This paper investigates the impact of surface texturing design on the tribological performance of aviation spur gears. A thermal elastohydrodynamic lubrication (TEHL) model is established to optimize the geometric parameters of the micro-dimple patterns, which are subsequently fabricated on the gear surfaces via laser etching technology. The thermal mitigation, vibration damping, and wear resistance of the enhanced gear pairs are systematically evaluated on an FZG standard test rig across a wide range of rotational speeds, torques, and lubrication regimes. The experimental results demonstrate substantial performance upgrades: under flooded lubrication, the textured pinion configuration can achieve significantly temperature and vibration reduction up to 30.0% and 22.8%, respectively; under starvation lubrication, the texturing advantage shifts to the gear, which substantially promotes temperature reduction up to 43.2% and 28.0% reduction in wear rate, compared to the untextured baseline. Mechanistic analysis reveals that under flooded lubrication, the textured pinion is more effective in suppressing pitting and scuffing due to enhanced micro-hydrodynamic effects and convective heat dissipation. Conversely, under starved lubrication, the textured gear markedly alleviates abrasive and adhesive wear by acting as oil reservoirs for secondary lubrication and trapping wear debris. This study underscores the efficacy of TEHL-guided surface texturing in optimizing the dynamic and tribological behavior of gear transmissions, offering crucial design guidelines for next-generation aviation gearboxes.

PurposeThis paper aims to experimentally investigate the effect of surface texture on the stick-slip behavior of the guideway of machine tools, and to find significant pattern and optimal parameters to suppress the stick-slip.Design/methodology/approachA method using the root mean square (RMS) of force acceleration are introduced to evaluate the stick-slip with groove and dimple patterns, as well as different surface roughness and contact modes.FindingsSmooth surfaces are more prone to stick-slip phenomena. Circular dimples show better anti-stick-slip performance compared to groove textures, while the area density of dimple textures is the key parameter.Practical implicationsUnder low-speed conditions, the guideway of machine tools may exhibit a stick-slip phenomenon, which compromises the stability of micro-feeding, positioning and processing accuracy and may even reduce the service life of cutting tools and guideways.Originality/value RMS of force acceleration is suggested for quantitative assessment of stick-slip. The design frame of dimple pattern to suppress stick-slip is proposed.

In this work, a line-contact reciprocating friction test apparatus was designed to measure the coefficient of friction (CoF) under sliding-rolling condition. This apparatus employed dual motors to independently control the cylinder’s rotational motion and the reciprocating motion of the specimen, allowing an adjustable slide-to-roll ratio (SRR). To achieve cross-validation of the CoF, the measurement system combines a torque sensor and a load cell to measure friction torque and force, respectively. The reliability of the apparatus was verified through repeated experiments under lubricated conditions. This device provides an effective experimental approach for evaluating the CoF under rolling-sliding line-contact conditions.

Ferrofluid (FF) droplets can be manipulated without direct mechanical contact, but reproducible deformation on conventional hydrophobic or superhydrophobic substrates is often limited by contact-line pinning and nanoparticle contamination. Here, we investigate magnetic-field-induced deformation and presplitting of FF droplets on a nonmagnetic slippery liquid-infused porous surface (SLIPS). The effects of magnet geometry, droplet volume, particle mass fraction, and droplet-magnet distance were examined using side-view imaging and image-based profile analysis. As the magnet approached the SLIPS, the apparent contact angle and base width decreased, whereas the droplet height increased, followed by strongly nonlinear deformation near the presplitting stage. Droplet morphology depended on both magnetic field intensity and field gradient. Among the tested parameters, FF particle mass fraction had the strongest influence on deformation mode, while droplet volume mainly caused proportional geometric scaling. Larger magnets generated stronger fields and steeper gradients, extending the effective actuation range and increasing the splitting distance. Finally, symbolic-regression models were developed to predict normalized droplet height and width, achieving R2 values of 0.94 and 0.89, respectively. The resulting empirical correlations describe presplitting FF droplet deformation on SLIPS within the tested parameter range.

