Lubricants

High-speed train brake pads are safety-critical consumable components whose wear condition affects braking safety, maintenance scheduling, and component life utilization. This study assesses the predictive potential and limitations of sparse life-cycle maintenance records for brake-pad wear-rate estimation when continuous degradation trajectories are unavailable. A dataset of 54 valid brake-pad life-cycle records was constructed, including replacement date, accumulated mileage, wear per 10,000 km, installation position, motor/trailer classification, and train identifier. Linear regression, ridge regression, random forest, Gaussian process regression, and quantile regression were evaluated under leave-one-out cross-validation. Random forest produced the numerically best aggregate LOOCV point-prediction metrics, with a mean absolute error of 0.0823 mm/10,000 km, a root mean square error of 0.1030 mm/10,000 km, and an R² of 0.6008; relative to the global-mean baseline, MAE and RMSE were reduced by 39.0% and 36.8%, respectively. The P10–P90 quantile interval achieved an empirical coverage of 62.96% and an average width of 0.2165 mm/10,000 km, with 11 observations exceeding the P90 upper bound, indicating undercoverage in the upper tail. Feature-importance analysis showed pronounced temporal stratification. Removing replacement year/month reduced random forest LOOCV R² from 0.6008 to 0.2440, whereas leave-one-train-ID-out grouped validation yielded R² = 0.5687; expanding-window chronological validation was materially weaker (R² = −0.0590 for the full retrospective feature set). These results indicate that the temporal descriptors capture dataset-specific temporal structure and may partly act as statistical proxies for unrecorded time-varying conditions; they should not be interpreted as physical determinants, and prospective temporal transferability remains unverified. As a secondary application of the prediction outputs, the point prediction and upper conditional quantile were linked with current pad thickness, the allowable thickness limit, and planned operating mileage, to illustrate a preliminary maintenance-screening interface. This interface is intended as a preliminary maintenance-screening procedure rather than a validated replacement policy. The results show that sparse maintenance records contain record-level predictive information for brake-pad wear-rate estimation, while temporal dependence, upper-tail undercoverage, and the absence of field decision-outcome validation currently limit direct operational use.

To address the inferior lubricity of synthetic cutting fluids compared with oil-based cutting fluids, a strategy is proposed to improve the cutting performance by exploiting the electroosmotic effect to enhance penetrability at the friction interfaces in the cutting zone. The triboelectrification potential and tribo-emission of charged particles were measured at the accessible major flank face–workpiece interface to characterize the electrical behavior of an alumina ceramic–AISI 52100 steel friction pair. Taking the rake face–chip interface as a representative case, the distribution characteristics of the tribo-induced electric field (TIEF) and the electroosmotic flow field of the cutting fluid within an interfacial capillary were analyzed using COMSOL Multiphysics 5.5 simulations, based on the measured electrical boundary conditions and zeta potentials. Turning tests on AISI 52100 steel with alumina ceramic tools were also conducted under the lubrication of cutting fluids with distinct electroosmotic properties. The simulations indicate that the TIEF can drive electroosmotic flow toward the interior of the interface. The experiments show that the electroosmotic performance of the cutting fluid is positively correlated with its cutting performance. The simulated TIEF intensity increases with increasing cutting speed and depth, and the electroosmotic regulation of cutting performance is correspondingly enhanced.

Three two-dimensional Tp-based covalent organic frameworks, namely TpPa-1, TpPa-2, and TpBD, were synthesized and incorporated into Shell Helix H6 lubricating oil (SO) to investigate their potential as lubricant additives in commercial lubricating oils. Tribological tests demonstrated that all three Tp-based frameworks enhanced lubrication performance, with TpPa-1 exhibiting the best overall performance. Under a 5 N load, the coefficient of friction (μ) and wear rate decreased by 35.5% (to 0.091) and 55.9% (to 4.1 × 10⁻⁶ mm³/(N·m)), respectively. Under a 10 N load, μ and wear rate decreased by 38.3% (to 0.095) and 60.9% (to 4.8 × 10⁻⁶ mm³/(N·m)), respectively. The lubrication mechanism was attributed to interlayer sliding of the Tp-based framework nanosheets and the formation of a protective tribofilm containing iron oxides and deposited Tp-based frameworks, which filled wear pits and reduced wear volume.