Patent Description:
A conventional machine bolt incudes a conventional male, helically threaded region and can be used to assemble two unthreaded components with the use of a threaded nut. A conventional threaded engagement between a machine bolt and a nut may undesirably loosen, such as, for example, under transverse vibration conditions and pivoting applications where a repeated torsional load is experienced. Conventional threads may also be cross-threaded during assembly and/or may require controlled torqueing to achieve a desirable pre-load. Furthermore, conventional threads may have a significantly variable clamp load if torqued with conventional means due to friction related variability.

A conventional shoulder bolt includes a shank with an unthreaded section encompassing a larger diameter "stand-off" or spacer portion in addition to a threaded section. The stand-off faces the workpiece and is intended to provide free pivoting movement or control of an installed clamp on the assembled pieces. A shoulder bolt may include a conventional male helically threaded section and, therefore, may present some of the drawbacks discussed above.

A conventional lock bolt is a structural two-piece fastener that utilizes a pin and a fastening collar. A permanent joint is created between the pin and the fastening collar when the fastening collar is swaged onto the pin. The fastening collar can deform onto annular rings of the pin and can be back extruded during installation, resulting in a desirable clamp load or pre-load. However, a lock bolt may be difficult to disassemble so that the underlying structure into which the lock bolt is installed can be serviced or modified. A conventional shoulder lock bolt may experience issues similar to those of a conventional lock bolt.

Providing a fastener design that maintains a repeatable desired clamp load, resists cross-threading, is efficient to assemble, and can be efficiently disassembled presents challenges.

<CIT> discloses a rivet and method of riveting. <CIT> discloses a rivet fastener.

One aspect according to the present disclosure is directed a multi-piece fastener comprising a fastening collar and a pin. The fastening collar comprises a first collar end, a second collar end, an inner collar surface extending from the first collar end to the second collar end and defining a collar cavity, and an external collar surface configured to receive a torque. The pin comprises a first pin end, a second pin end, and a shank extending intermediate the first pin end and the second pin end. The shank comprises a tapered threaded portion. The pin is configured to be at least partially received in the collar cavity. The inner collar surface of the fastening collar is configured to be deformed onto the tapered threaded portion and secured to the shank. The fastening collar is configured to be removable from the shank of the pin after deformation by applying a torque to the external collar surface.

Another aspect according to the present disclosure is directed to a method for fastening using a multi-piece fastener. The multi-piece fastener comprises a fastening collar and a pin. The fastening collar comprises a first collar end, a second collar end, an inner collar surface extending from the first collar end to the second collar end and defining a collar cavity, and an external collar surface. The pin comprises a first pin end, a second pin end, and a shank extending intermediate the first pin end and the second pin end. The shank comprises a tapered threaded portion. The pin is configured to be at least partially received in the collar cavity. The method comprises inserting the first pin end of the pin of the multi-piece fastener into a bore in a structure. The method further comprises deforming the inner collar surface of the fastening collar onto the tapered threaded portion of the pin, thereby securing the fastening collar to the pin.

It will be understood that the inventions disclosed and described in this specification are not limited to the aspects summarized in this Summary. The reader will appreciate the foregoing details, as well as others, upon considering the following detailed description of various non-limiting and non-exhaustive aspects according to this specification.

The features and advantages of the examples presented herein, and the manner of attaining them, will become more apparent, and the examples will be better understood, by reference to the following description taken in conjunction with the accompanying drawings, wherein:.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate certain embodiments, in one form, and such exemplifications are not to be construed as limiting the scope of the appended claims in any manner.

Various examples are described and illustrated herein to provide an overall understanding of the structure, function, and use of the disclosed multi-piece fasteners, fastening collars, pins, and methods of fastening. The various examples described and illustrated herein are non-limiting and non-exhaustive. Thus, the invention is not limited by the description of the various non-limiting and non-exhaustive examples disclosed herein. Rather, the invention is defined solely by the claims. The features and characteristics illustrated and/or described in connection with various examples may be combined with the features and characteristics of other examples. Such modifications and variations are intended to be included within the scope of this specification. The various embodiments disclosed and described in this specification can comprise, consist of, or consist essentially of the features and characteristics as variously described herein.

