中性腐蚀环境下钢丝的微动疲劳行为

在自制的微动疲劳试验机上开展中性腐蚀环境下单根钢丝的微动疲劳实验,考察在相同接触载荷下,不同振幅对钢丝的微动疲劳行为的影响,并用扫描电子显微镜观察疲劳钢丝的磨痕和断口形貌,研究钢丝微动疲劳断裂机制.结果表明:在较大的振幅下,钢丝的微动区均处于滑移状态,而在较小振幅下,钢丝的微动区从滑移状态逐渐转变为黏着状态;磨损机制主要为磨粒磨损、疲劳磨损、腐蚀磨损和塑性变形;钢丝疲劳寿命随着微动振幅的增大而减小;钢丝的疲劳断口可分为3个区域,即疲劳源区、裂纹扩展区及瞬间断裂区.     

Fretting wear behaviors of steel wires under friction-increasing grease conditions

Fretting wear tests were performed on the self-made fretting wear rig to investigate fretting wear behaviors of steel wires under friction-increasing grease conditions. The results demonstrated that the fretting regimes were dependent on displacement amplitudes and normal loads. The friction coefficient exhibited different variation trends in different fretting regimes. Friction-increasing grease changed the fretting running behavior and had a very good wear resistance for steel wires. Wear was slight in partial slip regime. Mixed regime was characterized by plastic deformation, fatigue cracks and abrasive wear. Slip regime presented main damage mechanisms of abrasive wear, fatigue wear and oxidation.     

Experimental Study of the Fretting Wear Behavior of Incoloy 800 Alloy at High Temperature

The fretting wear behavior of the nuclear power material Incoloy 800 was investigated in this study. A PLINT high-temperature fretting tester was used on an Incoloy 800 cylinder against a 304SS cylinder at vertical cross contact under different temperatures (25, 300, and 400°C). During testing, a normal load of 80 N was applied, and the displacement amplitudes ranged from 2 to 40 µm. The fretting wear mechanism at high temperatures and the kinetic character of the materials of the Incoloy 800 steam generator tube were analyzed. Results showed that the fretting running regimes varied little with ncreasing temperature, and some microcracks were observed in both the mixed fretting regime (MFR) and the partial slip regime (PSR) at high temperatures. Slight abrasive wear and microcracks were the main wear mechanisms of the Incoloy 800 alloy in PSR, whereas those in the MFR and the gross slip regime were oxidative wear, abrasive wear, and delamination.     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

Friction behavior of quenched and tempered steel in partial and gross slip conditions in fretting point contact

Tangential traction caused by friction in contacting surfaces is a major factor in fretting fatigue that increases stress levels and leads to a reduction in fatigue life. Friction in fretting contact was studied in partial, mixed and gross slip conditions on quenched and tempered steel. Measurements were made with sphere-on-plane contact geometry for polished and ground surfaces. Friction was evaluated from on-line energy ratio and, after the tests, from wear marks. A maximum friction coefficient of over 1.0 was measured at mixed slip zone with polished surfaces, whereas ground surfaces promote lower values in similar operating conditions. The friction coefficient dependence on load cycles and loading frequency is also presented and briefly discussed. The friction data and understanding thus gained is to be used for evaluation of crack initiation with the numerical fretting fatigue model.     

带有微动磨损缺口钢丝的疲劳特性

在自制的微动磨损试验机上进行钢丝的微动磨损试验,将微动磨损后的钢丝试样在液压伺服疲劳试验机上进行不同应力比和不同应力幅下的疲劳试验。结果表明,钢丝的微动磨损深度随微动时间和接触载荷的增加而增加,磨损缺口处的应力集中使其成为了裂纹萌生源,也使钢丝试样的疲劳寿命大大降低,微动磨损后钢丝试样的疲劳寿命和磨损深度呈反比关系。通过钢丝疲劳断口的SEM形貌分析了其疲劳断裂机制,断口对应不同的疲劳阶段,可分为裂纹萌生区、裂纹扩展区和裂纹瞬断区。     

