Effect of Steel Surface Roughness and Expanded Graphite Condition on Sliding Layer Formation

The aim of the research was to evaluate the influence of the initial roughness of a steel pin cooperating with a graphite ring—dry and wet—on the mechanism of sliding layer formation. A ring–pin friction pair was used for the study, where the rings were made of expanded graphite, while the pins were made of acid-resistant steel. In the first case, the steel pin interacted with a dry graphite ring, and in the second case, the graphite rings were moist. To determine the effect of initial surface roughness, the pins were divided into three roughness groups. To determine changes in surface geometry due to material transfer, the Ra and Rz parameters were measured. This project investigated how the initial roughness value of the steel surface pin cooperating with expanded graphite influences the formation of the sliding layer. Increasing the initial roughness of the steel surface interacting with the graphite contributes to faster layer formation and reduced roughness. The state of the expanded graphite—dry and wet—influences the formation of the sliding layer of graphite—a wet graphite component causes a faster smoothing of the steel surface. The running time of the wear apparatus has an effect on the resulting layer. The highest roughness group is the most favorable from the viewpoint of sliding layer formation.     

Influence of Test Conditions on Sliding Wear Performance of High Velocity Air Fuel-Sprayed WC–CoCr Coatings

Sliding wear performance of thermal spray WC-based coatings has been widely studied. However, there is no systematic investigation on the influence of test conditions on wear behaviour of these coatings. In order to have a good understanding of the effect of test parameters on sliding wear test performance of HVAF-sprayed WC–CoCr coatings, ball-on-disc tests were conducted under varying test conditions, including different angular velocities, loads and sliding distances. Under normal load of 20 N and sliding distance of 5 km (used as ‘reference’ conditions), it was shown that, despite changes in angular velocity (from 1333 rpm up to 2400 rpm), specific wear rate values experienced no major variation. No major change was observed in specific wear rate values even upon increasing the load from 20 N to 40 N and sliding distance from 5 km to 10 km, and no significant change was noted in the prevailing wear mechanism, either. Results suggest that no dramatic changes in applicable wear regime occur over the window of test parameters investigated. Consequently, the findings of this study inspire confidence in utilizing test conditions within the above range to rank different WC-based coatings.     

Influence of Lateral Movement on Level Behavior of Adhesion Force Measured Repeatedly by an Atomic Force Microscope (AFM) Colloid Probe in Dry Conditions

An atomic force microscope (AFM) was operated to repeatedly measure the adhesion forces between a polystyrene colloid probe and a gold film, with and without lateral movement in dry conditions. Experimental results show that the adhesion force shows a level behavior without lateral movement and with a small scan distance: the data points are grouped into several levels, and the adhesion force jumps between different levels frequently. This was attributed to the fact that when the cantilever pulls off the sample, the contact area of the sample is not exactly the same between successive contacts and jumps randomly from one to another. Both lateral velocity and material wear have little influence on level behavior. However, with a medium scan distance, level behavior is observed only for some measurements, and adhesion forces are randomly distributed for the other measurements. With a large scan distance, adhesion forces are randomly distributed for all measurements. This was attributed to the fact that the cantilever pulls off the sample in many different contact areas on the scanning path for large distances. These results may help understand the influence of lateral movement and imply the contribution of asperities to adhesion force.     

Pin-on-Disc Modelling with Mesh Deformation Using Discrete Element Method

The pin-on-disc test is a standard sliding wear test used to analyse sliding properties, including wear contour and wear volume. In this study, long-term laboratory test performance is compared with a short-term numerical model. A discrete element method (DEM) approach combined with an Archard wear model and a deformable geometry technique is used. The effect of mesh size on wear results is evaluated, and a scaling factor is defined to relate the number of revolutions between the experiment and the numerical model. The simulation results indicate that the mesh size of the disc has a significant effect on the wear contour. The wear depth and wear width follow a normal distribution after experiencing a run-in phase, while the wear volume has a quadratic relation with the number of revolutions. For the studied material combination, the calibration of the wear coefficient shows that the wear volume of the pin-on-disc test accurately matches the simulation results for a minimum of eight revolutions with a wear coefficient lower than 2 × 10⁻¹¹ Pa⁻¹.     

Electrical Contact Performance of Cu Alloy under Vibration Condition and Acetal Glue Environment

In view of the serious sliding electrical contact performance caused by external vibration and environmental contaminant, a study on the tribological characteristic and contact resistance of Cu alloy was conducted using a self-developed micro-load reciprocating electric contact device. Various glue concentrations (0%, 10%, 30%, and 50%) were prepared with anhydrous ethanol and deposited on the surface of a pure copper block via the deposition method. An external vibration source was installed on the sliding module to achieve vertical vibration. The results indicate that the final contact resistance and coefficient of friction (COF) in direct metal contact are about 0.01 Ω and 0.3, respectively. At this time, the wear volume is 2 to 3 orders of magnitude higher than the condition with glue residual. As glue concentration is above 10%, residual glue on the surface of Cu alloy hinders efficient contact between friction pairs, resulting in higher contact resistance. Glue exhibits lubrication, anti-wear, and insulation properties. External vibration causes friction pairs to briefly separate, leading to a lower glue removal capacity than that under non-vibration conditions. The contact resistance with glue addition under vibration conditions is higher than that under non-vibration conditions at 3 × 10⁴ cycles. The dominant oxide product is CuO, which has a limited effect on contact resistance.     