Any references herein to "various embodiments", "some embodiments", "one embodiment", "an embodiment", "non-limiting embodiment", or like phrases mean that a particular feature, structure, or characteristic described in connection with the example is included in at least one embodiment. Thus, appearances of the phrases "in various embodiments", "in some embodiments", "in one embodiment", "in an embodiment", "in a non-limiting embodiment", or like phrases in the specification do not necessarily refer to the same embodiment. Furthermore, the particular described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features, structures, or characteristics of one or more other embodiments without limitation. Such modifications and variations are intended to be included within the scope of the present embodiments.

In this specification, unless otherwise indicated, all numerical parameters are to be understood as being prefaced and modified in all instances by the term "about," in which the numerical parameters possess the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameter. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described herein should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Also, any numerical range recited herein includes all sub-ranges subsumed within the recited range. For example, a range of "<NUM> to <NUM>" includes all sub-ranges between (and including) the recited minimum value of <NUM> and the recited maximum value of <NUM>, that is, having a minimum value equal to or greater than <NUM> and a maximum value equal to or less than <NUM>. Any maximum numerical limitation recited in this specification is intended to include all lower numerical limitations subsumed therein, and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited. All such ranges are inherently described in this specification.

The grammatical articles "a", "an", and "the", as used herein, are intended to include "at least one" or "one or more", unless otherwise indicated, even if "at least one" or "one or more" is expressly used in certain instances. Thus, the foregoing grammatical articles are used herein to refer to one or more than one (i.e., to "at least one") of the particular identified elements. Further, the use of a singular noun includes the plural, and the use of a plural noun includes the singular, unless the context of the usage requires otherwise.

As used herein, "intermediate" means that the referenced element is disposed between two elements but is not necessarily in contact with those elements. Accordingly, unless stated otherwise herein, an element that is "intermediate" a first element and a second element may or may not be adjacent to or in contact with the first and/or second elements, and other elements may be disposed between the intermediate element and the first and/or second elements.

Providing a fastener design that maintains a repeatable desired clamp load, resists cross-threading, is efficient to assemble, and can be efficiently disassembled presents challenges. The present disclosure provides a multi-piece fastener that can be configured to achieve a repeatable desirable clamp load, resists cross-threading, and be easily installed and disassembled. Various embodiments of a multi-piece fastener according to the present disclosure allow the multi-piece fastener to be installed in a structure in an efficient manner and to be disassembled and uninstalled so as to allow access to, and enable repair and/or modification of, the structure.

<FIG> and <FIG> illustrate a non-limiting embodiment of a multi-piece fastener <NUM> according to the present disclosure. The multi-piece fastener <NUM> can be configured to be installed in a bore in a structure (for example, as shown and described with respect to <FIG>). The multi-piece fastener <NUM> can include at least two components, for example a fastening collar <NUM> and a pin <NUM>, as illustrated in <FIG>. In other non-limiting embodiments (not shown), a multi-piece fastener according to the present disclosure can comprise three or more components. In various non-limiting embodiments, the multi-piece fastener <NUM> can consist of a two-piece assembly including, for example, the fastening collar <NUM> and the pin <NUM>. In certain non-limiting embodiments, the multi-piece fastener <NUM> can comprise a lockbolt. In certain non-limiting embodiments including a lockbolt, the lockbolt can be a structural lockbolt fastener, such as, for example, a structural rivet, a structural bolt, or a structural stud.

Again referring to <FIG>, the fastening collar <NUM> of the multi-piece fastener <NUM> can comprise a first collar end <NUM>, a second collar end <NUM>, an elongate portion <NUM> intermediate the first collar end <NUM> and the second collar end <NUM>, an external collar surface <NUM>, and an inner collar surface <NUM>. The elongate portion <NUM> can define a longitudinal axis, A<NUM>, of the fastening collar <NUM> and/or the multi-piece fastener <NUM>. The inner collar surface <NUM> extends from the first collar end <NUM> to the second collar end <NUM>. The inner collar surface can define a collar cavity <NUM> that extends through the elongate portion <NUM>, from the first collar end <NUM> to the second collar end <NUM>.

