Research On Failure Mechanism Of 20Cr2Ni4A Heavy-duty Gears Based On Material Characteristics

The heavy-duty gear is the core component of the transmission system of large mechanical devices(bulldozers,excavators,armored vehicles,etc.).Its main function is to transmit motion and torque according to the specified speed ratio.In the study of the fatigue performance of heavy-duty gears,the gear transmission efficiency is reduced and the meshing is not in place due to the micro-damage of the tooth surface pitting,gluing,wear,etc.caused by contact fatigue;the bending fatigue directly causes the tooth root to crack or even Forming a broken tooth phenomenon,causing a major accident.In engineering structures and mechanical equipment,most parts are subjected to cyclic reciprocating alternating loads,which makes the bending fatigue failure phenomenon extremely common,which puts high requirements on the fatigue resistance of the parts steel.The main factors affecting the bending fatigue performance of steel parts of heavy-duty parts are surface defects and internal defects,such as scratches,pits and inclusions on the surface;holes,micro-cracks and inclusions on the surface.In order to improve the fatigue properties of steel materials and improve the bending fatigue life,researchers have done a lot of work,especially in the analysis of the characteristics of inclusions on the failure mechanism of steel has obtained a lot of constructive theory.Therefore,it is important to accurately test the bending fatigue life of heavy-duty gears,analyze the bending fatigue performance,optimize the gear design,improve the gear performance,monitor the equipment failure caused by bending fatigue failure,and avoid major accidents during service.Based on the material characteristics of heavy-duty gear steels,the paper takes the shape characteristics,mechanical properties and interactions between the inclusions in the steel as the starting point,and explores the influence of the characteristics of inclusions on the bending fatigue performance of heavy-duty gear parts.A high-precision heavy-duty gear bending fatigue tester was designed to test the fatigue life,in order to analyze the main principles of steel failure from the microscopic point of view,and the following three research results were obtained.(1)According to the analysis of the inclusions on the surface of the heavy-duty gear steel,the difference between the two steel non-metallic inclusions is visually counted,and the hardness and elastic modulus of the two main inclusions are measured according to the existing data,and according to the fatigue The curve model is mathematically fitted,and a set of semi-quantitative empirical formulas for predicting bending fatigue associated with inclusions is proposed.Its expression appears in Section 3.5.It is verified by regression analysis that the formula can accurately predict heavy-duty gears based on inclusion properties.The bending fatigue life.(2)Guided by the test method specified by the national standard,combined with the test conditions,the equivalent calculation is based on the root stress,and three kinds of stress levels meeting the test conditions are selected;the performance of the test gear and the test machine are tested to ensure the feasibility of the test and Accuracy,the fatigue test was completed according to the experimental procedure.The bending fatigue performance of the heavy-duty gear made of 20Cr2Ni4 A grade steel was measured for the first time.The fatigue life data under different stresses are obtained.The residual stress test and microscopic analysis of the broken teeth are carried out.The performance of the gears is accurately evaluated by the characteristics of the crack propagation fatigue crack propagation.(3)Through the preliminary test and the related research at home and abroad,the advantages of single-tooth loading high-frequency fast and uniformity of meshing loading force are integrated,and a new heavy-duty transmission gear bending fatigue testing machine is designed.The experimental machine mainly has three innovations.The first can be engaged by the meshing type,which is more suitable for the actual service form of the gear.The second can be used for variable angle loading and the gear life detection in all directions.The third can be used to adjust the load stress to meet the weight.The range of loading stresses required to carry the gear.This paper focuses on the key parts of the transmission system-heavy-duty transmission gears,focusing on the study of the bending fatigue mechanism of the inclusions on heavyduty gears,and provides the basic data and technical support for the development of a new generation of high-performance heavy-duty transmission gear in China and the improvement of the power density of the army mobile platform.