Relationship between Sound Absorption Property and Microscopic Structure Determined by X-ray Computed Tomography in Urethane Foam Used as Sound Absorption Material for Automobiles

Abstract

Recently, the application of porous soundproof materials to automobiles is changing from the use of sound insulation materials to the use of sound absorption materials. A method for attaining high absorption performance in the low-frequency region without increasing the material weight is thus needed. We investigated the use of X-ray computed tomography (CT) scanning for investigating the microscopic structure of soft urethane foam, a low specific gravity resin material, in a nondestructive manner. Our testing reveals that it is an effective tool for observing the microscopic organizational structure of a low specific gravity resin material and that the cell size of urethane foam, as measured by X-ray CT, affects the sound absorption characteristics. It also shows that reducing cell size shifts the peak frequency of the sound absorption coefficient downward.