SUMMARY

Fluid-borne noise is a significant problem for hydraulic circuits, especially for mobile applications. The problems cause by fluid-borne noise range from leakage to fatigue cycles to operator discomfort and hearing loss. Previous work has shown adding compliance to the system can treat the noise and its associated problems. One method is to include a syntactic foam – a term or art for a host matrix with specific inclusions; in this case a voided polymer. The compliance of the foam is a function of its void fraction, and the voids are created by collapsed microspheres. At elevated system pressures, up to 35 MPa, the voids lose their volume and the noise control effectiveness of the foam is diminished. This work uses pressurized voids to prevent the voids from shrinking as drastically. The pressure is of the voids is increased by permeating a gas into the microspheres before casting them into the foam. The microsphere is then chemically locked in order to prevent the pressure from permeating out. The polymer matrix for the foam should be very compliant itself while being able to interface well with the oil. For the purposes of this work a coated silicone is used as the host matrix. Experimental measurements of the noise control effectiveness of foams incorporating the pressurized microspheres show an improvement over the previous generation.