Patent Publication Number: US-2013239399-A1

Title: Expandable fastener assembly with deformed collar

Description:
BACKGROUND 
     1. Field of Technology 
     This disclosure generally relates to expandable fastener assemblies and methods of using the same. 
     2. Description of the Related Art 
     Fastener assemblies are often used to interconnect a plurality of workpieces, such as a stack of plates or other structural members. Conventional fastener assemblies have a bolt and a collar that cooperate to apply a clamp-up force to the workpieces. For example, two workpieces can be joined together by overlapping the workpieces to create a joint. A fastener assembly can be installed at the joint by drilling a hole through the overlapping portions of the workpieces and positioning a rod in the hole. The workpieces are clamped between a head of the rod and the collar. Unfortunately, these types of joints are susceptible to fatigue damage and have undesired electrical properties. 
     Contaminates (e.g., moisture, chemicals, debris, and other foreign substances) can become lodged between faying surfaces of joints resulting in increased wear and corrosion. Cyclic loading can lead to fatigue problems. The fastener assembly may allow the workpieces to move relative to one another, which may result in fretting, excessive stresses at the interface of the hole and fastener assembly, vibrations, and the like. In aerospace applications, conventional joints may thus have a relatively short in-service life. 
     Aircraft are often made of lightweight composite structures that are unable to withstand high electrical currents as well as their metallic counterparts. Composite structures may be damaged by high electrical currents caused by lightning strikes because composite structures do not readily conduct away the electrical currents and electromagnetic forces generated by lightning strikes. Electrical currents tend to not pass through the composites structures (e.g., carbon fiber structures) with poor electrical conductivity and instead pass through highly conductive materials, such as metals. Metal fastener assemblies can conduct electrical currents between layers of composite structures. Unfortunately, loosening of the components of the fastener assembly may result in movement between these components of the fastener assembly, movement of the workpiece, and the accumulation of contaminates at the faying surfaces. These problems may result in arcing or other electrical related problems that may cause fires or explosions. Conventional fastener assemblies may thus be unsuitable for many aerospace applications. Additionally, conventional sleeve/bolt systems have a tendency to cause damage in composite laminates when tolerances stack up to make interferences relatively high. Leading edges of conventional bolts are too abrupt for use with thin-walled sleeves. Shear loading along the holes of composite workpieces may be damaged (e.g., delamination), during installation. 
     BRIEF SUMMARY 
     Some embodiments disclosed herein include fastener assemblies adapted to apply desired clamp-up forces to workpieces. The fastener assemblies can be installed in openings in the workpieces in order to hold together the components of the workpieces. In some embodiments, the fastener assemblies can be installed in a joint of an aircraft. The installation can have desirable mechanical characteristics, electrical characteristics, and the like for enhancing performance, even after extended use under cyclic loading, static loading, or both. 
     In some embodiments, an installation includes a workpiece and a fastener assembly. The fastener assembly includes a swaged collar, an inner member, and an expanded outer member. The outer member is between the inner member and the workpiece. The swaged collar is coupled to the outer member or the inner member, or both. The inner member, in some embodiments, has a relatively narrow section, a relatively wide section, and a mandrel section between the narrow section and the wide section. A portion of the outer member is in an expanded state and is between the wide section and the workpiece. The workpiece is captured between the collar on one side of the workpiece and a head of the outer member on another side of the workpiece. In some embodiments, the workpiece comprises multiple components that are held together by the fastener assembly. 
     In some embodiments, a method of fastening together a multi-piece workpiece having an opening is provided. The opening extends between a first side and a second side of the workpiece. The method includes positioning a hollow expandable fastener through the opening. An inner member is positioned within the hollow expandable fastener. The inner member includes a mandrel section and is on the second side of the workpiece. The inner member is moved through the expandable fastener to radially expand at least a portion of the fastener. A collar is positioned on the first side of the workpiece. The collar, in some embodiments, is radially compressed onto coupling features of the expanded fastener to capture the workpiece between a head of the fastener and the collar. 
     In some embodiments, an installation comprises a workpiece, a swaged collar, an inner member, and a radially expanded outer member. The workpiece has an opening. The swaged collar has a first end, a second end, and a main body extending between the first end and the second end. The main body includes an inner surface defining the passageway. The inner member has a narrow section, a propping section, and a mandrel section between the narrow section and the propping section. The radially-expanded outer member is in the opening of the workpiece. The inner surface of the collar has been compressed against at least one locking feature of the expanded outer member to fix the collar and the outer member together. The outer member has been expanded from an unexpanded state to an expanded state by the mandrel section. The propping section keeps the outer member in the expanded state to maintain an interference fit and/or induced fatigue enhancing compressive stresses in the workpiece produced when the outer member is expanded from the unexpanded state to the expanded state. In some embodiments, the unexpanded outer member can fit in the opening with a clearance fit. 
