Finite Element Simulation Of The Influence Of 20CrMnTi Pitting Corrosion On Stress Concentration

As one kind of the traditional gear steel,20CrMnTi still occupies about 50%of the automobile gear market due to its excellent comprehensive performance.Pitting corrosion often occurs on the surface of gear teeth under actual working condition.The stress concentration produced from the pitting corrosion will accelerate the fatigue crack to sprout and develop around the pit,and result in the early fracture and failure of the components.Currently,the real mechanism of the fatigue failure caused by pitting corrosion as well as the definite critical condition is not clear.In this way,it is very significant to investigate the influence rule of the pitting corrosion on20CrMnTi stress concentration and gear fatigue.On the basis of the true morphology of the 20CrMnTi pitting corrosion obtained through the immersion test,this thesis parameterizes the modeling through the software of Solidworks,and applies the ANSYS Workbench software to carry out the static analysis and transient analysis on the modules to implement the finite element simulation.The specific contents are as follows:1.The hemispherical and semi-ellipsoidal pitting corrosion models with various sizes were established by applying Solidworks software.The influence of the three-dimensional size changes of the pit on the Stress Concentration Factor?SCF?wassimulatedbyANSYSWorkbench.Theempirical equations[K=0.8659-0.1442?w/l?²+1.149?w/l?-0.0743?r/l?²+0.2555?r/l?+0.3522?w/l??r/l?]of the SCF for the depth ratio of pit?r/l?and the width ratio of pit?w/l?were established with the aim to predict the approximate SCF of the pits whose three-dimensional size has been known.2.Through the numerical simulation analysis which influences the relationship mutually between the pits,we can obtain as follows:the mutual coupling effects of the two pits parallel to the tensile direction will reduce the stress concentration.When the spacing is 0mm,the stress concentration factor decreases by 9.2%compared with the single pit,when the spacing is greater than 1.2mm,the stress concentration factor is close to a single pit,and the interaction is negligible;the stress concentration factor increases sharply when the two-point pits are close together and perpendicular to the tensile direction;When the spacing is 0mm,the maximum stress value is as high as30.82?₀,which is 93%higher than the stress concentration factor of a single pit.which is a relatively dangerous distribution of pitting.The nucleation of the secondary pit at the bottom of the original pit has high crack nucleation potential due to its high stress concentration.For the constant depth of the secondary pit,the larger the diameter of the secondary pit is,the more favorable it is to moderate the secondary pit to intensify the stress concentration of the primary pit.3.The dynamic contact process of 20CrMnTi gear component with pitting corrosion was simulated,and the influence of pitting position on the contact stress concentration distribution as well as the fatigue life during the gear's dynamic meshing process was explored.The research results indicate as follows:when the pit defect is located in the nodal circle,the most serious stress concentration will be produced,the contact stress is as high as 749.87Mpa,the contact fatigue life of the active wheel is minimum of 5014.6 times,which is only 5%of the life without defects,the failure form will be changed from the bending fatigue of the tooth root of the drive wheel during the period without defect to the contact fatigue failure of the gear teeth with the pitting corrosion.In addition,the closer the pit is to the edge of the gear teeth,the more serious the stress concentration is,and the lower the fatigue life of the gear is.