In this work, a bio-inspired surface texture was developed to regulate lubricant migration and interfacial lubrication. Reciprocating friction tests in horizontal and vertical orientations were conducted to examine how thermal gradients and gravity influence the lubrication behavior of textured surfaces. Results demonstrated that surface texturing can effectively reduce friction and control lubricant loss under different directional forces. In simulated point-to-plane contact of the rotating pair tests under low-speed, light-load rotation, the textures enhanced resistance to centrifugal effects and improved lubrication stability. These findings confirm the potential of biomimetic surface designs for improving point-to-plane lubrication in complex operating conditions, with promising applications in aerospace bearings and precision motion systems.

Abstract This study investigated the fretting wear behavior of Ti-6Al-4V ball-on-flat laser-textured surfaces using a self-designed experiment platform. Dimple textures with area ratios of 10%, 30%, and 50% were tested under dry and lubricated conditions, 4 N and 20 N loads, and displacement amplitudes ranging from 25 µm to 200 µm. It was observed that under dry friction, textures did not alter the sliding regime. The energy wear-rate increased monotonically with the area ratio under a load of 4 N, but it demonstrated an initially increasing and then decreasing trend under a load of 20 N due to the increased contact stress and restricted debris evacuation. Under oil lubrication, the synergistic effect of lubrication and surface texture modified the sliding regime, expanded the effective friction-reduction range, and shortened the running-in time. This synergy was load-dependent: low-area-ratio surfaces excelled under the low load, while high-area-ratio surfaces performed better under the high load due to the superior oil storage and load-bearing. Furthermore, lubrication complicated the wear mechanisms, with the energy wear-rate governed by the coupling of load and displacement amplitude.

ABSTRACT In this work, a specially designed test fixture was used to investigate the effect of dimple surface texturing on the fretting fatigue performance of a Ti6Al4V dovetail joint. The novel geometry of the fretting pair offered simultaneous investigation under cylinder‐on‐flat and flat‐on‐flat contact configurations. Tests were conducted using a servo‐hydraulic fatigue machine under an axial cyclic load of 11 kN, a stress ratio of 0.05, and a frequency of 10 Hz. The dimple surface textures having densities of 19.6%, 12.6%, and 8.7% were fabricated using laser surface texturing. Microscopic investigations were conducted using an optical microscope, a scanning electron microscope, and a three‐dimensional wear microscope. An enhanced fretting fatigue life was observed at the highest texture density of 19.6%, causing a delay in the crack initiation and reducing the crack growth. SEM revealed a large amount of wear debris, oxidation, spalling, and debris at the higher texture densities.

In this study, a flat-on-flat contact configuration was designed to study the effects of temperature, frequency, load, and displacement on the fretting wear performance of self-mated Ti-6Al-4V pairs, based on orthogonal experiments. The results show that the energy friction coefficient decreased with increasing temperature, displacement, and frequency, but increased with higher load. The wear rate decreased with rising temperature, frequency, and load, but increased with greater displacement. Significance analysis identified frequency and temperature as the dominant factors affecting both friction and wear. At high temperatures, the formation of a protective ‘third-body’ layer through oxidative wear helped suppress wear. Additionally, the debris distribution at high frequencies created a ‘micro-roller’ effect, which contributed to a lower friction coefficient.

In this study, the friction behaviour of GCr15/45 steel line-contact friction pairs with four different surface textures was experimentally investigated under time-varying sliding-to-rolling ratio (SRR) conditions. Machine-learning models were applied to predict the coefficient of friction (CoF) and its fluctuation characteristics, while CFD simulations were used to interpret the lubrication mechanism. Unlike previous studies, which mainly focused on steady sliding or fixed SRR conditions, this work considered dynamic rolling-sliding contact with continuously varying SRR. The results showed that while all textured surfaces reduced the CoF and suppressed friction fluctuations, the elliptical texture (codenamed VET) with the major axis perpendicular to the motion direction exhibited the best performance. CFD analysis of the VET surface revealed that enhanced rolling contribution reduced the hydrodynamic friction coefficient. Two regression algorithms, namely eXtreme Gradient Boosting (XGBoost) and k-nearest neighbours (KNN) achieved the best prediction performance for the CoF and its standard deviation, with R² values of 0.95 and 0.93, respectively. Shapley additive explanation (SHAP) analysis revealed that low SRR mainly contributed to CoF reduction, whereas high SRR dominated friction-fluctuation suppression. This study provides an experimental and interpretable machine-learning approach, supported by CFD analysis, for predicting and understanding textured-surface friction under dynamic rolling-sliding contact.

