Processing and properties of co‐injected resin transfer molded vinyl ester and phenolic composites

Abstract Vacuum Assisted Resin Transfer Molding type processes have been proven to be cost effective manufacturing techniques for large composite structures. However, their use has been limited to a single resin system. A large variety of composite structures require multiple resins to serve different purposes while being integrated into a single structure. Co‐Injection Resin Transfer Molding (CIRTM) is a new manufacturing process, developed at the University of Delaware's Center for Composite Materials in collaboration with the U.S. Army Research Laboratory, that enables the user to manufacture multi‐layer hybrid composite parts in a single processing step (1). In this paper, CIRTM is used to manufacture a dual layered structure consisting of a vinyl ester layer for structural integrity and a phenolic layer for fire, smoke, and toxicity protection. The two resins are simultaneously injected into a mold filled with a stationary fiber bed and are co‐cured. Resin separation is maintained by a 0.0254 mm (0.001 in) thick polysulfone film sandwiched between two layers of 0.165 mm (0.0065 in) thick adhesive. A Differential Scanning Calorimeter (DSC) is used to select the optimum cure cycle for all of the materials. Mechanical testing is used to evaluate the performance of the interphase formed between dissimilar materials. Short beam shear (SBS) is used to evaluate the overall quality of the part produced. Double cantilever beam (DCB) is used to quantify the fracture toughness of the interphase, and the wedge test is used to evaluate the durability of the interphase. Experimental results show that co‐injected, co‐cured materials offer properties equivalent, or in some cases, superior, to those provided by single injection resin composites. This case is used to develop and present a methodology that can be followed to co‐inject different resins.