     In some embodiments, a fastener assembly is installed in an opening of a workpiece and comprises a collar, an outer member, and an inner member. The outer member is configured to be positioned in the opening of the workpiece. The outer member includes a longitudinally-extending passageway, a coupling section, a head, and an expandable section between the coupling section and the head. The coupling section is adapted to protrude from the workpiece and to be coupled to the collar. The inner member includes a narrow section, a propping stem, and a mandrel section between the narrow section and the propping stem. The propping stem is dimensioned and configured to prop the expandable section of the outer member after the mandrel section radially expands the expandable section in the opening of the workpiece. In some embodiments, the outer member is radially expanded from an initial configuration for placement in the opening of the workpiece to an expanded configuration to cold work the workpiece and/or to produce an interference fit with the workpiece. The outer member in the initial configuration can provide a clearance fit with the opening of the workpiece. 
     In some embodiments, a method for fastening together a multi-component workpiece having an opening extending between a first side and a second side is provided. The method includes positioning a hollow outer member in the opening of the workpiece. A portion of an inner member on the second side of the workpiece is moved within the hollow outer member. The inner member includes a mandrel section. At least a portion of the outer member and the workpiece is expanded using the mandrel section of the inner member. The collar is positioned on the first side of the workpiece such that the collar surrounds the outer member. The collar is swaged. In some embodiments, swaging the collar includes forming longitudinally-extending grooves along an exterior of the collar. 
     In some other embodiments, a swaging assembly for an installation apparatus includes a housing and an actuating device. The housing has a first end, a second end, and a bore extending between the first end and the second end. The actuating device includes a passageway and a plurality of spaced apart bearing elements surrounding the passageway. The actuating device is movable through the bore towards the second end such that the bearing elements swage a collar of a fastener assembly protruding from a workpiece against which the swaging assembly is placed. 
     In some embodiments, a fastener assembly can include an inner member, an outer member, and a collar. The wall thickness of the outer member can be sufficiently large to ensure that the outer member induces compressive stresses in the workpiece and/or an interference fit with a workpiece when the outer member is radially expanded. In some embodiments, the wall thickness of the outer member can be generally equal to a wall thickness of the collar. 
     In some embodiments, a fastener assembly includes an inner member, an outer member, and a collar. The inner member can radially expand the outer member to form an interference fit with the workpiece. The workpiece can comprise a composite material. For example, the workpiece can comprise one or more composite panels and one or more metal panels. The workpiece can be a stack of different types of panels, and the outer member can form interference fits with each of these panels. Advantageously, the outer member can be inserted through the stack with a clearance fit to minimize, limit, or substantially prevent damage of any of the panels, including composite panels, if any. In some embodiments, the outer member can be radially expanded a sufficient amount to produce compressive stresses in the workpiece. For example, the workpiece can be comprised mostly or entirely of metal in which compressive stresses can be induced without cracking the workpiece. If the workpiece comprises composite materials, the compressive stresses can be kept below a level that causes damage to the workpiece. In some embodiments, compressive stresses that improve fatigue performance may not be produced in the workpiece. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. 
         FIG. 1  is a side elevational view of an installation including a multi-component workpiece and an expandable fastener assembly that has a deformed collar, according to one illustrated embodiment. 
         FIG. 2  is a partial cross-sectional view of an installation of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the installation of  FIG. 2 . 
         FIG. 4  is a detailed view of the fastener assembly of  FIG. 3 . 
         FIG. 5  is an isometric view of an expandable fastener assembly installed in a multi-component workpiece. The workpiece and a collar of the fastener assembly are shown cut-away. 
         FIG. 6  is an isometric view of the fastener assembly and the workpiece of  FIG. 5 . The workpiece, the collar, and an expandable outer member are shown cut-away. 
         FIG. 7  is a pictorial view of an inner member of an expandable fastener assembly, according to one embodiment. 
         FIG. 8  is a side elevational view of the inner member of  FIG. 7 . 
         FIG. 9  is a side elevational view of the inner member of  FIG. 7  after the inner member has been broken apart. 
         FIG. 10  is a detailed view of the inner member of  FIG. 8 . 
         FIG. 11  is a detailed view of a mandrel section of an inner member, in accordance with one embodiment. 
         FIG. 12  is a side elevational view of an installation apparatus for installing an expandable fastener assembly, in accordance with one embodiment. 
         FIG. 13  is an elevational view of the installation apparatus installing an expandable faster assembly in a workpiece. A puller unit of the installation apparatus is shown partially cut-away. 
         FIG. 14  is a cross-sectional view of a swaging assembly, in accordance with one embodiment. 
         FIG. 15  is a pictorial view of an expandable outer member ready for installation in an opening of a workpiece, in accordance with one illustrated embodiment. The workpiece is shown cut-away. 
         FIG. 16  is a pictorial view of an inner member spaced from an expandable outer member in a hole of a workpiece. The workpiece is shown cut away. 
         FIG. 17  is a pictorial view of a deformable collar ready for placement over an expandable outer member assembled with an inner member. The workpiece is shown cut away. 
         FIG. 18  is a pictorial view of a swaging assembly ready for installing an assembled fastener assembly. The workpiece is shown cut away. 
