US3821871A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Fatigue resistant fasteners
Assignee: Boeing Co
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Filing: 1973-05-03
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Granted: 1974-07-02
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Expires: 1993-05-03
Abstract
Abstract A flush head fastener pin for use in aircraft structural joints which are countersunk for surface flushness. The pin is shaped and adapted to preload the joint material surrounding the countersink to create a predetermined residual stress pattern in that region for improvement of fatigue life. Preferred embodiments of a straight shank bolt, a tapered shank bolt, and a rivet are presented. Each pin embodiment has a 70* conical head and a concave transition portion of specified radius and smoothness interconnecting the head with the shank. The 70* head and transition portion cooperate to conformably deform and preload the countersunk region of the hole, which is preferably provided with a convex surface of specified radius at the base of the countersink, and a conical surface having a greater cone angle than that of the pin. The straight shank bolt embodiment further discloses a hardened convex lead-in portion of specified shape and smoothness extending between the shank and the threads to prevent galling of the hole during installation of the bolt.
Inventors
- 👤 H Schmitt
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 16:02
CPC Classifications
F; F16; F16B; F16B19/00; F16B31/00; F16B31/06; F16B35/00; F16B35/04; F16B35/06; F16B4/00; F16B4/004; Y; Y10; Y10T; Y10T29/00; Y10T29/49; Y10T29/49826; Y10T29/49908; Y10T29/49938; Y10T29/49943; Y10T403/00; Y10T403/75
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
302 words
A flush structural joint for transferring load between an overlapping pair of structural members comprising: walls on said members forming a concentric hole passing therethrough, said walls including a circular shank accommodating portion extending from an outer surface of one of said members and a concentric countersink portion of increased diameter which extends to the opposite outer surface of the other of said members, said countersink having an outer portion adjacent the outer surface of the other of said members, and an inner portion of reduced diameter adjacent to said shank accommodating portion, said inner portion including a convex surface extending to and tangent with the walls of said shank accommodating portion, said convex surface having a minimum radius of curvature of at least 0.015 inches; a fastener for creating an interference fit against said inner portion of said countersink comprising: a circular shank which fits into said shank accommodating portion of said hole, said shank having a predetermined maximum diameter, a circular flush head connected to one end of said shank and nested within said countersink, a transition portion interconnecting said head and said shank comprising a concavely curved surface having a minimum radius of curvature of a value greater than 15% of said predetermined maximum diameter, a fastening end section connected to the opposite end of said shank from said flush head and protruding out of said hole to allow a securing load to be applied to said members to retain the fastener in said hole; wherein said transition portion is forced into the convex surface of said inner portion of said countersink to radially expand and preload the material surrounding the countersink to cause a prestressed condition to exist therein which tends to prevent fatigue cracks from developing around said countersink when said members are subject to repetitive loadings.
Claim 2
Dependent Claim
302 words
A flush structural joint for transferring load between an overlapping pair of structural members comprising: walls on said members forming a concentric hole passing therethrough, said walls including a circular shank accommodating portion extending from an outer surface of one of said members and a concentric countersink portion of increased diameter which extends to the opposite outer surface of the other of said members, said countersink having an outer portion adjacent the outer surface of the other of said members, and an inner portion of reduced diameter adjacent to said shank accommodating portion, said inner portion including a convex surface extending to and tangent with the walls of said shank accommodating portion, said convex surface having a minimum radius of curvature of at least 0.015 inches; a fastener for creating an interference fit against said inner portion of said countersink comprising: a circular shank which fits into said shank accommodating portion of said hole, said shank having a predetermined maximum diameter, a circular flush head connected to one end of said shank and nested within said countersink, a transition portion interconnecting said head and said shank comprising a concavely curved surface having a minimum radius of curvature of a value greater than 15% of said predetermined maximum diameter, a fastening end section connected to the opposite end of said shank from said flush head and protruding out of said hole to allow a securing load to be applied to said members to retain the fastener in said hole; wherein said transition portion is forced into the convex surface of said inner portion of said countersink to radially expand and preload the material surrounding the countersink to cause a prestressed condition to exist therein which tends to prevent fatigue cracks from developing around said countersink when said members are subject to repetitive loadings.
Claim 3
Dependent Claim
67 words
The joint of claim 1 wherein said circular flush head comprises a conical surface having a selected given cone angle within the range of from 60* to 85*, said conical surface of said head being arranged to bear against a conical surface of the countersink to thereby radially expand and preload the material surrounding the countersink when said flush head is forced into position in said countersink.
Claim 4
Dependent Claim
35 words
The joint of claim 2 wherein said conical surface of said countersink has an initial unstressed cone angle which is at least 4* different from said selected given cone angle of said circular flush head.
Claim 5
Dependent Claim
64 words
The joint of claim 1 wherein said fastening end section comprises an externally threaded section having a thread major diameter smaller than the minimum diameter of said shank, and wherein the joint includes an internally threaded nut means for engagement with said threaded section to retain the head of the fastener in a seating engagement with said countersink by tightening of said nut means.
Claim 6
Dependent Claim
103 words
The joint of claim 4 wherein said shank is tapered approximately 0.020 inch per inch along the entire length of said shank and said predetermined maximum diameter defines the larger end of said shank located adjacent said transition portion, the diameters of the wall of the tapered shank being greater than the initial corresponding diameters of said hole by at least 0.001 inches to thereby expand and preload the material surrounding said shank accommodating portion of said hole to cause a tensile prestress condition to exist therein which tends to prevent fatigue cracks from developing around said shank accommodating portion of said hole.
Claim 7
Dependent Claim
65 words
The joint of claim 4 wherein said fastener further comprises a lead-in portion for cold working the shank accommodating portion of the walls of said hole during insertion of said fastener, said lead-in portion comprising: a convex surface having a radius adjoining and tangent to said shank which has a value within the range of from 20% to 60 % of said predetermined maximum diameter.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-07-01 | 1977-12-31 | 1978-07-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-07-01 | 1981-12-31 | 1982-07-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-07-01 | 1985-12-31 | 1986-07-02 | $7700.00 | Window Closed / Lapsed |