Blind fastener

Abstract

The fastener includes a sleeve, a core bolt, and an insert. The sleeve includes a tubular portion and an internal thread. The core bolt includes a cylindrical portion, a threaded portion having an external thread, and a thread run-out between the cylindrical portion and the threaded portion. The core bolt is disposed within the sleeve, and the external thread engages with the internal thread. The insert is disposed within the sleeve and surrounds a portion of the core bolt. The insert abuts and is held between the internal thread and the thread run-out at a pre-installation position. The insert is compressed between the internal thread and the thread run-out by the installation operation of the core bolt simultaneously with the generation of a compressive load on the sleeve. The insert deforms and facilitates the formation of a spherical portion within the sleeve in response to the compression.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of co - owned, concurrently filed U.S. Provisional Patent Application No. 63 / 352,780, entitled "BLIND FASTENER," filed on June 16, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to fasteners, and more particularly to blind fasteners for securing together carbon fiber reinforced composite workpieces that are exposed to impacts due to lightning strikes.

Background Art

[0003] Blind fasteners are commonly used to secure multiple workpieces together when only limited physical or visual access is possible to one side of the workpiece. Carbon fiber reinforced composites tend to be used in aircraft structures because they have good strength - to - weight ratios, stiffness, and resistance to fatigue - induced damage. Also, there is a tendency to design natural laminar flow wings and hybrid laminar flow wings to improve fuel efficiency. Such wings generally have thinner cross - sections with restricted access to the interior of the wing.

[0004] Aircraft are frequently struck by lightning. This is particularly important for carbon fiber reinforced composite structures that inherently have low electrical conductivity, as metal fasteners are often the main path for lightning strike currents that are not well - distributed on the surface of composite aircraft structures. In such situations, the lightning strike current can generate a harmful ignition source by arc discharge between the fastener and the composite structure. The main danger from lightning strikes is arc discharge by the fastener, which creates a potential ignition source for fuel vapors, but Joule heating of the material, plasma activation, and vaporization of the material along the fastener / structure assembly can cause substantial physical damage to the fastener and the surrounding structure.

[0005] Carbon fiber reinforced composites typically consist of a binding polymer, commonly referred to as a matrix, and high-strength carbon fibers. The orientation of the carbon fibers, the ratio of the matrix to the fibers, and the composition of both the fibers and the matrix can be adjusted to achieve specific target properties for a particular application. The mechanical, electrical, and environmental properties of carbon fiber reinforced composites can also be affected by various types of additives that can be introduced into the binding matrix.

[0006] A wide range of manufacturing techniques have been developed, many of which employ a certain lamination manufacturing process where the fibers are combined into unidirectional or woven fabric layers and then stacked on top of each other in a quasi-isotropic laminate such as 0°, +60°, or -60°. In some cases, the matrix is combined with individual layers. In other cases, the matrix is injected into the stacked layers after the individual layers are stacked. Manufacturing techniques continue to evolve to reduce costs, but two-dimensional stack layers are far more common than three-dimensional stacks. Variations of two-dimensional stack technology are generally used to create aircraft structural sections such as fuselages and wings. Some techniques allow for large-scale integration of features, but to form an assembly, the subsections need to be mechanically joined with fasteners. This is especially true when subsections are constructed from different materials.

[0007] One of the challenges is that subsections, or individual components, have inherent anisotropic mechanical and electrical properties where their structure is a product of the properties of the stacked layers. Thus, the development of composite aircraft structures has led to a greater demand for mechanical fasteners that are electrically compatible with composite structures due to being significantly less conductive than those used in metallic aircraft structures, which are more susceptible to lightning strike damage. The anisotropic resistance properties and the increase in contact resistance directly affect the current path and the resulting electric field within the electrically connected regions of the aircraft sections joined by the fasteners. These electrical irregularities also directly affect the electromagnetic response of the aircraft to high frequencies.

