| Gear contact fatigue is an important factor limiting the development of high-end equipment such as helicopters,wind power,and ships to high power density,long life,and high reliability.The factors affecting the contact fatigue failure of gears are complex and multi-sources.Structural factors such as gear macroscopic geometry,lubrication conditions,and load excitation will directly affect gear contact service behavior;surface integrity characteristics such as surface roughness,hardness gradient,and residual stress are also closely related to gear contact fatigue failure forms.In addition,the microstructure characteristics of gear materials also play an important role in the fatigue performance.Although there are currently plenty of rolling contact fatigue related studies that incorporate the influence of material microstructure characteristics,most of them have neglected the description of the anisotropic mechanical properties of the internal crystals of the material,and lacked scientific understanding of the degradation process of the mechanical properties of key material points under long-term cyclic loading.The evolution of fatigue damage on the meso-scale in the process and its internal mechanism urgently need to be further explored.Therefore,it is important to break through the limitations of traditional gear fatigue analysis methods based on the assumption of material homogeneity,construct a numerical model of gear contact fatigue with crystal plastic coupling damage on the meso-scale,and study the effect of gear material microstructure and crystal mechanical property degradation on gear contact fatigue failure.The works mentioned above has important theoretical value and engineering significance.This paper takes a 2 MW wind turbine gear as the research object to study the failure mechanism of gear contact fatigue,builds a numerical model of gear contact fatigue analysis that couples slip system damage to the crystal microstructure characteristics,and reveals the gear contact fatigue damage mechanism from the aspects of material microstructure,fatigue damage accumulation,and degradation of crystal mechanical properties.The main research contents of this paper are as follows:(1)Construct a gear contact fatigue numerical model based on the theory of crystal plastic coupling damage.Through experimental testing and Voronoi computer graphics methods,the gear material microstructure test characterization and geometric topology reconstruction are carried out.Importing microstructure features of gear near surface layer material based on Python programming.Based on the Fatemi-Socie multiaxial fatigue criterion,the damage parameters on the slip system are derived,and the damage is coupled with the crystal plastic theory.The evolution of the back stress of the slip systems are introduced to consider the influence of the gear cyclic load conditions on the stress-strain response,and the micro-scale fatigue damage constitutive equation is developed based on the ABAQU UMAT user-defined subroutine programming,so as to construct a numerical model of the contact fatigue of the gear with crystal-plastic coupling damage.(2)Determination of contact fatigue constitutive parameters of gears with crystalplastic coupling damage.The gear contact fatigue crystal plasticity coupled damage constitutive equations contain a series of material parameters.In order to accurately describe the mechanical response of the key material points near the surface in the gear contact fatigue process,the constitutive parameters need to be formulated.By constructing two different monotonic tensile models,the influence of constitutive parameters of different single crystal materials,the number of crystal grains,and the geometric size of the model on the mechanical properties of macroscopic poly-crystals can be determined,and finally determine the constitutive parameters.(3)Research on contact fatigue damage behavior of gears on the meso-scale.Based on the construction of a damage-coupled crystal plasticity numerical model,a numerical simulation of gear high-cycle fatigue damage was carried out,and the influence of the introduction of crystal anisotropy on the stress and strain distribution of the subsurface layer was compared and analyzed,and the evolution of the stress and strain field and fatigue damage of the subsurface layer of the gear after cyclic loading were studied.The elastic constant of the material and the critical shear strength of the slip system of each crystal evolve with the number of cycles are studied.The evolution of gear contact fatigue damage on the meso-scale and the internal mechanism of gear contact fatigue failure are investigated respectively.(4)Carry out research on the influence of gear contact fatigue damage parameters.Study the influence of different load levels on the contact mechanics state,damage accumulation and performance degradation during gear service,explore the influence of different initial crystal orientation characteristics on the initiation position and fatigue life of gear contact fatigue cracks.Summarize the influence law of gear operating condition load and microstructure characteristics on its contact fatigue behavior,and provide theoretical support for the anti-fatigue design and manufacture of high-performance gears. |
