The contact behaviors of rough surfaces are critical in tribology, yet predicting their load-area relationship across the entire contact regime remains challenging. This article presents a novel semi-analytical model for line contact between unidirectional rough surfaces and rigid planes under the plane-strain condition. Finite element simulations are performed for both elastic and elastic-perfectly plastic rough solids to capture the load-area relationship up to complete contact. The results reveal a gradual deviation from linearity at higher loads due to asperity interactions. To account for this nonlinear behavior, a general unified load-area formulation covering the full contact regime is established by integrating the simulation results with the theoretical line contact model at light loads. The accuracy of this advanced model is validated through direct finite element simulations on typical rough surfaces.
Laser powder bed fusion (LPBF) enables the fabrication of Ti-6Al-4V components with complex geometries for biomedical and aerospace applications; however, the as-built surfaces often require additional postprocessing to meet wear and corrosion performance requirements. In this study, an in situ nitrogen-assisted laser surface remelting step is integrated into the LPBF workflow to enhance near-surface performance without external coatings or secondary treatments. The effect of this process intervention on surface integrity and functional response is systematically evaluated. Electron backscatter diffraction (EBSD) reveals pronounced grain refinement and texture modification within the remelted surface layer, while Fourier transform infrared (FTIR) spectroscopy is employed solely as a qualitative tool to indicate nitrogen-related surface bonding. As a result of the remelting process under a nitrogen environment, significant improvements in functional performance are achieved, with the wear volume reduced by 54% and the nanohardness increased by 18-22% compared to the as-built condition. Electrochemical measurements further indicate enhanced corrosion resistance, reflected by a 14% reduction in corrosion current density (Icorr). These results demonstrate that in situ laser remelting under a nitrogen atmosphere can serve as an effective manufacturing strategy for improving the surface durability of LPBF Ti-6Al-4V components.
A closed-form analytical expression for the critical speed of dry-contact interfaces is developed. The model explicitly incorporates the influence of sliding velocity on heat diffusion, providing a realistic representation of the underlying thermal behavior. It further accounts for Newtonian cooling of friction-generated heat at the interface, while incorporating the effects of surface waviness. In addition, the surface roughness characteristics of both contacting bodies are systematically integrated into the formulation. The influence of disk thickness is also considered to improve the model's physical realism. The proposed critical speed expression is validated against several previously reported experimental and numerical results, showing excellent agreement, with deviations of less than 10% in certain cases.
This study investigates the wear behavior of T6 heat-treated Al7068/(SiC + fly ash) metal matrix composites fabricated using the casting process. The dry sliding wear behavior of Al7068/(SiC + fly ash) composites in both solution-treated and T6 heat-treated states was investigated using a pin-on-disc tribometer. The influence of critical parameters, such as heat treatment condition, sliding distance, and sliding velocity, on wear-rate (WR) and coefficient of friction (CoF), was systematically examined. The worn surfaces under high-load conditions were further characterized through scanning electron microscopy. The analysis indicated that the dominant wear mechanisms included delamination, abrasive action, oxidative wear, and adhesive interactions. To predict tribological responses, various machine learning algorithms, including random forest (RF), gradient boosting (GB), support vector machine (SVR), and artificial neural network (ANN), were developed and evaluated. For WR prediction, SVR demonstrated the best performance, achieving the highest coefficient of determination (R-2) of 97.62% and the lowest root-mean-square error (RMSE) of 0.118901. It was closely followed by the ANN model, which attained an R-2 of 97.35% and an RMSE of 0.125644. GB and RF showed comparatively lower accuracy, indicating their limited effectiveness for this dataset. In the case of CoF prediction, SVR outperformed all other models with superior accuracy (R-2) of 94.95%, minimal error values, an RMSE of 0.009847, and a mean absolute error (MAE) of 0.008138, while ANN and GB also demonstrated competitive performance. The findings demonstrate that integrating heat treatment approaches with data-driven modeling provides an efficient way to predict and analyze the tribological behavior of Al7068/(SiC + fly ash) aluminum composites.
The effects of adding nano-size zirconium oxide (ZrO2) particles were investigated on the friction, wear, and flash temperature of carbon-fiber reinforced poly-ether-ether-ketone (PEEK)-matrix composites with solid-state lubricant polytetrafluorethylene (PTFE). A fabrication technique, using the hot pressing method, is developed to manufacture the composite with distinct nanoparticle dispersions of different volume fractions of ZrO2. The morphology and microstructure of the nanocomposite were characterized with differential scanning calorimetry and X-ray diffraction, and also with scanning electron microscopy and a high-resolution optical microscope. The nano-oxide addition on changes in glass transition, melting, and crystallinity of PEEK matrix with PTFE fillers and carbon fibers in the composite was thoroughly examined. Tribological tests of the composite were conducted using a pin-on-disk tribometer. The effect of nano-ZrO2 dispersion on friction, wear, and flash temperature of the composite sliding in different directions on principal material planes was investigated. The tribological properties of the nanocomposite were very sensitive to the addition of even a small amount of nano-size ZrO2, but the effect depended on sliding directions and planes due to processing-induced carbon fiber orientation. The maximum reductions in coefficient of friction (64%), specific wear-rate (82%), and flash temperature (49%) were obtained by adding up to 5% (by volume) nano-ZrO2 to the PEEK/PTFE blend matrix. The mechanisms and characteristics of reduction in friction, wear, and flash temperature were addressed. The critical and complex interaction between carbon fibers and ZrO2 nanoparticles during friction and wear was discussed.
