CompositesWorld
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NEWS CompositesWorld.com 25 Reversible Bonds between dissimilar materials can further increase stresses. Lastly, mechanical fasteners are heavy and, significantly, can corrode. Properly executed, adhesive bonds (gener- ally with thermoset polymers) are lightweight, protect surface aesthetics, and are stronger than surrounding material. e adhesive bond is preferred for joining composites because, unlike mechanical fasteners, it spreads joint stresses evenly over the entire surface-to-surface contact area. Bonding also is preferable for multi-material assemblies because the adhesive's flexibility can better accommodate those differences in CLTE. Adhesive bonds, however, are typically perma- nent, making removal of components for repair or replacement impractical. at could change. A multi-year research program involving the American Chemistry Council's Plastics Division (ACC-PD, Wash- ington, DC, US) and Michigan State Univer- sity (MSU, East Lansing, MI, US), has yielded surprisingly effective results in its quest to develop reversible adhesive joints that can be debonded and rebonded multiple times. is capability could facilitate composites use in mixed-material vehicle structures because it gives adhesively bonded joints the durability and the reversibility of mechanically fastened joints at reduced weight. Fortuitous timing is project came about when separate research efforts at MSU and ACC-PD intersected. ree years ago, MSU — through its Composite Vehicle Research Center (CVRC) headed by Dr. Lawrence Drzal, university distinguished professor and a renowned expert on composites, nanocom- posites, and surface chemistry — submitted a proposal in response to a US Department of Bonding dissimilar materials without loss of production speed As the auto industry moves toward use of multi- material vehicle structures, the capability to structur- ally join components of unlike composition (photo, far left), keep them together during vehicle use life despite differences in coefficients of linear-thermal expansion (CLTE), then separate them for repair or recycling becomes an important consideration. Just as important, automakers want joining processes (near left, top) to take less than 1 minute, to keep up with assembly line speeds (near left, bottom). Sources | General Motors Co. (top) / American Chemistry Council (bottom) Seeking fastener-like bond reversibility Adhesive bonds spread stresses over the entire surface-to-surface contact area, can better accommo- date differences in CLTE, and provide better surface aesthetics than mechanical fasteners. But unlike most fasteners, adhesive joints are permanent, preventing debonding for subcomponent repair and reassembly, or end-of-life recycling. Debondable/rebondable structural adhesive bonds could facilitate composites use in mixed-material vehicle structures and give those joints the reversibility of mechanical fasteners at reduced weight. Source | American Chemistry Council and Michigan State University Testing electromagnetic nanoparticle performance Researchers from the American Chemistry Council's Plastics Div. and Michigan State University take a measurement as a electromagnetic coil excites ferromagnetic nanoparticles in an adhesive used to bond a small assembly. The team has demonstrated that an adhesive joint can be rapidly unbonded in the presence of an electromagnetic field, then rebonded again with another round of electromagnetic energy. At 4% particle loading, the joint has good impact and strength, but takes 10 minutes to heat and unbond or rebond. At 12-16% loadings, there is a small drop in mechanicals but the joint heats to unbond/rebond temperature in <20 seconds. Source | Michigan State University and the American Chemistry Council