Remnant Life Estimation of Automotive Components by Resonance Fatigue Method

In today’s commercial vehicle scenario, designing and developing a component which will never fail throughout its lifespan is next to impossible. For a long time especially in the field of automotive, any crack initiation shall deem the component as failed and the design requires further modification. This paper deals with studying the failure of one such component and understanding the effect the crack has on the overall life of the component i.e. understanding the remnant life of the component. The component under study was gear shift lever bracket and is mounted on the engine exhaust manifold. It experiences two types of loads: inertial load due to the engine vibration and gear shift load. Frequent failures were observed in the field and in order to simulate it at lab, an accelerated test approach was adopted. The engine operating speed was used to identify the possible excitation frequency which the component might experience. In order to simulate the gear shift forces a known weight was put simulating the shift forces which was approx. 5.25 kg. With the setup, the component was excited in its operating range and resonance was studied. It was observed that the resonance of the structure fell close to the engine idling rpm. This was critical as the amount of time the vehicle will be in idling will be predominantly high (Mining tipper application) and thereby increasing the damage on the component. Strain levels & accumulated damage on the component were studied. The test was continued further after the initiation of crack. On further continuation it was found that the resonance of the component started to fall below the engine excitation frequency, without much change in the crack behavior. This test was conducted for different materials and designs to understand the behavior and the effect was studied thereby helping us understand the remnant life of the component.