Zhongrong Zhou

Macroscale liquid superlubricity has profound significance for energy conservation and emission reduction. However, it suffers from low tolerance to high roughness, which seriously hinders the application in engineering friction systems. Although conventional understanding holds that wear debris accumulations increase friction and wear, the anti‐wear metal oxides (e.g., Fe ₂ O ₃ and Cr ₂ O ₃ ) in the debris from steel friction pairs are expected to form a protective oxidation film and reduce surface roughness. Here, a strategy using the synergetic effects of wear debris‐converted tribofilm and hydroxylated carbon nanotubes (CNTs) to promote the low‐wear superlubricity on high‐roughness steel surfaces ( R _a ≈ 57 nm) is reported. The wear rate (4.41 × 10 ⁻⁸ mm ³ Nm ⁻¹ ) is reduced by 64% while achieving a low coefficient of friction (COF ≈ 0.005). The debris is manipulated to convert into a protective oxidation film and reduce surface roughness via surface design. Then, the increase in metal hydroxides generated by tribochemical reactions allows the formation of a strengthened hydrogen bond network and the stronger adsorption of the CNTs, reducing friction and wear. This work, which turns wear debris into a “treasure”, can offer a new insight into the role of wear debris in promoting low‐wear superlubricity for highly rough engineering steel.

History of tribology researches in China is reviewed briefly in this paper. Development stages are divided and some memorable events in tribology researches in China are introduced in my personal view. The statistics of the funding from National Natural Science Foundation of China (NSFC) and of published research papers on tribology in the database of Web of Science are analyzed in order to better understand the state-of-the-art of tribology researches in China, including most active research institutions and fields. In addition, major research contents are obtained according to keywords and main achievements in tribology related to lubrication, lubricating materials, superlubricity, wear, biotribology and bionictribology, nanotribology, surface engineering, tribology in extreme conditions, and machine elements, particularly for recent years, are summarized. This paper shows that tribology is a rapid developing discipline in China has been one of the most important contributors in world tribology.

The braking system of high-speed trains is directly related to the operation safety of the train. The brake pads, which play a crucial role, will inevitably undergo uneven wear in long-term use, posing safety hazards to train braking. As the trains are in normal operating condition for long periods, it is difficult to collect usable uneven wear data, and there is a situation of data imbalance. This paper proposes a trade-off contrastive learning network (TCLN), utilizing the differences between data and balancing the weights of different classes, which can realize the condition monitoring under the data imbalance of brake pads. First, data augmentation is employed to provide sufficient and diverse data for contrastive learning, and nonlinear features are extracted by a quadratic convolutional neural network. Then, the designed class-weighted method is utilized to improve the characterization ability of the minority class data and realize the equidistant representation of features for each class, which in turn achieves the purpose of paying equal attention to all classes. Finally, the effectiveness of the proposed method is verified using the dataset collected from the scaling experiments, and the results show that the proposed method has higher accuracy and efficiency compared to other methods, which can still accurately identify the brake pad condition when the data are highly imbalanced.

Accurately evaluating particle surface micro-texture levels and distribution at different wavelength scales of granular material is critical to optimise service stability of granular material under long-term dynamic loads. Firstly, generalised regression neural network (GRNN) and empirical mode decomposition (EMD) were adopted to impute missing data points and remove the arc-shaped tendency of granular materials’ particle wear raw surface profile. Then, granular materials’ particle surface micro-texture levels and their distribution within constant bandwidth narrow band spectrum and octave/fractional octave band spectrum were obtained with spectral analysis method, which could characterise granular materials’ particle surface properties at different wavelength scales. Fourteen types of parent rocks of granular materials were tested with a modified micro tribological experiment simulating tribological behaviour among particle contact interfaces under dynamic loads. A contrastive analysis with traditionally used surface mean roughness was performed. The results indicate that the micro-texture levels and their distribution obtained in this study can detect the level of the exact texture scales (i.e. 32 and 2 μm wavelengths) significantly influencing the kinetic friction coefficient of granular materials, while surface mean roughness can only represent the global surface property. A high correlation was found between normalised micro-texture level (i.e. 32 μm) and Moh's hardness and coefficient of friction.

In this in vitro study, the restoration of acid-eroded enamel surface morphology and anti-wear properties under two conditions, mono-remineralization (treated with remineralization alone) and impact-remineralization (treated with cyclic impact followed by remineralization), are characterized to determine the effect of occlusal loading on enamel remineralization. Compared with the mono-remineralized surface, the impact-remineralized surface demonstrates better anti-wear performance, as manifested by a higher hardness and elastic modulus, as well as a lower friction coefficient and wear volume. Loading on the eroded enamel surface induces the fragmentation of hydroxyapatite nanoparticles, which aids crystal deposition and fusion during subsequent remineralization. In summary, owing to the enamel microstructure, occlusal loading can promote the restoration of enamel anti-wear properties by enhancing remineralization. Remineralization enhancement through occlusal-loading-induced nanoparticle fragmentation plays a significant role in preventing human teeth from excessive wear.

Commercial bisphenol A‐glycol methacrylate (BisGMA)/triethyleneglycol‐dimethacrylate (TEGDMA) have been widely used as dental restorative material; however, the poor mechanical and anti‐wear properties greatly limited their applied range. In this study, iron‐containing hydroxyapatite (FeHA) nanoparticles that mimic the chemical composition and microstructure of natural bamboo rat incisor enamel were synthesized and used as reinforcement in BisGMA/TEGDMA resins. The as‐prepared polycrystalline FeHA have a rod like morphology with uniformly dispersed iron. The effects of nanoparticle–resin weight ratios on the mechanical properties, tribological properties, and bioactivity of FeHA‐BisGMA/TEGDMA resins were investigated. In vitro bioactivity of the studied resin composites in artificial saliva showed that a dense and continuous apatite layer was formed on the surface of the resin composite. Findings revealed that doping a suitable content of FeHA nanoparticle, especially at 0.75 wt% FeHA, would significantly improve the tribological and mechanical properties as well as bioactivity of the dental resin composites.

The purpose of this study is to achieve better understanding of associated mechanisms and to recommend and identify new strategies to develop new rock breaking technology for Tunnel Boring Machines (TBMs). Tunnel Boring Machine tunnelling mainly depends upon the rock breakage caused by cutters moving on a rock surface in a rolling and sliding motion while under the action of thrust force. The rock breaking behaviour is controlled by the mechanical interaction between the cutters and the rock. Due to the high hardness and high abrasiveness of rock, the cutters have to work under very high thrust force and suffer heavy‐load‐impact and abrasive wear, causing serious wear and low rock breaking efficiency. Rock‐boring organisms exist in nature, which achieve drilling and/or tunnelling in rocks through a tribochemical interaction. This phenomenon is called bioerosion and the organisms are natural ‘TBMs’ to some degree. In this study, the interaction between TBM cutters and rock is presented, and current measures to improve cutter wear and rock breaking efficiency and their limitations are reported. Then, the connotation, mechanism and typical cases of bioerosion are presented. Finally, inspired by bioerosion, a new chemically assisted rock breaking technology is proposed for TBMs.