According to Myers, once the laminate is exposed to a magnetic field, it creates an effect akin to a human nervous system that sends pain messages to the brain. If the laminate is unscathed, it will display a uniform magnetic signature, but if an area is damaged, there will be a secondary magnetic signature that looks different.
For Myers, choosing carbon fiber and epoxy made sense due their commercial availability and widespread use in military applications. However, determining the exact material formulation was a challenge. Because Terfenol-D is only 1 to 300 microns in diameter, one of the biggest obstacles the team faced was how to spread it thinly and evenly throughout the laminate.
Myers says that combining compression-molded chopped carbon fibers and epoxy separately would make it difficult to overcome that obstacle, which is why he chose prepreg. “Epoxy [in CFRP prepreg] has a low level of tackiness before curing, which allows us to spread a thin layer of the magnetostrictive material on the prepregs as we build the composite laminate,” says Myers.
Myers is using the process to create beam specimens that can fit into Instron testing machines, which are used to evaluate the mechanical properties of materials and components. His team has created several electromagnetic coils which, along with data acquisition technology, help simultaneously generate an excitation field and read the output from the Terfenol-D.
Currently, the team is using what Myers calls a “surrounding scan” to get a general overview of damage in a structure. The next step of the research, he says, is to refine the system so it can display damage to one part of a structure at a time through a single-sided scan. Within 10 to 20 years, he envisions the Army incorporating a real-time data collection system for structured health monitoring based on his technology.
Thermoplastics for Construction
Project: Hybrid composite/concrete beam plate
School: University of Maine
Location: Orono, Maine
Principal Investigators: Bill Davids and Roberto Lopez-Anido
At the University of Maine, graduate students Camerin Seigars and Benjamin Smith at the school’s Advanced Structures and Composites Center (ASCC) are working with the Engineering Research and Development Center (ERDC) at the U.S. Army Corps of Engineers to develop a proof of concept for a novel concrete I-beam with a thermoplastic composite reinforcement. The goal, according to the students’ advisor, civil engineering professor Roberto Lopez-Anido, Ph.D., P.E., is to showcase what thermoplastics can offer, including recyclability, corrosion resistance, quick assembly, impact resistance and a high strength-to-weight ratio.