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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Frequency effects in fretting wear

The effect of frequency of vibration on fretting wear has been investigated in the 10 – 1000 Hz range with additional experiments at 20 000 Hz. Fretting tests were performed with two materials, a low carbon steel (AISI 1018) and an austenitic stainless steel (AISI 304). The experiments showed that two cases of fretting contact can be distinguished and related to the displacement amplitude. If the amplitude is low, the contact situation is characterized by partial stick at the interface. At these conditions the wear rate (measured as the volume of material removed per cycle) is little affected by frequency. However, in low amplitude fretting material damage by surface degradation and fatigue crack initiation is usually of more concern than the actual wear itself. Both of these parameters are found to be greatly accelerated by an increase in frequency. In high amplitude fretting, in contrast, gross slip occurs at the interface and wear becomes the dominant damage mode. At these conditions variations in frequency appear to have little effect on fretting wear and related mechanisms. Therefore, in the case of fretting at high displacement amplitudes, it may be possible to apply high frequency fretting to obtain accelerated testing conditions.     

Fretting wear mechanisms of Zircaloy-4 and Inconel 600 contact in air

The fretting wear behavior of the contact between Zircaloy-4 tube and Inconel 600, which are used as the fuel rod cladding and grid, respectively, in PWR nuclear power plants was investigated in air. In this study, number of cycles, slip amplitude and normal load were selected as the main factors of fretting wear. The results indicated that wear increased with load, slip amplitude and number of cycles but was affected mainly by the slip amplitude. SEM micrographs revealed the characteristics of fretting wear features on the surface of the specimens such as stick, partial slip and gross slip which depended on the slip amplitude. It was found that fretting wear was caused by the crack generation along the stick-slip boundaries due to the accumulation of plastic flow at small slip amplitudes and by abrasive wear in the entire contact area at high slip amplitudes.     

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.

     

The effect of number of cycles on the critical transition boundary between fretting fatigue and fretting wear

The object of the present study was to investigate the influence of number of cycles on the critical amplitudes of tangential force and displacement, identifying the transition from a mixed stick-slip regime (fretting fatigue) to a gross slip regime (fretting wear) over a wide range of test conditions. Fretting experiments were conducted on three metal specimen combinations: copper/copper; stainless steel/stainless steel; copper/stainless steel. All experiments took place in air, at ambient temperature, using a crossed-cylinder geometry. Normal loads of 3.4 and 11.4 N were applied with frequencies ranging from 10 to 800 Hz. In most cases, n = 1.2×10⁴ and n = 6×10⁶ were adopted as the representative lower and higher number of cycles, respectively. At different numbers of cycles, critical amplitudes of tangential force and displacement were measured. The scars fretted under separately selected conditions were examined by scanning electron microscopy.

It was found that the critical amplitudes of both tangential force and displacement dropped with increasing number of cycles for all test combinations, but there was an upper limit above which the drop of critical transition values no longer occurred with further increases in the number of cycles. The micromorphology of fretting scars (in a mixed stick-slip regime) revealed that the stick zone has shrunk after a larger number of cycles under the conditions of constant amplitude of tangential force and displacement, and that the damage mechanisms vary for different combinations, although they are all characterized by a central stick zone surrounded by a slip annulus. It was suggested that the decrease of critical amplitudes after a larger number of cycles results from the shrinkage of the stick area, which may be a complex process related to plastic deformation, strain hardening, and the change of stress distribution on the contact surfaces.     

Contact conditions in fretting

The influence of displacement amplitude, normal load and frequency of oscillation on the contact conditions in fretting have been explored by analysis of dynamic tangential force measurements. The fretting characteristics of two materials, a low carbon steel (AISI 1018) and an austenitic stainless steel (AISI 304), were investigated using a crossed-cylinder testing geometry. It was found that three regimes of fretting can be distinguished with increasing displacement amplitude. The two low amplitude regimes are characterized by a condition of partial stick at the interface, the difference between the two regimes being as to whether the bulk displacement in the stick region is accommodated by predominantly elastic or plastic shear. In contrast, in the third, high amplitude, regime gross slip takes place over the whole contact area. In this paper the physical significance of the critical amplitudes that define the two fretting regime transitions is discussed. In particular, results on the relationships between the two critical amplitudes and the applied normal load and frequency of oscillation are given.     

