A timely trend in gear transmission involves the replacement of steel with polymers. Nevertheless, the absence of fundamental durability data for polymer gears impedes their reliable application during power transmission. The expensive and time-consuming gear fatigue experiments make it impossible to rely merely on experimental data. In this study, a strategy for contact fatigue life prediction of polymer gears via an experimental-simulated hybrid data-driven model is presented. The hybrid data are established with a certain mixture ratio of experimental and simulation data and are augmented by the conditional tabular generative adversarial network (CTAB-GAN) algorithm. This specific algorithm was combined with the extreme gradient boosting (XGBoost) algorithm to predict the contact fatigue life of gears made from different polymer materials, with the prediction accuracy controlled within a 3-fold scatter band. Moreover, an empirical predictive formula for contact fatigue life was developed. The hybrid data-driven model, which merges experimental and simulated data, allows for efficient estimation of fatigue life and material selection strategies, generating insight into the anti-fatigue design of polymer gears.

The rapid evolution of advanced equipment that utilizes gears, including aviation engines, helicopters, and wind turbines, imposes escalating demands for enhanced reliability, prolonged lifespan, increased power density, and sustained durability of gears. Gear contact fatigue issues, associated with materials, geometries, and operating conditions, are crucial to modern gear design. To date, enormous theoretical and experimental studies have been conducted to understand gear contact fatigue mechanisms. To compile and categorize key investigations within a broad and active research field, this work reviews recent studies of gear contact fatigue. Emphasizing theories, tests, and anti-fatigue design approaches, this work aims to provide a comprehensive overview of recent developments in this significant area of research.

Under harsh service conditions and complex loading environments, gearbox cases in aero-engines are required to be both structurally robust and lightweight. A key design challenge is balancing weight reduction with control of bearing bore misalignment, which is an important performance metric. To address this issue, a topology optimization method for the gear transmission case is proposed, considering both mechanical and inertial loads. The approach is based on the solid isotropic material with penalization(SIMP) interpolation model. Inertial load effects on attached components are incorporated into the optimization model, which imposes constraints on case stress, critical bearing bore misalignment, and volume fraction of the optimized region. The objective is to minimize the weighted structural compliance of the case under multiple loading conditions. The proposed method achieves a 7.1% reduction in case weight and simultaneously decreasing maximum von Mises stress, total deformation, and critical bearing bore misalignment by 7.1%, 3.1% and 11.1%, respectively.

Polyetheretherketone (PEEK) gears are high-performance polymer gears widely used in automobiles, drones, robots, and other fields. However, the complex failure mechanism of PEEK gears and the lack of basic data on loading capacity lead to a shortage of a reasonable design basis in power transmission applications. To address the unclear failure mechanism and the lack of fundamental durability data of PEEK gears, fatigue performance tests of PEEK helical gear pairs under oil-jet lubrication were carried out, and the contact stress and bending stress were calculated. The failure mechanism were investigated by using scanning electron microscopy and other equipment. Experimental results show that the primary failure modes of PEEK gears under oil-jet lubrication were tooth surface pitting failure and tooth root fatigue fracture. The critical transition relationship between PEEK gear contact fatigue failure and bending fatigue failure was identified, and an evaluation method for the failure form of PEEK gears was proposed. When the ratio of contact stress to bending stress of the PEEK gear was smaller than 1.02, the PEEK gear mainly suffered from root fatigue fracture; when the ratio of contact stress to bending stress was larger than 1.10, the PEEK gear mainly suffered from tooth surface pitting failure. When the ratio was in the range from 1.02 to 1.10, there was a critical failure threshold between tooth surface contact fatigue and root bending fatigue.

The Lundberg–Palmgren (L–P) fatigue life formula, as a statistical fatigue theory, has been widely used in the industry. However, its direct applicability is limited to the components treated by surface strengthening technologies. Rolling contact fatigue tests and surface integrity measurements of American Iron and Steel Institute (AISI) 9310 rollers with several surface treatments were performed to address this issue. Based on these results, a modified L–P fatigue model was proposed, enabling the consideration of surface modification including surface roughness, residual stress, and hardening introduced by different surface treatments. Compared with the original L–P fatigue formula, its results are more accurate for surface strengthened specimens. Furthermore, this method can assess the contact fatigue life of gears treated by surface strengthening techniques.

