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New analytical model of elastic-plastic contact for three-dimensional rough surfaces considering interaction of asperities

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Friction 2022年第2期10卷 217-231页

作者： Yuqin WEN Jinyuan TANG Wei ZHOU Lin LI caichao zhu State Key L aboratory of High Performance Complex Manufacturing Central South University.Changsha 410083.China Hunan Provincial Key Laboratory of High Efficiency and Precision Machining of Difficult-to-Cut Material Hunan University of Science and TechnologyXiangtan 411201China State Key Laboratory of Mechanical Transmission Chongqing UniversityXiangtan 400044China

The contact calculation of three-dimensional real rough surfaces is the frontier field of tribology and surface science.In this study,we consider the interaction and elastic-plastic deformation characteristics of asperities and further,propose an analytical contact calculation method for rough surfaces considering the interaction of asperities.Based on the watershed algorithm,the rough surface is segmented and the asperities are reconstructed into ellipsoids.According to the height relationship between the asperities,the definition of the deformation reference height of the matrix between each couple of asperities is provided.Subsequently,the calculation formula of the substrate deformation is provided according to the local contact pressure considering the elastic-plastic deformation of the asperity,and the contact state under a specific load is determined using the iterative correction method.The results correspond with those of finite element numerical calculation and the study reveals the following:(1)compared with the results obtained without considering the asperity interaction,contact area,distance,and stiffness will be reduced by 6.6%,19.6%,and 49.5%,respectively,when the influence of asperity interaction is considered;(2)the interaction of the asperities has the greatest influence on the surface contact distance and stiffness.Under the same load,the existence of asperity interaction will reduce the contact distance,area,and stiffness;(3)considering the interaction of the asperities,the higher asperity will bear more load,but it will simultaneously reduce the contact of the surrounding area and increase that of the distant area.The calculation method proposed in this study has the advantages of high calculation efficiency and accuracy,thus,providing the calculation basis and method for subsequent studies on service performance of rough surfaces,such as the calculation of contact stiffness and fatigue performance analysis of rough surfaces.

关键词： calculation method contact analysis interaction of asperities rough surface

Numerical study on fatigue crack propagation behaviors in lubricated rolling contact

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Chinese Journal of Aeronautics 2021年第9期34卷 24-36页

作者： Haifeng HE Huaiju LIU caichao zhu Andrea MURA State Key Laboratory of Mechanical Transmissions Chongqing UniversityChongqing 400044China Department of Mechanical and Aerospace Engineering Politecnico di TorinoTorino 10129Italy

The surface-initiated Rolling Contact Fatigue(RCF)including pitting and micro-pitting is one of the key issues affecting the reliability of tribological components such as gears and bearings used in various devices.In this work,a surface-initiated crack Finite Element(FE)model which considers the effect of lubricant on crack faces was developed to investigate surface-initiated RCF using an automatic crack propagating Python script.Different lubricating states,initial crack parameters and loading conditions were simulated to analyze the evolution of crack propagation and the Stress Intensity Factors(SIFs).The RCF crack propagation path and life were predicted by employing the Maximum Tangential Stress(MTS)criterion coupled with the Paris’s law.A typical RCF failure is predicted in the numerical simulation.Results reveal that the lubricating pressurization dominates the surface-initiated RCF.In addition,the initial crack angle has a significant effect on the RCF crack propagation path and the fatigue life.

关键词： Fatigue crack propagation Finite element Life prediction Lubricating states Rolling Contact Fatigue(RCF) Stress Intensity Factors(SIFs)

Simulation of the fatigue-wear coupling mechanism of an aviation gear

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Friction 2021年第6期9卷 1616-1634页

作者： Boyu ZHANG Huaiju LIU caichao zhu Yibo GE State Key Laboratory of Mechancial Transmissions Chongqing UniversityChongqing 400044China Shanghai Peentech Equipment Tech.Co.Ltd. Shanghai 201800China

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.

关键词： gear contact fatigue tooth wear surface roughness damage accumulation

Effects of elastic support on the dynamic behaviors of the wind turbine drive train

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Frontiers of Mechanical Engineering 2017年第3期12卷 348-356页

作者： Shuaishuai WANG caichao zhu Chaosheng SONG Huali HAN The State Key Laboratory of Mechanical Transmissions Chongqing University Chongqing 400030 China CSIC (Chongqing) Haizhuang Windpower Equipment Co. Ltd.Chongqing 401122 China

The reliability and service life of wind turbines are influenced by the complex loading applied on the hub, especially amidst a poor external wind environment. A three-point elastic support, which includes the main bearing and two torque arms, was considered in this study. Based on the flexibilities of the planet carrier and the housing, a coupled dynamic model was developed for a wind turbine drive train. Then, the dynamic behaviors of the drive train for different elastic support parameters were computed and analyzed. Frequency response functions were used to examine how different elastic support parameters influence the dynamic behaviors of the drive train. Results showed that the elastic support parameters considerably influenced the dynamic behaviors of the wind turbine drive train. A large support stiffness of the torque arms decreased the dynamic response of the planet carrier and the main bearing, whereas a large support stiffness of the main bearing decreased the dynamic response of planet carrier while increasing that of the main bearing. The findings of this study provide the foundation for optimizing the elastic support stiffness of the wind turbine drive train.

