Structural and Acoustic Damping Characteristics of Polyimide Microspheres

Abstract

A broad range of tests have been performed to evaluate the capability of tiny lightweight polyimide spheres to reduce sound and vibration. The types of testing includes impedance tube measurement of propagation constant, sound power insertion loss for single and double wall systems, particle frame wave characterization and beam vibration reduction. The tests were performed using spheres made of two types of polyimide and with varying diameter. Baseline results were established using common noise reduction treatment materials such as fiberglass and foam. The spheres were difficult to test due to their inherent mobility. Most tests required some adaptation to contain the spheres. One test returned obvious non-linear behavior, a result which has come to be expected for treatments of this type. The polyimide spheres are found to be a competent treatment for both sound and vibration energy with the reservation that more work needs to be done to better characterize the non-linear behavior.

Damping of Structural Vibration Using Lightweight Granular Materials

“…The measured frame wave speed in Table 1 was much smaller compared to those of the airborne wave propagation which ranges from 100-200 m/s [9]. When the lightweight particles are treated in small cavities of structures, the first resonant response of the particles is from the frame wave propagation since the frame wave is much slower than the airborne wave.…”

“…It has been shown that the conduction of energy into the granular material and subsequent dissipation [3][4][5][6][7][8][9] increase vibration damping significantly. It has been suggested that the maximum loss factor occurs at quarter wavelength resonances inside the granular material [7][8].…”