Metal foams are used in various industries due to the great variety of properties they possess such as high strength-to-weight ratio, high energy absorption, and the ability to endure extreme conditions. However, despite their desirable properties, traditional metal foams lack acoustic absorption properties because of their stochastic open porous structure—a function of the foaming process. Additive manufacturing (AM) can allow the fabrication of more complex foams; however, current metal AM methods provide significant processing and scalability challenges, especially in printing aluminum parts. Here, we present an alternative method for fabricating open-celled aluminum sound absorbers with controlled cellular architectures. The method relies on modeling the cellular templates using an implicit, field-based modeling method. The templates are then fabricated by combining polymer-based AM techniques and converted into aluminum Duocel® foams using ERG Aerospace Corporation’s proprietary foaming technology. The acoustical properties of the fabricated foams are then measured using a normal incidence impedance tube method. Our results show that this method allows the fabrication of highly complex cellular architectures that may be optimized to obtain application-specific multifunctional performance.

Additive manufacturing allows the cost-effective fabrication of cellular porous structures with tailorable geometries. Structures with small pore sizes offer improved acoustical performance; however, they often result in increased structural weights and are difficult to produce using low-cost additive manufacturing methods. Here, we leverage our recent work demonstrating the fabrication of fibrous structures using 3D printing, to develop multifunctional porous structures with enhanced acoustical properties. Our method allows the addition of fibers to a structural host, which helps improve the acoustical performance without a significant weight or flow-reduction penalty. In this presentation, we outline the fabrication method and study the effect of adding fibers to the acoustical performance of porous structures with periodic gyroid unit cells. The effect of fibers on the acoustical impedance and flow resistance is studied using an impedance tube and a flow bench, respectively. We then use an inverse characterization method to analyze the effects of changing fiber and structural parameters on the acoustical performance. Our results show that adding fibers to porous host structures can drastically improve their broadband noise reduction potential.