[0008] The tendency to use more carbon fiber reinforced composites, as well as natural laminar wings and hybrid laminar wings, creates a need for blind fasteners that have a low inherent contact resistance between the components of the fastener assembly itself and a low contact resistance between the fastener and the surrounding composite structure. Such fasteners allow lightning strike currents to be conducted from one structural element to another and through the surrounding structure with relatively little adverse effect. As the current and electric fields develop within the aircraft structure, the low electrical continuity between the fastener surface and the internal joint due to the interface resistance becomes important in affecting the distribution of the current flow. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0009] In some embodiments, the fastener includes a sleeve having a first end and a second end opposite the first end, a tubular portion having an outer surface, an inner surface, an internal thread formed within the inner surface of the second end, and a head located at the first end, a core bolt having a first end and a second end opposite the first end, a cylindrical portion proximate the first end of the core bolt, an external thread portion proximate the second end of the core bolt, and a core bolt including a thread run-out between the cylindrical portion and the threaded portion, the core bolt being configured to be disposed within the sleeve, the external thread being configured to be threadedly engaged with the internal thread of the sleeve, an insert being disposed within the sleeve and configured to surround a portion of the core bolt proximate its second end, the insert being sized and shaped such that when the fastener is in the pre-installed position, it abuts and is held between the internal thread of the sleeve and the thread run-out of the core bolt, the insert being configured to be compressed between the internal thread of the sleeve and the thread run-out of the core bolt by the installation operation of the core bolt on the sleeve simultaneously with the generation of a compressive load on the sleeve by the installation operation of the core bolt, and the insert being configured to deform and facilitate the formation of a spherical portion within the sleeve in response to the compression of the insert.

[0010] In some embodiments, the core bolt includes an outer surface, and the insert is configured to fill a void between the outer surface of the core bolt proximate its second end and the inner surface of the sleeve proximate the second end of the tubular portion of the sleeve, and the insert is configured to provide an electrically conductive path between the sleeve and the core bolt. In some embodiments, the sleeve is composed of steel. In some embodiments, a first coefficient of friction between the inner surface of the sleeve and the outer surface of the core bolt, and a second coefficient of friction between the inner surface of the sleeve and the outer surface of the insert are selected to facilitate sliding contact between the sleeve and the core bolt and between the sleeve and the insert during attachment of the fastener.

[0011] In some embodiments, the sleeve includes a first layer on the outer surface of the sleeve, the first layer includes a first hardness, the sleeve includes a second layer on the inner surface of the sleeve, the second layer includes a second hardness, and the second hardness is greater than the first hardness. In some embodiments, the first layer is a coating. In some embodiments, the coating is composed of a metal-based coating. In some embodiments, the coating is selected from the group consisting of silver, gold, nickel, cadmium, copper, and lead, or alloys thereof. In some embodiments, the coating is composed of bronze. In some embodiments, the second layer is composed of an oxide layer. In some embodiments, the sleeve includes a third layer on the second layer. In some embodiments, the second layer is composed of carbon and the third layer is composed of nitrogen and carbon.

[0012] In some embodiments, the insert is composed of copper. In some embodiments, the insert is composed of Monel® alloy. In some embodiments, the insert includes a coating. In some embodiments, the coating is selected from the group consisting of silver, gold, and nickel. In some embodiments, the sleeve includes a band annealed portion proximate to the insert. In some embodiments, the core bolt includes a head at its first end, and the head of the sleeve includes a pocket sized and shaped to receive the head of the core bolt. In some embodiments, the head of the sleeve is configured to be attached to accessible holes of a plurality of workpieces, and the spherical portion is configured to be located on the blind side of the workpiece.

[0013] In some embodiments, the fastener includes a sleeve having a first end and a second end opposite the first end, a head located at the first end, a first portion proximate to the first end and having a first inner diameter, a second portion adjacent to the first portion and having a second inner diameter smaller than the first inner diameter of the first portion, a third portion proximate to the second end and having an internal thread, and a step located between the first portion and the second portion, a tubular portion, a core bolt including a first end and a second end opposite the first end of the core bolt, a cylindrical portion proximate to the first end of the core bolt, an external thread portion proximate to the second end of the core bolt, and a core bolt including a thread run-out between the cylindrical portion and the external thread portion, the core bolt being configured to be disposed within the sleeve, the external thread being configured to be thread-engaged with the internal thread of the sleeve, an insert being disposed within the sleeve and configured to surround a portion of the core bolt proximate to its second end, the insert being sized and shaped such that when the fastener is in the pre-mounted position, it abuts and is held between the internal thread of the sleeve and the thread run-out of the core bolt, the insert being configured to be compressed between the internal thread of the sleeve and the thread run-out of the core bolt by the mounting operation of the core bolt on the sleeve simultaneously with the generation of a compressive load on the sleeve due to the mounting operation of the core bolt, the insert being configured to deform and facilitate the formation of a spherical portion within the sleeve in response to the compression of the insert.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0015] For example, as shown in FIG. 10, in some embodiments, the fastener 10 includes a core bolt 12, a sleeve 14, and an insert 16. In some embodiments, the sleeve 14 is sized and shaped to receive the core bolt 12 and the insert 16, which is described in further detail below.