The external collar surface <NUM> is configured to receive a torque such that the fastening collar <NUM> can be rotated about the longitudinal axis, A<NUM>, by forcibly contacting the external collar surface <NUM> and rotating the fastening collar <NUM>. For example, the external collar surface <NUM> can comprise a first surface region 114a comprising at least one of a substantially flat side, a rib, a spline, an indent, a knurl, a lobe, a bore, a tab, or a similar structural feature. For example, the in various non-limiting embodiments, first surface region 114a can be selected from square nut portion, a hex nut portion, a knurled nut portion, and a splined nut portion.

In various non-limiting embodiments, the external collar surface <NUM> further comprises a second surface region 114b adjacent to the first surface region 114a, and the second surface region 114b can comprise a substantially cylindrical shape or an alternative shape suitable to be deformed by an anvil of a multi-piece fastener installation tool. In certain non-limiting embodiments, the external collar surface <NUM> consists of the first surface region 114a and the second surface region 114b. In various non-limiting embodiments, the external collar surface <NUM> comprises a third surface region (not shown).

Again referring to <FIG>, in various non-limiting embodiments the pin <NUM> of the multi-piece fastener <NUM> can comprise a first pin end <NUM>, a second pin end <NUM>, and a shank <NUM>. The shank <NUM> can comprise a shape suitable to be received within the collar cavity <NUM> of the fastening collar <NUM>. In various non-limiting embodiments, the shank <NUM> has a generally cylindrical shape. The shank <NUM> can be intermediate the first pin end <NUM> and the second pin end <NUM> and can be dimensioned so that it can be inserted into and extend at least partially through the collar cavity <NUM>. When the shank <NUM> is inserted in the cavity <NUM>, the first pin end <NUM> can be disposed adjacent to the second collar end <NUM>, and the second pin end <NUM> can be disposed adjacent to the first collar end <NUM>.

In various non-limiting embodiments, the second pin end <NUM> can further comprise a head portion <NUM> configured to inhibit the pin <NUM> from traversing through a bore in a structure (as described with respect to <FIG> herein) beyond a predetermined distance. The head portion <NUM> can be configured to receive a torque such that the pin <NUM> can be rotated about the longitudinal axis, A<NUM>, by forcibly contacting the head portion <NUM> and rotating the pin <NUM>. For example, the head portion <NUM> can comprise at least one of a substantially flat side, a rib, a spline, an indent, a knurl, a lobe, a bore, a recessed socket, a tab, and a similar structural feature. For example, the head portion <NUM> can comprise one of a square head portion, a hex head portion, a knurled head portion, a splined head portion, and a recessed socket head portion.

The shank <NUM> comprises a tapered threaded portion <NUM> and, in various non-limiting embodiments, optionally further comprises a pull region <NUM> and/or a first region <NUM>, as further discussed below. The tapered threaded portion <NUM> can be intermediate the pull region <NUM> and the second pin end <NUM>. In various non-limiting embodiments, the tapered threaded portion <NUM> can be intermediate the first shank region <NUM> and the pull region <NUM>. In certain non-limiting embodiments, the first shank region <NUM> can comprise a substantially cylindrical shape.

The tapered threaded portion <NUM> comprises threads <NUM>. The threads <NUM> can be right handed threads or left handed threads. The threads <NUM> can be, for example, square threads, trapezoidal threads, buttress threads, another thread type, or a combination of thread types.

