Fast Prediction Of Fatigue Limit Of 20Cr2Ni4A Gear Steel Based On Infrared Thermography

20Cr2Ni4A is a high-quality alloy steel with high strength,toughness and hardenability,and has the characteristics of high abrasion resistance of surface hardening and good toughness after carburizing and quenching.It is widely used in the design and manufacture of heavy-duty gears for large mechanical equipment.Heavy duty gears are the core components of transmission systems for large mechanical devices?bulldozers,excavators,armored vehicles,etc.?,and their main function is to transmit motion and torque at a specified speed ratio.In practical engineering applications,heavy gears often cause various problems due to the influence of large load,strong strain and long period.Among them,the fracture failure caused by fatigue accounts for more than 80%of the failure of the whole structure,so the fatigue problem becomes the bottleneck restricting its safe application.Therefore,in mechanical design,it is necessary to first understand the fatigue properties of the material.For a long time,the traditional fatigue experiment method has played an important role in determining the fatigue performance parameters of materials.However,the traditional method has the disadvantages of long experiment cycle,high consumption and low efficiency,which restricts the improvement of economic benefit in the process of structural optimization design,and the fatigue performance of materials is not easy to obtain.Therefore,it is urgent to develop a new fatigue assessment method to meet the high requirements of modern design.The macroscopic manifestation of energy dissipation in fatigue process is the change of non-uniform temperature field on the surface of the material.Infrared thermal imaging technology provides a new method for fatigue research.Based on the infrared thermal image method and energy dissipation theory,this paper studies the variation of damage indexes such as surface temperature signal,stress state and inherent dissipation in the process of fatigue damage evolution of materials and components,and realizes the rapid prediction of fatigue performance parameters of materials and components and the evaluation of stress state.The results show that under the action of fatigue cyclic load,when the stress level is low,the temperature rise is very small and almost zero.As the cyclic stress level increases,the temperature rise begins to increase,and a distinct initial rapid temperature rise phase and a stable temperature rise phase occur.There is a good correlation between the initial temperature rise rate of the cyclic temperature rise curve and the stable temperature rise value.It grows linearly slowly in the early stage until the temperature rise rate increases rapidly at the critical stress,so the stable temperature rise value and the initial temperature rise rate are utilized to predict the fatigue limit.The Luong method and Crupi method in infrared thermal imaging method have better support of material energy dissipation theory.Under the symmetrical stress state of stress ratio R=-1,the fatigue limit 500MPa measured by group method is used as reference.The accuracy of Luong method is higher,The537.5MPa error predicted by the steady temperature rise increment?T_AS is about 7.5%,while the 298MPa error predicted by the Crupi method is up to-40.4%;Luong method is slightly more dangerous,and the Crupi law is too conservative,Therefore,the fatigue limit predicted by Luong method can be reduced by 50MPa as the fatigue limit of engineering.In the course of the experiment,it is found that because of the temperature fluctuation caused by environmental temperature and so on,the prediction results are dispersed,which affects the infrared prediction accuracy,so the method of data continuous processing is adopted,so that the prediction results can be determined uniquely,the prediction error can be greatly reduced,and the forecast errors will be decreased to less than 5%.Finally,the meshing state of the gear in the actual service environment is analyzed.Four processes are summarized according to the contact state between the meshing teeth,and the force position and force value of the meshing of the gear tooth surface are accurately calculated by the cantilever beam.The cantilever beam test method under bending stress state is used to quickly predict the bending fatigue limit value by infrared thermography.The results show that the infrared thermal imaging method can make predictions on gear parts feasible.In addition,based on the fatigue increment prediction method of strain increment,the intrinsic correlation between the heat dissipation and strain variation of materials under gradient alternating load is discussed.The feasibility of infrared thermal imaging to predict the fatigue limit of gear parts was initially explored.