Blind fastener

Abstract

A fastener includes a sleeve including: a first end and a second end; a tubular portion having an outer surface and an inner surface; a recess formed in the outer surface between the first end and the second end; and an internal thread located within the internal surface at the second end. The fastener includes a core bolt including a cylindrical portion, an external threaded portion, and a screw tail between the cylindrical portion and the threaded portion. The core bolt is configured to be disposed within the sleeve. The external threaded portion is configured to threadedly engage the internal thread of the sleeve. Mounting movement of the core bolt within the sleeve generates a compressive load on the sleeve. The groove is configured to facilitate formation of a ball portion in the sleeve in response to the compressive load.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of co-owned, co-pending U.S. Provisional Patent Application Serial No. 63 / 439,405, entitled "BLIND FASTENER," filed on January 17, 2023, the content of which is incorporated herein by reference in its entirety. Field of the Invention

[0003] The present invention relates to fasteners and, more particularly, to blind fasteners for securing workpieces together. Background of the Invention

[0004] Blind fasteners are commonly used to secure multiple workpieces together when there is limited physical or visible access on the blind side or non-accessible side of one of the workpieces. There is a trend to use carbon fiber reinforced composites in aircraft structures because these materials combine good strength-to-weight ratios, stiffness, and resistance to fatigue-induced damage, but they generally have low stiffness and strength throughout their thickness. There is also a trend towards natural laminar and hybrid laminar wing designs for higher fuel efficiency. Such wings typically have a thin cross-section and limited access inside the wing.

[0005] Carbon fiber reinforced composites typically consist of a combination of an adhesive polymer (commonly referred to as a matrix) and high-strength carbon fibers. The orientation of the carbon fibers, the ratio of matrix to fiber, and the composition of both the fiber and the matrix can be customized 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 introduced into the adhesive matrix.

[0006] A variety of manufacturing techniques have been developed, but many involve some form of layered manufacturing process that involves combining fibers into unidirectional or woven fabric layers and then stacking these layers on top of each other in a quasi-isotropic layup (e.g., 0°, +60°, or -60° relative to each other). In some cases, the matrix is combined with individual layers. In other cases, the matrix is injected into the stack after the individual layers are stacked. The two-dimensional stacked layer structure is the inherent cause of low stiffness and strength throughout the thickness perpendicular to the fiber direction.

[0007] Accordingly, the development of composite aircraft has led to a greater need for mechanical fasteners that combine high clamping force perpendicular to the fiber direction and a large head on the blind side to distribute the clamping force and thus reduce the bearing stress between the head and the composite structure. Additionally, there is a need to minimize the bearing stress at the corner where the fastener hole intersects the back surface of the structure to prevent delamination of the composite material at that location. Summary of the Invention

[0008] In some embodiments, a fastener includes a sleeve that includes: a first end and a second end opposite the first end; a tubular portion having an outer surface and an inner surface; wherein a groove is formed in the outer surface between the first end and the second end; wherein internal threads are formed in the inner surface at the second end, and a head is located at the first end; and a core bolt that includes a first end and a second end opposite the first end of the core bolt, a cylindrical portion near the first end of the core bolt, an external threaded portion near the second end of the core bolt, and a thread tail between the cylindrical portion and the threaded portion, wherein the core bolt is configured to be disposed within the sleeve, and wherein the external threaded portion is configured to threadedly engage the internal threads of the sleeve, wherein the installation movement of the core bolt within the sleeve creates a compressive load on the sleeve, and wherein the groove is configured to facilitate the formation of a bulb in the sleeve in response to the compressive load.

[0009] In some embodiments, the groove has a depth of from 0.001 inches to 0.005 inches. In some embodiments, the groove has a width of from 0.06 inches to 0.15 inches. In some embodiments, the groove extends circumferentially around the sleeve. In some embodiments, the groove extends circumferentially around the entire diameter of the sleeve. In some embodiments, the groove extends circumferentially partially around the diameter of the sleeve. In some embodiments, the groove includes a first boundary and a second boundary, wherein the first boundary extends circumferentially around the sleeve, and wherein the second boundary extends circumferentially around the sleeve.

