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.
We investigated several conditions for manufacturing polyurethane foam for motor vehicle application to clarify the effect of the material structure on sound absorption performance in the low-frequency region. The objective is to reduce material weight without reducing noise absorption performance. We investigated the relationship between the internal microscopic structure and absorption performance by 3D analysis of X-ray computed tomography scanning observations. We found that the microscopic structural parameters of the material cells affect the sound absorption frequency and that they have a strong relationship with tortuosity, which is an acoustic parameter of porous materials. We also found that reducing cell size and making the cell frames thicker shifts the peak frequency of the sound absorption coefficient downward.
In this paper, we propose a method suitable for increasing the dimensional accuracy in the bending of high-strength steel sheets with a small work load by controlling the amount of a punch indentation in V-bending. The optimal indentation for obtaining the desired bending angle exactly could be calculated by finite-element-method (FEM) simulation using many types of high-strength steel sheets with different material characteristics. This method is effective for reducing the work load and obtaining a small radius of curvature in bent steel sheets; thus, it is suitable for forming high-strength steel sheets, which have been used widely for the fabrication of automobiles.
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