Wear Mechanism Classification Using Artificial Intelligence

Understanding the acting wear mechanisms in many cases is key to predicting lifetime, developing models describing component behavior, or for the improvement of the performance of components under tribological loading. Conventionally scanning electron microscopy (SEM) and sometimes additional analytical techniques are performed in order to analyze wear appearances, i.e., grooves, pittings, surface films, and others. In addition, experience is required in order to draw the correct and relevant conclusions on the acting damage and wear mechanisms from the obtained analytical data. Until now, different types of wear mechanisms are classified by experts examining the damage patterns manually. In addition to this approach based on expert knowledge, the use of artificial intelligence (AI) represents a promising alternative. Here, no expert knowledge is required, instead, the classification is done by a purely data-driven model. In this contribution, artificial neural networks are used to classify the wear mechanisms based on SEM images. In order to obtain optimal performance of the artificial neural network, a hyperparameter optimization is performed in addition. The content of this contribution is the investigation of the feasibility of an AI-based model for the automated classification of wear mechanisms.     

Study on Lubrication Characteristics of Novel Forced Wave Generator of Harmonic Drive without Flexible Bearing

In contrast to the conventional forced wave generator which consists of cam and flexible bearing in harmonic drive, the novel forced wave generator retains cam but cancels flexible bearing. In this article, the lubrication characteristics of the novel forced wave generator in harmonic drive is studied. First, an elliptical sliding bearing (ESB) model of simplified structure between the novel forced wave generator and the flex spline is established. Further, the computational fluid dynamics (CFD) method is employed to study the effect of some factors on the lubrication characteristics of the ESB model including elliptical gap ratio, width, and rotational speed. According to the analysis, the elliptical gap ratio has a great impact and its optimal value is 3, which is used in the design of the novel forced wave generator. Last, the practical design of the novel forced wave generator in harmonic drive is given, which can provide a basis for design and optimization of a forced wave generator without flexible bearing of the harmonic drive.     

Experimental Investigations on Dry Sliding Wear Behavior of Kevlar and Natural Fiber-Reinforced Hybrid Composites through an RSM–GRA Hybrid Approach

The present work aimed to investigate the dry sliding wear behaviors of hybrid polymer matrix composites made up of Kevlar, bamboo, palm, and Aloe vera as reinforcement materials of varying stacking sequences, along with epoxy as the matrix material. Three combinations of composite laminates with different stacking sequences such as AB, BC, and CA were fabricated by a vacuum-assisted compression molding process. The influence of composite laminates fabricated through various stacking sequences and dry sliding wear test variables such as load, sliding distance, and sliding velocity on the specific wear rate and co-efficient of friction were investigated. Experiments were designed and statistical validation was performed through response surface methodology-based D-optimal design and analysis of variance. The optimization was performed using grey relational analysis (GRA) to identify the optimal parameters to enhance the wear resistance of hybrid polymer composites under dry sliding conditions. The optimal parameters, such as composite combinations of CA, a load of 5 N, a sliding velocity of 3 m/s, and a sliding distance of 1500 m, were obtained. Furthermore, the morphologies of worn-out surfaces were investigated using SEM analysis.     

种植体支抗关闭拔牙间隙磨牙位移趋势的有限元研究

目的 运用三维有限元方法分析种植体支抗滑动法关闭拔牙间隙时上颌第一磨牙的Von Mises等效应力及位移变化趋势.方法 建立三维有限元模型,模拟临床种植体支抗滑动法关闭拔牙间隙,分析牵引力为1.5N时,种植体距离弓丝不同高度(6、8、10、12 mm)与牵引钩距离弓丝不同高度(1、4、7、10 mm)时,上颌第一磨牙Von Mises等效应力及位移变化趋势.结果 当种植体高度大于或等于牵引钩高度时,上颌第一磨牙根分叉处应力值最大;小于牵引钩高度时,应力分布出现在颊侧颈部,且腭根的腭侧应力值变小.上颌第一磨牙位移趋势为:X轴,磨牙向远中旋转,且旋转角度随牵引钩高度的增加而变大;Y轴,磨牙向远中倾斜、旋转,且倾斜角度随牵引钩高度的增加而增大;Z轴,磨牙近中向验方倾斜移动,且倾斜位移随牵引钩高度增加而增加.结论 上颌第一磨牙的应力分布变化与种植体植入高度及牵引钩高度有关;其位移变化趋势为磨牙向远中倾斜和旋转,其倾斜的方向与种植体高度和牵引钩高度有关.     

考虑微观形貌时平面型推力滑动轴承润滑性能数值研究

选择平面型推力滑动轴承为研究对象,通过对粗糙表面的数值模拟,基于雷诺方程,构建了考虑微观形貌时的平面型推力滑动轴承润滑性能的计算模型。运用Matlab软件编程,针对一个具体的算例,采用数值计算研究了轴承工作时推力环旋转一周过程中最大油膜压力、承载能力、最小油膜厚度等参数的变化规律,发现其润滑性能与表面形貌有关;研究了转速、表面粗糙度等因素对推力滑动轴承润滑性能的影响规律,绘制了在保持全油膜润滑状态下速度和承载能力、摩擦力矩之间的关系曲线,并对这些曲线进行了分析。