了试验钢基于塑性应变幅及应变速率的超低周疲劳寿命预测公式,且2种公式均能较好地对其寿命进行预测。通过电镜扫描(SEM),分析了试验材料超低周疲劳下的微观断裂机理。研究结果表明,试验材料在超低周疲劳与低周疲劳下的疲劳性能,如循环响应特征、寿命预测公式以及微观断裂机理等方面均存在一定的差异。     

Effect of contact pad rigidity and fretting fatigue design curve

In fretting fatigue the nucleation and early propagation of fatigue crack depends on the state of stress near the contact edge. Contact pad rigidity is one of the factors that influence the stress state near the contact edge, there by influencing fretting fatigue strength. In the present study the effect of contact pad rigidity on fretting fatigue strength of turbine steels (Ni-Cr-Mo-V steel specimen with 12 Cr steel contact pads) were investigated. To study the effect of contact pad rigidity, contact pads with different pad foot height were used. FEA was performed to evaluate the stress distribution near the contact edge. The results showed that with increase in contact pad rigidity the fretting fatigue strength decreased. The results obtained were explained based on the stress distribution near the contact edge evaluated by using FEA. By combining the experimental results and FEA, fretting fatigue design curves were proposed.     

Fatigue Strength of Conventionally Cast Tool Steels and its Dependence of Carbide Microstructure

The axial fatigue strength at two million cycles was experimentally determined for two conventionally cast tool steels and successfully compared with results from a fatigue limit model. Specimens were tested both in the rolling and transverse direction and showed large differences in fatigue properties due to the segregated carbide microstructure. Rolling direction specimens experienced higher fatigue strength than the transverse direction specimens. This is due to smaller carbides present in the load affected cross section of the rolling direction fatigue test bars compared to the cross section of the transverse direction fatigue test bars. Fractographic analysis of failed specimens showed that large carbides had caused fatigue failure, which was also predicted by the model. Measured size distributions of carbides and inclusions were used as input data in the model. The probability that at least one particle will be present in the material volume having a size larger than the threshold value for crack propagation was calculated.     

弹簧钢55SiCrA轴向疲劳行为的试验研究

随着对汽车轻量化和安全性要求的不断提高,改善疲劳性能成为弹簧钢研究与开发的一个重要主题.在Amsler HFP 5000高频疲劳试验机上研究了弹簧钢55SiCrA轴向拉-压加载的疲劳性能,测定了其条件疲劳极限及S-N曲线,利用扫描电镜(SEM)和E-DAX对疲劳断口及夹杂物进行观察,对断口进行了宏观和微观分析,研究了疲...     

Physicomechanical aspects of fretting and fretting fatigue of metallic stiff joints

The models of fretting corrosion and fretting fatigue mechanisms and the processes in the contact zone of parts subjected to fretting fatigue are discussed. Experimental data on the fretting and fretting fatigue mechanisms and on the effect of fretting on the fatigue resistance of structural materials are presented.     

疲劳失效机理及热轧H型钢疲劳断口分析

介绍了疲劳断口类型、形貌及形成机理,并对热轧H型钢疲劳断口进行了分析,为今后型钢产品疲劳研究奠定基础。     

不同应力上限和加载速率下的黄砂岩疲劳特性研究

为研究黄砂岩单轴疲劳加载的特性,开展了不同应力上限和加载速率下的单轴疲劳荷载试验。试验结果表明：黄砂岩的疲劳试验曲线受到单轴压缩应力—应变曲线的控制,疲劳极限变形与峰后对应变形一致;砂岩疲劳过程的不可逆变形和耗散能密度均具有三阶段演化规律,依据倒“S”型损伤模型,验证了黄砂岩疲劳损伤三阶段演化规律;分析认为三阶段规律的本质是砂岩的塑性变形和内部孔隙微裂纹生成以及扩展速度的不同所呈现的结果。研究表明应力上限和加载速率对疲劳寿命有显著影响,根据所得应力—寿命公式,可以估计砂岩在一定条件下的疲劳寿命。     

Fretting Fatigue Behavior of 304 Austenitic Stainless Steel Considering the Effect of Mean Stress and Tensile Overload

