Contact Fatigue of Carbon Steel Gear Under Different Lubrication Conditions

A Hertzian contact fatigue test was proposed to simulate conventional rolling wear experiments, by which the wear behavior and phase transformation of 3mol%Y2O3-partially stabilized zirconia (3Y-PSZ) and 3Y-PSZ/20 mass%Al2O3 ceramics in water at 90°C were investigated. The Hertzian stress contact fatigue property was found to be greatly dependent on fracture strength and remarkably improved by the post-HIP treatment. The Hertzian contact stress was revealed to have minor influence on the water-assisted tetragonal-to-monoclinic phase transformation in Y-PSZ-based ceramics at temperatures as low as 90°C. The addition of Al2O3 into Y-PSZ effectively suppressed the low-temperature phase transformation, but it did not lead to the improvement in the contact fatigue property probably because the strength of the resultant composite was lower than the monolithic Y-PSZ; however, more work is required to completely understand the Hertzian stress contact fatigue behavior of composites.

Research on calculation of contact fatigue life of rough tooth surface considering residual stress

A methodology is proposed to study the interplay between tooth wear and contact fatigue under elastohydrodynamic lubrication condition. The modeling methodology includes the influence of contact fatigue on wear and the influence of wear on contact fatigue. First, the changes in film pressure and film thickness of oil at each meshing point caused by contact fatigue are introduced according to the surface wear model, and the change of wear model is analyzed to study the effect of contact fatigue on wear. Then, according to the elastohydrodynamic lubrication theory, the change in film pressure affected by tooth surface wear is analyzed to study the effect of wear on contact fatigue. Finally, the influence of lubrication conditions on the interplay between tooth surface wear and contact fatigue is analyzed. In addition, an experimental fatigue study is performed and introduced into the model predictions to improve the accuracy of the proposed methodology.

Numerical modeling and experimental investigation on fatigue failure and contact fatigue life forecasting for 8620H gear

Structural health monitoring has become a viable solution to monitor critical infrastructure components that show distress or are unable to pass current load ratings. This research introduces the concept of a composite layer bonded to concrete structures, which is capable of providing distributed sensing capabilities. The layer consists of carbon nanotubes that are deposited on a carrier, which form a continuous conductive skin that is exceptionally sensitive to changes in strain and the formation and propagation of micro-damage and macro-damage. It can be either structural, where the layer represents the reinforcement as well as the sensor, or nonstructural, where the layer acts as a sensing skin alone. Distributed sensing allows for increased detectability of forming or growing damage that cannot necessarily be captured with conventional point-type sensors such as strain gages or accelerometers. Once developed, this sensing skin may be able to give real-time feedback on changes in strain, temperature effects, and formation and propagation of damage. In this article, we present the fabrication and evaluation of an integrated structural sensing composite layer attached to a concrete beam specimen. The specimen was tested to failure in the laboratory. Experimental results are presented and discussed, and currently ongoing research is introduced.

Composite effects of residual stress and hardness gradient on contact fatigue performance of rough tooth surfaces and optimization design of detailed characteristic parameters

An experimental investigation of spur gear behavior was conducted with the aim of quantifying the impact of lubrication methods and conditions on the power losses and contact fatigue lives. Variations of dip and jet-lubrication were defined and these behaviors were observed as a function of the lubrication conditions. All measurements were performed using the same back-to-back test machine and the same spur gear test articles such that all evaluations were correlated. Power loss experiments were performed under both loaded and unloaded conditions to determine both load-independent (spin) and load-dependent (mechanical) losses. Sets of long-cycle contact fatigue experiments were performed under the same lubrication conditions to determine macro-pitting lives in a statistically meaningful manner. Results indicate that the spin power losses are impacted by the lubrication method significantly while the mechanical losses are not influenced. Contact fatigue lives from jet-lubricated tests are comparable to those under dip-lubricated conditions ones as long as jet velocities are sufficient.

An experimental investigation of spur gear behavior was conducted with the aim of quantifying the impact of lubrication methods and conditions on the power losses and contact fatigue lives. Variations of dip and jet-lubrication are defined, and these behaviors were observed as a function of the lubrication conditions. Both types of measurements were performed using the same type of back-to-back test machines and the same spur gear test articles such that their evaluations can be correlated. Power loss experiments were performed under both loaded and unloaded conditions to determine both load-independent (spin) and load-dependent (mechanical) losses. Sets of long-cycle contact fatigue experiments were performed under the same lubrication conditions to determine macropitting lives in a statistically meaningful manner. Results indicate that the spin power losses are impacted by the lubrication method significantly while the mechanical losses are not influenced. Contact fatigue lives from jet-lubricated tests are comparable to those under dip-lubricated conditions ones as long as jet velocities are sufficient.