The threads <NUM> are formed on the shank <NUM> in a helical path about the longitudinal axis, A<NUM>. The helical path can have a conical shape such that the radius of the helix transverse to the longitudinal axis, Al, varies along an axial length of the shank <NUM>. In this way, the fastening collar <NUM> can be retained on the pin <NUM> after deformation of the fastening collar <NUM> on the pin <NUM> due to contact of the inner collar surface <NUM> with the threads <NUM>. The contact between the inner collar surface <NUM> and the threads <NUM> can be reduced as the fastening collar <NUM> is removed from the pin <NUM> by rotation. The tapered threaded portion <NUM> can comprise a taper that extends along the longitudinal axis, A<NUM>, such that a dimension of the tapered threaded portion <NUM> gradually or incrementally decreases along the tapered threaded portion <NUM> in an axial direction towards the first pin end <NUM>. For example, referring to <FIG>, the tapered threaded portion <NUM> can define a taper angle, X, no greater than <NUM> degrees relative to the longitudinal axis, Al, such as, for example, no greater than <NUM> degrees, no greater than <NUM> degrees, no greater than <NUM> degrees, no greater than <NUM> degrees, or no greater than <NUM> degrees. In various non-limiting embodiments, the tapered threaded portion <NUM> can define a taper angle, X, of at least <NUM> degrees relative to the longitudinal axis, A<NUM>, such as, for example, at least <NUM> degree, at least <NUM> degree, at least <NUM> degree, at least <NUM> degrees, at least <NUM> degrees, at least <NUM> degrees, or at least <NUM> degrees. In certain non-limiting embodiments, the tapered threaded portion <NUM> can define a taper angle, X, in a range of <NUM> degree to <NUM> degrees relative to the longitudinal axis, A<NUM>, such as for example, in a range of <NUM> degree to <NUM> degrees relative to the longitudinal axis, A<NUM>, in a range of <NUM> degrees to <NUM> degrees relative to the longitudinal axis, A<NUM>, in a range of <NUM> degrees to <NUM> degrees relative to the longitudinal axis, A<NUM>, or in a range of <NUM> degrees to <NUM> degrees relative to the longitudinal axis, A<NUM>. In various non-limiting embodiments, a thread crest of the threads <NUM> of the tapered threaded portion <NUM> decreases along the tapered threaded portion <NUM> in an axial direction towards the first pin end <NUM>. In certain non-limiting embodiments, a diameter, φ2, of the shank <NUM> in the tapered threaded portion <NUM> proximal to the first pin end <NUM> is less than a diameter, φ<NUM>, of the shank <NUM> in the tapered threaded portion <NUM> proximal to the second pin end <NUM>. In various non-limiting embodiments, a diameter, φ<NUM>, of the shank <NUM> in the pull region <NUM> is less than the diameter, φ<NUM>, of the shank <NUM>. In certain non-limiting embodiments, the diameter, φ<NUM>, of the shank <NUM> is in a range of <NUM> to <NUM> (<NUM> inches to <NUM> inches). In various non-limiting embodiments, the diameter, φ<NUM>, of the shank <NUM> is a conventional outside diameter of a conventional lock bolt.

In certain non-limiting embodiments, the dimension of the tapered threaded portion <NUM> gradually or incrementally decreases along at least <NUM>% of the length, l, of the tapered threaded portion <NUM> in the axial direction towards the first pin end <NUM>, such as for example, at least <NUM>% of the length, l, at least <NUM>% of the length, l, at least <NUM>% of the length, l, or at least <NUM>% of the length, l.

Referring again to <FIG>, in various non-limiting embodiments of a multi-piece fastener according to the present disclosure, the first pin end <NUM> can comprise a pull region <NUM>, which is configured to be engaged by a multi-piece fastener installation tool (not shown) when installing the multi-piece fastener <NUM> in a bore in a structure. The pull region <NUM> can comprise an axial length, and in various non-limiting embodiments the pull region <NUM> can comprise a taper. In various non-limiting embodiments, the pull region <NUM> can comprise at least one of a generally smooth region, an annular shoulder, a groove, and a bore, and/or can comprise one or more other features configured to be engaged by a multi-piece fastener installation tool. For example, and without limitation, the pull region <NUM> can comprise grooves <NUM>, as illustrated in <FIG> and <FIG>, that can be engaged by a multi-piece fastener installation tool. In certain non-limiting embodiments, the multi-piece fastener installation tool can be a puller tool or a squeezer tool.

Referring again to <FIG>, the shank <NUM> of the pin <NUM> can define the longitudinal axis, A<NUM>, of the pin <NUM> and/or the multi-piece fastener <NUM>. The shank <NUM> can be configured to engage the fastening collar <NUM> in order to retain the shank <NUM> to the fastening collar <NUM>. Upon engagement between the shank <NUM> and the fastening collar <NUM>, the longitudinal axis of the pin <NUM> and the longitudinal axis of the fastening collar <NUM> can be substantially aligned along a longitudinal axis, Al, of the multi-piece fastener <NUM>.

