Blind Fasteners

Abstract

The fastener includes a sleeve having a first and second end, a tubular portion having an outer surface and an inner surface, a groove formed in the outer surface between the first end and the second end, and an internal thread located in the internal surface at the second end. The fastener includes a core bolt having a cylindrical portion, an external thread, and an incomplete thread between the cylindrical portion and the thread. The core bolt is configured to be disposed within the sleeve. The external thread is configured to threadably mate with the internal thread of the sleeve. Installation of the core bolt within the sleeve generates a compressive load on the sleeve. The groove is configured to facilitate formation of an expansion in the sleeve in response to the compressive load.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of commonly owned and co-pending U.S. Provisional Patent Application No. 63 / 439,405, entitled "BLIND FASTENER," filed January 17, 2023, which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION The present invention relates to fasteners, and more particularly to blind fasteners for securing multiple workpieces together. [Background technology]

[0003] Blind fasteners are commonly used to secure multiple workpieces together when physical or visual access to one blind or inaccessible side of the workpieces is limited. There is a trend toward using carbon fiber reinforced composites in aircraft structures because they combine a good strength-to-weight ratio, stiffness, and resistance to fatigue-induced damage. However, carbon fiber reinforced composites often have low stiffness and strength through their thickness. There is also a trend toward designing natural and hybrid laminar flow wings to improve fuel efficiency. These wings generally have thinner cross-sections with limited access to the interior of the wing.

[0004] Carbon fiber reinforced composites are typically composed of high-strength carbon fibers combined with a binding polymer, commonly referred to as a matrix. The carbon fiber orientation, matrix to fiber ratio, and composition of both the fiber and matrix can be tailored to achieve specific target properties for specific applications. Additionally, the mechanical, electrical, and environmental properties of carbon fiber reinforced composites can be influenced by various types of additives that can be introduced into the binding matrix.

[0005] A wide range of manufacturing techniques have been developed, but many employ some type of layered manufacturing process in which fibers are combined into unidirectional or woven layers and then stacked together in quasi-isotropic laminations, e.g., at 0°, +60°, or -60° angles. In some cases, a matrix is ​​combined with the individual layers. In other cases, a matrix is ​​infused into the stacked layers after the individual layers have been stacked. The two-dimensional layered structure inherently contributes to low stiffness and strength in the thickness direction, which is perpendicular to the fiber direction.

[0006] Therefore, the development of composite aircraft is driving demands for mechanical fasteners that combine high clamping forces perpendicular to the fiber direction with large expansion sections on the blind sides to distribute the clamping forces and reduce bearing stresses between the expansion sections and the composite structure. Additionally, there is a need to minimize bearing stresses at the corners where the fastener holes intersect with the backside of the structure to prevent composite delamination at these locations. Summary of the Invention [Means for solving the problem]

[0007] In some embodiments, the fastener comprises: a sleeve having a first end and a second end opposite the first end, a tubular portion having an outer surface and an inner surface, a groove formed in the outer surface between the first end and the second end, an internal thread formed in the internal surface of the second end, and a head provided on the first end; and a core bolt having a first end, 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 an incomplete thread portion between the cylindrical portion and the external thread portion, wherein the core bolt is configured to be disposed within the sleeve, the external thread portion configured to threadably engage the internal threads of the sleeve, installation of the core bolt within the sleeve generates a compressive load in the sleeve, and the groove is configured to facilitate formation of an expansion portion in the sleeve in response to the compressive load.

[0008] In some embodiments, the groove has a depth of 0.001 inch to 0.005 inch (0.0254 mm to 0.127 mm). In some embodiments, the groove has a width of 0.06 inch to 0.15 inch (1.524 mm to 3.81 mm). In some embodiments, the groove is circumferentially disposed around the sleeve. In some embodiments, the groove is circumferentially disposed around the entire diameter of the sleeve. In some embodiments, the groove is circumferentially disposed partially around the diameter of the sleeve. In some embodiments, the groove includes a first boundary and a second boundary, the first boundary being circumferentially disposed around the sleeve and the second boundary also being circumferentially disposed around the sleeve.

