In the automotive industry, a prediction of real fatigue life for engine moving parts, such as crankshaft and connecting rod, has been carried out by quantifying and normalizing laboratory data. Attempts to correlate a fractured morphology directly to the prediction of fatigue life have been unsuccessful because the failure of real part is accompanied by complex factors. We investigated the fracture behavior at different fatigue cycles to correlate morphology and fatigue life characteristics.

Microalloyed steel has been widely used mainly for cost saving and weight reduction by optimizing the component design. Thus, we investigated the correlation of fractured morphology especially fatigue striation vs. failure cycle characteristics. We carried out numerous experimental works on various cases and fatigue limit quantification to correlate the life cycle and failure propagation for microalloyed and alloyed steels. It is found that a new type of microalloyed crankshaft exhibit a similar fatigue limit compared to the high strength alloy steel.

Fatigue tests have been carried out with specimens machined from forged crankshafts. Rig tests have been performed with machined crankshaft of different materials. We also analyzed the actual stress by applying strain gauges on the surface of crankshaft and compared with result of Finite Element Analysis(FEA) for demonstrating consistency of rig test and simulation. From the above evaluation results, we can determine the safety factor of crankshaft and thus, enable to optimize the design and materials for maximizing the engine performance.