Fretting wear behaviors of a railway axle steel

Fretting damage was one of the most important reasons for the failure of the railway axle. Fretting wear (tangential fretting mode) tests of a railway axle steel (LZ50 steel) flats against 52 100 steel balls were carried out under different normal loads and displacement amplitudes on a hydraulic fretting wear rig. Dynamic analyses in combination with microscopic examinations have been performed. The experimental results showed that the fretting regimes of the LZ50 steel were strongly dependent upon the imposed normal loads and displacement amplitudes. The F_t/F_n curves exhibited different variation trends in different fretting running regimes. The fretting scars presented slight damage in partial slip regime. In mixed fretting regime, the trace of the plowing and plastic deformation flow can be observed on the fretting scars. The wear mechanism during this regime was the combination of the abrasive wear, oxidative wear and delamination accompanied with obvious plastic deformation. The detachment of particles and plowing traces were the main phenomena in slip regime. And, thicker debris layer covered the contact zone of the scar. The severe degradation in slip regime presented the main wear mechanisms of abrasive wear, oxidative wear and delamination.     

On the mechanisms of various fretting wear modes

According to relative motion directions for a ball-on-flat contact, there are four fundamental fretting wear modes, e.g., tangential, radial, torsional and rotational modes. In this paper, the mechanisms of these four fundamental fretting wear modes, particularly for the later three modes, have been reviewed from results obtained by the authors in combination with results from literature. Some general features have been reported. Differences both in running and degradation behavior have been discussed in detail. Results showed that some similar laws for three fretting regimes (partial slip regime, mixed regime and slip regime), fretting maps (running condition fretting map and material response fretting map), wear and cracking mechanisms obtained from the classic mode (i.e. tangential fretting) were also identified and useful to characterize the other modes. Nevertheless, the occurrence of relative slip for the radial fretting, the formation of mixed regime for the torsional fretting, the evolution of surface morphology for the rotational fretting were quite different compared to that of the classical fretting mode.     

690合金材料的微动磨损特性研究

利用微动磨损试验机,在载荷50N以及位移幅值为60μm、100μm、150μm的工况下,研究了690合金材料在常温下的微动磨损行为及其动力学特性,采用激光共焦扫描显微镜(LCSM)和扫描电子显微镜(SEM)观察磨痕微观形貌。结果表明,载荷和位移幅值对微动特征有很大的影响,微动运行完全处于滑移状态。在滑移区,滑移磨损严重、磨痕面积大。690合金材料的磨损机制主要表现为磨粒磨损与剥层的共同作用。     

Research on torsional fretting wear behaviors and damage mechanisms of stranded-wire helical spring

Wear on the local area of steel wires’ surface is attributed to torsional fretting on the working process of stranded-wire helical spring. A mathematical model to calculate normal contact force and angular displacement amplitude among the wires is established first when the spring is impacted. With the experimental parameters obtained from the model, the torsional fretting test, which stimulates torsional fretting among the wires in the working process of the spring, is realized successfully on a newly developed fretting tester. Torsional fretting behaviors are strongly dependent upon normal contact force, angular displacement amplitude, and number of cycles. There are three basic types of T-θ curves (short for torque), angular displacement curves during the process of torsional fretting, namely, parallelogram, elliptic, and linear T-θ curves. To analyze the damage mechanisms, distribution maps of oxygen in the wear scar of spring wires under different working conditions are revealed. The damage gets slight in the partial slip region, mainly with the abrasive wear and the slight oxidative wear, whereas the wear mechanisms are mainly the abrasive wear, the oxidative wear, and the delamination, accompanied with obvious plastic deformation in the mixed fretting and slip regions.

