Epoxy resins are of particular interest in structural composite applications because they provide a unique balance of chemical and mechanical properties as well as extreme processing versatility. Some of their most interesting applications are found in the aerospace industry where resins and fibers are combined to produce complex composites structures. Epoxy resins satisfy a variety of non-metallic composite designs in commercial and military aerospace applications including flooring panels, ducting, wings, etc. Epoxy composites are also used to produce lightweight parts for rails, bicycle frames, golf clubs, automobiles and musical instruments. These applications use complex epoxy formulations which will include multiple epoxy resins with modifiers for toughness or flexibility, fillers for strength.
Epoxy are just chemical solutions, when mixed with hardener then it provide stable shape after curing process.if we do not mix hardener then epoxy will not cure and ultimately composite will not form..