This present study aimed to clarify the effect of contact scale and surface topography of substrates with different roughnesses on the actual contact area, tangential stiffness, and tangential deformation of the substrate at micro- and macro-scales via finite element method (FEM) simulations, as well as the final tribological performances of MoS₂ coatings by experiments. The MoS₂ coatings were deposited on stainless steel (SS) substrates with different roughnesses, and the settings in the simulation models were based on the roughness of the SS substrates. The predicted tribological behavior of the simulation results was confirmed by the morphological and compositional analysis of the wear track using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), 3D profilometer, and Raman spectroscopy. The results showed that the substrate with a surface roughness of Ra 600 nm (R600), coated by MoS₂ nanosheets, exhibited excellent tribological properties at both micro- and macro-scales. At the micro-scale, the lubrication lifetime of R600 was as long as 930 cycles, while the substrates with surface roughnesses of Ra 60 nm (R60) and Ra 6 nm (R6) had a lubrication lifetime of 290 cycles and 47 cycles, respectively. At the macro-scale, the lifetime of the substrate R600 was 9509 cycles, which was nearly six times longer than the 1616 cycles of substrate R60. For the rough surface of substrate, the surface grooves could not only effectively preserve the lubricant but also continuously release them, ensuring that the lubricants with low shear strength were always present in the contact interface. It was further verified that the high surface roughness of the substrate reduced friction and wear by reducing the actual contact area and enhancing the tangential stiffness of asperities, thereby prolonging the lubrication lifetime. The wear mechanisms were discussed in terms of the morphology and chemical composition of the wear tracks.

Polymer self-lubricating composites are key in reducing energy consumption from friction, boasting self-lubrication, remarkable wear, and corrosion resistance. This study delves into the unexpected synergy between micro-aramid and nano-Al ₂ O ₃ in enhancing PTFE’s wear resistance. The results exhibit that the optimal hybrid of 15 vol.% micro-aramid and 1 vol.% nano-Al ₂ O ₃ particles enhanced the PTFE composites has carried out the best tribological properties, showing synergistic anti-friction and anti-wear effects and obtaining the very low wear rate of 8.73 × 10 ⁻⁷ mm ³ /Nm, which is decreased by 53% and 98.7% in comparison with separate enhancement of the PTFE composites with 15 vol.% micro-aramid and 1 vol.% nano-Al ₂ O ₃ , respectively. In-depth characterization and analysis of the friction interface are confirmed that PTFE generating carboxylic acid groups during the friction process chelated with the dual steel surface, micro-aramid producing the interaction of the strong polarity with the dual steel, and mechanical stress and high flash temperature promoting friction sintering of nano-Al ₂ O ₃ to enhance bearing capacity are cooperatively endowed a robustness protective tribofilm with easy shearing and high bearing properties, which effectively enhances the tribological properties of PTFE composites, providing a reference for the research and design of new nano composites with ultra-low wear and self-lubricating properties.

The current sorting process for winter jujubes relies heavily on manual labor, lacks uniform sorting standards, and is inefficient. Furthermore, existing devices have simple structures and can only be sorted based on size. This paper introduces a method for detecting surface defects on winter jujubes using convolutional neural networks (CNNs). According to the current situation in the winter jujube industry in Zhanhua District, Binzhou City, Shandong Province, China, we collected winter jujubes with different surface qualities in Zhanhua District; produced a winter jujube dataset containing 2000 winter jujube images; improved it based on the traditional AlexNet model; selected a total of four classical convolutional neural networks, AlexNet, VGG-16, Inception-V3, and ResNet-34, to conduct different learning rate comparison training experiments; and then took the accuracy rate, loss value, and F1-score of the validation set as evaluation indexes while analyzing and discussing the training results of each model. The experimental results show that the improved AlexNet model had the highest accuracy in the binary classification case, with an accuracy of 98% on the validation set; the accuracy of the Inception V3 model reached 97%. In the detailed classification case, the accuracy of the Inception V3 model was 95%. Different models have different performances and different hardware requirements, and different models can be used to build the system according to different needs. This study can provide a theoretical basis and technical reference for researching and developing winter jujube detection devices.

Lightweight materials with a density less than 3 g/cm³ as potential tribo-materials for tribological applications (e.g., space tribology) are always desired. Al₃BC₃ ceramic, a kind of ternary material, is one of the lightweight materials. In this study, dense Al₃BC₃ ceramic is prepared via a reactive hot-pressing process in a vacuum furnace. Its tribological properties are investigated in two unlubricated conditions (one is at elevated temperature up to 700 °C in air, and another is in a vacuum chamber of back pressures from 10⁵ Pa to 10⁻² Pa at room temperature) and lubricated conditions (i.e., water and ethanol as low-viscosity fluids). At 400 °C and lower temperatures in air, as well as in vacuum, the tribological property of Al₃BC₃ ceramic is poor due to the fracture of grains and formation of a mechanically mixed layer. The beneficial influence of adsorbed gas species on reducing friction is very limited. Due to the formation of lubricious tribo-oxide at 600 °C and 700 °C, the friction coefficient is reduced from ca. 0.9 at room temperature and 400 °C to ca. 0.4. In the presence of low-viscosity fluids, a high friction coefficient and wear but a polished surface are observed in water, while a low friction coefficient and wear occur in ethanol. A lubricious carbide-derived carbon (CDC) coating on top of Al₃BC₃ ceramic through high-temperature chlorination can be fabricated and the wear resistance of CDC can be improved by adjusting the chlorination parameters. The above results suggest that Al₃BC₃ ceramic is a potential lubricating material for some tribological applications.