[0009] In some embodiments, the blind side grip line of a first workpiece of the plurality of workpieces is between the first boundary and the second boundary of the groove. In some embodiments, the blind side grip line of a first workpiece of the plurality of workpieces is proximate to the first boundary. In some embodiments, the blind side grip line of a first workpiece of the plurality of workpieces is substantially aligned with the first boundary. In some embodiments, the blind side grip line of a first workpiece of the workpieces is proximate to the second boundary. In some embodiments, the blind side grip line of a first workpiece of the workpieces is substantially aligned with the second boundary.

[0010] In some embodiments, the sleeve includes a first layer on an outer surface of the sleeve, the first layer having a first hardness, and a second layer on an inner surface of the sleeve, the second layer having a second hardness, the second hardness being greater than the first hardness. In some embodiments, the first layer is a coating. In some embodiments, the coating is comprised 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 comprised of bronze. In some embodiments, the second layer is comprised of an oxide layer. In some embodiments, the sleeve includes a third layer on the second layer. In some embodiments, the second layer is comprised of carbon, and the third layer is comprised of nitrogen and carbon.

[0011] In some embodiments, the fastener further comprises an insert disposed within the sleeve and configured to surround a portion of the core bolt proximate its second end, the insert being sized and shaped to abut and be held between the internal threads of the sleeve and the incomplete threads of the core bolt when the fastener is in a pre-installation position, the insert being configured to be compressed between the internal threads of the sleeve and the incomplete threads of the core bolt by an installation action of the core bolt relative to the sleeve simultaneously with the application of a compressive load to the sleeve by the installation action of the core bolt, and the insert being configured to simultaneously deform and facilitate the formation of an expansion in the sleeve in response to compression of the insert. In some embodiments, the insert, together with the groove, is configured to simultaneously deform and facilitate the formation of an expansion in the sleeve in response to compression of the insert.

[0012] In some embodiments, the core bolt has an outer surface, and an insert is configured to fill a gap 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, the insert being configured to provide a conductive path between the sleeve and the core bolt. 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 installation of the fastener. In some embodiments, the core bolt includes a head at the first end, and the head of the sleeve includes a pocket sized and shaped to receive the head of the core bolt. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a side view of some embodiments of a fastener. [Figure 2] FIG. 2 is a side view of some embodiments of a fastener. [Figure 3] FIG. 3 shows a partial side cross-sectional view of some embodiments of a fastener. [Figure 4] 4 is a side cross-sectional view of the fastener of FIG. 2 taken along section line 4-4 and looking in the direction of the arrows. [Figure 5] FIG. 5 is a partial cross-sectional perspective view of several embodiments of a fastener. [Figure 6] FIG. 6 is a cross-sectional perspective view of several embodiments of fasteners. [Figure 7] FIG. 7 is a top perspective view of several embodiments of fasteners attached to multiple workpieces. [Figure 8] FIG. 8 shows several embodiments of fasteners attached to multiple workpieces in a minimum grip state (left) and a maximum grip state (right). [Figure 9]FIG. 9 shows several embodiments of fasteners attached to multiple workpieces in a minimum grip state and a maximum grip state with corresponding bulging of the fastener. [Figure 10] FIG. 10 shows several embodiments of a comparison of bulge formation between several embodiments of fasteners with grooves (right) and several embodiments of fasteners without grooves (left) in a minimum grip state. [Figure 11] FIG. 11 shows several embodiments of a comparison of bulge formation between several embodiments of fasteners with grooves (right) and several embodiments of fasteners without grooves (left) at maximum grip. [Figure 12] FIG. 12 shows a graph of bulge size versus drive angle for a comparison of bulge formation between several embodiments of fasteners with grooves and several embodiments of fasteners without grooves at minimum grip conditions. [Figure 13] FIG. 13 shows a graph of bulge size versus drive angle for a comparison of bulge formation between several embodiments of fasteners with grooves and several embodiments of fasteners without grooves at maximum grip. [Figure 14] FIG. 14 shows a graph of contact node force versus drive angle for a comparison of several embodiments of fasteners with grooves and several embodiments of fasteners without grooves at minimum grip. [Figure 15] FIG. 15 shows a graph of contact node force versus actuation angle for a comparison of several embodiments of fasteners with grooves and several embodiments of fasteners without grooves at maximum grip. [Figure 16] FIG. 16 is a partial cross-sectional perspective view of several embodiments of a fastener. [Figure 17] FIG. 17 is a cross-sectional perspective view of several embodiments of fasteners. [Figure 18] FIG. 18 is a perspective view of several embodiments of inserts for use in fasteners. [Figure 19]FIG. 19 is a side view and cross-sectional side view of several embodiments of the fastener shown in FIGS. 16-17, showing the fastener fully installed within multiple workpieces. [Figure 20] FIG. 20 is a side view and cross-sectional side view of several embodiments of the fasteners shown in FIGS. 16-17, showing the fasteners fully installed within multiple workpieces. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1-6, in some embodiments, fastener 10 includes a core bolt 12 and a sleeve 14. In some embodiments, sleeve 14 is sized and shaped to receive core bolt 12, which will be described in more detail below.

