Fastener including expander means and joint including the same

Claim 1

A structural joint comprising: a workpiece having a pair of opposite surfaces comprised of a plurality of overlapping contiguous metal elements, each of the elements having a respective hole, the holes being axially aligned to form a continuous passage extending between said surfaces defined by respective walls of the holes and having a central axis, the metal of which the elements are made having the inherent physical property of a compressive stress-compressive strain relationship in which a yield point exists such that, when compressive forces are exerted beyond said yield point and are then relaxed, the material returns to a different strength and size than would result were the yield point not exceeded, and is said to be ''''cold-worked''''; a unitary metallic combined metalworking tool and fastener pin in the said hole comprising a cylindrical shank having a central axis coincident with that of the passage, a solid annular expander section on said pin contiguous to the cylindrical shank and extending radially beyond the shank, fastener means at one end of the fastener pin, and a head at the other end, said expander section including an initial portion which is a smooth surface of revolution facing and sloping toward the fastener means with a progressively increasing diameter as it extends axially away from said fastener means, and a return portion contiguous and directly connected to both the initial portion and to the cylindrical shank, and having no diameter less than that of the cylindrical shank, the return means facing and sloping toward the head, the expander section lying closer to the fastener means than the cylindrical shank, and having a greatest diameter greater than that of the cylindrical shank, the head bearing against the workpiece surface at one end of the passage, the expander section having adjacent to the other end of the passage, some part of the expander section having contacted the passage wall at the said other end and the major portion of the axial length of the walls of the holes forming an intimate and substantially continuous interference fit with the cylindrical shank, and the fastener means including means in abutment with the workpiece surface as said other end of the passage, the joint having been produced by selecting the said greatest diameter of the expander section relative to the initial diameter of the passage so that expansion of the wall to the diameter of the expander section by expansive force exerted by the expander section will coldwork the metal which bounds said wall, and upon release of said expansive force, the wall would, absent restraint, return to a new diameter which is larger than the initial diameter of the passage prior to exertion of said expansive force and smaller than that of the expander section, and selecting the diameter of the cylindrical shank so as to be greater than said new diameter, and pressing the fastener pin into the passage until the fastener means projects beyond said other end of the passage and the head bears against the workpiece surface at said one end of the passage, thereby passing the expander section axially through the major portion of the length of the passage, burnishing said walls on the way, and inserting the cylindrical shank in the passage in intimate and substantially continuous interference fit with the workpiece throughout the major proportion of the axial length of the holes without further expansion of the walls after passage of the return portion, the metal of the workpiece contiguous to the cylindrical shank being coldworked by the expander section and thereby having a greater tensile strength than material laterally farther removed from the passage.