The collar cavity <NUM> of the fastening collar <NUM> can be configured to at least partially receive the shank <NUM> of the pin <NUM> therein. For example, the collar cavity <NUM> can comprise a shape suitable to receive the shank <NUM> of the pin <NUM>. The fastening collar <NUM>, including the inner collar surface <NUM>, can be configured to be at least partially deformed onto the shank <NUM>, including the tapered threaded portion <NUM>. For example, during and/or after introduction of the shank <NUM> into the collar cavity <NUM>, the elongate portion <NUM>, including at least a portion of the inner collar surface <NUM>, can be at least partially deformed (e.g., swaged) onto the tapered threaded portion <NUM> responsive to forcible contact between the fastening collar <NUM> and a multi-piece fastener installation tool. Deformation of the elongate portion <NUM> can secure the fastening collar <NUM> to the shank <NUM> of the pin <NUM>, securing the multi-piece fastener within a bore of a structure. The fastening collar <NUM> can be removed from the shank <NUM> after deformation by applying a torque to the external collar surface <NUM>, thereby rotating the fastening collar <NUM> about the longitudinal axis, A<NUM>, such that the fastening collar <NUM> backs off of threads <NUM>.

In various non-limiting embodiments, the pin <NUM> may comprise a breakneck groove (not shown) configured to fracture to separate all or a portion of the pull region <NUM> from the pin <NUM> upon installation of the multi-piece fastener <NUM> in a structure. In certain other non-limiting embodiments, the pin <NUM> does not comprise a breakneck groove but is configured to include one or more other features so that the pull region <NUM> of the pin <NUM> fractures during installation of the multi-piece fastener <NUM>. In various non-limiting embodiments of the multi-piece fastener <NUM>, the pin <NUM> does not comprise a breakneck groove or other feature configured to fracture upon installation of the multi-piece fastener <NUM>, and the pull region <NUM> remains intact after installation. Thus, according to various non-limiting embodiments, multi-piece fasteners according to the present disclosure may be installed in a structure without fracturing of a breakneck groove or other feature, or the fasteners may include a breakneck groove or other feature that fractures upon installation of the fastener into the structure.

The multi-piece fastener <NUM> can comprise at least one of a metal, a metal alloy, a composite material, or another suitable material. For example, in various non-limiting embodiments, the multi-piece fastener <NUM> can comprise at least one of aluminum, an aluminum alloy, titanium, a titanium alloy, nickel, a nickel alloy, iron, an iron alloy, and a carbon fiber composite material.

As illustrated in the non-limiting embodiments shown in <FIG>, the multi-piece fastener <NUM> can be installed into a bore <NUM> of a structure <NUM>. As illustrated, the bore <NUM> can extend through the structure <NUM> from a first side <NUM> to a second side <NUM>. The structure <NUM> can comprise, for example, at least one of a metal, a metal alloy, a composite material, or another suitable material. For example, in certain non-limiting embodiments, the structure <NUM> can comprise one or more of aluminum, an aluminum alloy, titanium, a titanium alloy, nickel, a nickel alloy, iron, an iron alloy, and a carbon fiber composite material. In various non-limiting embodiments, the structure <NUM> in which the multi-piece fastener <NUM> is installed comprises aluminum and/or an aluminum alloy, such as, for example, <NUM> aluminum alloy. In various embodiments the structure into which a fastener according to the present disclosure can be installed can be configured as at least one of an aerospace component or structure, an automotive component or structure, a transportation component or structure, a building and construction component or structure, or another component or structure.

The structure <NUM> can comprise a single layer of material or two or more layers of material. For example, as illustrated in <FIG>, the structure <NUM> can comprise a first layer 344a and a second layer 344b, which may be the same material or different materials. The first layer 344a can be positioned intermediate the second layer 344b and the fastening collar <NUM> when the multi-piece fastener <NUM> is installed. In various non-limiting embodiments, the first layer 344a is adjacent to or contacts the fastening collar <NUM>.

