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Mechanisms and kinetics of the early fatigue damage in crystalline materials

[ jeudi 20-09-2007 13:00 | anglais ]Mechanisms and kinetics of the early fatigue damage in crystalline materials Jaroslav POLAK Institute of Physics of Materials
Academy of Sciences of the Czech Republic
Žižkova 22, Brno, Czech Republic

Résumé :
Multiple aspects of the phenomenon of localization of the cyclic plastic strain in fatigue of crystalline materials are shown. The effect of localization on the shape of the hysteresis loop, on the internal dislocation structure and especially on the surface relief evolution of austenitic and ferritic stainless steels is demonstrated. Characteristic features of extrusion and intrusion formation using AFM, FEG SEM and FIB techniques are presented. The mechanisms of fatigue crack initiation are considered. The experimental findings concerning the surface relief formation and crack evolution are confronted with existing models of fatigue crack initiation.

Short crack growth kinetics in polycrystalline materials in plastic strain controlled loading is documented. The short crack growth law and its parameters are evaluated. It is shown that short crack growth law describes reasonably well the damage evolution and its integration leads to the Coffin-Manson law. Parameters of the short crack growth law and parameters of Coffin-Manson law are compared.