[0015] In some embodiments, the core bolt 12 has 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 has a cylindrical portion 24 with an outer surface 25. In some embodiments, the cylindrical portion 24 is proximate 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 has a threaded portion 26. In some embodiments, the threaded portion 26 is proximate the second end 20. In some embodiments, the threaded portion 26 includes external threads 28. In some embodiments, the external threads 28 have an outer diameter. In some embodiments, the outer diameter is smaller than the first diameter of the shank portion 22. In some embodiments, the core bolt 12 includes incomplete threads 30. In some embodiments, the incomplete threads 30 are 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 has an annular groove 32. In some embodiments, the annular groove 32 is adjacent to the incomplete threads 30. In some embodiments, the core bolt 12 includes a first head 34. In some embodiments, the first head 34 is proximate 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 splined head. In some embodiments, the second head 36 is configured to be engaged by a fastener installation 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 breakneck portion 37 after the fastener 10 has been installed.

[0016] 1-6, in some embodiments, the sleeve 14 has 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 adjacent the first end 40 and having a first inner diameter, and a second portion 46 adjacent the second end 42. In some embodiments, the sleeve 14 has an inner surface 66. In some embodiments, the second portion 46 has internal threads 48. In some embodiments, the internal threads 48 are located on the inner surface 66 of the second portion 46 of the sleeve 14. Referring to FIG. 3, in some embodiments, the sleeve 14 has a third portion 50 adjacent to the first portion 44. In some embodiments, the third portion 50 has 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 have an annular step 52 .

[0017] 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 has an outer surface 58. In some embodiments, the outer surface 58 of the tubular portion 38 of the sleeve 14 has an outer diameter. In some embodiments, the outer diameter of the outer surface 58 is sized and shaped to mount the sleeve 14 within aligned holes 115, 117 in multiple workpieces 110, 112 (see FIG. 7 ).

[0018] In some embodiments, sleeve 14 has a groove 72 disposed in its outer surface 58 (see FIG. 2 ). In some embodiments, groove 72 extends circumferentially within outer surface 58. In some embodiments, groove 72 extends circumferentially within outer surface 58 around the entire outer diameter of sleeve 14. In some embodiments, groove 72 extends circumferentially within outer surface 58 around a partial diameter of sleeve 14. In some embodiments, groove 72 has a depth between 0.001 inches and 0.005 inches. In some embodiments, groove 72 has a depth of 0.001 inches. In some embodiments, groove 72 has a depth of 0.002 inches. In some embodiments, groove 72 has a depth of 0.003 inches. In some embodiments, groove 72 has a depth of 0.004 inches. In some embodiments, groove 72 has a depth of 0.005 inches. In some embodiments, groove 72 has a first boundary 74 and a second boundary 76. In some embodiments, first boundary 74 is spaced from second boundary 76. In some embodiments, groove 72 has a width W. In some embodiments, width W extends from first boundary 74 to second boundary 76. In some embodiments, width W is between 0.06 inches and 0.1 inches. In some embodiments, width W is between 0.06 inches and 0.15 inches.

[0019] In some embodiments, the wall thickness T of sleeve 14 is between 0.01 inches and 0.05 inches. In some embodiments, the wall thickness T of sleeve 14 at the location of groove 72 is less than the wall thickness T of other portions of sleeve 14 that do not include groove 72.

