Abstract: A heating element for providing localized heating during the thermoplastic bonding of thermoset composite structures is disclosed. Various construction details are developed which disclose an apparatus and method for uniformly heating a bond line. In one embodiment, a heating element (22) includes a resistance heating material (24) sandwiched between two layers of electrical insulation (25) and encased within a layer of thermoplastic material (26). Low resistance electrical leads (28), which extend across the width of the resistance heating material, and a power supply (30) provide electrical energy to raise the temperature of the resistance heating material.

Abstract: A method of bonding metallic structures to thermoplastic composite structures is described. Various construction details have been developed which provide a method for producing a bond of sufficient strength to transmit rotational and axial loads between the metallic and thermoplastic composite structures. In one embodiment, the method includes the steps of knurling a mating surface of the metallic structure, coating the mating surface with a thermoplastic material to produce a bonding surface, and consolidating the bonding surface to the thermoplastic composite structure.

Abstract: A method to bond metallic structures to thermoset composite structures is described. Various construction details have been developed which provide a method for producing a bond of sufficient strength to transmit torsional and axial loads between the metallic and thermoset composite structures. In one embodiment, the method includes steps to form a bonding surface on a metallic structure by knurling a mating surface of the metallic structure and molding a thermoplastic material over the knurled surface. Further, the method includes steps to form a bonding surface on a thermoset composite structure by partially embedding a layer of dry fiber into a thermoplastic cone, coating the exposed dry fiber with thermoset resin, and curing the coated dry fibers into the thermoset composite structure. The final step is to fuse the two bonding surfaces by applying heat sufficient to melt the thermoplastic material.

Abstract: A pair of thermoset composite structures (19,19') are bonded together by a pair of adhesive strips (10,10'). An adhesive strip (10) is comprised of a layer of semi-crystalline thermoplastic material (12), a layer of amorphous thermoplastic material (14), a layer of dry fiber reinforcement (16) partially embedded in the layer of amorphous thermoplastic material (14), and a layer of thermosetting resin (18) covering the exposed fibers of the dry fiber reinforcement. An adhesive strip is bonded to the bonding surface (20) of the structure (19) during the curing process for the thermoset composite structure. A resistance heating element is placed between the bonding surfaces (20,20'), the bonding surfaces (20,20') are pressed together, and electrical energy is passed through the heating element (24) to heat the joint and fuse the thermoplastic adhesive layers together.

Abstract: A pair of thermoset composite structures (19,19') are bonded together by a pair of adhesive strips (10,10'). An adhesive strip (10) is comprised of a layer of semi-crystalline thermoplastic material (12), a layer of amorphous thermoplastic material (14), a layer of dry fiber reinforcement (16) partially embedded in the layer of amorphous thermoplastic material (14), and a layer of thermosetting resin (18) covering the exposed fibers of the dry fiber reinforcement. An adhesive strip is bonded to the bonding surface (20) of the structure (19) during the curing process for the thermoset composite structure. A resistance heating element is placed between the bonding surfaces (20,20'), the bonding surfaces (20,20') are pressed together, and electrical energy is passed through the heating element (24) to heat the joint and fuse the thermoplastic adhesive layers together.

Abstract: The method of manufacturing a multi-legged (preferably five) flexbeam for a hingeless flexbeam helicopter rotor, which flexbeam is of one-piece construction and made solely of composite materials, and includes full length plies of unidirectional high strength fibers extending from a first leg and splitting in passing through the hub portion of the flexbeam, and then extending into two substantially diametrically opposite legs, and having cross and unidirectional plies interspersed between the full length plies to effect the desired taper and shape of the flexbeam hub and legs, and wherein the final ply lay-up is made on a rotatable lay-up tool of dodecahedron shape.