The delamination theory of wear

A new theory for wear of metals is considered. The theory is based on the behavior of dislocations at the surface, sub-surface crack and void formation, and subsequent joining of cracks by shear deformation of the surface. The proposed theory predicts qualitatively that the wear particle shape is likely to be thin flake-like sheets and that the surface layer can undergo large plastic deformation. It also predicts a number of experimentally observed phenomena such as the difference in wear particle sizes and the dependence of fretting wear rate on displacement amplitude. All theoretical predictions are supported by experimental evidences. A wear equation is developed based on the proposed theory.     

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.     

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.     

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.     

Behavior of alloy Ti–6Al–4V under pre-fretting and subsequent fatigue conditions

The mechanical behavior and microstructural changes in Ti–6Al–4V were determined in fretting tests, followed by axial fatigue tests. Prior to fatigue testing, specimens were subjected to fretting conditions over a range of contact stresses and fretting displacements. Fretting frequency was 100 Hz. High cycle fatigue (HCF) tests were run at 1000 Hz. The fretting test involved a flat-on-flat, bare Ti–6Al–4V/bare Ti–6Al–4V fretting system. The fretting process typically generated very shallow surface cracks at the ends of the wear scar. Subsequently, these shallow cracks were observed to propagate in axial fatigue tests, reducing the fatigue life significantly. Evidence of frictional heating during fretting was observed in the formation of scale-like oxide in the wear scar. Formation of oxides appeared to increase with increasing contact stress. Increased oxygen content was detected in the near surface regions of specimens. Large near surface deformation was typically observed within the wear scar. The contact geometry and slight tilting of the stationary fretting pad influenced the character of the fretting scar and the fretting-induced cracking. Fracture surfaces exhibited featureless, battered surfaces at the crack origins followed by (a) cleavage-type crack propagation, (b) formation of fatigue striations, and (c) final ductile tearing.     

AZ91D镁合金微动磨损特性研究

采用液压高精度材料试验机考察了平面一球面接触的AZ91D镁合金摩擦副的微动磨损行为，分析了位移幅值、法向载荷和频率等参数对摩擦因数和磨损体积的影响，考察了不同实验条件下的磨斑形貌，并探讨了其磨损机理。结果表明：AZ91D镁合金的微动区域可分为部分滑移区、混合区和滑移区3个区域，粘着磨损、疲劳磨损和磨粒磨损分别是3个区域的主要磨损机制；磨损体积随着位移幅值和法向载荷的增加而增大，但却随着频率的增大而减小。在微动部分滑移区和混合区，摩擦因数随着位移增大迅速增加；在微动滑移区，摩擦因数随法向载荷的增大而减小，而位移幅值和频率对摩擦因数的影响较小。     

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.     

Development of a test device for the evaluation of fretting in point contact

Fretting wear and fatigue may occur between any two contacting surfaces, wherever short‐amplitude reciprocating sliding is present for a large number of cycles. A test device has been developed for the evaluation of fretting fatigue and wear in partial and gross slip conditions. Three similar sphere‐on‐plane contacts run at the same time. Normal force, tangential force or displacement amplitude and constant bulk stress can be controlled and measured separately. Reciprocating tangential displacement is produced with rotational motion, the amplitude and frequency of which can be adjusted and controlled accurately by an electric shaker. The number of load cycles for crack initiation and growth is determined with strain‐gauge measurements near the fretting point of contact. The contact surfaces are measured with 3D optical profilometer before fretting measurements to determine actual contact geometry. The measurements were done with quenched and tempered steel. The initial results indicate that cracks are mostly formed in partial slip conditions, whereas fretting wear is more heavily involved in gross slip conditions. The initiation of a crack occurs near the edge of the contact in the slip direction, where the calculated cracking risk has its maximum value in partial slip conditions. The number of cracks increases as the displacement amplitude, i.e. friction force, increases in partial slip conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

Study on rotational fretting wear of 7075 aluminum alloy

Rotational fretting wear tests in a ball-on-flat configuration have been successfully realized on a special rotational fretting rig developed from an ultra-low-speed reciprocating rotational driver. The rotational fretting behavior of 7075 aluminum alloy against 52 100 steel was studied under different angular displacement amplitudes and normal loads. The results showed that both F_t?θ and F_t/F_n curves can be used to characterize the rotational fretting running behavior, which exhibited different curve shapes and variation trends in different fretting running regimes. The rotational fretting behavior of 7075 aluminum alloy was strongly dependent on the angular displacement amplitude, normal load and number of cycles. The wear of 7075 aluminum alloy was characterized by slight attrition in the partial slip regime, while a combination of delamination, abrasive and oxidative wear was found in the slip and mixed fretting regimes. The formation of a central bulge probably due to plastic flow was observed under gross slip condition of the rotational fretting mode.     