[0010] In some embodiments, the blind side clamping line of the first workpiece among a plurality of workpieces is located between the first boundary and the second boundary of the groove. In some embodiments, the blind side clamping line of the first workpiece among a plurality of workpieces is close to the first boundary. In some embodiments, the blind side clamping line of the first workpiece among the workpieces is substantially aligned with the first boundary. In some embodiments, the blind side clamping line of the first workpiece among the workpieces is close to the second boundary. In some embodiments, the blind side clamping line of the first workpiece among the workpieces is substantially aligned with the second boundary.

[0011] In some embodiments, the sleeve includes a first layer on an outer surface of the sleeve, where the first layer has a first hardness, and a second layer on an inner surface of the sleeve, where the second layer has a second hardness, and where the second hardness is greater than the first hardness. In some embodiments, the first layer is a coating. In some embodiments, the coating consists 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 consists of bronze. In some embodiments, the second layer consists of an oxide layer. In some embodiments, the sleeve includes a third layer above the second layer. In some embodiments, the second layer consists of carbon and the third layer consists of nitrogen and carbon.

[0012] In some embodiments, the fastener further includes an insert configured to be disposed within the sleeve and around a portion of the core bolt near its second end, where when the fastener is in a pre-installed position, the insert is sized and shaped to abut the internal threads of the sleeve and the thread tail of the core bolt and remain between the internal threads of the sleeve and the thread tail of the core bolt, where the insert is configured to be compressed between the internal threads of the sleeve and the thread tail of the core bolt by the installation movement of the core bolt relative to the sleeve, while generating a compressive load on the sleeve by the installation movement of the core bolt, and where the insert is configured to deform simultaneously with the sleeve in response to compression of the insert and facilitate the formation of a ball portion within the sleeve. In some embodiments, the insert is configured to deform simultaneously with the sleeve in response to compression of the insert and combine with a groove to facilitate the formation of a ball portion within the sleeve.

[0013] In some embodiments, the core bolt includes an outer surface, where the insert is configured to fill a void between the outer surface of the core bolt near its second end and the inner surface of the sleeve near the second end of the tubular portion of the sleeve, and where the insert is configured to provide an electrical conduction 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 its first end, and where the head of the sleeve includes a recess sized and shaped to receive the head of the core bolt. Description of the Drawings

[0014] Figure 1 and Figure 2 are side views of some embodiments of the fastener;

[0015] Figure 3 are partial side cross-sectional views of some embodiments of the fastener;

[0016] Figure 4 is Figure 2 a side cross-sectional view of the fastener taken along section line 4-4 and viewed in the direction of the arrow;

[0017] Figure 5 is a partial cross-sectional perspective view of some embodiments of the fastener;

[0018] Figure 6 is a cross-sectional perspective view of some embodiments of the fastener;

[0019] Figure 7 is a top perspective view of some embodiments of the fastener installed in multiple workpieces;

[0020] Figure 8 illustrates some embodiments of the fastener installed in multiple workpieces in the minimum clamping state (left figure) and the maximum clamping state (right figure);

[0021] Figure 9 illustrates some embodiments of the fastener installed in multiple workpieces in the minimum clamping state and the maximum clamping state, in which corresponding ball portions of the fastener are formed;

[0022] Figure 10 illustrates some embodiments of a comparison of ball portion formation between some embodiments of the fastener with a groove in the minimum clamping state (right figure) and some embodiments of the fastener without a groove (left figure);

[0023] Figure 11 illustrates some embodiments of a comparison of ball portion formation between some embodiments of the fastener with a groove in the maximum clamping state (right figure) and some embodiments of the fastener without a groove (left figure);

[0024] Figure 12 illustrates a graph of ball portion size versus drive angle for a comparison of ball portion formation between some embodiments of the fastener with a groove and some embodiments of the fastener without a groove in the minimum clamping state;

