DESIGN OPTIMISATION AND LIFE ESTIMATION OF SPLIT HUB GEOMETRY OF FSAE CAR

摘要

Hub in the car faces high vibrations and centrifugal stresses. This calls for proper design and analysis. The life cycle of any formula car should be less which is adequate for racing purpose. This work is focused in analyzing low cycle fatigue and conducting vibratory analysis of a split hub of FSAE car. Stress concentration factor is significant in machine elements which give rise to localized stresses for any change in design of surface or abrupt change in cross section. This member acts as stress riser which leads to localized stresses in turn leading to peak stresses introducing cracks. These cracks may propagate and leads to catastrophic failure of machine elements and these conditions leads to fatigue analysis to calculate life. Two approaches are employed here. Based on linear elastic finite element analysis Neuber stresses are calculated from fictive elastic results. Strain Amplitude approach is followed by Coffin-Manson equation to determine Fatigue life. The failure induced by fretting fatigue due to two contact surfaces subjected to an oscillatory loading serves as premature crack nucleation which will gradually become a prominent issue during the running of car. In some cases it reduces the life due to micro slip at the edge of contact. The split pieces of hub talk to each other and create wear which is calculated by fretting. These rotary parts call for structurally rigid geometry. Modes with relatively high mode participation factor can be readily excited by the base vibrations. Vibratory stresses arise due to engine and rotating wheels acts like excitation frequencies which may lead to possible resonance. Campbell diagram is effectively used to modify the stiffness in turn design. Also an approach is done for design optimization of fillet stresses at Sharp edges caused due to bending strength of the split pieces. Optimization of diameter, contact region, root land dimensions is done to ensure stress distribution is uniformly spread along the fillet radius on both pieces of hub which otherwise may lead to crack initiation considering all peak stresses. Design of Experiments technique and optimization methods are used to improve structural integrity by finding the peak sectional stress. Design optimization is done using screening method to ensure strength of material.