Fretting Wear Behavior of Laser Peened Ti-6Al-4V

This work deals with the influence of laser peening on the fretting wear behavior of Ti-6Al-4V. Laser peening was carried out on Ti-6Al-4V. The laser-peened surface was characterized by transmission electron microscopy. Surface roughness, nanoindentation hardness, residual stress, and tensile properties of the material in both laser-peened and unpeened conditions were determined. Fretting wear tests were conducted at different normal loads using a ball-on-flat contact geometry. Laser peening resulted in the formation of nanocrystallites on the surface and near-surface regions, increased hardness, and compressive residual stress. Laser peening did not affect the tensile properties and surface roughness significantly. There was no considerable difference between the values of the tangential force coefficient of laser-peened and unpeened samples. The fretting scar size, wear volume, and wear rate of laser-peened specimens were lower than those of unpeened samples. This may be attributed to an increase in surface hardness due to strain hardening and grain refinement at the surface and near-surface regions, higher compressive residual stress, and higher resistance to plastic deformation of laser-peened samples.     

恒定动能作用下薄壁管的冲击微动磨损行为研究

在新型冲击微动磨损试验机上对四种常见材料的薄壁管(不锈钢、铜合金、纯钛和铝合金)进行了冲击磨损试验,考察了材料属性、冲击能量对薄壁管损伤行为的影响。对其冲击动力学行为、磨损行为进行了分析。研究结果表明,不同材料金属管的能量吸收率、冲击接触力和冲击管变形有显著差异;同一种材料,随着初始冲击动能的增大,冲击过程中接触力、冲击管变形和冲击吸收能也在增大。通过分析磨痕微观形貌和磨痕轮廓,发现薄壁管的冲击磨损抵抗性能与材料属性密切相关;随着初始冲击动能的增加,材料损伤加剧,其损伤机制为疲劳磨损。     

Investigation on the Fretting Wear Behavior and Mechanisms of Alloy 690TT during the Transformation from Mixed Regime to Partial Slip Regime Induced by Elevated Temperature

Fretting wear of Alloy 690TT can occur in the steam generator of a nuclear power plant, in which the interfacial conditions are changed as the temperature varies. In this study, the gradual transformation from the mixed fretting regime (MFR) to the partial slip regime (PSR) occurred with an increase in test temperature. Correspondingly, there was a competition in wear modes due to the formation of a nanostructured tribologically transformed structure (TTS), presence of delamination cracking, nucleation of fatigue cracks, and oxidation. Delamination within the TTS dominated first. As the area of TTS and the plastic deformation region was reduced, fatigue cracks began to initiate. Oxidation was accelerated by an increase in the test temperature, and that effect resulted in reduced wear volume of Alloy 690TT in the MFR.     

Evaluation of fretting wear based on the frictional work and cyclic saturation concepts

It is time consuming or even impossible to simulate the whole process of fretting wear, since it always involves millions of cyclic loadings. This paper focuses on the modeling and evaluation method of fretting wear for the typical bridge type fretting test with a flat pad. The frictional work on the contact interface is chosen as the parameter to evaluate the fretting wear. To verify the fretting wear model, the predicted wear profile is compared with that obtained by the experimental results. Fretting wear always includes plastic deformations due to the edge stress singularity. The effect of cumulative plastic deformation is also taken into account in the wear model. The role of the coefficient of friction at the contact interface on the fretting wear has also been discussed.     

Fretting wear of Ti-48Al-2Cr-2Nb

An investigation was conducted to examine the wear behavior of gamma titanium aluminide (Ti-48Al-2Cr-2Nb in atomic percent) in contact with a typical nickel-base superalloy under repeated microscopic vibratory motion in air at temperatures from 296–823 K. The surface damage observed on the interacting surfaces of both Ti-48Al-2Cr-2Nb and superalloy consisted of fracture pits, oxides, metallic debris, scratches, craters, plastic deformation, and cracks. The Ti-48Al-2Cr-2Nb transferred to the superalloy at all fretting conditions and caused scuffing or galling. The increasing rate of oxidation at elevated temperatures led to a drop in Ti-48Al-2Cr-2Nb wear at 473 K. Mild oxidative wear was observed at 473 K. However, fretting wear increased as the temperature was increased from 473–823 K. At 723 and 823 K, oxide disruption generated cracks, loose wear debris, and pits on the Ti-48Al-2Cr-2Nb wear surface. Ti-48Al-2Cr-2Nb wear generally decreased with increasing fretting frequency. Both increasing slip amplitude and increasing load tended to produce more metallic wear debris, causing severe abrasive wear in the contacting metals.