     

Torsional Fretting Wear Behavior of Bonded MoS2 Solid Lubricant Coatings

The effects of applying a bonded MoS₂ solid lubricant to a 1050 steel substrate were investigated using a torsional fretting wear apparatus. Tests were conducted under a normal load of 50 N with angular displacement amplitudes ranging from 0.1 to 5°. Wear scars were examined using scanning electron microscopy, energy-dispersive X-ray spectrometry, optical microscopy, and surface profilometry. The MoS₂ coating exhibited different torsional fretting regimes than those of the substrate. Fretting regimes of the coating were primarily in the partial slip regime (PSR) and the slip regime (SR) with no mixed fretting regime. The width of the PSR narrowed. Due to the lubricating effects of the coating, the friction torque was consistently lower than that of the substrate. The damage to the coating in the PSR was very slight, and its granular structure remained even after 1,000 cycles. The damage mechanism to the SR coating was a combination of abrasive wear, oxidative wear, and delamination. The MoS₂ coating had potential to alleviate torsional fretting wear.     

Investigation into effects and interaction of various fretting fatigue variables under slip-controlled mode

Fretting fatigue behavior of unpeened and shot-peened Ti–6Al–4 V was investigated using a dual-actuator test setup which was capable of applying an independent pad displacement while maintaining a constant cyclic load on the specimen. The fretting regime was identified based on the shape of the hysteresis loop of tangential force versus relative slip range and the evolution of normalized tangential force. The fretting regime changed from stick to partial slip and then to gross slip with increasing relative slip range, and the transition from partial to gross slip occurred at a relative slip range of 50–60 μm regardless of the applied cyclic load, surface treatment, contact load and contact geometry. The fretting fatigue life initially decreased as the relative slip range increased and reached a minimum value, and then increased with increase of the relative slip range due to the transition in fretting regime from partial slip to gross slip. Shot-peened specimens had longer fatigue life than unpeened specimens at a given relative slip range, but the minimum fatigue life was found to be at the same value of relative slip range for both shot-peened and unpeened specimens. Tangential force was directly related to relative slip and this relationship was independent of other fretting variables.     

基于双重扩展自适应卡尔曼滤波的汽车状态和参数估计

准确实时地获取行驶过程中的状态信息是汽车动态控制系统研究的关键,为此提出了一种新的汽车状态估计器。建立了包含不准确模型参数和未知时变统计特性噪声的非线性汽车动力学模型,针对该非线性系统提出一种双重扩展自适应卡尔曼滤波算法（DEAKF）。该算法采用两个卡尔曼滤波器并行运算,状态估计和参数估计互相更新,同时将带遗忘因子的噪声统计估值器嵌入到状态校正过程和参数校正过程之间,以解决系统的噪声时变问题。基于ADAMS的虚拟试验和实车试验结果表明,该算法的状态估计精度高于EKF方法和DEKF方法的状态估计精度,同时具有良好的模型参数校正能力,对汽车动态控制系统中估计器的设计具有理论指导意义。
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Effect of Cold Rolling on the Fretting Wear Behavior and Mechanism in Inconel 600 Alloy

The fretting test was carried out using an SRV IV fretting test rig in order to investigate the fretting wear behavior and mechanism in Inconel 600 alloy at room temperature. The materials were rolled to different reductions before the test. The effect of cold rolling on the friction coefficient and wear volume was subsequently investigated. The surface and cross-sectional morphologies of the wear scar were studied by scanning electron microscopy (SEM), laser scanning confocal microscopy (LSCM), and electron back-scattering diffraction (EBSD). The results indicated that the cold rolling had a different effect on wear behavior in different slip regimes. In the stick regime, cold rolling strongly decreased the wear volume, although it did not affect the friction coefficient. The 25% rolled specimen had the minimum wear volume. The mechanisms of as-received and 50% rolled specimens were delamination and oxidation wear, whereas for the 25% rolled specimen, cracking was the main wear mechanism. In the gross slip regime, cold rolling had little effect on the friction coefficient or wear volume. The fretting wear process gave rise to a decrease in the Σ3 grain boundary, an increase in local misorientation, and a change in the crystal orientation.     

Third body effects on friction and wear during fretting of steel contacts

Fretting wear proceeds through particle detachment from the contacting surfaces which, while trapped in the contact zone, can affect the frictional and wear response. Ball-on-flat fretting experiments were carried out between steel specimens under gross slip regime. A transition in the coefficient of friction was linked to a critical contact pressure. The microstructure and chemical composition of the third body evolve with the applied pressure. The evolution of the friction coefficient is strongly dependent on the third body properties. The wear is controlled by the applied load and thus the real contact area within the wear track.     