         FIG. 19  is a cut-away view of a swaging assembly ready to deform a collar of an expandable fastener assembly, according to one illustrated embodiment. 
         FIG. 20  is a cut-away view of the swaging assembly of  FIG. 19  after deforming the collar, according to one illustrated embodiment. 
         FIG. 21  is a cut-away view of the swaging assembly after breaking apart the inner member, according to one illustrated embodiment. 
         FIG. 22  shows the swaging assembly separated from the installed fastener assembly, according to one illustrated embodiment. 
         FIG. 23  is a pictorial view of a swaging assembly, according to one illustrated embodiment. 
         FIG. 24  is a bottom view of the swaging assembly of  FIG. 23 . 
         FIG. 25  is a cross-sectional view taken along a line  25 - 25  of  FIG. 24 . A jaw assembly is shown removed. 
         FIG. 26  is a cross-sectional view of the swaging assembly taken along a line  25 - 25  of  FIG. 24 , wherein the swaging assembly includes a jaw assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various aspects of the representative embodiments. One skilled in the art, however, will understand that the embodiments may be practiced without these details. The fastener assemblies, installation apparatuses, and processes disclosed herein can be used to couple together workpieces and, in some embodiments, may improve in-service performance of these workpieces, such as electrical performance, mechanical performance, fatigue performance, or the like. The fastener assemblies can be expandable fastener assemblies installed in different types of workpieces and at a wide range of locations. The term “expandable fastener assembly” refers to a fastener assembly both in a pre-expanded state and an expanded state, unless the context dictates otherwise. 
     Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” 
     The terms “proximal” and “distal” are used to describe the illustrated embodiments and are used consistently with a description of non-limiting exemplary applications. The terms “proximal” and “distal” are used in reference to the user&#39;s body when the user operates an installation apparatus to install fasteners assemblies, unless the context clearly indicates otherwise. It will be appreciated, however, that the illustrated embodiments can be located or oriented in a variety of desired positions. 
     As used in this specification and the claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the context clearly dictates otherwise. 
       FIGS. 1-3  show an expandable fastener assembly  100  installed in a multi-component workpiece  108 . The workpiece  108  includes a first structural member  110  and a second structural member  120  that overlaps the first structural member  110  to form a lap joint  124 . The fastener assembly  100  includes a deformable collar  130 , an expandable outer member  140  extending through the workpiece  108  and the collar  130 , and an inner member  145  extending through the outer member  140 . The workpeice  108  is captured between a flange  150  of the collar  130  and a head  160  of the outer member  140  to reduce, limit, or substantially prevent relative movement between the members  110 ,  120 . The illustrated collar  130  and head  160  are positioned on first and second sides  143 ,  144  of the workpiece  108 , respectively. A user on the first side  143  of the workpiece  108  can install the fastener assembly  100 . 
     As used herein, the term “expandable outer member” is a broad term and includes, but is not limited to, a fastener, bushing, sleeve (including a split sleeve), fitting, structural expandable member (e.g., expandable members that are incorporated into structural workpieces), or other one-piece or multi-piece structures suitable for installation in a workpiece. An expandable outer member can be expanded from a first configuration to a second configuration. In some embodiments, for example, the expandable outer member  140  is a hollow fastener that is radially expanded from an initial pre-expanded state to a post-expanded state in order to create a desired fit, such as an interference fit, with an inner surface  154  forming an opening  155 , illustrated as a through-hole in the workpiece  108 . The term “expandable outer member” refers to an outer member both in a pre-expanded state and post-expanded state, unless the context clearly dictates otherwise. The illustrated outer member  140  is in a post-expanded state. 
     Various types of expansion processes may be employed to install the fastener assembly  100 . In a cold expansion process, for example, the expandable outer member  140  is radially expanded without appreciably raising the temperature of the outer member  140  to produce residual stresses in the workpiece  108 . The residual stresses can significantly increase fatigue life by reducing the applied stresses at the opening  155  to reduce the stress intensity factor and to increase the crack growth life. In some embodiments, the magnitude of the peak residual compressive circumferential stress at the opening is less than or about equal to the compressive yield stress of the workpiece  108 . The compressive stress zone may span one radius to one diameter from the edge of the opening  155 . A balancing zone of tensile stresses can be located beyond the circumferential compressive stress zone. The compressive stresses in the workpiece can be sufficient to alter fatigue performance of the workpiece to increase the service life of the workpiece by, for example, at least about 10×, 30×, or 50×. The illustrated expanded fastener assembly of  FIGS. 1-3  may induce compressive stresses in the workpiece  108  for enhanced fatigue performance. 
