Carbon Fiber Reinforced Rigidizable Space Structures

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Carbon Fiber Reinforced Rigidizable Space Structures S. A. Sarles, T. Bullion, O. T. Mefford, J. S. Riffle and D. Leo, Macromolecules and Interfaces Institute and Center for Intelligent Material Systems and Structures, Virginia Tech, Blacksburg, VA 24060 A. B. Brink and M. H. Brink Hydrosize Technologies, Raleigh, NC ABSTRACT In attempts to provide an active solution for the rigidization of flexible space structures, internal resistive heating is applied to a novel thermosetting resin. Carbon-fiber tow coated in UNyte Set 201A, which cures at ~150°C, was heated by passing electric current through the reinforcing material. Using a proportional-integral (PI) controller, precise temperature control of the heating process was established. Samples cured via controlled internal resistive heating were heated to 160°C and underwent material consolidation in less than 7 minutes. A change in material stiffness was measured to be almost two orders of magnitude greater than that of an uncured material. INTRODUCTION Rigidizable materials and methods for causing structural stiffening of inflatable space structures have been addressed in many ways [1-3]. Previous methods employ both active and passive techniques for inducing rigidization, including: thermal curing, passive cooling, UV curing, strain-hardening, inflation gas reaction, foam inflation, and solvent evaporation. In general, three types of materials are typically used as rigidizable materials: Aluminum laminates, constructed from layers of polymeric film (i.e. Kapton or Mylar) and aluminum film, are rigidized by inflating the structure such that the aluminum experiences plastic deformation [2,4,5]. Thermoplastic materials soften when heated and harden when cooled, allowing them to be used in passive cooling rigidization [6]. In contrast, a thermoset is “a polymer that can be caused to undergo cross-linking to produce a network polymer” [7]. When a thermoset crosslinks, the resulting networked structure has higher rigidity, dimensional stability, and resistance to heat and chemicals. These materials, unlike thermoplasts, are not reversible, have a limited storage life prior to deployment, and require heat in order to cure. Additionally, thermosets can be rigidized actively with resistive heaters or passively, via solar radiation in the form of UV curing [8,9]. The mechanical properties offered by cured thermosets make this material very suitable for space applications. ILC Dover used embedded resistive heating elements to cause material consolidation on a thermosetting resin that cured at 120°C for 45 minutes [1]. Recent work at Clemson, by Naskar and Edie [10], focused on the active consolidation of a carbon-fiber tow coated in ULTEM (GE) resin. Instead of using heating elements, electrical current was passed through the carbon-fiber reinforcement which provided internal resistive heating. Their work validated this method by showing that the ULTEM, when heated to ~380°C, underwent rigidization but lacked the ability to precisely control temperature. Furth