Abstract:

This Memorandum is concerned with the material damping of metals and their alloys. It may be considered to provide background information for ESDU 09006. Damping from external factors, such as lubrication, riveted joints and viscoelastic additions to the structure, are excluded from consideration. In the Item the main energy dissipation mechanisms responsible for material damping are presented. The first part of the Item is devoted to linear material damping, which is amplitude-independent but frequency-dependent. Most processes responsible for linear damping are relaxation processes, such as macroscopic and microscopic thermoelastic relaxations, point-defect relaxations and relaxations due to dislocations and grain boundary viscosity. Thermoelastic damping is present in all metals and alloys. However, it can only be identified at low frequencies, since at higher frequencies metals have damping which varies little with frequency. With some exceptions linear damping does not provide high values of loss factors. Nonlinear damping in metals and alloys is amplitude-dependent and frequency-independent. The main mechanisms responsible for nonlinear damping are associated with amplitude-dependent dislocations, magnetostriction, the heterogeneous structure of materials and phase transformations, all of which can give rise to relatively high damping with SDC values above 10%.