[0016] Referring to FIGS. 1 and 2, in some embodiments, the core bolt 12 includes a first end 18, a second end 20 opposite the first end 18, and a shank portion 22 between the first end 18 and the second end 20. In some embodiments, the shank portion 22 includes a cylindrical portion 24 that includes an outer surface 25. In some embodiments, the cylindrical portion 24 is adjacent to the first end 18. In some embodiments, the shank portion 22 is a smooth cylindrical shank portion. In some embodiments, the shank portion 22 has a first diameter. In some embodiments, the shank portion 22 includes a threaded portion 26. In some embodiments, the threaded portion 26 is adjacent to the second end 20. In some embodiments, the threaded portion 26 includes external threads 28. In some embodiments, the external threads 28 have a major diameter. In some embodiments, the major diameter is smaller than the first diameter of the shank portion 22. In some embodiments, the core bolt 12 includes a thread runout 30. In some embodiments, the thread runout 30 is located between the cylindrical portion 24 and the threaded portion 26. In some embodiments, the core bolt 12 is configured to be disposed within the sleeve 14. In some embodiments, the core bolt 12 includes an annular groove 32. In some embodiments, the annular groove 32 is adjacent to the thread runout 30. In some embodiments, the core bolt 12 includes a first head 34. In some embodiments, the first head 34 is adjacent to the first end 18. In some embodiments, the first head 34 is a flush head. In some embodiments, the core bolt 12 includes a second head 36. In some embodiments, the second head 36 is located at the first end 18. In some embodiments, the second head 36 is a spline head. In some embodiments, the second head 36 is configured to be engaged by a fastener attachment tool. In some embodiments, the second head 36 is removably attached to the first head 34. In some embodiments, the second head 36 is removably attached to the first head 34 by a breakneck portion 37.In some embodiments, the second head 36 is removed from the fastener 10 at the neck portion 37.

[0017] Referring to FIGS. 3-6, in some embodiments, the sleeve 14 includes a tubular portion 38. In some embodiments, the tubular portion 38 includes a first end 40, a second end 42 opposite the first end 40, a first portion 44 proximate the first end 40 and having a first inner diameter, and a second portion 46 proximate the second end 42. In some embodiments, the sleeve 14 includes an inner surface 66. In some embodiments, the second portion 46 includes an internal thread 48. In some embodiments, the internal thread 48 is located on the inner surface 66 of the second portion 46 of the sleeve 14. Referring to FIG. 7, in some embodiments, the sleeve 14 includes a third portion 50 adjacent to the first portion 44. In some embodiments, the third portion 50 includes a second inner diameter that is smaller than the first inner diameter of the first portion 44. In some embodiments, the sleeve 14 includes an annular step 52. In some embodiments, the annular step 52 is located between the first portion 44 and the third portion 50. In some embodiments, the sleeve 14 does not include an annular step 52.

[0018] In some embodiments, the sleeve 14 includes a head 54. In some embodiments, the head 54 is located at the first end 40 of the tubular portion 38. In some embodiments, the head 54 is an enlarged head. In some embodiments, the head 54 includes a pocket 56. In some embodiments, the pocket 56 is sized and shaped to receive the first head 34 of the core bolt 12. In some embodiments, the sleeve 14 includes an outer surface 58. In some embodiments, the outer surface 58 of the tubular portion 38 of the sleeve 14 includes an outer diameter. In some embodiments, the outer diameter of the outer surface 58 is sized and shaped to allow the sleeve 14 to be mounted within aligned holes of a plurality of workpieces 110, 112.