[0020] 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 complementary to and configured to mate with the internal threads 48 of the sleeve 14. In some embodiments, the core bolt 12 is configured to be engaged by a fastener installation tool 200 (see FIG. 7 ).

[0021] In some embodiments, the sleeve 14 is constructed of A286 (AISI 660) steel. In some embodiments, A286 steel is an austenitic precipitation hardened stainless steel. In some embodiments, the sleeve 14 is constructed of 300 series stainless steel. In some embodiments, the sleeve 14 is constructed of 304L stainless steel. In some embodiments, the sleeve 14 is constructed of 316L stainless steel. In some embodiments, the sleeve 14 is constructed of a copper-nickel alloy. In some embodiments, the steel may have a soft layer on the outer surface 58 of the sleeve 14. In some embodiments, the term "soft" as defined herein means that the layer on the outer surface 58 of the sleeve 14 has a hardness of less than Rc30 on the Rockwell Hardness C scale.

[0022] 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, a first layer on the outer surface 58 of the sleeve 14 includes a first hardness. In some embodiments, a 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 sleeve 14 has a selectively soft, deformable outer surface and a selectively hard inner surface.

[0023] 7 and 8, in some embodiments, the fastener 10 is configured to be installed within aligned holes 115, 117 in multiple workpieces 110, 112. In some embodiments, the fastener 10 is assembled and pre-installed within the multiple workpieces 110, 112. In some embodiments, the workpiece 110 has an accessible side 113. In some embodiments, the workpiece 112 has a blind side 114. In some embodiments, the accessible side 113 is opposite the blind side 114. In some embodiments, the fastener 10's attachment does not have physical or visual access to the blind side 114. In some embodiments, each of the aligned holes 115, 117 in the workpieces 110, 112 has an inner diameter. In some embodiments, each of the workpieces 110, 112 is comprised of a composite material. In some embodiments, each of the workpieces 110, 112 is comprised substantially of a composite material.

[0024] In some embodiments, the groove 72 is located within the outer surface 58 of the sleeve 14 such that a back grip line or plane AA of the workpiece 112 of the blind side 114 lies between a first boundary 74 and a second boundary 76 of the groove 72 (see FIG. 8 ). In some embodiments, the back grip line AA of the blind side 114 of the workpiece 112 is proximate to the first boundary 74. In some embodiments, the back grip line AA of the blind side 114 of the workpiece 112 is proximate to the second boundary 76. In some embodiments, the back grip line AA of the blind side 114 of the workpiece 112 is aligned with the first boundary 74. In some embodiments, the back grip line AA of the blind side 114 of the workpiece 112 is aligned with the second boundary 76. In some embodiments, the back grip line AA of the blind side 114 of the workpiece 112 is substantially aligned with the first boundary 74. In some embodiments, the back grip line AA of the blind side 114 of the workpiece 112 is substantially aligned with the second boundary 76 .

[0025] In some embodiments, groove 72 is configured to function as a hinge to facilitate the formation of bulge 70 without significantly increasing compressive stresses at corners 78 of hole 117 and blind sides 114 of workpiece 112 (see FIG. 7). In some embodiments, the hinge function of groove 72 reduces the likelihood of delamination of workpiece 112 at corners 78.

[0026] 7 and 9-11, in some embodiments, the groove 72 facilitates the formation of a bulge 70 against the surface of the blind side 114 of the workpiece 112 at all gripping ranges of the fastener 10 when the core bolt 12 is installed within the sleeve 14. In some embodiments, axial stresses on the sleeve 14 are concentrated in the bulge 70 when the sleeve 14 is compressed by tightening the core bolt 12 during installation of the fastener 10.

[0027] In some embodiments, the grooves 72 allow sleeves 14 with thicker wall thicknesses to buckle at lower axial forces during installation of the fastener 10, thereby requiring less drive torque. FIG. 10 shows some embodiments comparing bulge 70 formation between a fastener 10 with grooves 72 (shown on the right) and a fastener without grooves 72 (shown on the left) at minimum grip of four turns of the core bolt 12 against the sleeve 14. In some embodiments, the fastener on the left side of the illustration (without grooves) has a uniform sleeve wall thickness of 0.027 inches. In some embodiments, the fastener 10 on the right side of the illustration (with grooves 72) has stepped sleeve wall thicknesses of 0.027 inches and 0.025 inches with an undercut length of 0.1 inches.