     As used herein, the term “workpiece” is broadly construed to include, without limitation, a structure suitable for receiving the fastener assembly  100 . Workpieces can have at least one opening in which the fastener assembly  100  is installed and can be made, in whole or in part, of one or more metals (e.g., steel, aluminum, titanium, or the like), polymers, plastics, composites, resins, combinations thereof, or the like. Multi-component workpieces can include any number of panels, sheets, or other components capable of being coupled together using the fastener assembly  100 . The illustrated workpiece  108  includes two flat panels  110 ,  120  mated together; however, any number of panels (e.g., three or more panels) can be held together using the fastener assembly  100 . In other embodiments, the workpiece  108  can be a single panel. Such workpieces can be made, in whole or in part, of a composite material, such as a multi-laminate panel. The fastener assembly  100  can help inhibit, limit, or substantially prevent damage, such as delamination. Hybrid workpieces can be made of a wide range of different materials, including composite materials and metals. In some embodiments, the workpiece is a hybrid workpiece includes one or metal panels and one or more composite panels. 
     In some embodiments, the workpiece includes a plurality of panels. At least one of the panels can comprises a composite material (e.g., a fiber-reinforced composite material) and at least one of the panels comprises another material, such as a metal. A clearance fit can be produced with each of the panels to insert the outer member  140  into the workpiece. An interference fit is produced with each of the panels when the outer member  140  is expanded. In some embodiments, a hybrid workpiece includes one or metal panels and one or more composite panels. In some embodiments, the workpiece includes only metal panels or only composite panels. Any number of panels can be connected together using the fastener assembly  100 . 
     With continued reference to  FIGS. 1-3 , the collar  130  has been deformed to couple the collar  130  to the expanded outer member  140 . The outer member  140  can be tensioned to inhibit or prevent loosening of the collar  130 . The head  160  of the outer member  140  and the collar  130  can compress the workpiece  108  to limit, minimize, or substantially prevent fretting of the panels  110 ,  120 . 
     The collar  130  provides generally uniformly distributed stresses (e.g., contact stresses) in a region of an outer surface  123  of the panel  120  proximate the opening  155  to avoid unwanted stress concentrations. For example, if the workpiece  108  is made of a composite material that is susceptible to cracking or delaminating, the flange  150  and/or head  160  can have a radial thickness sufficiently large to keep compressive stresses in the workpiece  108  at or below an acceptable level to limit, reduce, or eliminate cracking or delamination. The fastener assembly  100  can also enhance the desired electrical conductivity of the workpiece  108  and, in some embodiments, maintains the integrity of coatings, including platings, or any other treatments on the workpiece  108 , even coating on faying surfaces. The outer member  140  can insulate the workpiece  108  from the inner member  145  such that an electrical current can pass through the inner member  145 . 
     Referring to  FIG. 4 , the collar  130  includes a main body  180  extending generally longitudinally from the flange  150  and a passageway  190  extending between opposing ends  200 ,  210  of the collar  130 . The illustrated collar  130  is a swagable collar. The term “swagable collar” refers to a collar both in a pre-swaged state and a post-swaged state, unless the context clearly dictates otherwise. A swaging process has been performed to axially and rotationally fix the swaged collar  130  shown in  FIG. 4  to the outer member  140 . 
     The expandable outer member  140  of  FIG. 4  includes a tubular main body  250  extending generally longitudinally from the head  160  and a longitudinally-extending passageway  260  extending between opposing ends  270 ,  280 . The tubular main body  250  includes a radially expandable portion  213  and a coupling section  235 . The expandable portion  213  extends from the head  160  through the panels  110 ,  120 . At least a substantial portion of the opening  155  can be radially expanded to produce a desired fit with the expandable portion  213 . The axial length of the expandable portion  213  can be selected based on the thickness T of the workpiece  108 . For example, the axial length of the expandable portion  213  can be slightly less than, equal to, or slightly greater than the thickness T of the workpiece. Substantially all of the longitudinal length of the expandable portion  213  is in an expanded state. For example, at least 90% of the length of the expandable portion  213  can be expanded. Thus, most of the opening  155  between the head  160  and collar  130  is also expanded. 
     The expandable portion  213  can protrude from the first side  143  of the workpiece  108  such that the entire opening  155  is expanded. The coupling section  235  includes a plurality of locking features  220  proximate the end  270 . The locking features  220  are illustrated as external grooves that can bear against an inner surface  217  of the collar  130 . The external grooves  220  can be helical external threads, an array of spaced apart grooves, or the like. The locking features  220  can also be bumps, ridges, projections, recessed regions, combinations thereof, or the like. The locking features  220  and the inner surface  217  can lock together to axially fix and/or rotationally fix the collar  130  to the outer member  140 . 
     The inner surface  217  can be a generally smooth tubular surface and can be made, in whole or in part, of a material with a yield strength that is less than the yield strength of the material of the locking features  220 . When the inner surface  217  is compressed against the locking features  220 , the locking features  220  can cause appreciable deformation (e.g., plastic deformation, elastic deformation, or both) of the inner surface  217 . In this manner, the collar  130  can be locked to the expandable outer member  140 . In some embodiments, the coupling section  235  has one or more coupling features (e.g., internal threads, a bonding layer, an adhesive, etc.) that facilitate coupling with the locking features  220 . 
