Core materials offer a wide range of properties and benefits for composite manufacturers. However, research labs, universities and supplier companies are continually expanding, adapting and answering the demands of new composite applications.

Greener, Quieter Sandwich Composites

Three composite manufacturing researchers from the University of Delaware investigated the material properties of cork-sandwich composites and concluded that cork shows significant promise for use in aerospace, commuter rail and wind-energy technology. Dr. Jonghwan Suhr, an assistant professor in the university’s Department of Mechanical Engineering and affiliated faculty member of the Center for Composite Materials (CCM), said the most important discovery was finding just how well natural cork reduces sound transmission and vibration when used in cork-sandwich composites.

During the research project, Suhr served as an advisor to the lead researcher, Arthur James Sargianis, who completed his master’s degree in mechanical engineering at the University of Delaware in May 2012. Sargianis took first-place honors at the 2012 Society for the Advancement of Material and Process Engineering’s National Student Research Symposium for his paper, “Natural Material Based Sandwich Composites with Enhanced Noise Mitigation.” Published in 2012, the paper detailed Sargianis’ findings as he researched the potential benefits of using cork as a core material.

Sargianis’ research with cork was selected from a group of six finalists in the U.S. in the master’s degree category, according to the university. A third team member, Hyung-ick Kim, is also a postdoctoral researcher at the CCM and an expert in mechanical characterization of advanced materials.

“After researching with natural materials, we found that cork had interesting properties that we need to improve the acoustics,” Suhr says. Traditional composite beams radiate noise at a very small frequency range — around 2.5 kilohertz whereas aluminum beams begin radiating noise at five kilohertz. “We tested the cork core material in a sandwich-composite configuration and found that it virtually doesn’t generate any noise.”

The team had several goals in mind for the research project, says Suhr. One was improving the acoustical properties of sandwich composites so that less noise is transmitted. A secondary goal was reducing vibration and a third priority was to incorporate “greener” materials that lessen the environmental impact.

The academic team also explored the underlying mechanical properties that contribute to poor acoustical performance in sandwich composites. “If the wave speed is faster than the air, then it radiates all noise from the sandwich composite structure,” Suhr says. In order to slow down the wave speed in a structure, the team surmised that a certain set of physical properties must be in place for solving the problem, and cork possessed those properties, he says.