Viscoelastic properties, specifically mechanical damping and stiffness, of biological and high-damping composite materials were studied experimentally using the Broadband Viscoelastic Spectroscopy (BVS) and Resonant Ultrasonic Spectroscopy (RUS) techniques. For a human tibia, a relative minimum in damping over a frequency range of I to 100 Hz was observed which is inconsistent with the hypothesized optimal "design" for bone as a shock absorber. Furthermore, wet bone exhibited a larger viscoelastic damping tan δ than dry bone over a broad range of frequency using BVS. For a bovine femur it was difficult to distinguish the three separate damping peaks in the RUS spectrum due to the broadness of the peaks, caused by the high tan δ.

A high-damping viscoelastic ceramic, lead metaniobate, was studied in torsion and bending over more than ten decades of time and frequency. Damping at audio and sub-audio frequency was lower than at ultrasonic frequency. The damping at the highest frequencies approached 0.09 which was previously observed at ultrasonic frequencies.

Several RUS scans from 50 to 500 kHz were conducted on cubical specimens of various materials including brass, aluminum alloys, and polymethyl methacrylate (PMMA). Since the higher modes are closely spaced, fundamental torsion modes for each specimen were studied to measure damping and stiffness. Tan δ via RUS and BVS for PMMA and In-Sn corresponded in the frequency range where the methods overlapped. Experiments were performed using negative stiffness inclusions in a positive-stiffness matrix. The resulting composites exhibited extreme mechanical damping and large stiffness anomalies, as a consequence of the high local strains that result from the inclusions deforming more than the composite as a whole.