Additionally, in various non-limiting embodiments, the first pin end <NUM> can be sized and configured to facilitate alignment of the pin <NUM> with the bore <NUM>, thereby allowing the first pin end <NUM> to readily move into and through the bore <NUM>. In various non-limiting embodiments, the head portion <NUM> can be sized and configured to inhibit the pin <NUM> from traversing into the bore <NUM> beyond a predetermined distance.

As illustrated in <FIG>, the first pin end <NUM> of the pin <NUM> was positioned in alignment with the second side <NUM> of the bore <NUM> and inserted through the bore <NUM>. The fastening collar <NUM> was positioned over the first pin end <NUM>, and the first pin end <NUM> has been inserted into the collar cavity <NUM> of the fastening collar <NUM>. In the arrangement shown in <FIG> the fastening collar <NUM> has not yet been deformed about the pin <NUM>.

With reference to <FIG> and <FIG>, and as will be understood by those having ordinary skill in the multi-piece fastener art, the jaws of the collet of a multi-piece fastener installation tool (e.g., a fastening collar installation tool) can close around and forcibly engage the pull region <NUM> of pin <NUM>. Upon engagement, the collet can apply an axial force to the pull region <NUM> of the pin <NUM>. The collet can retract into a housing of the multi-piece fastener installation tool, and the pin <NUM> also moves as the collet retracts due to the engagement between the pull region <NUM> and the collet. As the pin <NUM> moves in this way, an anvil of the installation tool can forcibly contact the fastening collar <NUM> with an axial force and urge the fastening collar <NUM> along the pin <NUM> in a direction away from the first pin end <NUM>. The movement of the fastening collar <NUM> can decrease a gap, if present, between the first layer 344a and the second layer 344b of the structure <NUM> and forcibly contact the fastening collar <NUM> with the structure <NUM>.

When the anvil of the multi-piece fastener installation tool imparts a sufficient force to the fastening collar <NUM>, the elongate portion <NUM> can be at least partially deformed onto the pin <NUM>. For example, the inner collar surface <NUM> can be deformed onto the tapered threaded portion <NUM> of the shank <NUM> of the pin <NUM> intermediate the first layer 344a and the first pin end <NUM>. The deformation of the inner collar surface <NUM> onto the tapered threaded portion <NUM> can form threads <NUM> in the inner collar surface <NUM> of the fastening collar <NUM>. Since the threads <NUM> are formed on the inner collar surface <NUM> during the installation process by contact with the threads <NUM> of the tapered threaded portion <NUM>, the threads <NUM> and the threads <NUM> can be substantially aligned such that they are not cross-threaded. In various non-limiting embodiments, since the fastening collar <NUM> is deformed onto the pin <NUM>, the multi-piece fastener <NUM> is vibration resistant, similar to a conventional lock bolt.

The deformation of the elongate portion <NUM> can secure the fastening collar <NUM> to the pin <NUM> and thereby secure the multi-piece fastener <NUM> to at least a portion of the structure <NUM>. In that way, for example, the first layer 344a and second layer 344b of the structure <NUM> are secured together. After installation of the multi-piece fastener <NUM> into the structure <NUM>, the fastening collar <NUM> and the head portion <NUM> of the pin <NUM> are applying a clamping force to the structure <NUM>. In the arrangement shown in <FIG>, the fastening collar <NUM> was deformed onto tapered threaded portion <NUM> and threads <NUM> formed as a result of the deformation, thereby the fastening collar <NUM> is secured to the pin <NUM>. The gap between the first layer 344a and the second layer 344b of the structure <NUM> in <FIG> has been decreased as shown in <FIG>.

As illustrated in <FIG>, the pin <NUM> may not fracture after installation into the structure <NUM>. Alternatively, the pin <NUM> may fracture (not shown) after installation into the structure <NUM> as a result of force applied to the pin <NUM> by the multi-piece fastener installation tool. For example, the pin <NUM> may fracture along a breakneck groove, if present, after installation into the structure <NUM>.