[0025] Figure 13 illustrates a graph of ball portion size versus drive angle for a comparison of ball portion formation between some embodiments of the fastener with a groove and some embodiments of the fastener without a groove in the maximum clamping state;

[0026] Figure 14 illustrates a graph of contact node force versus drive angle for a comparison between some embodiments of the fastener with a groove and some embodiments of the fastener without a groove in the minimum clamping state;

[0027] Figure 15A contact node force vs. drive angle graph illustrating a comparison between some embodiments of a fastener having a groove in a maximum clamping state and some embodiments of a fastener without a groove;

[0028] Figure 16 is a partial cross-sectional perspective view of some embodiments of a fastener;

[0029] Figure 17 is a cross-sectional perspective view of some embodiments of a fastener;

[0030] Figure 18 is a perspective view of some embodiments of an insert employed by a fastener; and

[0031] Figure 19 and Figure 20 are Figures 16 to 17 a side view and a cross-sectional side view of some embodiments of the fastener shown, the fastener being fully installed in a plurality of workpieces. DETAILED DESCRIPTION

[0032] Referring Figures 1 to 6 , in some embodiments, the fastener 10 includes a core bolt 12 and a sleeve 14. In some embodiments, the sleeve 14 is sized and shaped to receive the core bolt 12, which will be described in further detail below.

[0033] 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 an outer diameter. In some embodiments, the outer diameter is less than the first diameter of the shank portion 22. In some embodiments, the core bolt 12 includes a thread tail 30. In some embodiments, the thread tail 30 is positioned 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 tail 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 flat head. In some embodiments, the core bolt 12 includes a second head 36. In some embodiments, the second head 36 is positioned 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 installation tool. In some embodiments, the second head 36 is detachably attached to the first head 34. In some embodiments, the second head 36 is detachably attached to the first head 34 by a necking portion 37. In some embodiments, after the fastener 10 is installed, the second head 36 is detached from the fastener 10 at the necking portion 37.

[0034] Still referring to Figures 1 to 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 adjacent to the first end 40 and having a first inner diameter, and a second portion 46 adjacent to the second end 42. In some embodiments, the sleeve 14 includes an inner surface 66. In some embodiments, the second portion 46 includes internal threads 48. In some embodiments, the internal threads 48 are positioned on the inner surface 66 of the second portion 46 of the sleeve 14. Referring to Figure 3, in some embodiments, the sleeve 14 includes a third portion 50 adjacent to the first portion 44. In some embodiments, the third portion 50 has a second inner diameter that is less 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 positioned between the first portion 44 and the third portion 50. In some embodiments, the sleeve 14 does not include an annular step 52.

[0035] In some embodiments, the sleeve 14 includes a head 54. In some embodiments, the head 54 is positioned 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 recess 56. In some embodiments, the recess 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 has an outer diameter. In some embodiments, the outer diameter of the outer surface 58 is sized and shaped such that the sleeve 14 can be installed within the alignment holes 115, 117 of a plurality of workpieces 110, 112 (see Figure 7 ).

[0036] In some embodiments, the sleeve 14 includes a groove 72 in its outer surface 58 (see Figure 2 ). In some embodiments, the groove 72 extends circumferentially within the outer surface 58. In some embodiments, the groove 72 extends circumferentially within the outer surface 58 around the entire outer diameter of the sleeve 14. In some embodiments, the groove 72 extends circumferentially only partially within the outer surface 58 around the diameter of the sleeve 14. In some embodiments, the groove 72 has a depth of from 0.001 inches to 0.005 inches. In some embodiments, the groove 72 has a depth of 0.001 inches. In some embodiments, the groove 72 has a depth of 0.002 inches. In some embodiments, the groove 72 has a depth of 0.003 inches. In some embodiments, the groove 72 has a depth of 0.004 inches. In some embodiments, the groove 72 has a depth of 0.005 inches. In some embodiments, the groove 72 has a first boundary 74 and a second boundary 76. In some embodiments, the first boundary 74 is spaced apart from the second boundary 76. In some embodiments, the groove 72 has a width W. In some embodiments, the width W extends from the first boundary 74 to the second boundary 76. In some embodiments, the width W is from 0.06 inches to 0.1 inches. In some embodiments, the width W is from 0.06 inches to 0.15 inches.

