Mobilite des dislocations lors de la sollicitation cyclique de l'aluminium polycristallin

Abstract

This paper is concerned with the study of microscopic mechanisms which control the cyclic deformation of pure polycrystalline aluminum (5N). By TEM technique, a dislocation cell structure has been observed from the first fatigue cycles. Fatigue loops, obtained under total or plastic strain-control conditions, and ultrasonic attentuation measured during the fatigue test itself, were analyzed in order to provide information on the dynamic behaviour of dislocations. According to the fatigue parameters, several mechanisms of interactions have been identified: at low fatigue amplitude, the dislocation-point defect interaction plays an important role; at higher fatigue amplitude, the interaction between dislocations is predominant. The athermal behaviour of this last mechanism suggests that long distance interactions are involved: they have been ascribed to internal stress necessary to ensure the compatibility of deformation between cell wall and the cell inside.