Material Modeling of High-Pressure Compliant Syntactic Foams

Syntactic foam, specifically a host urethane embedded with hollow microspheres, has been shown to be an effective method to treat pressure pulsations, also known as noise, within a hydraulic system; however, the current generation of foam becomes less effective with increasing system pressure, particularly ineffective above 7 MPa. Material modeling predicts that increasing the initial internal pressure of a microsphere will allow voids within the foam to retain their size at pressures up to 35 MPa and the foam will remain compliant at those pressures. Noise is attenuated by an expansion chamber lined with syntactic foam when the system pressure causes embedded microspheres to collapse, which leaves a gaseous void within the host urethane, greatly reducing the effective bulk modulus of the foam. Predicted material properties are then used in conjunction with a previously developed linear acoustic model to predict the effectiveness of developmental syntactic foams. Changing the mechanical properties of the current host urethane does not have a drastic impact on the overall performance unless the properties have been reduced to the approximate order as the properties of the void. The factors with the most consequence on noise control effectiveness are the internal pressure of the microspheres and system pressure.