High-pressure compliant syntactic foam for hydraulic noise control

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Gruber, Elliott R.
Cunefare, Kenneth A.
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Pressure fluctuations within a hydraulic system, commonly known as noise, create problems, such as leaks and breakout noise, within the system and necessitate treatment. Prior work has demonstrated the effectiveness of a flow-through expansion chamber with a syntactic foam liner; the device is known as a suppressor. Syntactic foam is a term of art which refers to a material fabricated from a host matrix and specifically selected inclusions to alter the engineering properties of the composite body. The syntactic foam used to treat noise is a voided polymer; the voids are created by hollow microspheres which collapse when exposed to a critical value of hydrostatic pressure. The voids within the host polymer increase the effective compliance to the foam; the increase in compliance decreases the noise within the system. As the system pressure increases, the voids within the foam shrink, reducing the compliance of the foam and its noise control effectiveness. The current work seeks to find a method to limit the voids from contracting with increasing system pressure. The work is conducted by increasing the internal pressures of the microspheres and fluorinating their surface to inhibit loss of internal pressure before fabrication. The increased pressure within the microspheres prevents voids created by the collapsed microspheres from losing volume as drastically as unpressurized voids at higher pressures. The result is functional noise control at elevated pressure, up to the maximum system operating pressure of 35 MPa.
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