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Carbon fiber and fiber-reinforced materials have played a role in automotive manufacturing for decades, with recent years seeing entire vehicles made out of the material, albeit on a limited scale.

Having the strength and stiffness of metal, but at a much-reduced weight, such composites have taken on a critical role in improving the overall fuel efficiency of vehicles, since lighter vehicles require less energy to go the same distance as heavier ones.

As their adoption continues to increase, examining their reliability and durability has become a foremost concern.

Fred N. Peebles Professor and UT-Oak Ridge National Laboratory Joint Institute of Advanced Materials Chair of Excellence Dayakar Penumadu is leading a team that might have just the answer for that.

“Auto manufacturers like these materials because they don’t corrode, are easier to recycle, and help the manufacturers to produce more eco-friendly cars, but there is a real challenge in joining different pieces together,” said Penumadu, who also works out of the Department of Civil and Environmental Engineering. “Our study aims to solve some of the complex hybrid material joining issues between carbon and glass fiber reinforced polymer composites and metals through the use of Smart Joint technology, intellectual property we have developed that integrates fiber optic sensing.”

Smart Joints can provide on-demand health assessment for adhesively joined material systems, overcoming a major challenge for evaluating state of bonded joint during manufacturing, during service in real world and harsh-conditions, and evaluation of the joints after an accident. Penumadu expects wide application of this technology for aerospace industry immediately, where the use of carbon fiber composites is growing rapidly and qualified bonding of materials has been a key challenge.

Building off some of his own prior research, Penumadu and the team integrated fiber optic sensors into joints between carbon fiber reinforced composite material and aluminum using a special adhesive developed by Dow Chemical for a project with Ford.

Those results were published recently as “Smart Adhesive Joint with High-Definition Fiber-Optic Sensing for Automotive Applications” in the journal Sensors.

The team then put the joined materials through a series of tests designed to see how it held up under thermally induced external stresses and resulting residual stresses for E-coat pain process commonly used in auto industry. They tested the durability of the smart joint system by putting it through a simulated painting process that automobiles undergo, where temperatures approach 375 degrees.

Their breakthrough was a big step forward in allowing samples to tested and data collected in real time, something that Penumadu noted could have a big impact for composites and efforts to have more eco-friendly vehicles.

“The standards Europe has adopted call for a reduction of more than 30 percent of emissions for cars and vans by 2030, and since major companies like Ford, General Motors, and Volkswagen are global entities, they will need to meet that target.”

Joining of composites is a key aspect of successfully integrating these new class of materials into the automotive industry. When that happens, it will be thanks in part to Penumadu’s work.