[0028] 11 shows several embodiments comparing bulge 70 formation between a fastener 10 with grooves 72 (shown on the right) and a fastener without grooves 72 (shown on the left) at maximum grip at 2.5 turns of core bolt 12 against sleeve 14. In some embodiments, the fastener on the left side of the illustration (without grooves) has a uniform sleeve wall thickness of 0.027 inches. In some embodiments, the fastener 10 on the right side of the illustration (with grooves 72) has a stepped sleeve wall thickness of 0.027 inches and 0.025 inches with an undercut length of 0.1 inches.

[0029] Figure 12 shows a graph of bulge size versus drive angle comparing bulge 70 formation at minimum grip between fastener 10 with grooves 72 and several embodiments of fasteners without grooves 72. Figure 13 shows a graph of bulge size versus drive angle comparing bulge 70 formation at maximum grip between fastener 10 with grooves 72 and several embodiments of fasteners without grooves 72.

[0030] Figure 14 shows a graph of contact node force versus drive angle comparing fastener 10 with groove 72 and several embodiments of fasteners without groove 72 at minimum grip. Figure 15 shows a graph of contact node force versus drive angle comparing fastener 10 with groove 72 and several embodiments of fasteners without groove 72 at minimum grip. In some embodiments, groove 72 helps delay the onset of clamping force (i.e., preload) when installing fastener 10. In some embodiments, fastener 10 is configured to have equal or greater preload at a selected grip condition at a particular target torque when installing fastener 10.

[0031] FIG. 15 shows Table 1 showing the diameter, preload, and ultimate tensile strength (UTS) of the fastener 10 and associated expansion 70 under minimum or maximum grip conditions compared to target values.

[0032] 16 and 17 , in some embodiments, the fastener 10 includes an insert 16 disposed between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12. 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 threads 26 of the core bolt 12. In some embodiments, the insert 16 surrounds the entire threads 26 of the core bolt 12. In some embodiments, the insert 16 is sized and shaped to abut and be held between the internal threads 48 of the sleeve 14 and the partial threads 30 of the core bolt 12 when the fastener 10 is in a 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 partial threads 30 of the core bolt 12 when the fastener 10 is in a pre-installed position.

[0033] Referring to FIG. 18 , in some embodiments, the insert 16 has 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 the insert 16 defines an opening 64. In some embodiments, the opening 64 extends from the first end 60 to the second end 62 of the insert 16. In some embodiments, the insert 16 has an outer surface 65. In some embodiments, the insert 16 has a tubular shape. In some embodiments, the inner surface 63 is cylindrical. In some embodiments, the insert 16 has an inner diameter. In some embodiments, the inner diameter of the insert 16 is larger than the outer diameter of the external threads 28 of the core bolt 12 (see FIGS. 16 and 17 ). In some embodiments, the insert 16 has an outer diameter. In some embodiments, the outer diameter of the insert 16 is smaller than the minimum inner diameter of the sleeve 14. In some embodiments, the insert 16 is constructed of copper. In some embodiments, the insert 16 is constructed of Monel® alloy. In some embodiments, the insert 16 is coated. In some embodiments, the insert 16 is coated with a highly conductive coating. In some embodiments, the coating is comprised of a conductive metallic material. In some embodiments, the coating is comprised of silver. In some embodiments, the coating is comprised of gold. In some embodiments, the coating is comprised of nickel. In some embodiments, the coating is comprised of cadmium. In some embodiments, the coating has a low coefficient of friction. In some embodiments, the coefficient of friction is less than 0.50.

[0034] 19 and 20 , in some embodiments, during installation of the fastener 10, the insert 16 is compressed between the annular step 52 of the sleeve 14 and the incomplete threads 30 of the core bolt 12 by the installation of the core bolt 12 relative to the sleeve 14. In some embodiments, the length of the insert 16 is configured so 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, such that the insert 16 fills the void between the core bolt 12 and the sleeve 14 when the fastener 10 is fully installed within the workpiece 110, 112. In some other embodiments, during installation of the fastener 10, the insert 16 is compressed between the internal threads 48 of the sleeve 14 and the incomplete threads 30 of the core bolt 12 by the installation of the core bolt 12 relative to the sleeve 14, which generates a compressive load on the sleeve 14.