[0037] In some embodiments, the sleeve 14 has a wall thickness T of from 0.01 to 0.05 inches. In some embodiments, the wall thickness of the sleeve 14 at the location of the groove 72 is thinner than the wall thickness T of other portions of the sleeve 14 that do not include the groove 72.

[0038] In some embodiments, the first diameter of the cylindrical portion 24 of the core bolt 12 is sized and shaped such that the core bolt 12 can 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 the internal threads 48 of the sleeve 14 and are configured to engage the internal threads of the sleeve in a threaded manner. In some embodiments, the core bolt 12 is configured to be engaged by a fastener installation tool 200 (see Figure 7 ).

[0039] In some embodiments, the sleeve 14 is constructed of A286 (AISI 660) steel. In some embodiments, A286 steel is an austenitic precipitation hardening stainless steel. In some embodiments, the sleeve 14 is constructed of a 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 is modified to include 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 scale C.

[0040] 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 from 8.0 to 8.5 on the Mohs scale. In some embodiments, the first layer on the outer surface 58 of the sleeve 14 has a first hardness. In some embodiments, the second layer on the inner surface 66 of the sleeve 14 has 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 includes a selectively soft deformable outer surface and a selectively hard inner surface.

[0041] Reference Figure 7 and Figure 8, in some embodiments, the fastener 10 is configured to be installed in the alignment holes 115, 117 of 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 includes an accessible side 113. In some embodiments, the workpiece 112 includes a blind side 114. In some embodiments, the accessible side 113 is opposite the blind side 114. In some embodiments, the installer of the fastener 10 does not have physical or visible access to its blind side 114. In some embodiments, each of the alignment holes 115, 117 in the workpieces 110, 112 has 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 composed of substantially a composite material.

[0042] In some embodiments, a groove 72 is located within the outer surface 58 of the sleeve 14 such that the rear clamping line or plane A-A of the blind side 114 of the workpiece 112 is between the first boundary 74 and the second boundary 76 of the groove 72 (see Figure 8 ). In some embodiments, the rear clamping line A-A of the blind side 114 of the workpiece 112 is close to the first boundary 74. In some embodiments, the rear clamping line A-A of the blind side 114 of the workpiece 112 is close to the second boundary 76. In some embodiments, the rear clamping line A-A of the blind side 114 of the workpiece 112 is aligned with the first boundary 74. In some embodiments, the rear clamping line A-A of the blind side 114 of the workpiece 112 is aligned with the second boundary 76. In some embodiments, the rear clamping line A-A of the blind side 114 of the workpiece 112 is substantially aligned with the first boundary 74. In some embodiments, the rear clamping line A-A of the blind side 114 of the workpiece 112 is substantially aligned with the second boundary 76.

[0043] In some embodiments, the groove 72 is configured to act as a hinge to facilitate the formation of the ball portion 70 (see Figure 7 ), without significantly increasing the compressive stress at the corner 78 of the hole 117 and the blind side 114 of the workpiece 112. In some embodiments, the hinge function of the groove 72 reduces the likelihood of delamination of the workpiece 112 at the corner 78.

[0044] Referring to Figure 7 and Figures 9 to 11 , in some embodiments, when the core bolt 12 is installed within the sleeve 14, the groove 72 facilitates the formation of the ball portion 70 against the surface of the blind side 114 of the workpiece 112 within all the clamping ranges of the fastener 10. In some embodiments, when the sleeve 14 is compressed by tightening the core bolt 12 during the installation of the fastener 10, the axial stress on the sleeve 14 is concentrated on the ball portion 70.

