The Effect Of Geometrical Parameter And Mean Stress To Fatigue Life Of Stepped Shaft

Under the imburse of the talents project fund of Gansu Province and technicality step & characteristic study of Lanzhou University of Technology, the effect of geometrical parameter and mean stress to fatigue life of stepped shaft was investigated in this paper, the available parameters to the application of anti-fatigue design in engineering was obtained.In this paper, the main factors influencing the fatigue life were discussed based on fatigue strength theory,geometric model of stepped shaft was proposed. The local stress-strain method of fatigue life prediction was discussed, combined with prediction of the multiaxial fatigue life, the life prediction model which takes equivalent strain as the damage parameter was obtained. The basic principle of material plastic mechanics was discussed, three-dimensional finite element model of stepped shaft was established with the software of ANSYS. Elastic-plasticity and nonlinear cyclic stress-strain relationship of 40Cr steel was used in the finite element model of the stepped shaft. The parameters of the stepped shaft transition fillet radius, diameter ratio and stress ratio were considered, the stress and strain at stepped shaft transition fillet was analyzed.Von Mises equivalent stress was choose to be the damage parameter of low cycle fatigue life prediction, low cycle fatigue life of shaft was calculated combined with finite element analysis results.The calculation result shows that the low cycle fatigue life of the stepped shaft increases with the increases of transition fillet radius, reduce as the increases of diameter ratio (D/d) or stress ratio (R). The reason of transition fillet radius and diameter ratio influences on the fatigue life is that, the stress coefficient factor of the transition fillet radius changed with the transition fillet radius and diameter ratio. The stress concentration factor will increase and the fatigue life will reduce as the r reducing or D/d increasing.The reason of stress ratio affecting the fatigue life is that the increasing stress ratio leads to the raising average stress and enhances the elongated part of the cycle which result in the decrease of the fatigue life of stepped shaft.