Interaction Between Gear Surface Wear and Contact Fatigue

Surface contact fatigue is the main failure mode in many mechanical components, such as gears, bearings, and cam-followers. A fatigue life prediction model is proposed for finite line contact under starved thermal elastohydrodynamic lubrication (TEHL) condition in this paper. Then, the effects of inlet oil-supply thickness, slide-to-roll ratio (SRR), and operating conditions on the lubrication performance and fatigue life are investigated. The results show that the lubrication characteristics and fatigue life of finite line contact are obviously different from those of fully flooded situation by introducing the starved lubrication condition. For example, the severe starved conditions lead to a significant increase in friction coefficient and decreased fatigue life. The variation of SRR has an important influence on the fatigue life. With the increase of SRR, the fatigue life decreases firstly and then increases. The stress concentration occurs near the surface when speed is low. In addition, under the low-speed situation, rotation speed variation has little effect on the fatigue life.

Vibration-based updating of wear prediction for spur gears

Based on “slice method,” the improved time-varying mesh stiffness (TVMS) calculation model of helical gear pair with tooth surface wear is proposed, in which the effect of friction force that obtained under mixed elastohydrodynamic lubrication (EHL) is considered in the model. Based on the improved TVMS calculation model, the dynamic model of helical gear system is established, then the influence of tooth wear parameters on the dynamic response is studied. The results illustrate that the varying reduction extents of mesh stiffness along tooth profile under tooth surface wear, in addition, the dynamic response in time-domain and frequency-domain present significant decline in amplitude under deteriorating wear condition.

The effects of nanotexturing on oil film thickness and shape under pointcontact elasto-hydrodynamic lubrication (EHL) conditions were experimentally investigated. A disk-onball friction tester with an optical interferometer was used to measure oil film thickness and to observe the oil film shape. Periodic groove structures with a spiral, perpendicular, or parallel shape and with various groove depths and distances were formed by irradiation of a femtosecond laser onto the surface of steel balls. These nanotextured balls were tested under a load of 20 N and at rotational speeds from 1.0 to 3.0 m/s. Most of the balls with nanotexturing had a thicker oil film than those without texturing. The groove depth and angle were the key parameters determining the thickness of the oil film as they controlled the amount of side leakage of oil from the contact point. Optimization of these parameters resulted in an oil film that was almost twice as thick as that on the ball without texturing.

The influence of the heat transfer field on anomalous film formation under elastohydrodynamic lubrication (EHL) conditions was studied. Liquid lubricant film shapes between a transparent disc and steel ball friction pair were investigated by white light optical interferometry. The fatty alcohol 1-dodecanol was used as the representative lubricant to develop anomalous film shapes. A sapphire disc and glass disc, which have different thermal conductivities, were used as the transparent bounding surface. Experiments were performed wherein the applied load, sliding conditions and ambient temperature were varied. The temperature of the lubricant film was estimated by a simple model with the measured traction coefficient. The estimated temperature and maximum Hertzian pressure were compared with the phase diagram of 1-dodecanol obtained using a diamond anvil cell to investigate the phase state of the lubricant film. It was found that the anomalous film shape was stably formed in the solid-state regime of the phase diagram whereas the film exhibited unique characteristics such as the collapse behaviour in high sliding conditions and liquid-like behaviour of the traction with a remaining thickened film part in the liquid state regime.

An improved mesh stiffness model of helical gear pair considering axial mesh force and friction force influenced by surface roughness under EHL condition

The surface quality of cold rolled strip is related to a greater extent on the rolling oil film thickness, and there are many factors that affect the oil film thickness. Considering the various factors comprehensively, an integrated mathematical model is established, such as roughness of rolls and strips, elastohydrodynamic lubrication, friction heat and plastic deformation heat in the rolling zone, viscosity varying with temperature and pressure, etc. A series of equations are developed, such as the Reynolds equation of partial membrane hydrodynamic lubrication based on average flow theory, equation of oil film thickness on rough elastic surface, the thermal interface equations between strip, oil film and roller surface, surface asperity contact pressure equation, lubricant viscosity and density equations, motion equation of the oil film, etc. This model is solved by finite difference method to get the film pressure, oil film thickness, and temperature distribution in the rolling zone. The average rolling pressure, the roll, and strip temperature calculated by the model are very close to the field test results. Comparing the minimum film thickness calculated by the model with the regression formula of other literature test, the error is less than 10%. The minimum oil film thickness is analyzed. It increases with the decrease of the rolling force and is approximately proportional to the rolling speed and lubricant viscosity.

