CompositesWorld
Issue link: https://cw.epubxp.com/i/919214
JANUARY 2018 24 CompositesWorld WORK IN PROGRESS » As the auto industry moves toward use of multi-material vehicle structures, the ability to structur- ally join dissimilar materials and keep them together during the vehicle's useful life, yet also separate them for repair, rejoin them and then separate them again at end-of-life for recycling has become increasingly important. is is especially important for primary vehicle structures. ese are far more safety critical than interior or exterior panels and, therefore, it's vital to prevent unwanted separation during vehicle operation. ey are also costlier to replace, which makes them highly desirable targets for repair rather than the junkyard if damaged. Problems with conventional joining methods e conventional structural joining technologies — welding, mechanical fastening (with its associated hardware) and adhesive bonding — each fall short of ideal in this new multi-material reality. Effectively executed, welding produces strong joints but permanently links components, making it difficult to separate and repair subcomponents, and then rejoin them to the assembly. Also, welding is limited to certain metals and to thermoplastics, and is impractical for thermosets and for multi- material systems. Mechanical fastening is a well-known industry standard for joining, and, in most cases, it is revers- ible. A damaged component can be disconnected from a larger assembly, and then a repaired or a replacement part can be reattached to the assembly. Although this approach works well with metal-to-metal assemblies, it is less desirable for assemblies that feature composite (and/or plastic) components because fasteners require drilling, or molding in, holes. Fasteners not only disrupt surface aesthetics, but also concentrate stresses, so provide opportunities for cracks or interlam- inar separation to begin. Furthermore, coefficient of linear-thermal expansion (CLTE) differences Ferromagnetic nanoparticles in thermoplastic adhesives make it possible to debond and rebond adhesive joints, using electromagnetic energy. Reversible multi-material adhesive bonds By Peggy Malnati Contributing Writer