[0019] Referring to FIG. 8, in some embodiments, insert 16 includes a first end 60, a second end 62 opposite the first end 60, and an inner surface 63. In some embodiments, the inner surface 63 of insert 16 forms an opening 64. In some embodiments, the opening 64 extends from the first end 60 of insert 16 to the second end 62. In some embodiments, insert 16 includes an outer surface 65. In some embodiments, insert 16 has a tubular shape. In some embodiments, the inner surface 63 is cylindrical in shape. In some embodiments, insert 16 has an inner diameter. In some embodiments, the inner diameter of insert 16 is larger than the major diameter of the external thread 28 of core bolt 12. In some embodiments, insert 16 has an outer diameter. In some embodiments, the outer diameter of insert 16 is smaller than the minimum inner diameter of sleeve 14. In some embodiments, insert 16 is composed of copper. In some embodiments, insert 16 is composed of Monel® alloy. In some embodiments, insert 16 is coated. In some embodiments, insert 16 is coated with a high conductivity coating. In some embodiments, the coating is composed of a conductive metal material. In some embodiments, the coating is composed of silver. In some embodiments, the coating is composed of gold. In some embodiments, the coating is composed of nickel. In some embodiments, the coating is composed of cadmium. In some embodiments, the coating includes a low coefficient of friction. In some embodiments, the coefficient of friction is less than 0.50.

[0020] Referring to FIGS. 9 - 15, in some embodiments, the first diameter of the cylindrical portion 24 of the core bolt 12 is sized and shaped to allow the core bolt 12 to be installed within the sleeve 14. In some embodiments, the external threads 28 of the threaded portion 26 of the core bolt 12 are configured to be complementary to, or threadedly engage, the internally threaded portion 48 of the sleeve 14. In some embodiments, the core bolt 12 is configured to be engaged by a fastener installation tool. In some embodiments, the insert 16 is disposed within the sleeve 14. In some embodiments, the insert 16 surrounds at least a portion of the threaded portion 26 of the core bolt 12. In some embodiments, the insert 16 surrounds the entire threaded portion 26 of the core bolt 12.

[0021] Referring to FIGS. 16 and 17, in some embodiments, the fastener 10 is configured to be installed within aligned holes 115, 117 of a plurality of workpieces 110, 112. In some embodiments, the fastener 10 is assembled and pre-installed within a plurality of workpieces 110, 112. In some embodiments, the workpiece 110 includes an accessible side surface 113. In some embodiments, the workpiece 112 includes a blind side surface 114. In some embodiments, the accessible side surface 113 is on the opposite side of the blind side surface 114. In some embodiments, the fastener 10's fixture has no physical or visual access to its blind side surface 114. In some embodiments, each of the aligned holes 115, 117 of the workpieces 110, 112 includes an inner diameter. In some embodiments, each of the workpieces 110, 112 is composed of a composite material. In some embodiments, each of the workpieces 110, 112 is substantially composed of a composite material. In some embodiments, the insert 16 is sized and shaped to abut and be held between the internal thread 48 of the sleeve 14 and the thread runout 30 of the core bolt 12 when the fastener 10 is in its pre-installed position. In some embodiments, the insert 16 is sized and shaped to abut and be held between the annular step 52 of the sleeve 14 and the thread runout 30 of the core bolt 12 when the fastener 10 is in its pre-installed position.

[0022] Referring to FIGS. 18 and 19, in some embodiments, during the installation of the fastener 10, the insert 16 is compressed between the annular step 52 of the sleeve 14 and the thread runout 30 of the core bolt 12 by the installation operation of the core bolt 12 relative to the sleeve 14, simultaneously with the installation operation of the core bolt 12. In some embodiments, the length of the insert 16 is configured such that the total volume of the insert 16 is complementary to the total volume of the void located between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12 so as to fill the void between the core bolt 12 and the sleeve 14 when the fastener 10 is fully installed within the workpieces 110, 112. In some other embodiments, during the installation of the fastener 10, the insert 16 is compressed between the internal thread 48 of the sleeve 14 and the thread runout 30 of the core bolt 12 by the installation operation of the core bolt 12 relative to the sleeve 14, simultaneously with the installation operation of the core bolt 12 that generates a compressive load on the sleeve 14.