Focusing on the need for stable and reliable face gear transmissions, this study develops a high-order topology modification strategy to precisely control meshing behavior. Guided by contact path optimization, four modification functions including fourth-order, fourth-order segmented, second-order, and double-crowned are established along the contact path and instantaneous contact line. Comprehensive tooth contact analysis (TCA) and loaded TCA simulations reveal that the method effectively controls the contact path and shapes the transmission error curve. The fourth-order segmented modification proves particularly robust, significantly improving contact distribution and eliminating edge contact. Consequently, this approach effectively increases transmission stability and contact pattern percentage while reducing deviation. This research provides a practical framework for designing high-performance face gear pairs, especially for critical applications such as helicopter transmissions.

The quasi-static shear mechanical behavior and damage mechanisms of high-silica woven fiber-reinforced phenolic interfaces after thermal-oxidative aging and fatigue were investigated through shear tests in conjunction with digital image correlation (DIC) and scanning electron microscopy (SEM). The residual shear strength of interface progressively decreases with increasing fatigue amplitude, cycles, and duration of thermal-oxidative aging. Up to 20,000 cycles, the residual strengths under fatigue loadings , , , and decreased by 8.9%, 12.9%, 21.3%, and 30.3%, respectively. At fatigue amplitude , thermo-oxidative aging for 36, 76, and 103 days caused reductions of 30.4%, 34.6%, and 38.4% relative to the unaged specimens. DIC and SEM reveal that interfacial shear damage initiates at defects along the biphasic interface, progresses through microcrack propagation with concurrent penetration into the interlaminar region, and ultimately results in crack coalescence and macroscopic delamination-induced instability failure. Under fatigue-dominated loading, damage is characterized by fiber fracture and interlaminar debonding, whereas thermo-oxidative aging suppresses fiber tearing but markedly exacerbates interlaminar debonding. Based on the equivalence principle of residual strength under fatigue loading-cycling-aging, a predictive model for residual shear strength was developed to account for the effects of thermal-oxidative aging and fatigue. Experimental validation showed that the model achieved an average relative error of approximately 10%, demonstrating good agreement with the measured data.

To explore the influence of surface textures, laser-processed grooved textures with varying area ratios were applied to TC4 (Ti-6Al-4V) alloy. Fretting wear tests were conducted using a plane-on-plane contact configuration under dry and grease-lubricated conditions. The results demonstrated that the grooved textures help store wear debris and reduce the energy friction coefficient. However, higher texture area ratios lead to increased contact stress and higher wear rates. Groove orientation also presents significant influence: the grooves in parallel to the direction of motion promoted debris removal, while the perpendicular grooves entrapped more debris. Under grease lubrication, the perpendicular grooves helped to squeeze the stored lubricant into the contact area and reduced the running-in period.

Ferrofluid (FF) droplets can be manipulated without direct mechanical contact, but reproducible deformation on conventional hydrophobic or superhydrophobic substrates is often limited by contact-line pinning and nanoparticle contamination. Here, we investigate magnetic-field-induced deformation and presplitting of FF droplets on a nonmagnetic slippery liquid-infused porous surface (SLIPS). The effects of magnet geometry, droplet volume, particle mass fraction, and droplet-magnet distance were examined using side-view imaging and image-based profile analysis. As the magnet approached the SLIPS, the apparent contact angle and base width decreased, whereas the droplet height increased, followed by strongly nonlinear deformation near the presplitting stage. Droplet morphology depended on both magnetic field intensity and field gradient. Among the tested parameters, FF particle mass fraction had the strongest influence on deformation mode, while droplet volume mainly caused proportional geometric scaling. Larger magnets generated stronger fields and steeper gradients, extending the effective actuation range and increasing the splitting distance. Finally, symbolic-regression models were developed to predict normalized droplet height and width, achieving R 2 values of 0.94 and 0.89, respectively. The resulting empirical correlations describe presplitting FF droplet deformation on SLIPS within the tested parameter range.

