| As one of the most important components of locomotive,gear transmission system is prone to a series of behaviors such as crack initiation,propagation and even tooth breakage in complex working environment,which may cause serious accidents and economic losses.Therefore,it is of great theoretical significance and engineering value to study the dynamic characteristics and crack propagation mechanism of gear transmission system with root crack for the safe operation of gear transmission system.The main contents of this paper are as follows:Firstly,based on the potential energy method,the time-varying meshing stiffness of the healthy gear and the tooth root crack fault gear were solved,and the change law of the single-tooth meshing stiffness and the double-tooth meshing stiffness under different crack parameters were analyzed,and the meshing stiffness was found to be decreasing with the increase of crack depth and angle.The dynamic model of the 6-DOF gear transmission system was established,and the time-varying meshing stiffness of the gear under different crack propagation depths was substituted into the dynamic equation to solve the vibration characteristics of the transmission system.It is concluded that the crack failure causes periodic vibration and impact of the transmission system,and the vibration and impact are intensified with the increase of the crack depth.By analyzing the time domain signal and calculating the sensitivity of different statistical indicators to different fault degrees,it is concluded that the pulse factor is more sensitive to the crack fault characteristics.Secondly,the finite element model of the transmission system was established by using ABAQUS finite element software,and the contact characteristics of the gear transmission system under the internal excitation of different center distance errors and tooth surface friction coefficient were analyzed.It is concluded that there is an optimal assembly center distance to reduce the meshing impact,and the tooth surface friction coefficient had little influence on the contact characteristics of the transmission system.Dynamic simulation software was used to establish locomotive multi-body dynamics model,wheel polygons of different orders and rail corrugation with different wave depths were selected to obtain the vibration displacement of driven gear under different working conditions,and it was applied as an external excitation to the finite element model to solve the contact characteristics of the transmission system.It is concluded that the existence of wheel-rail excitation intensifies the vibration of the transmission system,increases the contact force of the cracked tooth surface and the stress at the crack tip.The risk of gear tooth fracture increases,affecting the safety of locomotive operation.Finally,the natural characteristics of gears with different crack propagation depths were analyzed,and the change of natural frequency ratio with crack depth was obtained,which provided a reference for the design of gear box and other parts.The stress intensity factor of tooth root crack was solved by the contour integral method to explore the mechanism of tooth root crack growth,and different contact conditions are simulated by changing the size and application position of the load.In ABAQUS,the propagation finite element method was used to simulate the root crack propagation path,and the PHILSM value was extracted to reconstruct the crack surface,and the change rule of crack propagation depth was solved. |