[0023] In some embodiments, insert 16 is configured to be compressed between the internal threads 48 of sleeve 14 and the thread run - out 30 of core bolt 12 upon attachment of core bolt 12 to sleeve 14, simultaneously with the generation of a compressive load on sleeve 14 by the attachment operation of core bolt 12. In some embodiments, insert 16 is configured to deform and facilitate the formation of spherical portion 70 within the tubular portion 38 of sleeve 14 in response to the compression of insert 16. In some embodiments, insert 16 acts as a bearing during the attachment process, filling the void between the inner surface 66 of sleeve 14 and the outer surface 25 of core bolt 12 to form an electrically conductive path between core bolt 12 and sleeve 14. In some embodiments, the second head 36 is removed from the fastener 10 at the break - neck portion 37 after the fastener 10 has been attached within workpieces 110, 112. In some embodiments, the first head 34 of core bolt 12 is in the same plane as the accessible side surface 113 of workpiece 110. In some embodiments, the head 54 of sleeve 14 is in the same plane as the accessible side surface 113 of workpiece 110.

[0024] In some embodiments, sleeve 14 is composed of A286 (AISI660) steel. In some embodiments, A286 steel is an austenitic precipitation - hardening stainless steel. In some embodiments, sleeve 14 is composed of 300 - series stainless steel. In some embodiments, sleeve 14 is composed of 304L stainless steel. In some embodiments, sleeve 14 is composed of 316L stainless steel. In some embodiments, sleeve 14 is composed of a copper - nickel alloy. In some embodiments, the steel is modified to include a soft layer on the outer surface 58 of sleeve 14. In some embodiments, the term "soft" as defined herein means that the layer on the outer surface 58 of sleeve 14 has a hardness of less than Rc30 on the Rockwell C hardness scale.

[0025] In some embodiments, the steel is modified to include a hard layer on the inner surface 66 of the sleeve 14. In some embodiments, the term "hard" as defined herein means that the layer on the inner surface 66 of the sleeve 14 has a hardness of 8.0 to 8.5 on the Mohs scale. In some embodiments, the sleeve 14 includes a band annealing portion 72. In some embodiments, the first layer on the outer surface 58 of the sleeve 14 includes a first hardness. In some embodiments, the second layer on the inner surface 66 of the sleeve 14 includes a second hardness. In some embodiments, the second hardness of the inner surface 66 of the sleeve 14 is greater than the first hardness of the outer surface 58 of the sleeve 14. In some embodiments, the band annealing portion 72 is proximate to the insert 16. In some embodiments, the sleeve 14 includes a selectively soft conformable outer surface, a selectively hard inner surface, and an annealing portion between a first end 40 and a second end 42 proximate to the insert 16. In some embodiments, the band annealing portion 72 is band annealed by a laser or a radio frequency induction coil. In some embodiments, the band annealing portion 72 facilitates the formation of the spherical portion 70 against the surface of the blind side 114 of the workpiece 112 in all grip ranges of the fastener 10.

[0026] In some embodiments, the outer surface 58 of the sleeve 14 is coated with a soft, highly conductive coating. In some embodiments, the coating has sufficient electrical conductivity. In some embodiments, the coating is galvanically compatible with the sleeve 14. In some embodiments, the coating is galvanically compatible with the workpieces 110, 112. In some embodiments, the coating conforms to the respective unique microtexture of the inner surface formed by each of the holes of the workpieces 110, 112. In some embodiments, the coating is composed of a metal-based coating. In some embodiments, the coating is composed of silver. In some embodiments, the coating is composed of gold. In some embodiments, the coating is composed of nickel. In some embodiments, the coating is composed of cadmium. In some embodiments, the coating is composed of copper. In some embodiments, the coating is composed of lead. In some embodiments, the coating is composed of an alloy. In some embodiments, the coating is composed of bronze.

[0027] In some embodiments, the outer surface 58 of the sleeve is not coated. In some embodiments, the outer surface 58 of the sleeve 14 is microtextured. In some embodiments, the microtexture of the outer surface 58 of the sleeve 14 complements the microtexture unique to the inner surface forming each of the holes of the workpieces 110, 112. In some embodiments, the microtexture is between 25 microinches and 40 microinches.

