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An active approach for initiating rigidization in carbon-fiber reinforced polymer (CFRP) thermosets links controllable mechanical stiffening to inherent electrical resistivity. With direct applications toward the rigidization of ultra-lightweight, inflatable space structures, temperature-controlled resistive heating is used to create oncommand rigidization. As required by the on-orbit conditions in space, flexible, rigidizable structures demand stable and space-survivable materials that incorporate techniques for providing shape control and structural stiffening. Methods currently employed to achieve a mechanical hardening include many passive techniques:
UV curing, sub-Tg hardening, and hydro-gel evaporation. The benefits of a passive system (simplicity, energy efficiency) are offset by their inherent lack of control, which can lead to long curing times and weak spots due to uneven curing. In efforts to significantly reduce the transition time of the composite from a structurally-vulnerable state to a fully-rigidized shape and to increase control of the curing process, an active approach is taken. Specifically, temperature-controlled internal resistive heating initiates thermoset curing in a coated carbon fiber composite to form an electrically-controlled, thermally-activated material. Through controlled heating,
this research examines how selective temperature control can be used to prescribe matrix consolidation and material rigidization on two different thermosetting resins, U-Nyte Set 201A and 201B. Feedback temperature control, based on a PID control algorithm, was applied to the process of resistive heating. Precise temperature tracking (less than 1.1°C RMS or ±3.3% error) was achieved for controlled sample heating. Using samples of the thermoset-coated carbon-fiber tow, composite hardening through resistive heating occurred in 24 minutes and required roughly 1 W-hr/inch of electrical energy. The rigidized material was measured to be 14-21 times stiffer in bending than the uncured material. In addition, the cure completion of the resin was measured through differential scanning calorimetry (DSC).
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