Active Composite Rigidization Using Temperature-controlled Resistive Heating

An active approach for initiating rigidization in carbon-fiber reinforced polymer (CFRP) composites unites electrical resistivity to mechanical stiffening. Temperature control is implemented in efforts to reduce the curing time of the composite and to increase control of the curing process. Specifically, proportional-integral (PI) feedback control of internal resistive (Joule) heating establishes an electrically-controlled, thermally-activated material. Precise temperature tracking (less than 1C error at steady state) was achieved for controlled sample heating tests. The rigidization of these materials was quantified and compared for different curing profiles by measuring the increase in bending stiffness as well as verifying resin cure completion with DSC. Small samples of carbon-fiber tow (Toho Besfight G40-800 (12k)) coated with toughened epoxy Unyte powder resin (Hydrosize Technologies) were successfully rigidized (15 − 20 times stiffer than the flexible, uncured material) and fully-cured through a controlled heating routine in only 24 minutes and required less than 0.1 W-hr/cm of electrical energy. Experimental studies on how the prescribed curing profiles (including curing temperature and time) affect matrix consolidation and resin curing were performed and methods for reducing the curing time and energy were investigated.