Self-locking fastener, fastener system, and process

An improvement in a collar of the type having an axial bore with internal threads for threaded receipt on external threads of a pin, the bore having an axis, the collar and the pin being capable of cooperating together to develop a desired clamp-up load on a workpiece under the collar, the improvement comprising:

• (a) a plurality of substantially identical lobes on the outside of the collar, the lobes being equally spaced radially of the axis, and being spaced apart from each other in planes radial to the axis and containing the axis, the lobes containing a predetermined and equal volume of material, the surface of each lobe extending axially of the collar and being substantially parallel to the axis, and the lobes being capable of acting as wrenching surfaces for a driver;
• and
• (b) each of the lobes and the material of the collar radially inward of the lobes being plastically deformable to develop plastically deformed material within the bore corresponding to the predetermined volume of the lobe and a lock that rotationally couples the collar and pin together, the yield strength of the lobes and the plastically deformable material of the collar radially inward of the lobes and the surface curvature of the lobes coacting to produce the plastic deformation at a predetermined applied load of the driver on the lobes tangential with respect to the axis of the bore that corresponds to the desired clamp-up load on the workpiece, the applied load resulting from the reaction to the clamp-up load by the workpiece.

A fastener system comprising:

• (a) a collar having an axial bore and internal threads in the axial bore, the internal threads as viewed along the axis of the bore being circular;
• (b) at least one lobe on the outside of the collar for engagement by a driver, the lobe having a surface that substantially parallels the axis of the bore;
• (c) the lobe and collar material radially inward of the lobe being plastically deformable in response to radial compressive forces of predetermined magnitude applied by the driver in concert with a workpiece corresponding to the yield strength of the lobe and the material radially inward of the lobe such that with such deformation both the lobe and the material radially inward thereof flow radially inward with the lobe tending to merge into the balance of the collar and the radially inward material protrudes into the axial bore;
• (d) a pin having external threads for receipt of the internal threads of the collar;
• and
• (e) means of the pin for cooperating with the collar and applying a clamp-up load on a workpiece;
• whereby, upon reaching the yield strength of the lobe and material radially inward thereof, during the development of a clamp-up load on a workpiece, the lobe and radially inward material flow radially inward against the pin to rotationally lock the pin and collar together.

A self-locking and load determining fastener system comprising:

• (a) a pin for receipt in a hole in a workpiece and having an externally threaded section;
• (b) a collar having a right cylindrical bore with an axis, a workpiece bearing end for compressively engaging a workpiece in an axial direction, and internal threads in the bore for threaded receipt on the external threads of the pin;
• and
• (c) at least one axially extending lobe on the lateral outside of the collar, the surface of the lobe paralleling the axis of the bore, the lobe surface configuration and the physical strength of the lobe and material of the collar radially inward of the lobe and toward the axis of the bore effecting plastic deformation of the lobe and such material to form a plastically yielded zone in response to a predetermined radial compressive load on the lobe, the predetermined radial compressive load being directly a function of a load applied to the lobe by a driver which is tangential with respect to the axis of the bore, the plastically yielded zone having the lobe merged into the balance of the collar and the material radially inward of the lobe protruded into the cylindrical bore;
• whereby, progressively threading the collar with the driver onto the threads of the pin while the collar compressively bears on the workpiece increases the resistance of the collar to such threading and upon reaching a predetermined resistance the predetermined radial compressive load is reached and the plastically yielded zone created, the plastically yielded zone bearing against the pin and creating a rotational lock between the collar and the pin.