Failure Investigation of the Front Coil Spring of a 160 cc Motorcycle

Coil springs in motorcycles are crucial components in the vehicle's suspension system, where they are used in the front or rear to absorb the impact energy experienced by the wheels. In this study, the coil spring experienced a failure in the form of fracture, prompting several tests to analyze the mechanism and causes of this failure. The conducted tests include visual observation, chemical composition testing, metallographic testing, hardness testing, and FEM simulation. The visual observation results indicate that the failure experienced by the coil spring is due to fatigue fracture, as defined by the presence of crack initiation, crack propagation (beachmark), and final rupture. The chemical composition testing reveals that the material used is SAE 9254 Steel, that is a low-alloy steel. The microstructure formed consisted of ferrite and pearlite phases, attributed to the absence of quenching and tempering processes during the coil spring's production. The hardness testing results show an average hardness of 216,6 HV, confirming the absence of quenching and tempering in the coil spring production process. The FEM simulation results show that the stress does not exceed the yield strength of the material.