Abstract: The crack propagation characteristics of a kind of diesel crankshaft are studied by measuring the crack growth rate using the frequency sweep method. This method is based on resonant fatigue test rig. According to the regularity that the resonance frequency will drop as the crankshaft’s crack growth, the method tracks the crack size’s growth rate dynamically by scanning the spectra of the resonant system. After the crankshaft is broken and actual shape and size of the crack are available, finite element modal analyses are conducted to accurately calculate the crack size at various test-cycle time point. The frequency sweep method is a more capable method than normal methods. It can be directly applied to a component even with complex structure and has been treated by all kinds of technology processing. As a corresponding result, the crack growth rate curve plotted herein would synthetically reflect many influence factors on the crack propagation behavior, such as geometric parameters, precision of machine tooling and reinforcing treatments, etc. 4 crankshaft specimens are tested and the result shows that a 3-section feature exists in the Paris region of the curve. According to the specimens’ fracture surface profile, it is concluded that the feature’s formation is chiefly due to the stress ratio’s sudden change during crack propagating, which is caused by surface residual stress of the .

Key words: Crack growth rate, Engine crankshaft, Frequency sweep method, Residual stress