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The use of stress relaxation experiments for obtaining information about dislocation dynamics is discussed in view of the different empirical relationships between dislocation velocity and stress. Experimental results are presented to show that the applicability of either relation is determined by the internal state of the specimen and can be varied by varying the amount of plastic strain.

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High damping materials find numerous uses in the field of vibration and noise reduction in more or less complex structures. The high damping required in such structures can be structural damping or materials damping, although the distinction is not always clear-cut. Damping depends on a number of external parameters such as temperature, vibration amplitude, frequency, magnetic field etc. The material microstructure determines largely the mechanisnt(s) responsible for the damping level in a certain field of external parameter values. A number of possible processes for structural damping will be discussed as well as some o f the physical mechanisms responsible for materials damping in composite materials, polycrystalline materials, polymers, amorphous materials, etc. These mechanisms are based on micro- or macromolecular restructuration within the materials as caused by effects of dislocations and various types of interfaces (e.g. domain, twin, interphase or grain boundaries)

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