Tooth profile deviation is one of the main factors causing vibration and noise in transmission systems. In order to explore the influence of the randomness of tooth profile deviation on the dynamic characteristics of spur gears, this paper conducted a study on the nonlinear dynamics of spur gear pairs based on random tooth profile deviation. Firstly, based on the consideration of the characteristics of tooth profile deviation, combined with the tolerance constraint characteristics of gear tooth profile, the variation characteristics of random tooth profile deviation under a certain tolerance were analyzed. Secondly, based on the TCA (tooth contact analysis) method, the solution method for the meshing error of spur gears was studied, and the influence of random tooth profile on meshing error was explored. Finally, based on the previous meshing error solution method, a nonlinear dynamic model of spur gear considering multi tooth meshing state was constructed, and the influence of the randomness of tooth profile deviation within a certain tolerance constraint range on the dynamic characteristics of spur gear transmission system under different working conditions was analyzed. The results indicate that the research method proposed in this article can be used to analyze the effects of different tooth profile deviations and their randomness on the meshing of gear teeth, providing a reference for predicting the impact of tooth profile tolerances at different accuracy levels and designing gear accuracy.

The composite structure of fiber shell and skirt of solid rocket motor will bear multiple tensile loads throughout its service life. In view of this problem, the composite structure of fiber shell and skirt of solid rocket motor is taken as the sample. According to the relevant test standards and the actual loading conditions of solid rocket motor, the tension-tension fatigue test scheme is developed. The static tensile tests are carried out on the fatigued samples to obtain residual failure load after each fatigue condition; The CT scan tests are carried out on the fatigued samples to obtain the porosity of the adhesive layer. The porosity of the adhesive layer is used to characterize the damage of the sample during the fatigue, and the relationship between the residual failure load of the sample and the porosity of the adhesive layer is constructed. It is found that the residual failure load decreases with the increase of load level and cycles. A processing method of load level-cycles equivalence principle is proposed referring to the time-temperature equivalence principle. A load level-cycles equivalence model has been established. The proposed model is verified, and the mean error is less than 5%, which shows that the proposed model is valid and feasible.

Porous copper with adjustable structures was successfully prepared from a low-cost H62 Cu-Zn alloy using onestep chemical/electrochemical dealloying method. The effects of dealloying conditions on the porous microstructure and dealloying mechanism were investigated. The results show that during chemical dealloying, the dealloying mechanism remains constant, involving only atomic diffusion and dissolution. This leads to a consistent bicontinuous porous structure across all chemical dealloying conditions. In contrast, applying additional potentials not only accelerates the atomic diffusion and dissolution, but also shifts the dealloying mechanism from asynchronous corrosion to galvanic corrosion, and forms various porous structures. Notably, hierarchical porous Cu is only fabricated by precisely controlling the dealloying potential at intermediate levels around 0.2 V. The finally dealloying morphology arises from the competition between diffusion and dissolution, and similar porous morphologies are achieved by keeping Ds at comparable levels. The nano-hardness and elasticity modulus of all dealloyed H62 alloys are reduced depending on their structure. However, the prepared bimodal porous Cu exhibits a higher nano-hardness of 0.28 +/- 0.04 GPa compared to most reported porous metals, which is beneficial for its service performance and lifespan.

