Method of joining workpieces with a rivet fastener system

A method of joining workpieces by setting a two-piece rivet assembly, which rivet assembly comprises a rivet with a head and a central axis, a solid shank of substantial length, and a tubular upsettable portion extending beyond said solid shank formed by a recess in the end of said rivet opposite from the head, there being an abutment surface at the intersection of the solid shank and the tubular upsettable portion and a core pin inside the recess adapted at least partially to abut said abutment surface, said method comprising:

• inserting said rivet through holes in said workpieces until the head abuts one workpiece and the core pin extends beyond another workpiece, holding said head against said one workpiece while applying an axial force on said upsettable portion to form a bulbular upset head, during at least the terminal portion of the formation of the bulbular upset head, simultaneously applying an axial end force to the core pin to press it axially against said abutment surface to cause the solid shank to expand principally as a consequence of columnar axial loading.