Radius filler for wet composite layup

A cured composite structure, comprising:

• a composite base member comprised of reinforcing fibers embedded in resin, and having a radius cavity extending along a length of the composite base member;
• a radius filler element extending continuously along a length of the radius cavity and having radius filler side surfaces, the radius filler element being formed of a radius filler material;
• a mixture zone bonding the radius filler side surfaces to the composite base member and comprised of a hardened mixture of the resin and the radius filler material;
• wherein:
• the radius filler material is contiguous and homogenous throughout the radius filler element, excluding the mixture zone;
• and
• the mixture zone has a higher strength than the radius filler material, and a higher strength than the resin in a cured state without the radius filler material.

A cured composite structure, comprising:

• one of a composite stringer or a composite spar of an aircraft, including:
• a composite base member comprised of reinforcing fibers embedded in resin and having a radius cavity extending along a length of the composite base member;
• a radius filler element extending continuously along a length of the radius cavity and having radius filler side surfaces, the radius filler element being formed of a radius filler material;
• a mixture zone bonding the radius filler side surfaces to the composite base member and comprised of a hardened mixture of the resin and the radius filler material;
• wherein:
• the radius filler material is contiguous and homogenous throughout the radius filler element, excluding the mixture zone;
• and
• the mixture zone has a higher strength than the radius filler material, and a higher strength than the resin in a cured state without the radius filler material.