Method of repairing a core stiffened structure

A method of repairing a rotor blade, the method comprising:

• removing a damaged portion of the rotor blade to provide a first core member within a cavity of the rotor blade;
• installing an uncured composite shelf onto the first core member in the cavity;
• bonding the uncured composite shelf onto the first core member with an adhesive;
• concurrently curing the uncured composite shelf and the adhesive to form a cured composite shelf bonded to the first core member;
• bonding a second core member having a plurality of cells to the cured composite shelf;
• depositing a foam mixture into a cell of the second core member;
• allowing the foam mixture to expand and fill the plurality of cells in the second core member so as to form an expanded foam;
• trimming the expanded foam;
• and
• securing a skin patch over the second core member;
• wherein the cured composite shelf provides a shear transfer medium between the first core member and the second core member.