Effect of mean stress on fretting fatigue behavior of 304 austenitic stainless steel has been investigated by conducting fretting fatigue tests at a constant contact pressure of 100 MPa under three different mean stresses i.e., 0, 350 and 450 MPa. For comparisons, plain fatigue tests were also carried out. The influence of tensile overload on fretting fatigue life was also investigated. The results showed that with an increase in mean stress, the reduction in fatigue strength due to fretting increased drastically from 51% at 0 MPa mean stress to 71% at 450 MPa mean stress. The application of tensile overload during fretting fatigue had significant influence on the fretting fatigue lives when the tensile overload was above yield strength. The fretting variables, i.e., tangential stress and relative slip amplitude were measured during fretting fatigue tests. Fracture surfaces were examined using scanning electron microscope. The results have been discussed based on the tangential stress measurement, relative slip amplitude evaluation during fretting fatigue and fracture surface examinations.     

An experimental investigation of fretting fatigue in Ti-6Al-4V: the role of contact conditions and microstructure

A systematic investigation of the fretting fatigue behavior of the titanium alloy Ti-6Al-4V in both the mill-annealed (MA) and the solution-treated and overaged (STOA) conditions was carried out. A sphere-on-flat fretting fatigue device was used that facilitated real-time control and monitoring of all the relevant parameters such as the contact geometry, contact (normal and tangential) loads, and bulk alternating stress. While different sets of experiments were conducted to examine the influence of the bulk stress, the tangential load, and the normal load, respectively, on fretting fatigue response, the effect of microstructure on fretting fatigue was explored with experiments on the acicular, Widmanstätten, and martensitic microstructures as well. In experiments where the contact loads were maintained constant and the bulk stress was varied, fretting reduced the fatigue strength of Ti-6Al-4V. For this case, the “strength reduction factor” was higher for the experiments with higher tangential loads. For cases where the bulk stress and the normal or the tangential loads were maintained constant, lower fretting fatigue lives were obtained at larger tangential loads and at smaller normal loads. Of all the microstructures studied, preliminary results on the martensitic structure suggest an enhanced fretting fatigue resistance, compared to the basic STOA or the MA microstructure. Using the measured maximum static friction coefficient for Ti-6Al-4V, the experimentally observed contact and stickzone radii were found to exhibit good agreement with analytical predictions. Furthermore, conditions for crack initiation were determined through the application of the recently developed adhesion model for fretting fatigue. The model predictions of weak adhesion and crack initiation were validated with experimental observations of stick-slip behavior and fretting fatigue failures, respectively.     

Fretting fatigue behavior of surface modified biomedical titanium alloys

Fretting is a form of adhesive wear normally occurring at the contact points gradually leading to premature failure of load bearing medical implants made of titanium alloys. The aim of this work is to characterize the fretting fatigue damage features of PVD TiN coated, plasma nitrided, ion implanted, laser nitrided and thermally oxidized Ti-6Al-4V and Ti-6Al-7Nb contact pairs. The surface layers were characterized. The damage progression during fretting process is apparently explained with tangential force coefficient curves. Plasma nitrided pairs showed highest fretting fatigue life compared to others. PVD TiN coated pairs have experienced early failures due to third body mode of contact interaction with irregular tangential force coefficient pattern. Ion implanted layers showed similar damage as unmodified alloys. Laser nitrided and thermally oxidized pairs experienced early failures due to brittle and irregular modified layers.     

超音速等离子喷涂NiCr-Cr_3C_2涂层的组织结构与微动磨损性能

采用超音速等离子喷涂法在1045钢表面制备NiCr-Cr_3C_2涂层,分析涂层的微观结构及化学成分以及涂层的晶粒结构,利用MICROMET-6030显微硬度仪和Nano-test 600纳米压痕仪测定涂层的显微硬度与弹性模量,通过油润滑微动摩擦磨损试验测试涂层的微动磨损性能。结果表明,NiCr-Cr_3C_2涂层为明显的层状结构,具有单晶、纳米多晶与过渡区共存的复杂晶体学结构,显微硬度HV0.3高达998,约为基体材料硬度的3倍,弹性模量为224.6GPa;涂层的微动摩擦因数随载荷增大而减小,随温度升高而增大。喷涂层的抗微动摩擦磨损性能较基体优异,摩擦因数及体积磨损量分别比基体降低36.7%和55.6%。涂层的磨损机理以磨粒磨损和疲劳剥落为主。