关键词： wind turbine drive train elastic support,dynamic behavior frequency response function

Study on contact fatigue of a wind turbine gear pair considering surface roughness

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Friction 2020年第3期8卷 553-567页

作者： Heli LIU Huaiju LIU caichao zhu Zhangdong SUN Houyi BAI State Key Laboratory of Mechanical Transmissions Chongqing UniversityChongqing 400030China Hubei University of Automotive Technology Shiyan 442002HubeiChina Chongqing Wangjiang Industrial Co.Chongqing 400071China

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.

关键词： carburized gear contact fatigue surface roughness residual stress Dang Van criterion

Mesh Force Modelling and Parametric Studies for Compound Oscillatory Roller Reducer

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Chinese Journal of Mechanical Engineering 2021年第4期34卷 151-167页

作者： Changxu Wei Chaosheng Song caichao zhu Chengcheng Liang Long Hu The State Key Laboratory of Mechanical Transmissions Chongqing UniversityChongqing 400030China

A compound oscillatory roller reducer(CORR)with a first-stage gear transmission and a second-stage oscillatory roller transmission is presented.The transmission principle of oscillatory roller transmission is introduced,and the tooth profile equation of the inner gear is derived.The analytical model of mesh force considering the installation errors and manufacturing errors is proposed.Then,parametric studies considering different errors on the mesh force are conducted.Results show that the design parameters are significant factors for mesh force.The mesh force is reduced by 17%as the eccentricity of disk cam increases from 2.5 mm to 4 mm.When the radius of the movable roller increases from 7 mm to 20 mm,the mesh force decreases by 8%.As the radius of disk cam increases from 125 mm to 170 mm,the mesh force is decreased by 26.5%.For the impacts of errors,the mesh force has a noticeable fluctuation when these errors exist including the manufacturing error of disk cam,the installation error of disk cam and the manufacturing error of movable roller change.The prototype of the reducer is manufactured and preliminary run-in test proved the feasibility of the transmission principle.

关键词： Compound oscillatory roller reducer Kinematic principle Mesh force modelling Misalignments Parametric study

Evaluation of contact fatigue risk of a carburized gear considering gradients of mechanical properties

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Friction 2020年第6期8卷 1039-1050页

作者： Wei WANG Huaiju LIU caichao zhu Jinyuan TANG Chenxu JIANG State Key Laboratory of Mechanical Transmissions Chongqing UniversityChongqing 400030China State Key Laboratory of High Performance Complex Manufacturing Central South UniversityChangsha 410083China College of Aerospace Engineering Chongqing UniversityChongqing 400044China

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.

关键词： carburized gear multiaxial stress hardness gradient pitting spalling

Examination on the wear process of polyformaldehyde gears under dry and lubricated conditions

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Friction 2021年第3期9卷 538-550页

作者： Guoda YU Huaiju LIU Ken MAO caichao zhu Zehua LU State Key Laboratory of Mechanical Transmissions Chongqing UniversityChongqing 400030China School of Engineering the University of WarwickCoventry CV47ALUK

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.

关键词： polyformaldehyde gear lubrication wear surface damage

Tribological behavior of coated spur gear pairs with tooth surface roughness

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Friction 2019年第2期7卷 117-128页

作者： Huaiju LIU Heli LIU caichao zhu Peitang WEI Jinyuan TANG State Key Laboratory of Mechanical Transmissions Chongqing University State Key Laboratory of High Performance Complex Manufacturing Central South University

Coating is an effective way to reduce friction and wear and to improve the contact-fatigue lives of gear components, which further guarantees a longer service life and better reliability of industrial machinery. The fact that the influence coefficient linking the tractions and stress components could not be expressed explicitly increases the difficulty of coated solids contact analysis. The complicated tribological behavior between tooth surfaces influenced by lubrication and surface roughness further adds difficulty to the coated gear pair contact problems. A numerical elastohydrodynamic lubricated(EHL) contact model of a coated gear pair is proposed by considering the coupled effects of gear kinematics, coating properties, lubrication, and surface roughness. The frequency response function and the discrete convolute, fast Fourier transformation(DC-FFT) method are combined to calculate the surface deformation and the subsurface stress fields at each meshing position along the line of action(LOA). The Ree-Eyring fluid is assumed to incorporate the non-Newtonian effect, which is represented in the generalized Reynolds equation. Influences of the ratio between the Young's modulus of the coating and the substrate on the contact performance, such as pressure, film thickness, tooth friction coefficient, and subsurface stress field, are studied. The effect of the root mean square(RMS) value of the tooth surface roughness is studied by introducing the roughness data, deterministically measured by an optical profiler.

关键词： coating gear elastohydrodynamic lubrication (EHL) surface roughness