[0045] In some embodiments, the recess 72 enables the sleeve 14 with a thicker wall thickness to buckle at a lower axial force during installation of the fastener 10, which in turn requires a lower driving torque. Figure 10 Illustrated are some embodiments comparing the formation of the ball portion 70 between the fastener 10 with the recess 72 (right figure) and the fastener without the recess 72 (left figure) under minimum clamping when the core bolt 12 rotates four (4) turns relative to the sleeve 14. In some embodiments, the fastener on the left side of the figure (without the recess) has a uniform sleeve wall thickness of 0.027 inches. In some embodiments, the fastener 10 on the right side of the figure (with the recess 72) has a stepped sleeve wall thickness of 0.027 inches and 0.025 inches, and the undercut length is 0.1 inches.

[0046] Figure 11 Illustrated are some embodiments comparing the formation of the ball portion 70 between the fastener 10 with the recess 72 (right figure) and the fastener without the recess 72 (left figure) under maximum clamping when the core bolt 12 rotates two and a half (2.5) turns relative to the sleeve 14. In some embodiments, the fastener on the left side of the figure (without the recess) has a uniform sleeve wall thickness of 0.027 inches. In some embodiments, the fastener 10 on the right side of the figure (with the recess 72) has a stepped sleeve wall thickness of 0.027 inches and 0.025 inches, and the undercut length is 0.1 inches.

[0047] Figure 12 Illustrated is a graph of the drive angle comparing the ball portion size for the formation of the ball portion 70 between some embodiments of the fastener 10 with the recess 72 and the fastener without the recess 72 under minimum clamping. Figure 13 Illustrated is a graph of the drive angle comparing the ball portion size for the formation of the ball portion 70 between some embodiments of the fastener 10 with the recess 72 and the fastener without the recess 72 under maximum clamping.

[0048] Figure 14 Illustrated is a graph of the contact node force vs. the drive angle comparing some embodiments of the fastener 10 with the recess 72 and the fastener without the recess 72 under minimum clamping. Figure 15 Illustrated is a graph of the contact node force vs. the drive angle comparing some embodiments of the fastener 10 with the recess 72 and the fastener without the recess 72 under minimum clamping. In some embodiments, the recess 72 facilitates the formation of a delayed clamping force (i.e., preload) during installation of the fastener 10. In some embodiments, the fastener 10 is configured to have an equal or greater preload at a selected clamping state at a specified target torque during installation of the fastener 10.

[0049] Figure 15Table 1 is illustrated, which is an example of fastener 10 in a minimum or maximum clamping state and the associated ball diameter 70, preload, and ultimate tensile strength (UTS), compared to their target values.

[0050] Reference Figure 16 and Figure 17 , in some embodiments, fastener 10 includes insert 16 located between inner surface 66 of sleeve 14 and outer surface 25 of core bolt 12. In some embodiments, insert 16 is disposed within sleeve 14. In some embodiments, insert 16 surrounds at least a portion of threaded portion 26 of core bolt 12. In some embodiments, insert 16 completely surrounds threaded portion 26 of core bolt 12. In some embodiments, when fastener 10 is in a pre-installed position, insert 16 is sized and shaped to abut inner threads 48 of sleeve 14 and tail 30 of core bolt 12 and remain between the inner threads of the sleeve and the tail of the core bolt. In some embodiments, when fastener 10 is in a pre-installed position, insert 16 is sized and shaped to abut annular step 52 of sleeve 14 and tail 30 of core bolt 12 and remain between the annular step of the sleeve and the tail of the core bolt.