The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears. Meanwhile, the coexistence of tooth contact fatigue damage and tooth profile wear leads to a complicated competitive mechanism between surface-initiated failure and subsurface-initiated contact fatigue failures. To address this issue, a fatigue-wear coupling model of an aviation gear pair was developed based on the elastic-plastic finite element method. The tooth profile surface roughness was considered, and its evolution during repeated meshing was simulated using the Archard wear formula. The fatigue damage accumulation of material points on and underneath the contact surface was captured using the Brown-Miller-Morrow multiaxial fatigue criterion. The elastic-plastic constitutive behavior of damaged material points was updated by incorporating the damage variable. Variations in the wear depth and fatigue damage around the pitch point are described, and the effect of surface roughness on the fatigue life is addressed. The results reveal that whether fatigue failure occurs initially on the surface or sub-surface depends on the level of surface roughness. Mild wear on the asperity level alleviates the local stress concentration and leads to a longer surface fatigue life compared with the result without wear.

This study presents the results of detailed wear process examination on polyformaldehyde gears under both dry and lubricated conditions. A multi-purpose durability test rig was employed to study the wear performance of polyformaldehyde gear pairs. The wear behaviors of polyformaldehyde gears under dry and oil-lubricated operating conditions were characterized via measurements of gear tooth surface micro-topography and tooth profile deviation. Under the dry running condition, a hump and a gully appear on the tooth surface in the pitch line area of the driving gear and the driven wheel, respectively. The largest amount of wear was observed around the tooth root of the driving gear. However, the gear tooth wear pattern with lubrication is different from that under the dry running condition.

Carburized gears are widely used in geared machines such as wind turbines. Contact fatigue problems occur in engineering practice, reducing reliabilities of machines. Contact fatigue failures are related to many factors, such as gradients of mechanical properties of the hardening layer. In this work, an elastic-plastic contact model of a carburized gear is developed based on the finite element method to evaluate contact fatigue failure risk, considering variations in hardness and strength. The Dang Van multiaxial equivalent stress is calculated via Python coding within the Abaqus framework. The gradient of yield strength along the depth from case to core is considered. The concept of local material fatigue failure risk is defined to evaluate the probability of pitting failure. The effects of design factors, such as the case hardening depth (CHD), surface hardness, and contact pressure on fatigue failure risk, are studied. As the CHD increases or the surface hardness decreases, the risk of deep spalling failure reduces. The increase in surface hardness leads to a decreased risk of pitting failure, while the variation in CHD hardly affects the pitting failure risk.

Contact fatigue issues become more and more crucial in gear industry as they significantly affect the reliability and service life of associated mechanical systems such as wind turbine gearboxes. The contact fatigue behavior is mostly determined by the mechanical properties of materials and stress fields near the contact area, which is further influenced by the lubrication and surface roughness due to pressure fluctuations. In this study, a numerical model incorporating the lubrication state, tooth surface roughness, residual stress, and mechanical properties of the material is developed to determine the contact fatigue behavior of a megawatt level wind turbine carburized gear. The variations of the hardness and residual stress along the depth were characterized by the Vickers hardness measurement and X-ray diffraction test, respectively. The elastohydrodynamic lubrication theory was applied to predict the contact pressure distribution, highlighting the influence of the surface roughness that stemed from the original measurement through an optical profiler. The stress histories of the studied material points during a complete contact loading cycle were fast calculated using the discrete- concrete fast Fourier transformation (DC-FFT) method. Modified Dang Van diagrams under different working conditions were determined to estimate the contact fatigue failure risk. The effect of the root mean square (RMS) value of the surface roughness on the failure risk at critical material points were discussed in detail. Results revealed that the surface roughness significantly increases the contact fatigue failure risk within a shallow area, and the maximum risk appears near the surface.