•A random multi-shots peening model considering the initial hardness gradient and residual stress conditions of a carburized rollers is developed.•The influence of shot peening coverage on detail ...evolution of surface morphology and residual stress is investigated.•The ratio between the layer thickness of compressive residual stress and the critical depth of maximum compressive stress generally lies in the regime of 3.6–4.3 after shot peening.
Shot peening is becoming a widely used surface strengthening technique for various key mechanical components for its enhanced influence on the fatigue performance. This technique allows to strengthen the mechanical properties of material via introduce a certain depth of compressive stress layer and change the surface topography. The relation of the shot peening processing parameters, the surface integrity including residual stress and the surface roughness remains a large unmet practical need. In this paper, the residual stress and surface topography obtained by various shot peening treatments were experimentally and theoretically examined. A random multi-shots peening model of a carburized roller, accounting for the initial hardness gradient and residual stress was developed. The measured residual stress and surface roughness present good agreements with the predicted results. Both the experimental and simulated results reveal that the axial and tangential residual stress components tend to be consistent after shot peening. In addition, the influence of peening coverage on detailed evolution of surface topography and residual stress is investigated. It is found that the ratio between the layer thickness of compressive stress and the critical depth of maximum stress generally lies in the regime of 3.6–4.3 after shot peening. As the coverage increases from 100% to 400%, surface roughness parameters Sa, Sq, S5z, Sku decrease, while the maximum magnitude of compressive stress fluctuates in the range of 1105∼1230 MPa. This work could act as an advisory reference for shot peening engineering practices.
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•The studies on gear transmission efficiency and dynamics are reviewed.•The studies on gear contact fatigue and wear-contact fatigue competitive phenomenon are reviewed.•The conflicting gear ...performance requirements and implications on lubrication are discussed.
Increasingly demanding performance standards and operating requirements are driving the growing interest on lubrication technologies in gear transmission systems. Optimized gear lubrication methods and lubricant compositions are necessary to meet the industrial challenges of higher load, speed, temperature and performance expectations in multiple powertrain applications, including automotive, aeronautical and marine. Numerous theoretical and experimental studies have been dedicated to gear lubrication, especially on lubrication modelling and composition of lubricants. Improvements on lubrication methods and conditions can reduce friction, suppress wear and scuffing, and increase gear flank capacity and fatigue life. In order to compile and categorize key investigations in an expansive field with substantial recent research, this work reviews gear lubrication papers with focus on gear efficiency, contact fatigue and dynamics. Furthermore, some accompanying results obtained by the authors are included.
•An systematic experimental investigation is conducted to identify the failure modes of the lubricated PEEK gears under different loading conditions through the enclosed power flow test rig, ...supplemented with the measurements on wear, vibration and the surface micro-topography.•S evere thermal damage occurs on the tooth surface of the PEEK gear under dry contact operation, while the no thermal damages are observed under the lubrication condition due to the fact that the heat accumulation on the tooth surface is dissipated effectively.•Experimental results reveal that the pitting-induced tooth breakage occurs under light and moderate loading conditions, while the tooth root breakage dominates under the heavy duty loading conditions.
An experimental investigation is conducted to identify the failure modes of the lubricated PEEK gears under different loading conditions through the enclosed power flow test rig, supplemented with the measurements on wear, vibration and the surface micro-topography. The FZG C type gear pair is selected while the mating driving gear is chosen with the material of C45. Experimental results reveal that the pitting-induced tooth breakage occurs under light and moderate loading conditions, while the tooth root breakage dominates under heavy duty loading conditions. The measurement of the wear and the tooth surface micro-topography help to identify that the micro-pits near the pitch line lead to the final tooth breakage under moderate loading conditions. Meanwhile, the insufficiency of the bending strength under heavy loading conditions is the cause of the tooth root fracture.
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.
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•A high-power-density design method via adaptive NSGA-III and surrogate sub-models for polymer gear systems is outlined.•The key factors affecting the operating performance of polymer ...accessory gearbox are explained.•Compared with metallic design scheme, the polymer scheme achieves a 49 % weight reduction and power density with 22.5 kW/kg.
There is a growing and prevalent trend in the power transmission field of high-performance polymers replacing metallic materials given the strict light-weight requirement. Polymer gears exhibit a low elasticity modulus, high-temperature sensitivity, and increased geometric design flexibility, presenting technical challenges to the straightforward application of metallic design methods to polymer gear systems. This study is centred on the development of a high-power-density polymer gear transmission system for the accessory unit of a gas turbine engine, utilising an adaptive NSGA-III algorithm and surrogate sub-models. A comprehensive assessment indicator for the operating performance of the transmission system is suggested, encompassing gear strength, bearing temperature, and shaft torsional stiffness. The model made it possible to simultaneously optimise forty-six structural parameters, including gear tooth module, web thickness, and bearing clearance. In contrast to the original steel design scheme, the optimised polymer gear transmission system indicated a 49% reduction in weight and a 1.96-fold increase in power density. This presents a method for substituting steel with polymers for effective power transmission.
•The injection molding lunker defect is detected by X-ray CT and the polymer gear fatigue model considering lunker is established considering the thermal-elastic-plastic constitutive behavior.•The ...effects of loading condition and the lunker defect on the POM gear fatigue life are studied numerically and experimentally.•The failure mode competitive mechanism of POM gears reveals that the final failure mode is more sensitive to the loading condition, but the presence of injection molding lunker rises the possibility of tooth root breakage.
Polymer gears manufactured with injection molding have been widely used in many industries, but the unavoidable injection molding lunker defects limit the loading capacity and the further use of polymer gears in power transmissions. In this work, injection molding lunker defects are detected by X-ray CT and a polymer gear fatigue model with lunker defect is established considering the thermal-elastic-plastic constitutive material behavior. Durability tests are also conducted, and the fatigue lives correspond well with simulation results. Results reveal that the lunker defect jeopardizes the loading capacity of tooth root under medium or heavy loading conditions, while the tooth flank failure is significantly influenced by the loading condition.
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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 discreteconcrete 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.
In this study, a comprehensive finite-element-based method, utilizing the continuum damage mechanics (CDM) theory and the linear elastic fracture mechanics (LEFM) theory, is proposed to predict the ...total gear bending fatigue life including the crack initiation and propagation. The developed gear finite element model has been validated following the ISO standard result. The contribution of crack propagation to the overall lifetime is addressed. Simulated results indicate that the gear bending fatigue life, especially the crack initiation life, highly depends on the loading level. In addition, the gear bending fatigue crack initiation life dominates the total life.
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.
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