[0051] Reference Figure 18 , in some embodiments, insert 16 includes first end 60, second end 62 opposite first end 60, and inner surface 63. In some embodiments, inner surface 63 of insert 16 forms orifice 64. In some embodiments, orifice 64 extends from first end 60 to second end 62 of insert 16. In some embodiments, insert 16 includes outer surface 65. In some embodiments, insert 16 has a tubular shape. In some embodiments, the shape of inner surface 63 is cylindrical. In some embodiments, insert 16 has an inner diameter. In some embodiments, the inner diameter of insert 16 is greater than the outer diameter of external threads 28 of core bolt 12 (see Figure 16 and Figure 17 ). In some embodiments, insert 16 has an outer diameter. In some embodiments, the outer diameter of insert 16 is less than the minimum inner diameter of sleeve 14. In some embodiments, insert 16 is made of copper. In some embodiments, insert 16 is made of alloy. In some embodiments, insert 16 is coated. In some embodiments, insert 16 is coated with a highly conductive coating. In some embodiments, the coating is made of a conductive metal material. In some embodiments, the coating is made of silver. In some embodiments, the coating is made of gold. In some embodiments, the coating is made of nickel. In some embodiments, the coating is made 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.

[0052] Reference Figure 19 and Figure 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 shank end 30 of the core bolt 12 by the installation movement of the core bolt 12 relative to the sleeve 14, and this compression occurs simultaneously with the installation movement 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 installation of the fastener 10, the insert 16 is compressed between the internal threads 48 of the sleeve 14 and the shank end 30 of the core bolt 12 by the installation movement of the core bolt 12 relative to the sleeve 14, and said compression occurs simultaneously with the installation movement of the core bolt 12, thereby generating a compressive load on the sleeve 14.

[0053] In some embodiments, the insert 16 is configured to be compressed between the internal threads 48 of the sleeve 14 and the shank end 30 of the core bolt 12 by the installation movement of the core bolt 12 relative to the sleeve 14, while generating a compressive load on the sleeve 14 by the installation movement of the core bolt 12. In some embodiments, the insert 16 is configured to deform simultaneously with the tubular portion 38 of the sleeve 14 in response to compression of the insert 16 and facilitate the formation of the ball portion 70 within the tubular portion of the sleeve. In some embodiments, the insert 16 is configured to deform simultaneously with the tubular portion 38 of the sleeve 14 in response to compression of the insert 16 and promote the formation of the ball portion 70 within the tubular portion of the sleeve in combination with the groove 72. In some embodiments, the insert 16 is configured to act as a bearing during the installation process and fill the void between the inner surface 66 of the sleeve 14 and the outer surface 25 of the core bolt 12 to form an electrical conduction path between the core bolt 12 and the sleeve 14.

[0054] 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 current-compatible with the sleeve 14. In some embodiments, the coating is current-compatible with the workpieces 110, 112. In some embodiments, the coating conforms to the inherent microtexture of each of the inner surfaces formed by the respective holes 115, 117 in 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 zinc. 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. In some embodiments, the coating is a polymer-based coating.

[0055] 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 is complementary to the inherent microtexture of the inner surfaces forming the holes 115, 117 in each of the workpieces 110, 112. In some embodiments, the microtexture is from 25 microinches to 40 microinches.

[0056] 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 and 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, 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 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 includes a bilayer. In some embodiments, the bilayer 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 bilayer is increased two to three times compared to the untreated inner surface 66 of the sleeve 14. In some embodiments, the microhardness of the inner surface 66 of the sleeve 14 is 8.0 to 8.5 on the Mohs scale.

[0057] 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 elevated temperatures. In some embodiments, the oxide layer grows to a thickness of several microns to provide a hard layer. In some embodiments, the hard layer separates the metallic counterparts of the core bolt 12 and the insert 16 from the metallic counterpart of the sleeve 14 during the sliding movement of the core bolt 12 and the insert 16 relative to the sleeve 14, thereby avoiding surface damage and wear and high friction. In some embodiments, the hard layer has a corundum-like fine-grained structure, resulting in a hard surface on the outer surface 58 of the sleeve 14 having a hardness of up to 9.0 on the Mohs scale.

[0058] 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 present invention. All such variations and modifications, including those discussed above, are intended to be included within the scope of the present invention.

