Short crack growth in polycrystalline materials

The early stages of fatigue damage in cyclic loading in several polycrystalline materials were studied. The initiation of fatigue cracks is influenced by a number of factors like the presence of inclusions, grain size and cyclic creep strain. The growth of short cracks was measured in symmetrical loading and in cycling with positive mean stress. The kinetics of short crack growth is affected by the presence of secondary cracks and can be approximated by an exponential law. The integrated crack growth law is equivalent to Coffin-Manson law allowing the interpretation of this law in terms of short crack growth.