Non-Polluting Composites Repair and Remanufacturing for Military Applications: Co-Injection Resin Transfer Molding

Vacuum-assisted resin transfer molding VARTM processes have been proven to be cost-effective manufacturing techniques for large composite structures. However, their use has been limited to single resin systems. A large variety of composite structures requires multiple resins to serve different purposes while being integrated into a single structure. Significant environmental cost savings are possible by replacing currently practiced sequential repair and manufacturing techniques with reduced-step co-cure processes enabled by the co-injection resin transfer molding CIRTM variant of the VARTM process. The CIRIM process was investigated to manufacture two dual-layered structures commonly required in Department of Defense DoD structures. The first consists of a vinyl-ester layer for structural integrity and a phenolic layer for flammability, smoke, and toxicity FST protection. The second consists of structural epoxy with a polyurethane layer for improved damage tolerance. In each case, the two resins are simultaneously injected into a mold filled with a stationary fiber bed and co-cured. Resin separation is maintained by a 1-mil-thick polysulfone film sandwiched between two layers of 6.5-mil-thick adhesive. Various tests have been performed to demonstrate mechanical, thermal, and rate-dependent performance of the improved structures.