[0035] In some embodiments, the insert 16 is configured to be compressed between the internal threads 48 of the sleeve 14 and the incomplete threads 30 of the core bolt 12 by the installation of the core bolt 12 relative to the sleeve 14, simultaneously with the application of a compressive load to the sleeve 14 by the installation of the core bolt 12. In some embodiments, the insert 16 is configured to deform simultaneously with and facilitate the formation of a bulge 70 in the tubular portion 38 of the sleeve 14 in response to the compression of the insert 16. In some embodiments, the insert 16 is configured to deform simultaneously with and facilitate the formation of a bulge 70 in the tubular portion 38 of the sleeve 14 in response to the compression of the insert 16, simultaneously with and facilitate the formation of the bulge 70, together with the groove 72. In some embodiments, the insert 16 is configured to function as a bearing during the installation process, filling a gap between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12 to form a conductive path between the core bolt 12 and the sleeve 14.

[0036] 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 unique microtextures on the inner surfaces formed by the holes 115, 117 of each of the workpieces 110, 112. In some embodiments, the coating is a metallic coating. In some embodiments, the coating is silver. In some embodiments, the coating is gold. In some embodiments, the coating is nickel. In some embodiments, the coating is lead. In some embodiments, the coating is cadmium. In some embodiments, the coating is copper. In some embodiments, the coating is lead. In some embodiments, the coating is an alloy. In some embodiments, the coating is bronze. In some embodiments, the coating is a polymeric coating.

[0037] In some embodiments, the outer surface 58 of the sleeve 14 is uncoated. In some embodiments, the outer surface 58 of the sleeve 14 is microtextured. In some embodiments, the microtexture on the outer surface 58 of the sleeve 14 complements the inherent microtexture on the inner surfaces forming the holes 115, 117 of each of the workpieces 110, 112. In some embodiments, the microtexture is between 25 microinches and 40 microinches.

[0038] In some embodiments, the inner surface 66 of the sleeve 14 has a layer with 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, a first coefficient of friction between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12 and a 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 installation 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, 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 interface between the inner surface 66 of the sleeve 14 and the outer surface 65 of the insert 16 is reduced by the presence of the oxide layer. In some embodiments, the oxide layer has a 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 has a double layer. In some embodiments, the double layer on the inner surface 66 of the sleeve 14 includes nitrogen and carbon in a first layer and carbon in a second layer. In some embodiments, the first layer on the inner surface 66 of the sleeve 14 is the innermost layer. In some embodiments, the first layer on the inner surface 66 of the sleeve 14 is the outermost layer. In some embodiments, the second layer on the inner surface 66 of the sleeve 14 is the innermost layer. In some embodiments, the second layer on 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 the double layer is increased 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.

[0039] In some embodiments, a thick, hard oxide layer is selectively grown on the inner surface 66 of the sleeve 14. In some embodiments, the selectively grown thicker oxide layer on the inner surface of the sleeve 14 provides sufficient protection against surface damage and results in lower friction. In some embodiments, the thick oxide layer forms slowly at high temperatures. In some embodiments, the oxide layer grows to a thickness of up to several microns to provide a hard layer. In some embodiments, the hard layer separates the metal counterparts of the core bolt 12 and insert 16 from the metal counterparts of the sleeve 14 during sliding action of the core bolt 12 and 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 fine-grained structure that provides a hard surface on the outer surface 58 of the sleeve 14 with a Mohs hardness of up to 9.0.

[0040] It should be understood that the embodiments described herein are merely exemplary in nature and that those skilled in the art may make numerous variations and modifications thereto without departing from the scope of the invention, and such variations and modifications are intended to be included within the scope of this disclosure.

