Tapered lead-in for interference fit fasteners
An assembly comprising first and second structural elements having aligned holes, a fastener that occupies at least respective portions of the holes without a surrounding sleeve, and a mating part that is coupled to the fastener. The fastener comprises: a head; a circular cylindrical shank extending from the head; a mating portion comprising external projections; and a transition portion disposed between the shank and the mating portion. The transition portion comprises a tapered lead-in section that meets the shank at a shank/lead-in intersection and a radiused lead-in section that meets the tapered lead-in section. The tapered lead-in section tapers gradually in a first axial direction toward the mating portion and has a first profile that is linear and a taper angle equal to or less than 20 degrees, while the radiused lead-in section curves abruptly in the first axial direction and has a second profile that is a circular arc having a radius.
1. An assembly comprising a first structural element having a first hole, a second structural element having a second hole aligned with the first hole of the first structural element, a fastener that occupies at least respective portions of the first and second holes in the first and second structural elements without a surrounding sleeve and extends beyond the second structural element, and a mating part that abuts the second structural element and is coupled to the fastener, wherein the fastener comprises:
a head;
a shank extending from the head, the shank comprising an external surface that is circular cylindrical;
a mating portion comprising external projections; and
a transition portion disposed between the shank and the mating portion,
wherein the transition portion comprises a tapered lead-in section that meets the shank at a shank/lead-in intersection and a radiused lead-in section that meets the tapered lead-in section, the tapered lead-in section tapers gradually in a first axial direction toward the mating portion and has a first profile that is linear and a taper angle equal to or less than 20 degrees, and the radiused lead-in section curves abruptly in the first axial direction and has a second profile that is a circular arc having a radius; and
wherein the mating portion has a maximum diameter less than a minimum diameter of the radiused lead-in section.
2. The assembly as recited in claim 1 , wherein the shank of the fastener and the first and second structural elements are in contact without a sleeve therebetween.
3. The assembly as recited in claim 1 , wherein one of the first and second structural elements is made of composite material and the other of the first and second structural elements is made of metallic material.
4. The assembly as recited in claim 1 , wherein the mating part comprises internal threads that are interengaged with the external projections of the mating portion of the fastener.
5. The assembly as recited in claim 1 , wherein the mating part comprises a swaged collar that is interengaged with the external projections of the mating portion of the fastener.
6. The assembly as recited in claim 1 , wherein the first profile is a profile of an external surface of the tapered lead-in section in a plane that intersects a central axis of the fastener, and the second profile is an external surface of the radiused lead-in section in the plane that intersects the central axis of the fastener.
7. The assembly as recited in claim 1 , wherein a maximum diameter of the tapered lead-in section equals a diameter of the shank and an external surface of the tapered lead-in section is a section of a right circular cone.
8. An assembly comprising:
a first structural element having a first hole;
a second structural element having a second hole aligned with the first hole of the first structural element;
a fastener comprising a head, a shank that extends from the head, a mating portion that extends beyond the second structural element, and a transition portion disposed between the shank and the mating portion, wherein the shank occupies at least respective portions of and contacts the first and second holes in the first and second structural elements, the mating portion comprises external projections, and the transition portion comprises a tapered lead-in section that meets the shank at a shank/lead-in intersection and a radiused lead-in section that meets the tapered lead-in section; and
a mating part that abuts the second structural element and is coupled to the mating portion of the fastener,
wherein the tapered lead-in section tapers gradually in a first axial direction toward the mating portion and has a first profile that is linear and a taper angle equal to or less than 20 degrees; and
wherein the mating portion has a maximum diameter less than a minimum diameter of the radiused lead-in section.
9. The assembly as recited in claim 8 , wherein the radiused lead-in section curves abruptly in the first axial direction and has a second profile that is a circular arc having a radius.
10. The assembly as recited in claim 8 , wherein the shank of the fastener and the first and second structural elements are in contact without a sleeve therebetween.
11. The assembly as recited in claim 8 , wherein one of the first and second structural elements is made of composite material and the other of the first and second structural elements is made of metallic material.
12. The assembly as recited in claim 8 , wherein the mating part comprises internal threads that are interengaged with the external projections of the mating portion of the fastener.
13. The assembly as recited in claim 8 , wherein the mating part comprises a swaged collar that is interengaged with the external projections of the mating portion of the fastener.
14. The assembly as recited in claim 8 , wherein the first profile is a profile of an external surface of the tapered lead-in section in a plane that intersects a central axis of the fastener, and the second profile is an external surface of the radiused lead-in section in the plane that intersects the central axis of the fastener.
15. The assembly as recited in claim 8 , wherein a maximum diameter of the tapered lead-in section equals a diameter of the shank and an external surface of the tapered lead-in section is a section of a right circular cone.
16. A fastener comprising a head, a shank that extends from the head, a mating portion, and a transition portion disposed between the shank and the mating portion, wherein the mating portion comprises external projections, and the transition portion comprises a tapered lead-in section that meets the shank at a shank/lead-in intersection and a radiused lead-in section that meets the tapered lead-in section, wherein:
the tapered lead-in section tapers gradually in a first axial direction toward the mating portion and has a first profile that is linear and a taper angle equal to or less than 20 degrees;
the radiused lead-in section curves abruptly in the first axial direction and has a second profile that is a circular arc having a radius; and
the mating portion has a maximum diameter less than a minimum diameter of the radiused lead-in section.
17. The fastener as recited in claim 16 , wherein the first profile is a profile of an external surface of the tapered lead-in section in a plane that intersects a central axis of the fastener, and the second profile is an external surface of the radiused lead-in section in the plane that intersects the central axis of the fastener.
18. The fastener as recited in claim 16 , wherein a maximum diameter of the tapered lead-in section equals a diameter of the shank and an external surface of the tapered lead-in section is a section of a right circular cone.
19. The fastener as recited in claim 16 , wherein the external projections are external threads.
20. The fastener as recited in claim 16 , wherein the external projections are external annular rings.