Theoretical And Experimental Researches Of20CrMnMo Gear Root Residual Stresses

Gears have been widely used in equipment manufacturing and other regions, due tothe important role in mechanical transmission. With the development of science andtechnology, the performance requirements of gears, such as high strengh, highefficiency and high reliability are also increased. Usually, fatigue failure is one of themain failure mode of gears, which will seriously influnence the transmissiveperformance and the service life. Shot blasting is one of the cold processing technologyfor matel surface which is usually used as a surface treatment process of gears. Recently,lots of researchs have been done by both domestic and international scholars on the shotpreening techniques and the residual compressive stress processed by shot peeningstrengthening, but those works have not been focused on the influence of residualcompressive stress on the gears performance. Although there are some conclusions, it islack of data to do verifications. In this thesis, the deeper correlation among the shotpeening process, the residual compressive stress and the bending fatigue strength will bestudied though the theoretical analysis, numerical simulation and experiment based onthe testing the residual stress of20CrMnMo gear root. The content of the researchembraces five principal sections:First, analyzing and discussing in detail to measuring principle of residual stress,considering the characteristic of testing object. And the X-ray and fixed is selectedas the testing method.Second, the testing20CrMnMo gears with same specification are divided into twogroups: one group is processed with peening strengthening, and the other is the controlgroup without the peening strengthening. The fixed method and the fixed0method are used to test the grouped gears respectively. The results indicate the fixed method is more precise and reliable.Third, the test results of residual stress of gear root between the peeningstrengthening group and the controls are analyzed, in order to acquire the reliable datathat the peening strengthening can improve the residual stress and the deep relationshipbetween the peening strengthening and the residual stress.Fourth, the finite element model the same with the actually working conditions isestablished in ANSYS based on the peening strengthening process to analysis thefactors that affect the distribution of residual stress. The relationships among the projectile velocity, projectile diameter and the residual pressure stress are discussed.Some ideas are developed to improve the residual pressure stress of gear root.Last, the fatigue strength experiment of four stress level is done based on thegrouping method and staircase method respectively in the electromagnetic resonancefatigue machine, and the P-S-N curves are matched. The influences of residual stress onthe improving the bending fatigue strength of gear root can be resulted combining theexperiment data and the test results of residual stress.