[0028] In some embodiments, the inner surface 66 of the sleeve 14 includes a layer having a higher surface hardness compared to the hardness of the untreated inner surface 66. In some embodiments, the inner surface 66 of the sleeve 14 has a surface hardness of 8.0 to 8.5 on the Mohs scale. In some embodiments, the first coefficient of friction between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12, and the second coefficient of friction between the inner surface 66 of the sleeve 14 and the outer surface 65 of the insert 16 are selected to facilitate sliding contact between the sleeve 14, the core bolt 12, and the insert 16 during the attachment of the fastener 10. In some embodiments, the first coefficient of friction is less than 0.5. In some embodiments, the second coefficient of friction is less than 0.5. In some embodiments, the friction at the interface between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12, and the friction at the interface between the inner surface 66 of the sleeve 14 and the outer surface 65 of the insert 16 are reduced by the presence of an oxide layer. In some embodiments, the oxide layer includes high hardness. In some embodiments, the oxide layer has a hardness of 8.0 to 8.5 on the Mohs scale. In some embodiments, the inner surface 66 of the sleeve 14 includes a double layer. In some embodiments, the double layer of the inner surface 66 of the sleeve 14 includes nitrogen and carbon in the first layer and carbon in the second layer. In some embodiments, the first layer of the inner surface 66 of the sleeve 14 is the innermost layer. In some embodiments, the first layer of the inner surface 66 of the sleeve 14 is the outermost layer. In some embodiments, the second layer of the inner surface 66 of the sleeve 14 is the innermost layer. In some embodiments, the second layer of the inner surface 66 of the sleeve 14 is the outermost layer. In some embodiments, the microhardness of the inner surface 66 of the sleeve 14 having a double layer increases by 2 to 3 times compared to when the inner surface 66 of the sleeve 14 is untreated. In some embodiments, the microhardness of the inner surface 66 of the sleeve 14 is 8.0 to 8.5 on the Mohs scale.

[0029] In some embodiments, a thick and hard oxide layer selectively grows on the inner surface 66 of the sleeve 14. In some embodiments, the thicker oxide layer selectively grown on the inner surface of the sleeve 14 creates sufficient protection against surface damage and results in lower friction. In some embodiments, the thick oxide layer is formed slowly at high temperature. In some embodiments, the oxide layer grows to a thickness of up to a few microns to provide a hard layer. In some embodiments, the hard layer separates the metal counterparts of the core bolt 12 and the insert 16 from the metal counterpart of the sleeve 14 during the sliding operation of the core bolt 12 and the insert 16 relative to the sleeve 14, thereby avoiding surface damage, galling, and high friction. In some embodiments, the hard layer has a corundum-like particulate structure on the outer surface 58 of the sleeve 14 that provides a hard surface with a maximum Mohs hardness of 9.0.

[0030] It should be understood that the embodiments described herein are merely exemplary in nature and that those skilled in the art can make many variations and modifications thereto without departing from the scope of the invention. Such modifications and variations are intended to be included within the scope of this disclosure.

Description of Reference Numerals

[0031] 10 Fastener 12 Core Bolt 14 Sleeve 16 Insert 18 First End 20 Second End 22 Shank Portion 24 Cylindrical Portion 25 Outer Surface 26 Threaded Portion 28 External Thread 30 Thread Run-Out 32 Annular Groove 34 First Head 36 Second Head 37 Necking Portion 38 Tubular Portion 40 First end 42 Second end 44 First part 46 Second part 48 Internal thread 50 Third part 52 Annular step 54 Head 56 Pocket 58 External surface 60 First end 62 Second end 63 Internal surface 64 Opening 65 External surface 66 Internal surface 70 Spherical part 72 Band annealing part 110, 112 Workpiece 113 Accessible side 114 Blind side 115, 117 Hole

Claims

1. A fastener comprising: A sleeve including a first end and a second end opposite the first end; A tubular portion having an outer surface, an inner surface, an internal thread formed within the inner surface of the second end, and a head located at the first end; A core bolt including a first end and a second end opposite the first end of the core bolt, a cylindrical portion adjacent to the first end of the core bolt, an external thread portion adjacent to the second end of the core bolt, and a thread run-out between the cylindrical portion and the threaded portion; wherein the core bolt is configured to be disposed within the sleeve, the external thread is configured to be threadedly engaged with the internal thread of the sleeve, an insert is disposed within the sleeve and configured to surround a portion of the core bolt adjacent to its second end, the insert is sized and shaped such that when the fastener is in a pre - installation position, it abuts and is held between the internal thread of the sleeve and the thread run - out of the core bolt, the insert is configured to be compressed between the internal thread of the sleeve and the thread run - out of the core bolt by the installation operation of the core bolt on the sleeve, simultaneously with the generation of a compressive load on the sleeve due to the installation operation of the core bolt, the insert is configured to deform and facilitate the formation of a spherical portion within the sleeve in response to the compression of the insert. A fastener.