Claims

1. A fastener, comprising: A sleeve, the sleeve comprising: A first end and a second end opposite the first end, A tubular portion having an outer surface and an inner surface; Wherein a groove is formed in the outer surface between the first end and the second end; Wherein an internal thread is formed in the inner surface at the second end, and a head is located at the first end; and A core bolt, the core bolt comprising a first end and a second end opposite the first end of the core bolt, a cylindrical portion near the first end of the core bolt, an external thread portion near the second end of the core bolt, and a thread tail between the cylindrical portion and the thread portion, Wherein the core bolt is configured to be disposed within the sleeve, and wherein the external thread portion is configured to engage the internal thread of the sleeve in a threaded manner, Wherein the installation movement of the core bolt within the sleeve generates a compressive load on the sleeve, and Wherein the groove is configured to facilitate the formation of a spherical portion within the sleeve in response to the compressive load.

2. The fastener according to claim 1, wherein the groove has a depth of from 0.001 inches to 0.005 inches.

3. The fastener according to claim 1, wherein the groove has a width of from 0.06 inches to 0.15 inches.

4. The fastener according to claim 1, wherein the groove extends circumferentially around the sleeve.

5. The fastener according to claim 4, wherein the groove extends circumferentially around the entire diameter of the sleeve.

6. The fastener according to claim 4, wherein the groove extends circumferentially partially around the diameter of the sleeve.

7. The fastener according to claim 1, wherein the groove includes a first boundary and a second boundary, wherein the first boundary extends circumferentially around the sleeve, and wherein the second boundary extends circumferentially around the sleeve.

8. The fastener according to claim 7, wherein the blind side clamping line of the first workpiece among the plurality of workpieces is located between the first boundary and the second boundary of the groove.

9. The fastener according to claim 8, wherein the blind side clamping line of the first workpiece among the plurality of workpieces is close to the first boundary.

10. The fastener according to claim 7, wherein the blind side clamping line of the first workpiece among the workpieces is substantially aligned with the first boundary.

11. The fastener according to claim 10, wherein the blind side clamping line of the first workpiece among the workpieces is close to the second boundary.

12. The fastener according to claim 7, wherein the blind side clamping line of the first workpiece among the workpieces is substantially aligned with the second boundary.

13. The fastener according to claim 1, wherein the sleeve includes a first layer on the outer surface of the sleeve, wherein the first layer has a first hardness, and a second layer on the inner surface of the sleeve, wherein the second layer has a second hardness, and wherein the second hardness is greater than the first hardness.

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

15. The fastener according to claim 14, wherein the coating is composed of a metal-based coating.

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

17. The fastener according to claim 15, wherein the coating is composed of bronze.

18. The fastener according to claim 13, wherein the second layer is composed of an oxide layer.

19. The fastener according to claim 13, wherein the sleeve includes a third layer above the second layer.

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

21. The fastener according to claim 1, further comprising an insert configured to be disposed within the sleeve and around a portion of the core bolt near its second end, wherein when the fastener is in a pre-installed position, the insert is sized and shaped to abut the internal threads of the sleeve and the thread tail of the core bolt and to be held between the internal threads of the sleeve and the thread tail of the core bolt, wherein the insert is configured to be compressed between the internal threads of the sleeve and the thread tail of the core bolt by the installation movement of the core bolt relative to the sleeve, while generating a compressive load on the sleeve by the installation movement of the core bolt, and wherein the insert is configured to deform simultaneously with the sleeve in response to compression of the insert and to facilitate the formation of a ball portion within the sleeve.

22. The fastener according to claim 21, wherein the insert is configured to deform simultaneously with the sleeve in response to compression of the insert and to combine with the groove to facilitate the formation of a ball portion within the sleeve.

23. The fastener according to claim 22, wherein the core bolt includes an outer surface, wherein the insert is configured to fill a void between the outer surface of the core bolt near its second end and the inner surface of the sleeve near the second end of the tubular portion of the sleeve, and wherein the insert is configured to provide an electrical conduction path between the sleeve and the core bolt.

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

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