The technique, developed by engineers at the Universities of Glasgow and Sydney, uses carbon nanotubes incorporated into plastic structures, which are architected and 3D-printed with precise arrangements of struts and spaces, giving them a lattice-like structure. By passing current through the carbon nanotubes via electrodes attached to the materials, an imaging technique called electrical impedance tomography (EIT) can monitor the structural health of the material as it experiences external loads.
The research “could help pave the way for new generations of ‘self-sensing’ metamaterials made with intricate lattice structures which are custom-designed to prioritise characteristics like weight, strength, impact resistance or flexibility,” a University of Glasgow announcement said.
“These materials could find use in medical implants, aircraft parts or the bodies of cars in the years to come, allowing detailed feedback on the condition of the materials used in the parts as they degrade with age or experience strains caused by impacts.”
The engineers believe their new research is the first reported use of in situ EIT to monitor damage in 3D-printed architected metamaterials. EIT is often used in medical settings to monitor hospital patients’ lung function, using electrodes to take continuous measurements of how electricity flows through materials such as human tissue. Analysis of these measurements enables images of the lungs to be reconstructed without invasive procedures, allowing changes to be tracked in real time.
In the team’s research, they used EIT to map changes in electrical conductivity across small lattice structures by measuring voltage differences through external electrodes as they were stretched until breaking point.
“Traditional sensing methods measure changes in electrical resistance/conductivity at specific points, which can work well for simple structures but cannot show what is happening throughout complex metamaterials,” the announcement said. The team used EIT to monitor changes in conductivity across the whole structure, rather than only individual points.
As the materials stretched, conductive pathways within the lattices changed, altering the way electricity flowed through the structures. These changes provided information about how the structures were deforming and where damage was developing.
A computer algorithm translated these changes into real-time maps showing where damage was developing and how it was progressing, including damage occurring away from the electrodes used to make the measurements.
The system also highlighted where damage was building up before the lattice broke, providing what could be the basis of an early-warning system in future applications. The findings were validated by comparing the system’s results with direct observations of the structures, confirming that it accurately identified where damage developed and where the structures eventually failed.
The maps produced by the algorithm could localise damage to within approximately one strut of its actual location. The researchers also pushed the limits of the system’s ability to detect damage by deliberately adding tiny cracks to some of the struts. They found that they were able to track the cracks as they spread outwards under increasing strain.
“In this research, we’ve developed a new way to map electrical changes across an entire 3D-printed lattice structure in real time. The output is somewhat like an MRI scan: just as an MRI can show what is happening throughout the body, our approach allows us to see how different parts of the lattice are responding while it is under strain,” said Professor Shanmugam Kumar of the James Watt School of Engineering.
“Conventional measurements can tell us what is happening at a particular location in a material or provide an overall, averaged indication of the structural health of the whole structure. However, they cannot show us in detail where damage is developing and how it is spreading throughout the structure. Our research shows that by combining carefully designed lattice structures with EIT we can obtain this much richer picture of structural behaviour, including detecting damage before the structure ultimately fails. The engineered lattice architectures enable control over sensing fidelity.
“This technique could open up potential applications in areas such as structural health monitoring and other advanced engineering systems, although further work is needed to develop and scale the technology for practical applications.”
The research was supported by the University of Sydney-University of Glasgow Ignition Grants and by a Vaibhav Fellowship awarded to Professor Kumar by the Indian National Academy of Engineering and India’s Department of Science and Technology.
The work was published in Advanced Functional Materials.
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