Coil spring failure and fatigue analysis

This paper presents the failure and fatigue analysis results of a coil spring removed from a personal vehicle after having failed in service. Using experimental procedures like visual observations, optical and scanning electron microscopy, the failed coil was examined in order to determine the causes of the fracture. Furthermore, the chemical composition of the material was determined and a hardness test performed. It was concluded that the continuous contact between the coils formed corrosion pits that served as crack initiation points leading to the final fracture. Based on these findings, the finite element model of the coil spring was built to run the stress analysis under stochastic variable dynamic loading. The quarter car model was used for the assessment of vehicle behaviour under dynamic loading. Matlab numerical routine was used to perform rainflow counting as well as Miner's cumulative damage assessment in accordance with Goodman failure criterion. The obtained results give prediction of the spring fatigue life. The results can be useful in the further design optimization of motor vehicle coil springs.