     The head  160  is in the form of a chamfered flange for seating in a countersink  237  of the workpiece  108 . The head  160  has a countersink  239  to receive a complementary shaped head  310  of the inner member  145 . An outer surface  315  of the head  160  is generally flush with an outer surface  311  of the panel  120  and an outer surface  313  of the head  310 . The configurations of the countersinks  237 ,  239  can be selected such that the head  160  and/or head  310  sit slightly above, at, or below the surface  311  of the panel  120 . The outer surfaces  311 ,  313 ,  315  can be made flush using various processes, such as a machining process, to be within a desired tolerance, for example, a manufacturing tolerance associated with the installation. The illustrated heads  160 ,  310  can reduce the occurrence of lightning strikes. 
     In other embodiments, the heads  160 ,  310  may protrude from the second side  144  of the workpiece  108 . For example, the head  160  can lie along and protrudes from the surface  311  of the panel  120 . 
     Referring to  FIGS. 4-6 , the inner member  145  is shown installed (i.e., after it has expanded the outer member  140  and has been broken apart). The inner member  145  includes a narrow section  300 , the head  310 , and a stem  320  between the narrow section  300  and head  310 . A mandrel section  330  is positioned between the narrow section  300  and the stem  320 . 
     The mandrel section  330  can expand the outer member  140 , and in some embodiments, the stem  320  can limit or substantially prevent constriction of the outer member  140 . The stem  320  can prop the expanded portion  213  to maintain desired compressive stresses in the workpiece  108 . The inner member  145  can be, without limitation, a fastener, a rod (e.g., a threaded rod), a bolt, a stud, a shank, a mandrel, or the like. The illustrated inner member  145  has a solid cross-section. 
     With continued reference to  FIG. 4 , a selected amount of residual compressive stress is induced in the workpiece  108  because of the radial expansion of the outer member  140 . The compressive stresses may enhance the fatigue life of the installation. The amount of radial expansion of the outer member  140  may be selected to achieve corresponding amounts of residual compressive stresses in the workpieces  110 ,  120 . The fastener assembly  100  is suitable for performing a cold expansion process. The process of cold expansion is broadly interpreted as any process that radially expands at least some of the material surrounding the opening  155  with appreciably raising the temperature of the workpiece  108 . It is further understood that cold working the opening  155  may or may not induce beneficial compressive residual stresses and may or may not produce fatigue-enhancing benefits in the structural workpiece  108 . Determining the desired amounts of stresses in the workpieces  110 ,  120 , the amount of interference between the outer member  140  and the inner member  145 , and the amount of interference fit between the outer member  140  and the collar  130  may be an iterative process to achieve specific design goals, for example, installing the assembly  100  into the workpiece  108  without damaging the workpiece  108 . In some embodiments, the interference fits are sufficient to keep the outer member  140  and/or inner member  145 , even without installing the collar  130 , from migrating under operation, vibration, and/or other types of loads. 
     If the workpiece  108  is made of a low strain material, over expansion may cause strains that may cause crack initiation, crack propagation, fracture, or the like. In addition, if the workpiece  108  is made of fiber-reinforced composites, excessive strains may cause delamination between layers, fiber de-bonding, or the like. The outer member  140  can be inserted into the workpiece  108  with a clearance fit to reduce, limit, or substantially prevent damage to the composite workpiece  108 . A high interference can be achieved without over-expanding the member  140  to limit, reduce, or substantially prevent damage associated with over expansion. The high interference fit can also increase the fatigue life of the workpiece  108  because the workpieces  110 ,  120  are held tightly together. The inner member  145  can prevent an appreciable amount of contraction of the expanded member  140  to achieve a wide range of high interference fits. 
       FIGS. 7-8  show the inner member  145  prior to installation. The inner member  145  includes a detachable section  340  coupled to the narrow section  300 . The detachable section  340  includes an engagement region  342  and a shank  346 . The detachable section  340  is a break away component and can be integrally formed with the narrow section  300 . In other embodiments, the detachable section  340  is a separate component that is detachably coupled to the narrow section  300  by an adhesive, weld, or the like. 
     The engagement region  342  can be releasably coupled to an installation apparatus and includes a plurality of engagement features  344   a ,  344   b ,  344   c ,  344   d  (collectively  344 ). In some embodiments, including the illustrated embodiment of  FIGS. 7 and 8 , the engagement features  344  are circumferential grooves spaced apart from each other with respect to a longitudinal axis  360  of the inner member  145 . The engagement features  344  can be other types of coupling features for temporarily or permanently coupling to installation apparatuses. 
     When a sufficient force is applied to the engagement region  342 , the inner member  145  breaks at the decoupling feature  350  to allow separation of the shank  346  and the narrow section  300 , as shown in  FIG. 9 . A cross-sectional area taken at  362  of the decoupling feature  350  is less than the cross-sectional areas of the other sections of the inner member  145 . The cross-sectional area at  362  can thus be the minimum cross-sectional area of the member  145 . The decoupling feature  350  may serve as a crack initiation site. Cracks can propagate generally along a plane that is substantially perpendicular to the longitudinal axis  360 .  FIG. 9  shows the detachable section  340  separated from the narrow section  300  after the decoupling feature  350  has fractured. 