Objective: To determine the prevalence and the extent of tooth wear of Binh Tri Thien Railway Management Company in 2011. Methodology: This quantitative research, cross-sectional study based on the data from 776 staff-workers whose age range from 18 to 55 years in Binh Tri Thien Railway Management Company, 2011. The severity of tooth wear was clinically evaluated directly according to Tooth Wear Index (TWI) described previously by Smith and Knight (1984). The materials which got at least one tooth surface wear from score-2 is known as tooth wear. The extent of tooth wear is determined by the average number of pathological tooth wear (≥ score-2) on each surface of the tooth. This research examined the relationship between the extent of tooth wear with age, gender, diet, oral hygiene habits and subfunctional activity. Results: The mean age of the sample was 39.88 ± 10.16. The mean age of men was 40.33 ± 10.06. The mean age of women was 37.51 ± 10.42. Prevalence of tooth wear in this study was 77.7%. Extent of tooth wear: the average number of pathological wear buccal surface: 0.36 ± 1.5, the average number of pathological wear lingual surface: 0.76 ± 2.25, the average number of pathological wear occlusal surfaces/ incisal edges: 8.22 ± 7.99, the average number of pathological wear teeth cervical: 1.98 ± 3.61. Research shows that gender, age, geography, habit of eating sour food, drinking alcohol, drinking carbonated beverage, brushing teeth immediately after eating sour, teeth grinding disability related statistical significantly with extent of tooth wear. Conclusion: The prevalence of tooth wear in this study was 77.7%. Gender, age, eating sour food habits, drink alcohol, drink carbonated beverages, teeth grinding disability statistically significant relation with the extent of tooth wear.

Experimental study on the influence of different carburized layer depth on gear contact fatigue strength

Enhancement of wear resistance on normal contact ratio spur gear pairs through non-standard gears

Comprehensive surface integrity evaluation during early stages of gear contact fatigue

The elastohydrodynamic lubrication model considering solid particles was set up. Taking effect of solid particles into account, the Reynolds equation was deduced. The elastohydrodynamic lubrication analysis of spur gear running-in was completed considering time-variant effect. Results show that oil film pressure in region 2 where particle is located increases dramatically but oil film thickness in region 2 decreases thinking about effects of solid particles. When particle size becomes greater oil film pressure increases obviously, oil film thickness diminishes. The minimum film thickness and maximum film pressure both diminish considering effects of solid particles. Keywords-solid particles; spur gears; running-in; time-variant effect; elastohydrodynamic lubrication

The film shape, pressure and temperature profiles have been measured in a disk machine under conditions of elastohydrodynamic lubrication. They were obtained with a new design of transducer which enables the various measurements to be accurately inter-related. In the case of the film shape and pressure measurements the corresponding theoretical solutions have been calculated and detailed comparison made. It has been shown that the sharp peaks of pressure near the outlet which are predicted in the theory are in practice considerably attenuated but do occur in the correct positions. The associated dip in film thickness is also much reduced. Johnson’s recent postulate that the position of the pressure spike should be a function of a single parameter has been examined and found to hold for this new range of experimental data.

PurposeThis study aims to research the time-varying mesh stiffness (TVMS) model for orthogonal face gear drives considering elastohydrodynamic lubrication (EHL) and provide a theoretical basis for understanding the dynamic characteristics of face gear drives.Design/methodology/approachConsidering EHL, a novel model is proposed to calculate the TVMS of orthogonal face gears using the deformation compatibility condition. First, the tooth surface equations of orthogonal face gears are derived according to the tooth surface generation principle. Then, the oil film thickness on the tooth surface of face gears is obtained by solving the governing equations of EHL. Furthermore, the proposed model is used to calculate the TVMS of face gears along the mesh cycle and is verified. Finally, the effects of module, tooth number of shaper cutter and pressure angle on mesh stiffness are analyzed.FindingsThe results indicate that when the contact ratio is greater than 1 and less than or equal to 2, the TVMS of face gears exhibits a phenomenon of double-single tooth alternating meshing where sudden changes occur. As the module increases, the overall mesh stiffness of face gears increases, and the magnitude of the sudden change at the moment of single-double tooth alternating meshing gradually increases. As the tooth number of shaper cutter and pressure angle increase, so does the TVMS of face gears. When the effect of oil film is considered, the calculated TVMS of face gears slightly increases overall and the increase in average oil film thickness leads to a rise in the TVMS. This study provides a theoretical basis for understanding the dynamic characteristics of face gear drives.Originality/valueThis study’s originality and value lie in its comprehensive approach, which includes conducting analysis based on loaded tooth contact, considering the influence of elastohydrodynamic lubrication, proposing a novel analytical–finite–element model, calculating TVMS of face gears, verifying the proposed model and analyzing the effects of typical structural parameters and oil film thickness.

New infinitely variable transmission (IVT) systems are under development for the automotive industry as a means to achieving significant fuel economy benefits. These systems rely on the lubricating fluid to transmit the drive train loads across the interface of the transmission components. This requires the development of new fluids that exhibit high traction properties under elastohydrodynamic lubrication (EHL) conditions. However, it has been reported recently that the traction performance of some fluids can reduce dramatically as temperature is reduced. This may place severe operational limits on IVT systems and suggests that the low-temperature traction properties of fluids for these systems should be studied in order to understand the mechanism for the observed reduction in traction. The work reported here is an experimental study aimed at identifying whether low temperature traction reduction is related to a fundamental change in rheological behavior specific to the fluids tested or to more generic changes in the EHL contact conditions. A series of model experiments were performed using a mini traction machine (MTM) on three high-viscosity polybutene samples. The results have been mapped against previously reported non-dimensional parameters used to identify different EHL regimes. The results show that dramatic reductions in traction occur when the contact transitions from the rigid piezo-viscous (RP) toward the rigid iso-viscous (RI) region. Similar results were also found for two other high-viscosity fluids of different molecular structure and lower traction properties. The results support the hypothesis that the reduction in traction observed at low temperature is due to a change in EHL contact conditions rather than being solely due to a change in the rheological performance of the test fluids.