Fracture morphologies are often formed as a result of plastic deformation at the crack tip. Therefore, it has been found that sizes of fracture morphologies (striation spacings, stretched zone width etc.) are correlated with fracture mechanics parameters. Such relationship makes possible the quantitative analysis of service failures of machines or structures.
In this paper, striation spacings were measured by transmission microscope fractography on the replica obtained from fatigue failed machine parts (gears, shaft and crane hook), and the values of applied stress amplitude or cycles given to propagate the crack until failure occurred were estimated using the relation between the striation spacing and stress intensity factor, ΔK. Fatigue tests or fatigue crack growth tests were carried out with the specimens taken from actually failed machine parts to know the fatigue properties for the parts. The combined fractographic fracture mechanics method was found very valuable in the quantitative analysis of fatigue failures of machine parts.