The configuration of certain embodiments of a multi-piece fastener according to the present disclosure allows the fastener to be disassembled and removed from the structure to provide access to the structure. For example, with reference to the multi-piece fastener <NUM> shown in <FIG>, subsequent to installation of multi-piece fastener <NUM> in structure <NUM>, a torque can be applied to the external collar surface <NUM> of the fastening collar <NUM> to rotate the fastening collar <NUM> about the longitudinal axis, A<NUM>. By rotating the fastening collar <NUM> in a suitable rotational direction, the fastening collar <NUM> is urged to move along the tapered threaded portion <NUM> of the pin <NUM> in an axial direction away from the second pin end <NUM>. This movement of the fastening collar <NUM> along the pin <NUM> reduces the interference of the threads <NUM> on the inner collar surface <NUM> with the threads <NUM> of the tapered threaded portion <NUM> of the pin <NUM> because of the relative disengagement of the matched tapers between threads <NUM> and <NUM>. When interference between the threads <NUM> of the fastening collar <NUM> and the threads <NUM> of the pin <NUM> is reduced to a suitable degree, the fastening collar <NUM> can be further rotated about the pin <NUM> in a fashion similar to a conventional nut, and removed from the pin <NUM>, as shown in <FIG>. The clamping force applied to the structure <NUM> by the multi-piece fastener <NUM> can be relieved by the removal of the fastening collar <NUM>, and the pin <NUM> can thereafter be removed from the bore <NUM> in the structure <NUM>.

Embodiments of multi-piece fasteners according to the present disclosure can be used in a method for fastening a structure. <FIG> illustrates steps of a non-limiting embodiment of such a method. The method illustrated in <FIG> can comprise inserting the first pin end <NUM> of a multi-piece fastener <NUM> according to the present disclosure into a bore <NUM> in a structure <NUM> (at step <NUM>). After inserting the first pin end <NUM> into the structure <NUM>, the first pin end <NUM> can be inserted into the collar cavity <NUM> of the fastening collar <NUM> (at step <NUM>). Subsequent to inserting the first pin end <NUM> into the collar cavity <NUM>, in certain non-limiting embodiments, the fastening collar <NUM> can be forcibly contacted with an anvil of a multi-piece fastener installation apparatus, urging the fastening collar <NUM> to move along the pin <NUM> in a direction away from the first pin end <NUM> (at step <NUM>). In various non-limiting embodiments, the pull region <NUM> of the pin <NUM> can be forcibly contacted with jaws of the collet of the multi-piece fastener installation apparatus (at step <NUM>). In various non-limiting embodiments, steps <NUM> and <NUM> can occur simultaneously. The inner collar surface <NUM> of the fastening collar <NUM> can be deformed onto the tapered threaded portion <NUM> of the shank <NUM> of the pin <NUM>, thereby securing the pin <NUM> to the fastening collar <NUM> and retaining at least a portion of the multi-piece fastener <NUM> in the structure <NUM> (at step <NUM>). Subsequent to deforming the inner collar surface <NUM>, the fastening collar <NUM> can be removed from the pin <NUM> by applying a torque to the external collar surface <NUM> (at step <NUM>).

Claim 1:
A multi-piece fastener (<NUM>) comprising:
a fastening collar (<NUM>) comprising
a first collar end (<NUM>),
a second collar end (<NUM>),
an inner collar surface (<NUM>) extending from the first collar end (<NUM>) to the second collar end (<NUM>) and defining a collar cavity (<NUM>), and
an external collar surface (<NUM>) configured to receive a torque; and
a pin (<NUM>) configured to be at least partially received by the collar cavity (<NUM>), the pin (<NUM>) comprising
a first pin end (<NUM>),
a second pin end (<NUM>), and
a shank (<NUM>) extending intermediate the first pin end (<NUM>) and the second pin end (<NUM>), wherein the shank (<NUM>) comprises a tapered threaded portion (<NUM>), and wherein the inner collar surface (<NUM>) is configured to be deformed onto the tapered threaded portion (<NUM>) and secured to the shank (<NUM>), and the fastening collar (<NUM>) is configured to be removed from the shank (<NUM>) after deformation by applying a torque to the external collar surface (<NUM>).