     The decoupling feature  350  can be an edge notch. Exemplary edge notches can include, without limitation, a circumferential groove having a generally U-shaped cross-section, V-shaped cross-section, or the like. Other types of edge notches or parting features can be used to control stress concentrations, crack initiation, and/or crack propagation such that the detachable section  340  is separable from the narrow section  300  without appreciably damaging to any significant extent other components of the fastener assembly  100 . 
       FIG. 10  shows the mandrel section  330  includes a first expansion portion  331  and a second expansion portion  333 . The first expansion portion  331  is connected to the narrow section  300 . The second expansion portion  333  is connected to the stem  320 . Angles of taper α, β of the expansion portions  331 ,  333 , respectively, can be selected based on the desired amount of expansion of the outer member  140 , rate of expansion of the outer member  140 , desired stresses/strains of the outer member  140  and/or the workpiece  108 . In some embodiments, the angle of taper α is equal to or greater than the angle of taper β. For example, the angle α can be at least 30 degrees greater than the angle β. Such embodiments are especially well suited for controlled expansion without producing significant amounts of longitudinally displaced material of the components, e.g., longitudinally displaced material of a sidewall of the outer member  140 . Surfaces  371 ,  373  of the mandrel section  330  can thus slide smoothly along the inner surface of the outer member  140 . 
       FIG. 11  shows a mandrel section  377  that has a longitudinally curved surface  379  for sliding smoothly along the outer member  140 . The mandrel section  377  can expand the outer member  140  without producing as much longitudinally material as the mandrel section  330  of  FIG. 10 . 
       FIG. 12  shows an installation apparatus  384  that includes an installation tool  386  for installing the fastener assembly  100 . Generally, the installation tool  386  includes an actuator unit  388  (illustrated as a puller unit) and a swaging assembly  396  (shown in dashed line) carried by the puller unit  388 . The puller unit  388  includes a grip  390 . A user can manually grasp the grip  390  for comfortably holding and accurately positioning the installation tool  386 . The illustrated grip  390  is a pistol grip. However, other types of grips can also be utilized. 
     The installation tool  386  can be driven electrically, hydraulically, pneumatically, or by any other suitable drive system. In some embodiments, the puller unit  388  houses a drive system capable of driving a component of the fastener assembly  100 , preferably along a predetermined path (e.g., a line of action), in a proximal direction and/or distal direction. A pair of fluid lines  392 ,  394  of the installation apparatus  384  provides pressurized fluid (e.g., pressurized gas, liquid, or a combination thereof) to a piston drive system that operates the swaging assembly  396 . 
     Referring to  FIG. 13 , the swaging assembly  396  includes an outer housing  398 , an actuating device  400 , and a biasing member  402  between the outer housing  398  and the actuating device  400 . The actuating device  400  is moved through the outer housing  398  towards the workpiece  108  to cause a swaging mechanism  404  to swage the collar  130 . The outer housing  398  is held against the workpiece  108  as the puller unit  386  pulls on the inner member  145  to remove the detachable section  340 . 
       FIG. 14  shows the outer housing  398  having a generally tubular main body  412 , a first end  413 , a second end  415 , and a bore  416  extending between the first end  413  and the second end  415 . The bore  416  is a longitudinally-extending passageway sized and dimensioned to closely surround the actuating device  400 . 
     The biasing member  402  pushes on the housing  398  and a retainer  420 , illustrated as a flange of the actuating device  400 , to move the actuating device  400  in a proximal direction to move a shoulder  422  of the actuating device  400  against a shoulder  414  of the outer housing  398 . The illustrated biasing member  402  is captured between a face  430  of the retainer  420  and an opposing face  432  of the outer housing  398 . The biasing member  402  can include, without limitation, one or more springs (e.g., helical springs, conical springs, and the like). In some embodiments, the biasing member  402  is a round wire helical compression spring surrounding a sleeve  406  of the device  400 . Although the embodiments illustrated herein show the biasing member  402  as a spring, it is understood that other mechanical devices known in the art that are capable of exerting a force can be used in place of the mechanical spring. 
     The sleeve  406  is closely received by the outer housing  398  and includes the shoulder  422 . An inner surface  487  of the sleeve  406  defines a passageway  489 . In the illustrated embodiment, the sleeve  406  is movable between a proximal position (e.g., when the shoulder  422  bears against the shoulder  414 ) and a distal position (illustrated in  FIG. 14 ). A distance of travel D of the actuating device  400  can be selected based on the dimensions of the outer housing  398  and the sleeve  406 . 
     The retainer  420  is coupled to an exterior surface  442  of the sleeve  406 . A stop  448  can limit, minimize, or substantially prevent relative movement between the retainer  420  and the sleeve  406 . The stop  448  of  FIG. 14  is a ring that is at least partially disposed within an annular recess  444  at a proximal end  450  of the sleeve  406 . 
