Analysis Of Dynamic Stress In Gears Based On Stress Wave Propagation

Gear system is widely used in power and motion transmission, the research about its strength and life has received much attention. Usually, dynamic-static method is used to calculate gear strength, which does not reflect the essence of the operating state of gear transmission. Gear faults occurring in recent years commonly are due to vibration, and the stress wave in gear is a hidden and mainly destructive factor affecting the strength and reliability of gear transmission, so the design criterion of gear needs to be improved. This paper for the first time introduces stress wave transfer theory to design of gear strength, and really realized the calculation of dynamic stress of gear and provides a kind of new meaningful thought for calculating stress of gear.This paper summarizes the basic theory of elastic dynamics. As a fundamental research, the paper takes a simple equal-section bar and rectangle-section taper bar as analyze examples, respectively, establishes their wave equations, and builds up a FE model to study their dynamic responses under a few circumstances such as being subjected to axial, radial, and being subjected to axial in the meantime with radial load.Finally the paper uses gear teeth of a spur gear as analyze object, builds up a complete 3D meshing model of a pair of spur gears by using UG, and carries out simulation research on the dynamic stress in gear meshing process by using LS-DYNA. The results show: (1) actually bigger dynamic stress mainly concentrates on contacting areas and near the root of teeth;(2) At lower rotation speed, the dynamic stress value calculated by method of wave theory is lower, so it can't bring gear breakage, but at higher rotation speed, stress is bigger than the one at lower speed, and bigger rotation speed causes bigger stress. When rotation speed reaches certain limit, the dynamic stress calculated by using wave theories has even greatly exceeded stress limit, this indicates that gear designing adopting conventional design way is unreliable in high speed transmission. (3) At higher rotation speed, the gear contacts not only on face of gear but also on back of gear according to simulation results, it means the rattling occurred in gear system, and the dynamic stress caused by impact load due to rattling can't be neglected. This further indicates that the effect of stress wave must be taken into account in the strength design of gear in high speed transmission.