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Damping in porous structures is enhanced by localized stresses in comparison with corresponding dense materials. An analytical model for mechanical damping in porous materials is suggested for the 'microplastic' range of deformation on the basis of the statistical mechanics of micro-heterogeneous materials. Two types of heterogeneity are considered: one-level porosity (directly sintered powder steels) and two-level porosity (larger pores in a carcass with smaller pores) on one hand, and fatigue-induced cracks on the other. Special emphasis is placed on the crackrelated contribution to damping using a Dugdale approach to crack-induced microplasticity.

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