Fatigue-based reliability in assessing the failure of an automobile coil spring under random vibration loadings

The paper presents an assessment of fatigue-based reliability in measuring failure random vibration loadings due to unexpected loads under various road conditions. Random loads were the main cause of fatigue failure in a component durability analysis. Acceleration signals were measured during a road test held on rural and highway road surfaces. These signals were captured from an accelerometer placed on a vehicle’s lower arm suspension system in a locally made sedan-type automobile. This arrangement enhanced the capacity for collecting acceleration signals using multi-body dynamics simulation, which would minimise the need for actual acceleration data measurements. Modal analysis was conducted to determine the natural frequencies and mode shapes of the geometry of a coil spring so that strain signals based on each mode shape could be obtained. As modal parameters occurred within the frequency range of road excitation, fatigue life prediction was not affected by instances of dynamic behaviour in the components in time domain. Fatigue life was analysed using the Dirlik, Lalanne and narrowband approaches in frequency domain. The Dirlik method predicted a good correlation for the measured acceleration and generated strain signals at 2.32 × 108, 2.55 × 108 and 1.51 × 108 blocks to failure, indicating that a coil spring could withstand the uneven road surface without failing prematurely. Hence, fatigue-based reliability can evaluate the hazards of rate-reliability, based on predictions of fatigue life data on component durability.