Dynamic Characteristics Analysis Of Spur Gear System With Tooth Root Crack Fault

Gear transmission, as an irreplaceable mechanical transmission component, iswidely used in equipment manufacturing industry based on its advantages such ascompact, accurate mechanism, high efficiency, and strong load capacity. Tooth rootcrack fault is generated where the maximum tangential tensile stress is located, whenthe root suffering bending stress is too much high on the condition of high speed andheavy load. The crack extending throughout tooth width occurs tooth breakage, whichaffects equipment’s normal operation. Therefore, acquaintance with the form reasonof crack and mastering working dynamic characteristics of cracked gear system are ofgreat theoretical significance and potential engineering value for fault monitoring,identifying and diagnosing.This thesis focuses on the dynamic characteristics of gear system with tooth rootcrack fault by using mechanical vibration method, which is supported by the programfor the National Natural Science Foundation of China (No.51075179). The maincontents of this presented work are listed as following:(1) Based on the equations of standard involute and gear root transition curveformed in generating method, the time-varying gear meshing stiffness calculationequations for healthy spur gear pair are derived in potential energy method. Variationlaw of five stiffness kinds and the relationship between comprehensive stiffness andsingle/dual meshing stiffness. The presented meshing stiffness calculation method isvalidated by comparing with ISO method and approximate regression method.(2) The root cracked gear meshing stiffness calculation equations are derived byconsidering the influence of crack on bending stiffness, axial compressive stiffnessand shearing stiffness for involute profile and root transition curve. Finite ElementAnalysis (FEA) is applied to calculate cracked gear meshing stiffness in ABAQUS.By comprising with FEA result, the proposed theoretical method of cracked gearmeshing stiffness is validated. The gear meshing stiffness with root crack faultreduces in a certain degree with the difference of meshing position and crack depth. (3) The usual4degrees of freedom (DOFs),5DOFs and6DOFs gear pairdynamic models are proposed. Each characteristics of the models and applicationscope are analyzed. A dynamic gear system model of6DOFs is established includingmeshing damping effect and surface Coulomb friction effect.(4) Acceleration characteristics, friction characteristics and other dynamicvibration characteristics are compared in time domain and frequency domain betweenfriction and non-friction dynamic models, among different crack depths models andamong single tooth crack, dual cracks and three cracks fault respectively. Analysisresults show that acceleration and other vibration characteristics oscillate in timedomain as cracked gear meshes in and meshes out. Crack depth have a greaterinfluence on oscillation amplitude. Crack induces the signal sideband of accelerationin the line-of-action direction in high frequency range, and the sideband ofacceleration in the off-line-of-action direction in whole frequency range. Sidebandbehavior is more significant as crack grows deeper.