THERMODYNAMIC DAMPING IN POROUS MATERIALS WITH SPHERICAL CAVITIES

When a material is subjected to an alternating stress field, there are temperature fluctuations throughout its volume due to the thermoelast ic effect. The resulting irreversible heat conduction leads to entropy production that in turn is the cause of thermoelastic 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 the porosity of th e material. A homogeneous, isotropic, elastic bar of cylindrical shape is consider ed with uniformly distributed spherical cavities under al ternating uniform axial stress. The analytical calculation of the dyna mic characteristics of the porous structure yielded the damping factor of the bar and the material damping factor Experimental results on po rous metals are in good correlation with an analysis.