THERMODYNAMIC DAMPING IN POROUS MATERIALS WITH ELLIPSOIDAL CAVITIES

When a material is subjected to an alternating stress field, there are temperature fluctuations throughout its volume due to thermoelastic e ffects. The resulting irreversible heat conduction leads to entropy pr oduction which, in turn, is the cause of thermodynamic damping. An ana lytical investigation of the entropy produced during a vibration cycle due to the reciprocity of temperature rise and strain yielded the cha nge of the material damping factor as a function of shape and magnitud e of the porosity of the material. A homogeneous, isotropic, elastic b ar of cylindrical shape is considered with uniformly distributed ellip soidal cavities under alternating uniform axial stress. The analytical calculation of the dynamic characteristics of the porous structure yi elded the change of the material damping factor as a function of shape and magnitude of the porosity of the material. A homogeneous, isotrop ic, elastic bar of cylindrical shape is considered with uniformly dist ributed ellipsoidal cavities under alternating uniform axial stress. T he analytical calculation of the dynamic characteristics of the porous structure yielded the damping factor of the bar and the material damp ing factor. Experimental results on porous metals are in good correlat ion with analysis. (C) 1997 Academic Press Limited.