Fretting Wear Behavior of Cu–Al Coating on Ti-6Al-4V Substrate under Dry and Wet (Lubricated) Contact Condition

The fretting wear behavior of Cu–Al coating was investigated with and without fatigue load under the dry and wet (lubricated) contact conditions. The Cu–Al coating was plasma deposited on titanium alloy, Ti-6Al-4V. Fretting regime was determined from the shape of fretting hysteresis loop. Fretting regime changed from partial slip to total (gross) slip at ∼15 μm of the applied relative displacement, and this transition point was independent of fatigue loading and contact surface (lubricated versus dry) conditions. Wet contact condition reduced frictional force during cycling, as evidenced by the lower-tangential force. Wear analysis using the accumulated dissipated energy approach did not show any effect of contact surface condition. In other words, the relationship between the accumulated dissipated energy and wear volume showed a linear relationship, and it was independent of loading and contact surface conditions, as well as of the fretting regime. Further, the relationship between the wear depth and accumulated dissipated energy did not show any effect of loading and contact surface conditions, as well as of the fretting regime up to instant when the maximum wear depth was equal to the coating thickness. The views expressed in this article are those of the authors and do not reflect the official policy or position of the United State Air Force, Department of Defense, or the U.S. Government.     

桨-毂轴承材料扭动微动磨损行为研究

采用面接触扭动微动形式,以动力定位系统可调距螺旋桨桨-毂轴承摩擦副材料(CuNiAl-42CrMo4)为对象,以不同的角位移幅值模拟海水波动影响下的微动磨损行为,并结合扫描电子显微镜和超景深三维显微镜对磨痕形貌进行分析,探究桨-毂轴承摩擦副材料扭动微动磨损规律。结果表明,随着角位移幅值的增加,扭动微动依次运行于部分滑移区、混合区、滑移区,摩擦因数减小,同时磨损量增加,微动损伤中剥层机制所占的比例逐渐增加,且由于疲劳裂纹扩展的不利影响,实际运行过程中要尽量避开混合区。     

Fretting behavior of shot peened Ti-6Al-4V under slip controlled mode

Fretting tests of shot peened Ti-6Al-4V were conducted under slip controlled mode using a dual actuator test setup which could apply an independent pad displacement at a given applied bulk stress. Fretting regime was identified based on the hysteresis loop of tangential force versus relative slip range and the evolution of tangential force. Fretting regime changed from partial slip to mixed slip and then to gross slip with increasing relative slip range, and the transition from mixed to gross slip occurred at a relative slip range of ∼50 μm regardless of the applied bulk stress magnitude for both shot peened and unpeened specimens. Fretting fatigue life initially decreased as the relative slip range increased and reached to a minimum value, and then increased with an increase of the relative slip range due to the transition in fretting regime from mixed slip to gross slip. Shot peened specimens had longer fatigue life than unpeened specimens at a given relative slip range, but the minimum fatigue life was at the same value of the relative slip range for both shot peened and unpeened specimens. The relationship between relative slip and fatigue life was also found to be independent of the applied bulk stress level. Further, tangential force was directly related to relative slip and this relationship was independent of other fretting variables.     

Fretting fatigue of zinc coated low carbon steel EN H320 M

The object of the present study was to investigate the influence of zinc coatings on steel sheets during fretting fatigue and fatigue tests. The influence of the fatigue stress range, normal pressure and amplitude of slip, on the fracture life was studied for both coated and uncoated EN H320 M steel. The wear produced by fretting was measured and compared with the fracture life evolution for different values of slip amplitude. The wear scars and the fracture surfaces were examined by scanning electron microscopy to identify the degradation mechanism. Although zinc films do not influence the fatigue life of the tested steel, when fretting is superposed on to a fatigue stress the coating markedly improves the fracture life.