CompositesWorld

JAN 2018

CompositesWorld

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JANUARY 2018 26 CompositesWorld WORK IN PROGRESS Testing shows extensive effectiveness in multi-material combinations The reversible adhesive bonding research has enabled successful attempts to join a wide variety of metals, plastics and composites to create multi-material assemblies. When resin/particle surface compatibility and substrate surface prep are rightly done, the team has achieved joint shear strengths in the 12-13 MPa (1,741-1,886 psi) range, which it says is better than epoxy structural adhesives. Source | Michigan State University and the American Chemistry Council Energy (DoE) program aimed at exploring light- weighting and multi-material joinery. At the time, researchers were working with graphene nanoparticles in thermoplastic polymers. ey already knew that applying microwave energy excited the nanoparticles, and that doing so heated and melted only the polymer in which nanoparticles were embedded. is led researchers to think the phenomenon could be harnessed to create reversible adhesive joints. e project received a grant and research began. ACC-PD's parallel roadmapping projects, done with industry and federal government partners, had identified "technology gaps" that were slowing the adoption of lightweight plastics and composites in vehicle applications. One such gap was the need for better joining technologies for multi-material structures. "Seeing the problem, our member companies decided to take the initiative and try to develop a solution," recalls Mike Day, an ACC-PD tech- nical consultant and career-retiree from DuPont (Wilmington, DE, US). While conducting a technology review for possible solutions to the bonding problem, ACC-PD discovered MSU's work and contacted the university a month into the DoE research program. Research detour Not long after collaboration began, the joint MSU/ACC-PD research team ran into a problem. Researchers checked how big commercial microwave-generation units were. "e biggest variable-frequency microwave ovens anyone seemed to be making were the size of home microwave ovens," recalls Dr. Mahmoodul Haq, MSU assistant professor – Department of Civil & Environmental Engineering. "ose were too small to be practical for field use — particularly for some of the structural applications we were envisioning." Until in-field microwave applica- tors were developed, it was back to the drawing board to find another nanoparticle that could be excited by energy transmitted by a device not so size-constrained. "Fortunately, there are lots of nanoparticles out there," he adds. "For example, we knew ferro- magnetic particles could be excited with elec- tromagnetic energy, and that to generate that energy, all we needed were small coils without all the surrounding structure you need to safely operate microwave systems." Making that shift put "rockets under the project," Haq recalls.

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