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Friction drive and wear control is a tough issue for linear standing-wave ultrasonic motors with intermittent contact and impact friction. For the widely recognized reduction of friction/wear, minimum quantity lubrication was adopted to improve the output performances and services for motors through friction regulation. Given different preload and driving voltages, the mechanical characteristics of motors with minimal quantity lubrication were investigated using a homemade test rig. Results show that output performances and driving efficiency under film lubrication differ from those of dry friction. The optimized driving voltage was reduced by 31.5% and the minimum startup voltage was reduced by 41.67% using film lubrication. Additionally, the output speed increased by 26.29%, and thrust decreased by 41.26% under uniform exciting conditions (e.g., 150 V at 39.14 kHz). The existence of film lubrication broadens the effective frictional contact boundary, and effective friction contribution enhances the driving efficiency (the maximum efficiency of motors increased by 14%). Furthermore, the singularity of the effect of preload is significantly improved after lubrication, and the friction interface of the stator/slider becomes more controllable. Suitable lubrication is critical to the improvement of startup performance and prone to realize low-voltage driving, and the combination of lubrication regulation and wear inhibition is conducive to the durability and reliability of motors. This study provides an additional alternative for performance improvement of linear standing-wave motors apart from frictional materials. [ABSTRACT FROM AUTHOR]

Coulomb friction model is modified with considering the preliminary distance of rigid bristles and shear stiffness of the contact surface. The degeneration in friction drive and wear behavior induced by nonlinear contact (i.e., impact, intermittent, and fretting) is outlined. Wear tests of LUSMs with V-shape transducers are conducted by a homemade reciprocating apparatus. Results show that chemical inertness, thermotolerance, elasticity as well as surface topography are critical for the contact interface of LUSMs A systematic approach involving, for instance, dynamic contact, friction model, and wear behavior provides new perspectives in improving service performances and promoting practical applications. [ABSTRACT FROM AUTHOR]

Despite good approval for excellent friction regulation, surface texturing seems to be a penalty area for gears mostly because of the traditional cognition of surface (micro-)pitting and structural similarity. Surface micro-textures were applied to the pinion flank to regulate the time-varying meshing stiffness and enhance the meshing characteristics. Results showed the stress regulation and smoothing capability of micro-textures in meshing process, the time-varying meshing stiffness increases by 4.75% and the frictional stability increased by 52%. Experiment results approve that the flank micro-textures can control friction and reduce torque by 26.2%. This study is significant for the systemic design of the dynamic performance and frictional meshing, especially for the gear engagement reliability in space without film lubrication. [Display omitted] • Surface pitting-like micro-textures were preset on flank surfaces of spur gears. • The symmetrical and continuous micro-textures near the pitch line were compared. • The micro-textures are capable to improve the meshing stiffness of gears. • Stress on flanks is rearranged for homogenize distribution after micro-texturing. • Micro-textures regulate the dynamic friction and increase friction stability. [ABSTRACT FROM AUTHOR]

• A new filler of carbon nanocage is first proposed for epoxy resin nanocomposite. • Carbon nanocage filler shows prominent physical confinement and self-lubrication. • Relative to neat epoxy, wear rate is reduced by 51.9% for the optimized sample. • Friction coefficient is reduced by 55.6% for the optimized sample. • The performances are attributed to the unique hollow structure of carbon nanocage. Epoxy resin (EP) nanocomposite materials with excellent tribological properties are highly desired for many engineering applications requiring low friction and wear. Adding carbon nanofiller is regarded as one of the most potential solutions to solve the serious dry wear problem of epoxy matrix. Herein, we report a new filler of carbon nanocages (CNC) prepared by the method of MgO templates to improve its dry friction performance through filling epoxy into the internal hollow space of CNC. Relative to neat epoxy, the friction coefficient (0.249) and wear rate (7.98 × 10−7 mm3 Nm−1) are reduced by 55.6% and 51.9% for the optimized CNC/EP nanocomposites, respectively. Even compared to typical graphene/epoxy nanocomposites, the wear rate is also reduced by up to 21.8%, as well as greatly enhancing the mechanical properties, thereby effectively protecting epoxy matrix and improving its dry friction. Such great tribological performance is attributed to unique structure of CNC, enabling the multi-functional collaboration of physical confinement, self-lubrication and wear-debris collection for CNC fillers, and making it the most potential carbon-based nanofiller for EP-based nanocomposite material system. More than that, it also provides insights for designing other advanced carbon-based nanofillers. [ABSTRACT FROM AUTHOR]