The study of crack initiation in sintered steel and mild steel under fatigue / Ahmad Ashari and Zaid Zahari

During the process of a fatigue failure, microcracks initially form and then coalesce or grow to macrocracks, which propagate until the fracture toughness of the material is exceeded and final fracture occurs. For the present purposes, in which we are generally considering metals in the usual range of grain size (2 to_200μm), a microcrack may be defined as smaller than a few grain diameters; a macrocrack may be taken as larger than this. This presentation will be concerned with the phenomenology of formation of microcracks, growth of microcracks to macrocracks (usually a slow step), and the subsequent slow growth of macrocracks at low values of the alternating stress intensity near threshold, Af<o. Comparison of the growth _of microcracks at high cyclic stress and the growth of macrocracks at low cyclic stress where AK is approximately the same will also be made.