Radial-draw bending of stainless steel tube

Abstract. Existing research on tooth surface wear of helical gears has insufficiently considered the complex and variable lubrication conditions between meshing tooth surfaces. This study constructed a mixed elastohydrodynamic lubrication (EHL) model based on the meshing characteristics of helical gears, analyzed the lubrication characteristics between the meshing tooth surfaces and the temperature changes induced by asperity contact and oil film shear, and introduced them into the improved Archard wear model to construct the surface wear calculation model under the mixed EHL conditions. Taking the changes in meshing characteristics of tooth profile during the tooth surface wear accumulation process as a connecting bridge, the mutual influence relationships among the tooth surface wear, lubrication characteristics, and tooth surface temperature rise were systematically clarified. The cumulative distribution law of tooth surface wear and the influence of tooth surface roughness, working conditions, and tooth profile parameters on the tooth surface wear depth were explored. The research indicates that the wear depth at the tooth root and top is deeper than that at the pitch position, the pinion's surface wear depth is greater than that of the gear, and the maximum wear appears at the pinion's tooth root. The wear depth under mixed EHL conditions is nearly 4 orders of magnitude lower than that under dry friction conditions. Reducing the magnitude of tooth surface roughness can effectively decrease the tooth surface wear depth. Appropriately increasing the velocity, module, tooth width, helix angle and tooth surface hardness is beneficial to improving the anti-wear ability of tooth surfaces. This study can provide a reliable theoretical basis for predicting and optimizing the tooth surface wear of helical gears under complex lubrication conditions.

The main purpose of this article is to establish the meshing theory for the offsetting Archimedes cylindrical worm drive, which consists of a cylindrical worm with asymmetric tooth profile and a plane worm gear. The equations of the tooth surfaces, the meshing function, the curvature interference limit function, and the curvature parameters are all obtained for the worm drive. By means of the developed reference-point-based meshing theory, the reference point located strictly on the tooth surfaces of a worm drive is determined via solving the system of nonlinear equations, in which no iteration is needed to perform this process. Based on the location of the reference point, the tooth surface boundaries are ascertained for the plane worm gear. The numerical case is carried out and the conjugate zone, the instantaneous contact lines, and the local meshing property parameters are acquired for the worm drive. The whole thread length of the cylindrical worm can almost be used and the conjugate zone can cover the whole tooth surface of the mating plane worm gear. In the meshing zone, not only the contact stress level between the tooth surfaces is relatively low, but also the lubrication condition is favorable. The comparative study on the meshing properties between the offsetting Archimedes cylindrical worm drive and the Archimedes conical worm drive is carried out.

Tooth surface roughness and lubrication status have significant influence on the contact performance and fatigue life of helical gear pair. Yet, despite the development in elastohydrodynamic lubrication-based contact analysis and solution of subsurface stress field, researches in subsurface stress field of helical gears considering both lubrication and surface roughness are not quite comprehensive. In this study, three-dimensional surface roughness of generating ground gear is measured, a finite line-contact mixed elastohydrodynamic lubrication model is established to perform the contact analysis, and, on this basis, the influence of tooth surface roughness on the subsurface stress field is studied. Results show that compared with the smooth surface, the overall level of subsurface stress is raised; maximum stress values and plastic zones occur in the close vicinity of tooth surface, which adds to the risk of surface failure; within sections in the valley regions of roughness, locations of maximum stresses are generally similar to the smooth surface situation, i.e. in relatively deep zones, while within sections in the peak regions, the majority of locations with maximum stresses shift much closer to the surface; contact pressure and stress status see only mild undulation between different sections distributed along the contact line, but intense changes between sections distributed along the entraining direction.

The contact characteristics of rough surfaces in line contact during running-in process

Two-dimensional Hertzian contact problem with surface tension

Contact fatigue is a main fatigue mode of gears such as those used in wind turbines, due to heavy duties occurring in engineering practice. The understanding of the gear contact fatigue should be based on the interaction between the local material strength and the stress state. Under the rolling–sliding motion, the multi-axial stress state makes the gear contact fatigue problem more complicated. A numerical contact model is proposed to evaluate the contact fatigue life of an intermediate parallel gear stage of a megawatt level wind turbine gearbox. The gear meshing theory is applied to calculate the geometry kinematics parameters of the gear pair. The gear contact is assumed as a plane strain contact problem without the consideration of the influence of the helical angle. The quasi-static tooth surface load distribution is assumed along the line of action. The elastic mechanics theory is used to calculate the elastic stress field generated by surface tractions. The discrete convolute, fast Fourier transformation method is applied to estimate the subsurface stresses distributions. In order to describe the time-varying multi-axial stress states during contact, the Matake, Findley, and Dang Van multi-axial fatigue criteria are used to calculate the critical planes and equivalent stresses. Both the statistic and the deterministic fatigue life models are applied by choosing the Lundberg–Palmgren (LP), Zaretsky models, respectively. The effect of the residual stress distribution on the contact fatigue initiation lives is discussed. In addition, the crack propagation lives are estimated by using the Paris theory.