Crack Failure Mechanism Research And Dynamic Response Analysis Of Gear Transmission System

With the rapid development of China’s economy,the machinery manufacturing industry moved closer to the "intelligent" and "high-end" direction.As machinery and equipment became more sophisticated and complex,the incidence of failure rates increased,and the forms of failure became more diverse.Because of its special internal structure,the stress-strain situation in a gearbox,as a common transmission device,is relatively complex and very prone to failure.As one of the more serious types of gearbox failure,broken tooth failure is a more serious type of failure.Its early manifestation is in the form of cracked gear teeth,so the study of cracked gear failure can provide a theoretical basis for early fault diagnosis of gearboxes.This paper takes the gear transmission system as the research object,studies the mechanism of tooth crack generation and expansion,analyzes the important internal parameters of gears,including time-varying mesh stiffness,constructs the gear transmission system dynamics model,studies the dynamic response of the gear transmission system,analyzes the fault characteristics and laws,and provides the theoretical basis for fault detection and diagnosis.The main research content of this paper is as follows:Firstly,the fatigue cracking fault expansion mechanism of gears is studied.Three types of crack fracture characteristic models are compared,and the crack tip stress and displacement fields of each characteristic model are analyzed.The crack expansion rate equation is described,and the different stages of crack expansion are investigated.Design crack expansion simulation experiments to simulate the tooth meshing process and determine the initial crack location.The effect of the support ratio and the initial crack position on the crack expansion path is considered,and the simulated crack expansion path is obtained using the finite element method and compared with the experimental crack path to determine the accuracy of the experimental method.Next,the variation law of the meshing stiffness of the sawtooth and random curve-shaped crack models is investigated.Based on the potential energy method,the meshing stiffness algorithm is improved to derive the meshing stiffness calculation formulae for the two models,calculate the meshing stiffness under different failure levels,and analyze the effect of different crack failure levels on the meshing stiffness and its components.Based on the finite element method,tooth surface stress analysis is carried out on gear models under different health conditions to study the effect of different degrees of cracking on the gear meshing characteristics,and the meshing stiffness of the two cracking models under different degrees of cracking is calculated and compared with the results of the potential energy method to verify the validity of the cracking models.Finally,the dynamic response and fault characteristics of the gearing system are investigated.A six-degree-of-freedom dynamics model is constructed to obtain the dynamic response of the gear system,taking into account the time-varying meshing stiffness and tooth surface friction.The response of the system under different levels of failure is analyzed,and crack fault characteristics are extracted using time and frequency domain analysis.Combined with the experimental signals,the simulation results of the gear dynamics model are compared to verify the accuracy of the model.The simulation signals are evaluated using time-and frequency-domain indicators to obtain methods and indicators suitable for evaluating gear faults and to provide guidance for gear system fault diagnosis.