Research For Fatigue Life Of Leaf Springs

Leaf spring is an elastic component often used in dependent-type suspension on modern vehicles, and its stress and fatigue strength characteristics are vital to the reliability and security in the vehicle riding. Based on the structure stress status research of leaf springs, this paper calculates the fatigue life of the leaf spring under cycle loading. And find out a solution to predict the fatigue life by combine FE analysis with program calculation.FEA model of its free status has been built using ANSYS APDL. To figure out the nonlinear contact condition of the leaf spring, we use contact element type to simulate the contact region of leaf spring, and treat with the elements' attributes properly. Then the initial stress was calculated with proper load and the assembly process simulation. The FEA assembly model was built according to the distortion of the leaf spring in the former phase in ANSYS APDL. The load case was simulated with contact of loading head and leaf spring. And the displacement control of the leaf spring center was transferred to the displacement at load point. Then after the load step options configuration, the leaf spring stress circulation under cycle loadings was calculated. The model was validated by the result compare between the rigid extracted from the simulation results and the one out of the rigid test of the leaf spring.The stress result of assembly process and loading process was exchanged with the ANSYS special function on external data file. And the stress of leaf spring under virtual condition was calculated by the operation of array vectors of model results, which were generated from the external data file.Using the S-N curve, and considering the influence on fatigue characteristics of the leaf spring real feature, we edited the calculationprogram in ANSYS postprocessor to calculate the fatigue life on the critical points of leaf spring. At last the result's validation was proven by the fatigue test of leaf spring.The results of the test and simulation reveal that based on the FE analysis, it is feasible to predict the fatigue life of the structure in the critical location when the S-N curve of the fatigue life applied. The meanings and conclusions can effectively instruct the design of leaf spring system.The results of the test and simulation reveal that based on the FEanalysis, the fine friction between leaves is no obvious influence upon the structure stress distribution. It can simulate the complete stress cycle including the initial stress in the assembly process, by composing stresses of two stages. Because of the sliding at the loading node, this special loading condition can be simulated by contact between the loading head and leaf spring. It is feasible to predict the fatigue life of the structure in the critical location when the S-N curve of the fatigue life applied. The meanings and conclusions can effectively instruct the design of leaf spring system.