As a typical rigid-flexible contact system, the water-lubricated rubber bearing-rotor system (WLRBRS) is prone to friction-induced vibrations under extreme operating conditions, which compromises the reliability and stealth performance of naval vessels. Traditional research methods are insufficient to deeply investigate the dynamic characteristics of contact interface, resulting in unclear mechanisms behind friction vibration. This study constructs a visualized friction interface, utilizing high-speed camera, vibration and force sensor, and employs digital image processing method to analyze the contact and dynamic characteristic of the WLRBRS. The research indicates that: Friction vibration originates from stick-slip at the contact interface. The occurrence of "Chatter" and "Squeal" is governed by whether the relative velocity of the friction pair is zero. The friction vibration of WLRBRS is essentially the coupling of bearing and rotor vibration.
This study employs a cartridge-type selector valve friction measurement experimental setup to investigate the frictional characteristics under three distinct conditions: pure water medium, different temperature conditions, and thermal particle coupling interactions. Comparative analysis reveals significant friction variation across conditions: the peak friction force measures merely 0.02 N in pure water, increases to 9.01 N under single thermal effects, and surges to 11.72 N under thermal particle coupling. When particles invade the clearance, partial retention occurs potentially causing valve spool sticking. Subsequent particle invasion simulations demonstrate that particles are typical flushed out in clustered formations, with retention rates inversely proportional to clearance flow velocity. These findings systematically analyze multifactorial influences on cartridge-type selector valve friction, providing fundamental data for mitigating valve sticking and optimizing structural design.
The application of ultra-high-strength steel (UHSS) enables effective automotive lightweighting, contributing to energy conservation and emissions reduction. However, the high forming forces associated with UHSS significantly intensify the complexity of friction behavior at the tool-workpiece interface during stamping operations. While conventional stamping friction models typically address isolated influencing factors, this study develops an integrated approach that simultaneously considers the effects of contact pressure, sliding velocity, temperature, and tool surface roughness-key parameters prevalent in industrial automotive stamping processes. By combining microscopic and macroscopic perspectives, a multifactor coupled friction model is established, offering a more comprehensive characterization than existing models. This model specifically investigates the effect of microscale surface morphology evolution on friction behavior. Statistical methods are employed to characterize the height distribution of both workpiece and tool surfaces, with surface microtopographical features captured using laser confocal microscopy. Contact regions on the tool surface were identified via MATLAB-based image processing, and asperities within these zones are geometrically modeled as elliptic paraboloids. Experimental friction data for carbide-free bainitic steel CFB1180 were analyzed under varying levels of SKD11 tool steel surface roughness and different temperatures to optimize the friction model, incorporating the combined effects of tool surface roughness and thermal conditions. More than 20 sets of orthogonal flat sliding friction tests were conducted to validate the effectiveness of the established multifactor stamping friction model under corresponding process parameters. The steady-state friction data were adopted for coefficient calculation, demonstrating a model prediction accuracy exceeding 90% compared with experimental measurements. Finally, the developed friction model was implemented via the VFRIC subroutine in ABAQUS finite-element software to simulate a U-shaped part bending-stretching process. Simulation results show close agreement with experimental measurements, with relative errors in springback angle predictions remaining below 10%. In industrial applications, the developed friction model is employed to presimulate sheet-forming operations under varying process conditions, predicting springback behavior and subsequently guiding process parameter adjustments for springback control.
This study investigates the onset of electrically induced damage in rolling element bearings (REBs). An electric discharge test rig (EDTR) was designed and developed to investigate the effects of load, speed, lubricant, and electrical power on bearing damage. In the EDTR, one race of a thrust ball bearing is used to control the motion of the balls, while the counter raceway was replaced by a polished bearing steel flat. This configuration allows for examination of the flat specimen for the extent and nature of damage, as well as re-polishing and subsequent use. The test bearings were comprised of a single steel ball and five ceramic balls to control the flow of electrical current. Key parameters, including lubricant film thickness, supply power, and applied thrust load, were systematically varied to evaluate their influence on the damage. The effect of electrical power was also investigated by applying both direct current (DC) and alternating current (AC). Surface profilometry was conducted along the running track to measure the damage morphology, followed by a statistical analysis of the pits created due to electric discharge. Surface analysis revealed two characteristic forms of electrically induced bearing damage (EIBD): discrete surface pitting along the running track and an indented surface profile in the central contact region, resulting from thermal softening and localized plastic deformation. The results show that electrical damage at the contact is a strong function of the lubricant film thickness. Thin films promote frequent discharge events and high pit density, whereas thick films limit discharge frequency but produce deeper pits when breakdown occurs. Increasing electrical power and load intensifies damage severity, increasing both pit density and surface indentation. Statistical analysis confirmed lubricant film thickness as the dominant factor governing EIBD, followed by electrical power.
The grease life of rolling bearings is strongly influenced by the lubricating film thickness, yet its transient evolution has not been extensively investigated. In this work, a mass balance framework is used to describe the competition between oil supply from grease bleed and oil loss at elastohydrodynamic lubrication (EHL) contacts, enabling the assessment of the characteristics of film thickness evolution over time. The analysis reveals an initial stabilization toward a characteristic film thickness plateau, resulting from a nearly constant early-stage oil supply and self-regulating nonlinear EHL losses. At longer times, the film thickness gradually decreases, governed by the characteristic time scale of grease bleed, indicating that oil availability and rate of supply control the long-term film behavior. The proposed framework provides a systematic basis for understanding film evolution in grease-lubricated cylindrical roller bearings and can be extended to incorporate more detailed physical mechanisms for accurate predictions.
