Damping capacity of carbon foam

An experimental measurement of dynamic elastic constants and damping capacity expressed by a loss factor in carbon foams is presented. Sample has been placed in free vibration mount in vacuum. Electromagnetic excitation and optical detection of free vibrations have been used. Elastic modulus and loss factor has been inverted from resonance frequencies and logarithmic decay measurement performed at several (up to 10) normal-mode resonances using Demarest’s theory of cube resonance. For samples under investigation dynamic shear modulus was found to be proportional to sample density and equal to 1 GPa for 0.5 kg/m3. Specific damping capacity was equal to 0.004 for 0.3 kg/m3 foam samples and 0.012 for 0.5 kg/m3 foam samples that cannot be explained by difference in foam structure and must be caused by difference in properties of the constitutive material. Technical problems, such as the contribution of parasitic damping to the loss factor are discussed in details.