Experimental and numerical analysis of a helical spring failure
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Results of experimental and numerical analysis of a broken motor vehicle helical spring are presented in this paper. Location of the fracture is on a first active coil of the spring. Experimental part of the research employed optical microscopy that revealed fractured surface microstructure and allowed for detection of inclusions. Corroded fracture surface limited scanning electron microscopy examination (SEM). Nevertheless, corrosion pits on the edge of the spring wire which served as crack initiation points could be detected by SEM along with radiating ridges left by the fracture front that propagated to the opposite edge of the wire. Optical emission spectrometer with glow discharge source sample stimulation was used to determine material chemical composition that is adequate to spring steel 61SiCr7. Additionally, hardness test was performed and obtained value was used to derive maximum tensile strength of the steel. Experimentally collected data served as input for numerical analysis of helical spring. Finite element analysis of a helical spring model was performed. Stress distribution was determined and fatigue life of the undamaged helical spring predicted. Results were compared with those obtained analytical. Causes of failure are outlined assessing the results of the performed experimental and numerical analysis. Insufficient corrosion protection and excessive contact between the coils caused damage that developed from initial crack to final fracture of the spring. Results obtained by this research are valuable in understanding fracture behavior of helical spring mounted in suspension system of various motor vehicles. Given the presented results, further improvements of spring design can be made in order to reduce failures.