     The swaging mechanism  404  includes a plurality of swaging elements  462   a ,  462   b ,  462   c ,  462   d  (collectively  462 ). The swaging elements  462  can be generally similar to each other, and accordingly, the following description of one of the swaging elements applies equally to the others, unless indicated otherwise. The swaging elements  462  can be circumferentially spaced about the sleeve  406  and can protrude inwardly from the inner surface  487  into the passageway  489 . In the illustrated embodiment, the swaging elements  462  are ball bearings, each positioned in a corresponding socket  464   a ,  464   b ,  464   c ,  464   c  (collectively  464 ) in a sidewall  469  of the sleeve  406 . For example, the swaging element  462   a  can rotate freely within the complementary socket  464 . The ball bearings  462  can be generally spherical bearings made, in whole or in part, of a hard material suitable for deforming collars. 
     The swaging mechanism  404  can include six swaging elements  462  spaced generally equally apart by about 30 degrees with respect to a longitudinal axis  491  of the actuating device  400 . The number of the swaging elements  462  may be greater or less than the illustrated exemplary number depending on various design objectives. For example, the swaging mechanism  404  can have more than six swaging elements  462  to increase the number of contact points created during the swaging process. 
       FIGS. 15-22  illustrate one method of installing the fastener assembly  100 . Generally, the expandable outer member  140  is positioned in the opening  155 . The inner member  145  is inserted into the expandable outer member  140 . The collar  130  is moved over the outer member  140  such that the workpiece  108  is between the collar  130  and the head  160  of the outer member  140 . The outer member  140  is expanded into the workpiece  108  using the mandrel section  330  of the inner member  145 . The collar  130  is fixed to the expanded outer member  140 . 
     Referring to  FIG. 15 , the outer member  140 , in a pre-expanded state, is inserted into the opening  155  of the workpiece  108 . A clearance fit, or other type of suitable fit, can be provided for convenient assembly. If the workpiece  108  is made of a composite material, a clearance fit can be provided to reduce, minimize, or substantially prevent damage to the workpiece  108  as the outer member  140  is placed within the opening  155 . The opening  155  can closely receive the outer member  140  to reduce the amount of expansion required to install the outer member  140 . 
     In the illustrated embodiment, the outer member  140  on the second side  144  of the workpiece  108  is moved sequentially through the first and second panels  120 ,  110 . When the head  160  is seated in the countersink  237 , the coupling section  235  protrudes from the first side  143  of the workpiece  108 . In some embodiments, a substantial portion of the coupling section  235  extends outwardly from the opening  155 . The illustrated coupling section  235  is spaced apart from the opening  155 . 
       FIG. 16  shows the outer member  140  positioned in the opening  155  and ready to receive the inner member  145 . The detachable section  340  of the inner member  145  is inserted into and advanced through the passageway  260  of the outer member  140  until at least a portion of the detachable section  340  projects outwardly from the inner member  140 . 
     As shown in  FIG. 17 , the collar  130  can be positioned on the first side  143  of the workpiece  108 . The collar  130  can be moved over the detachable section  340  and the outer member  140  such that the collar  130  rests against the workpiece  108 . The collar  130  surrounds at least a portion of the coupling section  235 . 
       FIG. 18  shows the swaging assembly  396  ready to receive the assembled fastener assembly  100  in an unexpanded state. A puller unit (e.g., the puller unit  388  illustrated in  FIG. 12 ) can be coupled to the detachable section  340  protruding outwardly from the collar  130 . The puller unit is activated to pull the inner member  145  proximally through the outer member  140  (indicated by the arrow  357  of  FIG. 18 ). The mandrel section  330  expands the outer member  140  as it passes through the outer member  140  and the stem  320  props the expanded portion  213  of the outer member  140  to limit, minimize, or substantially prevent contraction of the outer member  140 . During this process, the workpiece  108  is pulled against the swaging assembly  396 . As the head  310  seats in the head  160 , the puller unit compresses the workpiece  108  between the collar  130  and the head  160 . 
     When the mandrel section  330  moves through the outer member  140 , the mandrel section  330  radially expands the outer member  140  from an initial configuration to an expanded configuration to cold work, the workpiece  108  to produce an interference fit with the workpiece  108 , or the like. The outer member  140  can shield the inner surface  154  of the opening  155  to prevent, limit, or substantially eliminate damage to the workpiece  108 . The wall thickness of the outer member  140  can be increased to increase shielding. The outer member  140  remains stationary with respect to the workpiece  108  as the tubular main body  250  is expanded. The outer member  140  can control stresses induced in the workpiece  108  throughout a portion or the entire thickness of the workpiece  108 . 
     The outer surface  359  of the inner member  145  includes an outer perimeter  361  that is sized to be equal to (e.g., maximum tolerance conditions) or at least slightly smaller than the inner perimeter of the “radially expanded” outer member  140 . This relative sizing allows the stem  320  to follow the mandrel section  330  into the expanded outer member  140  and to prop open the outer member  140 . In some embodiments, the inner member  145  can be inserted into the outer member  140  without damaging an inner surface  263  of the outer member  140 . 
