Interference fastener

Claim 1

A metallic interference member adapted to be mounted on a metallic base member having a hole for receiving said interference member, said interference member comprising a body adapted to extend into the hole in the metallic base member, a plurality of axially extending waves form an outer surface on said body to interfere with inner surfaces of the hole in the metallic base member to thereby prestress the metallic base member around the hole to improve fatigue life of the metallic base member, said waves including a continuous series of evenly spaced crests and troughs having circular cross sections in planes perpendicular to a longitudinal axis of said interference member, said waves having an amplitude of between 0.001 and 0.005 of an inch and a crest diameter which is greater than the inside diameter of the hole in the metallic base member by an amount which is less than the amplitude of said waves to provide interference between the inner surface of the hole in the metallic base member and said crests to prestress the metallic base member around the hole, said crests being axially spaced apart by a distance of between 0.05 and 0.8 times the diameter of the hole in the metallic base member to provide for interference between the surfaces of the hole in the metallic base member and said body of the interference member at a plurality of axially spaced apart locations along said body, said crests having a cross-sectional configuration in an axial plane which is the same as the cross-sectional configuration of the crests of a sine wave and having leading and trailing surfaces which have the same angular slope relative to the longitudinal axis of the fastener to promote a flow of metal around the crests upon insertion of the fastener into the holes in the metallic member, each of said troughs having a sloping trailing surface portion which forms a smooth continuation of the leading surface of one of said crests and a sloping leading surface portion which forms a smooth continuation of a trailing surface of a next adjacent one of said crests with a continuously curving concave center surface portion interconnecting said leading and trailing surface portions to form said shank with a continuously curving outer surface which is free of stress inducing discontinuities and which facilitates insertion of said interference member into the hole in the metallic base member, said concave center surface portions of said troughs having radially innermost surface portions which are spaced from the inner surface of the hole in the metallic base member to thereby tend to minimize metal-to-metal contact between said body and said metallic base member to further facilitate insertion of said interference member into the hole in the metallic base member.