A Qualitative Model for Amplitude Dependent Dislocation Damping

A two-mechanism model for dislocation damping, which should be valid in the cases of rather dense Cottrell atmospheres, is proposed. The first mechanism arises from the movement of the vibrating dislocation inside the most dense (axial) region of the atmosphere, while the second one, which can be identified with the well-known mechanism by Granato and Lücke, takes place at higher amplitudes of vibration, arising from the movement of the dislocation in the (external) low-density region of the atmosphere. Both mechanisms involve an amplitude dependent and an amplitude independent component of the decrement. A butterfly-shaped hysteresis loop is obtained which is the synthesis of one loop of the type proposed by Nowick and by Weertmann and Salkowitz with two loops of the type proposed by Granato and Lücke. In addition, the results of some experimental measurements, carried out on 99.995% aluminium for checking the qualitative features of the model, have been reported.