Multi-Material Joining for Carbon Fiber Thermoplastic B-Pillar S. Yarlagadda, D. Heider, J.J. Tierney, B.Z. Haque, D. Roseman, N. Shevchenko, J.W. Gillespie Jr. Center for Composite Materials, University of Delaware A. Campbell, L. Keuthage, D. Rinehardt, BMW Group D. Fulk, R. Myers, National Center for Manufacturing Sciences Abstract Multi-material joining methods for carbon fiber reinforced thermoplastic structures are documented in this paper, for a B-Pillar design. The two-part Pillar is comprised of two different thermoplastic materials for the hat (Nylon-based) and spine (Elium-based) sections, respectively. It was also joined to a steel rocker at its base prior to high energy drop tower testing to demonstrate the overall Pillar crash performance. Adhesive bonding, adhesive selection, bonding cycle, and traction law development for modeling are presented along with Pillar assembly procedures. Overall performance of the joining approach was validated by full-scale high energy drop tower testing. Introduction Carbon fiber composites are becoming one of the preferred solutions for vehicles to achieve overall weight reduction in order to meet fuel economy and emission standards while maintaining safety requirements. Carbon fiber thermoplastic composites offer several additional advantages: higher levels of ductility and specific energy absorption; rapid processing; and recyclability and reuse. A project team funded by NHTSA consisted of NCMS, and two technology providers, BMW and UD- CCM, investigated computational tools for the design, optimization and manufacture of carbon fiber thermoplastic materials for vehicle side frame structures (e.g., B-pillar) subject to side-impact crash loading 1 . The B-pillar is the support post that connects a vehicle’s roof to its frame at the rear of the front occupant door and provides the major source of resistance to occupancy compartment intrusion during a side-impact collision. The B-pillar was designed using computer-aided design (CAD) and computer-aided engineering (CAE) tools. The design and crash performance were evaluated using both simulation and hardware (subcomponent and full scale B-Pillars) to satisfy vehicle safety requirements for passenger intrusion Within the scope of this project, BMW assisted UD- CCM by supplying vehicle design and safety requirements derived from full vehicle crash simulations as well as feedback and guidance on all project tasks. UD-CCM, conducted composite design, analysis and optimization, developed tooling and novel processing methods for forming and multi-material joining, and manufactured full- size carbon fiber thermoplastic B-pillar assemblies that were impact tested under equivalent full-energy, side- impact crash conditions. The overall goals of this project were met by the design, manufacture and testing of the carbon fiber thermoplastic B-pillar, that offered 60% weight savings over the steel baseline and satisfied the side-impact crash requirements established in the program. This paper documents the multi-material adhesive joining methodology used to downselect adhesive and surface pretreatments, adhesive traction law properties for model development, full-scale B-pillar assembly procedures and full-scale crash performance of the multi-material joining methods. Thermoplastic B-Pillar Design The final B-pillar design was a multi-material system with AS4/Nylon (Tencate) in the hat section, T700/Elium (Arkema) in the spine section and steel for the top and bottom rails (Figure 1). Following manufacture of the hat and spines, an adhesive joining method was proposed for assembly of the hat/spine and steel lower rail (rocker) into the full-scale test article for high energy drop tower testing. This required the selection of an adhesive system and appropriate pretreatments for compatibility to all three systems, joint strength assessment and failure modes, traction law development for modeling and simulation, and the final assembly process development. Adhesive Selection A number of adhesive systems were evaluated for bonding to thermoplastic resins and steel, with emphasis on high-elongation systems for crash performance. BMW recommended two systems – DOW Betaforce (polyurethane based) and Sikaforce 766 L30 (polyurethane), based on their experience with bonding thermoset composites on the BMW i-series. The Sikaforce system is not currently sold in the U.S. and was not considered. Two other systems were selected by UD-CCM, based on prior experience 2-5 – 3M AC240 (polysulfide based) and Plexus MA530 (methacrylate based). Both these systems are tough high-elongation systems with demonstrated performance in prior UD-CCM programs and are able to bond to a variety of surfaces. Surface SPE ANTEC ® Anaheim 2017 / 716
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Multi-Material Joining for Carbon Fiber Thermoplastic B-Pillar
S. Yarlagadda, D. Heider, J.J. Tierney, B.Z. Haque, D. Roseman, N. Shevchenko, J.W. Gillespie Jr.
Center for Composite Materials, University of Delaware
A. Campbell, L. Keuthage, D. Rinehardt, BMW Group
D. Fulk, R. Myers, National Center for Manufacturing Sciences
Abstract
Multi-material joining methods for carbon fiber
reinforced thermoplastic structures are documented in this
paper, for a B-Pillar design. The two-part Pillar is
comprised of two different thermoplastic materials for the
hat (Nylon-based) and spine (Elium-based) sections,
respectively. It was also joined to a steel rocker at its base
prior to high energy drop tower testing to demonstrate the