US3748948A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Fatigue resistant fasteners
Assignee: Boeing Co
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Filing: 1970-08-05
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Granted: 1973-07-31
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Expires: 1990-08-05
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 15:56
CPC Classifications
F; F16; F16B; F16B4/00; F16B4/004; F16B19/00
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
164 words
A countersunk head bolt for connecting an overlapping pair of structural members having an aligned concentric hole passing therethrough, and for preventing development of fatigue cracks around the countersunk region; said bolt comprising: a circular shank having a predetermined maximum diameter; a circular flush head carried by one end of said shank comprising a convex crown end having a radius of curvature of at least twice said predetermined maximum diameter and a conical surface having a given included cone angle of approximately 70*; a transition portion interconnecting said head and said shank comprising a concavely curved constant radius circular surface tangent to said head and said shank and hardened by cold rolling to a surface finish smoother than 32 RHR, said circular surface having a radius of curvature of a value of greater than 15 percent of said predetermined maximum diameter; and a fastening end portion comprising an externally threaded section having a major thread diameter smaller than the minimum diameter of said shank.
Claim 2
Dependent Claim
164 words
A countersunk head bolt for connecting an overlapping pair of structural members having an aligned concentric hole passing therethrough, and for preventing development of fatigue cracks around the countersunk region; said bolt comprising: a circular shank having a predetermined maximum diameter; a circular flush head carried by one end of said shank comprising a convex crown end having a radius of curvature of at least twice said predetermined maximum diameter and a conical surface having a given included cone angle of approximately 70*; a transition portion interconnecting said head and said shank comprising a concavely curved constant radius circular surface tangent to said head and said shank and hardened by cold rolling to a surface finish smoother than 32 RHR, said circular surface having a radius of curvature of a value of greater than 15 percent of said predetermined maximum diameter; and a fastening end portion comprising an externally threaded section having a major thread diameter smaller than the minimum diameter of said shank.
Claim 3
Dependent Claim
41 words
The fastener pin of claim 1 which includes a trimmed surface between said crown end portion and said conical surface which extends longitudinally less than 0.005 inches wherein said constant radius circular surface has a radius of at least 0.060 inches.
Claim 4
Dependent Claim
67 words
The bolt of claim 1 which further includes a lead-in portion interconnecting said shank and said fastening end portion, said lead-in portion having a maximum diameter smaller than said predetermined maximum diameter of said shank and comprising a convex surface tangent to the surface of said shank and having a nominal radius of curvature within the range of from 20 to 60 percent of said maximum diameter.
Claim 5
Dependent Claim
33 words
The bolt of claim 1 wherein said shank is tapered approximately 0.020 inch per inch along the entire length of said shank and said predetermined maximum diameter is located adjacent said transition portion.
Claim 6
Dependent Claim
193 words
A countersunk head rivet constructed of a material having an ultimate shear strength eXceeding 85,000 psi for connecting an overlapping pair of structural members having an aligned concentric hole passing therethrough, and for preventing development of fatigue cracks around the countersunk region; said rivet comprising: a circular cylindrical shank having a predetermined diameter; a circular flush head having a conical surface with an included cone angle of 70* held to close tolerances and a spherical convex crown end portion having a radius of curvature of at least twice said predetermined diameter; a transition portion interconnecting said head and said shank comprising a concavely curved constant radius circular surface tangent to said shank and hardened by cold rolling to a surface finish smoother than 32 RHR; and a fastening end lead-in portion comprising a convex circular surface tangent to said shank with a constant radius of curvature of a value ranging from 20 to 60 percent of said diameter; wherein said 70 cone angle and said transition portion are adapted to cooperate, upon the driving of said rivet to cause the rivet to expand to create residual stresses extending substantially throughout the countersunk region.
Claim 7
Dependent Claim
193 words
A countersunk head rivet constructed of a material having an ultimate shear strength eXceeding 85,000 psi for connecting an overlapping pair of structural members having an aligned concentric hole passing therethrough, and for preventing development of fatigue cracks around the countersunk region; said rivet comprising: a circular cylindrical shank having a predetermined diameter; a circular flush head having a conical surface with an included cone angle of 70* held to close tolerances and a spherical convex crown end portion having a radius of curvature of at least twice said predetermined diameter; a transition portion interconnecting said head and said shank comprising a concavely curved constant radius circular surface tangent to said shank and hardened by cold rolling to a surface finish smoother than 32 RHR; and a fastening end lead-in portion comprising a convex circular surface tangent to said shank with a constant radius of curvature of a value ranging from 20 to 60 percent of said diameter; wherein said 70 cone angle and said transition portion are adapted to cooperate, upon the driving of said rivet to cause the rivet to expand to create residual stresses extending substantially throughout the countersunk region.
Claim 8
Dependent Claim
25 words
The rivet of claim 5 which includes a trimmed surface between said crown end portion and said conical surface which extends longitudinally approximately 0.005 inches.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-07-30 | 1977-01-29 | 1977-07-31 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-07-30 | 1981-01-29 | 1981-07-31 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-07-30 | 1985-01-29 | 1985-07-31 | $7700.00 | Window Closed / Lapsed |