2. The fastener according to claim 1, wherein the core bolt includes an outer surface, the insert is configured to fill a gap between the outer surface of the core bolt adjacent to its second end and the inner surface of the second end of the tubular portion of the sleeve, and the insert is configured to provide an electrically conductive path between the sleeve and the core bolt.

3. The fastener according to claim 1, wherein the sleeve is made of steel.

4. The first coefficient of friction between the inner surface of the sleeve and the outer surface of the core bolt, and the second coefficient of friction between the inner surface of the sleeve and the outer surface of the insert are selected to facilitate sliding contact between the sleeve and the core bolt and between the sleeve and the insert during attachment of the fastener, the fastener according to claim 3.

5. The sleeve includes a first layer on the outer surface of the sleeve, the first layer having a first hardness, and a second layer on the inner surface of the sleeve, the second layer having a second hardness, the second hardness being greater than the first hardness, the fastener according to claim 4.

6. The first layer is a coating, the fastener according to claim 5.

7. The coating is composed of a metal-based coating, the fastener according to claim 6.

8. The coating is selected from the group consisting of silver, gold, nickel, cadmium, copper, and lead, or alloys thereof, the fastener according to claim 6.

9. The coating is composed of bronze, the fastener according to claim 6.

10. The second layer is composed of an oxide layer, the fastener according to claim 5.

11. The sleeve includes a third layer on the second layer, the fastener according to claim 10.

12. The second layer is composed of carbon, and the third layer is composed of nitrogen and carbon, the fastener according to claim 11.

13. The insert is composed of copper, the fastener according to claim 1.

14. The insert is composed of a Monel (registered trademark) alloy, the fastener according to claim 1.

15. The insert includes a coating, the fastener according to claim 1.

16. The coating is selected from the group consisting of silver, gold, and nickel, the fastener according to claim 15.

17. The sleeve includes a band annealing portion proximate to the insert, the fastener according to claim 4.

18. The core bolt includes a head at its first end, and the head of the sleeve includes a pocket sized and shaped to receive the head of the core bolt, the fastener according to claim 1.

19. The fastening device according to claim 1, wherein the head of the sleeve is configured to be attached to accessible holes in a plurality of workpieces, and the spherical portion is configured to be located on the blind side surface of the workpiece.

20. A fastening device, A sleeve, A sleeve having a first end and a second end opposite the first end, A tubular portion, A head located at the first end, A first portion proximate to the first end and having a first inner diameter, A second portion adjacent to the first portion and having a second inner diameter smaller than the first inner diameter of the first portion, A third portion proximate to the second end and having an internal thread, A tubular portion having a step located between the first portion and the second portion, A core bolt, A first end and a second end opposite the first end of the core bolt, A cylindrical portion proximate to the first end of the core bolt, An external thread portion proximate to the second end of the core bolt, A core bolt including a thread run-out between the cylindrical portion and the external thread portion, The core bolt is configured to be disposed within the sleeve, The external thread is configured to be threadedly engaged with the internal thread of the sleeve, An insert is disposed within the sleeve and is configured to surround a portion of the core bolt proximate to the second end thereof, The insert is sized and shaped such that when the fastening device is in the pre - attachment position, it is abutted and held between the step of the sleeve and the thread run - out of the core bolt, The insert is configured to be compressed between the internal thread of the sleeve and the thread run - out of the core bolt by the attachment operation of the core bolt to the sleeve, simultaneously with the generation of a compressive load on the sleeve due to the attachment operation of the core bolt, The fastening device, wherein the insert is configured to deform and facilitate the formation of a spherical portion within the sleeve in response to the compression of the insert.

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