Each year, the Air Force Office of Scientific Research awards research grants to young scientists and engineers through their Young Investigator Research Program. Among the 40 recipients this year was Assistant Professor Katie Matlack for her proposal, “Controlling Damage Mechanisms in Metamaterial Composites with Multiscale Interfaces.” She was the only award winner from the University of Illinois.

What began as a collaboration with the Air Force Research Lab during a summer faculty fellowship in 2018, her project will focus on creating structural composites that can control damage. Traditional engineering materials are subjected to damage due to high loads and vibrations from the system and surrounding environment. To address these issues, the researchers will create damage-tolerant composites with specific architectures and weak interfaces, that can also be tuned if the damaging loads change. The mechanisms under study include crack propagation, fracture toughness, and vibration. 

Previously, the research group developed metamaterials—materials engineered to have properties that are not naturally occurring—that can control mechanical wave propagation. Some metastructures they developed (see image), for example, have a periodic geometry that results in band gaps—frequencies that cannot propagate through the structure. In addition, the group studied how magnetorheological elastomers (MREs) can be used in metamaterials to tune their properties. These MREs stiffen in the presence of magnetic fields, which in turn causes the frequency-dependent properties to change. The researchers predict that these materials can also be used to improve damage tolerance of composites, by controlling fracture toughness and crack propagation paths in the material. The presence of band gaps in the composites will also contribute to mitigating damaging vibrations and improve mechanical dissipation.

With the three-year grant, Matlack will direct ink write 3D print new composites and test the effect of applied magnetic fields and different architectures on the dampening properties of the material, and on controlling crack propagation. They aim to predict how the magnetic properties affect both the mechanical and vibration properties of the composites, using experiments and finite element analysis. With this they will create engineered composites that can control how mechanical damage propagates in composites.

The desired outcomes of the research are advanced lightweight structural components to be used for U.S. Air Force-related applications. Automotive structures around engines are also among the possible applications for these materials that can prevent vibrations from propagating through a material.