Claims

1. A fastener comprising: A sleeve, a first end and a second end opposite the first end; a tubular portion having an outer surface and an inner surface; a groove formed in the outer surface between the first end and the second end; a sleeve having an internal thread formed within the inner surface of the second end and a head disposed at the first end; a core bolt having a first end, a second end opposite the first end, a cylindrical portion proximate the first end of the core bolt, a male thread portion proximate the second end of the core bolt, and an incomplete thread portion between the cylindrical portion and the male thread portion; Equipped with The core bolt is configured to be disposed within the sleeve, and the male thread portion is configured to threadably engage with the female thread of the sleeve; the installation action of the core bolt within the sleeve creates a compressive load on the sleeve; The fastener, wherein the groove is configured to facilitate the formation of a bulge in the sleeve in response to the compressive load.

2. The fastener of claim 1, wherein the groove has a depth of between 0.001 inches and 0.005 inches.

3. The fastener of claim 1, wherein the groove has a width between 0.06 inches and 0.15 inches.

4. The fastener of claim 1 , wherein the groove is circumferentially disposed about the sleeve.

5. 5. The fastener of claim 4, wherein said groove is circumferentially disposed around the entire diameter of said sleeve.

6. 5. The fastener of claim 4, wherein said groove is partially circumferential about a diameter of said sleeve.

7. 2. The fastener of claim 1, wherein the groove includes a first boundary and a second boundary, the first boundary being circumferentially around the sleeve and the second boundary being circumferentially around the sleeve.

8. 8. The fastener of claim 7, wherein a blind side grip line of a first workpiece of the plurality of workpieces is between the first boundary and the second boundary of the groove.

9. 9. The fastener of claim 8, wherein the blind side grip line of the first workpiece of the plurality of workpieces is proximate to the first boundary.

10. 8. The fastener of claim 7, wherein the blind side grip line of the first of the workpieces is substantially aligned with the first boundary.

11. 11. The fastener of claim 10, wherein the blind side grip line of the first of the workpieces is proximate the second boundary.

12. 8. The fastener of claim 7, wherein the blind side grip line of the first of the workpieces is substantially aligned with the second boundary.

13. the sleeve includes a first layer on the outer surface of the sleeve, the first layer having a first hardness; 10. The fastener of claim 1, wherein the sleeve includes 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.

14. 14. The fastener of claim 13, wherein the first layer is a coating.

15. 15. The fastener of claim 14, wherein the coating comprises a metal-based coating.

16. 16. The fastener of claim 15, wherein the coating is selected from the group consisting of silver, gold, nickel, cadmium, copper, and lead, or alloys thereof.

17. 16. The fastener of claim 15, wherein the coating is comprised of bronze.

18. 14. The fastener of claim 13, wherein the second layer comprises an oxide layer.

19. 14. The fastener of claim 13, wherein the sleeve includes a third layer over the second layer.

20. 20. The fastener of claim 19, wherein the second layer is composed of carbon and the third layer is composed of nitrogen and carbon.

21. 2. The fastener of claim 1, further comprising an insert disposed within the sleeve and configured to surround a portion of the core bolt proximate the second end thereof, the insert being sized and shaped to abut and be held between the internal threads of the sleeve and the incomplete threads of the core bolt when the fastener is in a pre-installation position, the insert being configured to be compressed between the internal threads of the sleeve and the incomplete threads of the core bolt by the installation action of the core bolt relative to the sleeve simultaneously with the application of a compressive load to the sleeve by the installation action of the core bolt, and the insert being configured to simultaneously deform and facilitate the formation of a bulge in the sleeve in response to the compression of the insert.

22. 22. The fastener of claim 21, wherein the insert, together with the groove, is configured to deform in response to compression of the insert simultaneously with and facilitate the formation of a bulge in the sleeve.

23. 23. The fastener of claim 22, wherein the core bolt has an outer surface, and the insert is configured to fill a gap between the outer surface of the core bolt proximate the second end thereof and the inner surface of the sleeve proximate the second end of the tubular portion of the sleeve, the insert being configured to provide a conductive path between the sleeve and the core bolt.

24. 24. The fastener of claim 23, wherein 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 installation of the fastener.

25. 2. The fastener of claim 1, wherein the core bolt includes a head at the first end thereof, and the head of the sleeve includes a pocket sized and shaped to receive the head of the core bolt.

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