Abstract:The ester base oil of dioctyl adipate (DOA) was oxidized in an oven at 200 °C for 30 h, and variations in the physicochemical and tribological properties were studied. To investigate the thermal-oxidation mechanism, the thermal-oxidation products were analyzed by gas chromatography-mass spectrometry (GC−MS), and the thermal-oxidation process was simulated using visual reactive force field molecular dynamics (ReaxFF MD). The results indicated that the total acid number (TAN) increased significantly because of the presence of 14% carboxylic acids and low molecular weight monoesters. The tribological properties were improved by the formation of the strongly polar carboxylic acids. Additionally, the increase in kinematic viscosity was limited due to the formation of high molecular weight polymerization products and low molecular weight degradation products. Thermal-oxidative degradation and polymerization mechanisms were proposed by combining ReaxFF MD simulations and GC−MS results.
The shock waves and micro-jets generated during the process of bubble collapse leads to cavitation damage for the materials surface of the hydraulic machinery equipment parts, which need to be...
The laser surface texture process will inevitably produce the edge of material surface texture bulges. Currently, laser processing bulges are generally polished directly, but this method ignores its impact on the friction pairs. In this paper, the tribological properties of polished and unpolished textured surfaces were investigated under dry friction, oil lubrication, and seawater lubrication conditions using three shapes of texture (grooves, square pits, and round pits) prepared on the surface of 316L stainless steel. The results show that the polished surface of 316L stainless steel texture increases wears, and the friction mechanism is mainly adhesive wear, while the unpolished surface of the texture has less wear, and the friction mechanism is mainly abrasive wear. The method and principle of using machining bulges to improve the wear resistance of friction pairs are discussed to address the differences in the tribological performance of entire friction pairs due to the influence of machining bulges of different shapes of texture.
Determining the nature of microscopic mechanism of friction and wear by experimental method is a challenge. Molecular simulation technology is an effective method for exploring microscopic friction mechanisms of polymers.
In this study, nanographite (NG), as a lubricant additive, and polyimide (PI) were used to fabricate NG/PI composites via a hot compression molding process. The tribological properties of the NG/PI composites with different NG mass contents (0-10 wt%) were tested using a reciprocating ball-on-disc contact tribometer matched with a GCr15 rubbing pair. The thermal stability, surface hardness, and compression strength of the composites were discussed. The results revealed that a small quantity of nanofillers greatly reduced the friction coefficient and increased the wear resistance of the NG/PI composites. Despite a minor decrease in mechanical performance, the composite with 5 wt% of NG filler exhibited improved tribological properties; it showed a 55.63% reduction in the friction coefficient and a reduction of 97.39% in the wear rate compared with neat PI. Moreover, an increase in the glass transition temperature (T g ) of the NG/PI composites indicated the enhancement of their thermal stability and wear resistance. Scanning electron microscopy (SEM) analyses showed that the main wear mechanism of the composites was fatigue wear. These findings suggest that the 5 wt% NG/PI composite could be a significant contribution to the field of tribological engineering plastics.
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