Magnetic fluids (MFs) are a kind of magnetically manipulated colloid, which may serve as an active lubricant. These fluids can be retained at the desired locations, by the application of an appropriately designed external magnetic field. In this research work, initially, centrifugal experiments were conducted to estimate the antispreading behavior of the MFs, in the presence of an external magnetic field. Later, the starvation behavior of a thrust ball bearing was investigated after lubricating it with an MF, under different magnetic field distributions and operating temperatures. The preliminary results presented that the application of an external magnetic field can maintain more residual MFs in the raceway at higher rotational speeds. Tribological tests showed that proper magnetic field distribution on the raceway may effectively inhibit the lubricant loss and prolong operation before the starvation of the bearing. In addition, an increased operating temperature of the bearing accelerated the occurrence of a starved state of lubrication.

Creep or thermocapillary migration is one of the major causes of lubricant loss mechanisms, leading to the failure of tribo-pairs. In this work, we have proposed the application of ferrofluids (FFs) to control lubricant creep and starvation. A specially designed test setup was used to observe the FF's creep behavior driven by temperature gradient. Tribological tests (having ball-on-flat contact configuration) were conducted to evaluate the effect of FF's creep on the starvation by considering the factors of temperature gradient, initial creep time and volume. Further experiments focused on the effect of magnetic field on anti-creep and lubrication behaviors of the FFs. Results showed that the creep distance increased with the increase in temperature gradient and volume. However, it reduced with the increment in magnetic field intensity and no creep was observed at the highest value of 90 kA/m. Tribological tests showed that the temperature gradient and volume both dominate the lubrication performance and starvation occurred at the highest temperature gradient or lowest volume. With the increase in magnetic field intensity, the FF was positioned in the frictional contact region, thus low and stable friction was achieved. Most importantly, with the application of magnetic field, the escaped FF was drawn back to replenish lubrication. Such replenishment mechanism, which conventional lubricant is restricted, is helpful to control the lubricant and prevent starvation.

In this study, we explored the evolution of mechanical properties in hydroxyl-terminated polybutadiene (HTPB) propellants under fatigue loading by performing fatigue tests with varying maximum stresses and cycle numbers, followed by uniaxial tensile tests on post-fatigue specimens. Residual elongation was used as a key parameter to characterize mechanical behavior, while scanning electron microscopy (SEM) provided insights into the mesostructural morphological changes that occur under different loading conditions, revealing the mechanisms responsible for variations in mechanical properties. The results show that, as the number of loading cycles increases, residual elongation decreases, with three distinct phases of decline-slow change, gradual decline, and rapid deterioration-depending on the stress levels. SEM analysis identified damage mechanisms such as "dewetting" and particle fragmentation at the mesostructural level, which compromise the material's structural integrity, leading to reduced residual elongation. A novel aspect of this study is the application of Williams-Landel-Ferry (WLF) theory to construct a master curve describing residual elongation decay. This approach enabled the development of a generalized model to predict the material's degradation under fatigue loading, with experimental validation of the fitted evolution model, offering a new and effective method for assessing the long-term performance of HTPB propellants.

Slippery liquid-infused porous surfaces have broad applications due to their excellent properties, but their performance under high-temperature conditions typical in industry remains underexplored. In this study, textured and slippery surfaces were fabricated via ultraviolet laser processing and chemical modification. The impact behaviors of water, mixture, and emulsion droplets on smooth, textured, and slippery surfaces were examined from 130 to 230 degrees C. Evaporation experiments revealed notably lower static Leidenfrost points for droplets on slippery surfaces-180, 180, and 190 degrees C for water, mixture, and emulsion, respectively-demonstrating the thermal stability of the slippery surface. Impact mode maps summarized droplet behaviors, and dynamic Leidenfrost points were identified, with water droplets showing values of 160, 160, 190, 130, and 130 degrees C across five surfaces at impact velocity V = 0.9 m/s. Changes in spreading factor and schematics elucidated that co-evaporation of lubricant and water stabilizes the vapor layer and enhances droplet bouncing. Numerical simulations revealed shorter solid-liquid contact times and clarified mechanisms of explosive bounce due to vapor flow variations among surface structures. Thermal resistance and heat transfer models for different surfaces were innovatively developed. These findings fill gaps in prior research lacking thermal considerations and offer theoretical insights for applications in surface self-cleaning, droplet manipulation, and thermal management.