Scanning electron micrograph of nickel-based superalloy open-cell foam.
New research shows that superalloy foam can better absorb the noise of ships and aircraft engines.
Engines and exhaust systems of jet aircraft are the main noise source of the aircraft, but the operating temperature of jet engines exceeds the operating temperature of materials commonly used for sound attenuation, such as polymer foam. One possibility to reduce aircraft engine noise is to combine conventional sound insulation with extremely heat-resistant metal superalloys, a method that has been applied to jet turbine blades.
A * STAR's Wei Zhai and Xu Song of the Singapore Institute of Manufacturing Technology and their colleagues said that conventional polymer foams can be used as a template for making heat-resistant sound-insulating superalloy metal foam. The team developed a technology in which they applied a slurry of a nickel-based superalloy to a polymer foam, then burned the polymer, leaving an open-cell metal foam with the same structure as the original polymer . Zhai says cheap polyurethane household cleaning sponges can be a good template for metal foam.
Xiang Yu and Fangsen Cui of A * STAR High Performance Computing Institute have jointly developed a predictive model for optimizing the pore structure of metal foams to meet specific needs. First, they produced a range of metal foam structures by coating them on polymer templates with various porosities and pore sizes. The researchers then tested the acoustic properties of these metal foams and obtained data on how foams with different pore structures absorb sound. This data forms the basis of the predictive model.
The research team found that sound absorption is usually better when the pores are smaller. The smaller the pores, the longer the path of sound waves in the material, which increases the transmission time and makes it difficult to transfer. The material suppresses acoustic energy by converting it into heat. This phenomenon is called the thermoviscous effect.
Zhai said that the next step is to better control the template replication process so that an adjustable pore size gradient can be formed within a single foam block. The sound absorption and mechanical properties of this gradient metal foam will be further improved. In addition to sound absorption, metal foam also has excellent properties-light weight, non-flammable, and high structural strength. These characteristics have great potential for aircraft and marine engine and exhaust components. The improved foam can be used as the core material of the sandwich structure composite material, which has both mechanical strength and sound damping properties in one component.