     The relative sizing of the mandrel section  330  and the stem  320  can also permit the stem  320  to be passed into the radially expanded outer member  140  so that the outer member  140  can produce an interference fit with the inner member  145 , which both supports and limits the radial contraction of the outer member  140 . In some embodiments, elastically, radially spring back of radially-expanded outer member  140  produces a secure interference fit therewith to achieve desired clamp-up forces, even relatively large clamp-up forces. 
     The opening  155  can be expanded without compromising the structural integrity of the workpiece  108 , even the free edges  483 ,  485  of the opening  155 . Because the workpiece  108  is not exposed to any appreciable frictional forces during the expansion process, damage (e.g., delamination) of the one or both of the panels  110 ,  120  can be kept at or below a desired level, even in material proximate to the free edges  483 ,  485  shown in  FIG. 15 . The composition, dimensions, and configuration of the outer member  140  can be selected to minimize, limit, or substantially prevent undesired stresses (e.g., shear stresses) in the workpiece  108  while producing desired stresses (e.g., compressive stresses) in the workpeice  108 . 
     Referring to  FIG. 19 , an outer surface  493  of the collar  130  is a generally cylindrical surface. The actuating device  400  contacts and bears against the outer surface  493 . The actuating device  400  is moved distally towards the flange  150  of the collar  130 . A gripping mechanism of the puller unit pulls on the inner member  145  to keep the puller unit against the workpiece  108  while the swaging elements  462  roll along the outer surfaced  493 . 
     As the swaging elements  462  roll along the outer surface  493 , the swaging elements  462  compress the collar  130  against the expanded outer member  140 . The swaging elements  462  cooperate to radially displace the collar  130  inwardly so as to press the inner surface  217  of the collar  130  against the locking features  220 . Each swaging element  462  can produce a longitudinally-extending swage groove. The grooves can have an arcuate cross-section, including a generally U-shaped cross-section, or other suitable cross-sections. As used herein, the term “groove” includes, but is not limited to, a generally long narrow furrow or channel. In some embodiments, the swaging elements  462  can push material of the collar  130  towards the workpiece  108  to increase the clamp-up forces. Each of the swaging elements  462  can cause a flow of material ahead of the interface between the swaging elements  262  and the collar  130 . This flow of material can be pushed towards the flange  150  and results in significantly increased clamp-up forces. 
       FIG. 20  shows a plurality of grooves  495  circumferentially spaced from one another about the collar  130 . The depths and widths of the grooves  495  can be increased by increasing the compressive forces applied by the swaging elements  462 . The illustrated grooves  495  extend generally longitudinally along the collar  130 . The grooves  495  can extend along most of the longitudinal length of the main body  180  to lock a substantially portion of the longitudinal length of the collar  130  to the outer member  140 . 
     At full stroke, the swaging elements  462  are proximate the flange  150 . After completing the swaging process, the puller unit can break off the exposed detachable section  430 . A sufficient axial load can be applied to the inner member  145  to fracture the inner member  145  at or near the decoupling feature  350 .  FIG. 21  shows the inner member  145  after it is broken. A fracture surface  512  of the inner member  145  can be flush or adjacent to the end  270  of the member  140 . 
       FIG. 22  shows the installed fastener assembly  100  and the swaging assembly  396  separated from the assembly  100 . The swaging assembly  396  can be separated from the installed fastener assembly  100  after the detachable section  340  is removed. 
     The outer member  140  can contribute to the clamp-up of the workpiece  108 , along with the swaged collar  130 , to enhance performance (e.g., improve conductivity) and may result in some compliance that inhibits or precludes failure of the fastener head  160  in single shear loading conditions. The illustrated fastener assembly  100  can also be conveniently dissembled. When the inner member  145  is removed, the outer member  140  can spring back (e.g., contract inwardly) and, in some embodiments, can allow for the joint to be disassembled without damage to the workpieces  110 ,  120 . The wall thickness of the outer member  140  can be sufficiently large to allow the inner member  145  to be slide out of the outer member  140  that remains generally stationary. In contrast, conventional thin-walled sleeve/bolt assemblies may come out together resulting in unwanted damage to workpiece, especially when the workpiece is made of a composite material. 
     The outer member  140  can have an outer diameter that is slightly less than 0.25 inches and a wall thickness that is equal to or greater than about 0.03 inches. Such an outer member  140  can be installed in a 0.25 inch diameter hole. The outer member  140  can be radially-expanded into the workpiece  108  to form an integral part of the fastener assembly  100 . In some embodiments, the outer member  140  has a wall thickness of about 0.04 inches and is made, in whole or in part, of steel (e.g., stainless steel), titanium, or the like. The inner member  145  can be made of a relatively hard material, such as stainless steel, suitable for radially-expanding the outer member  140 . The dimensions and configurations of the inner member  145  and outer member  140  can be selected based on the installation configuration. 
     The fastener assembly  100  can provide enhanced electrical conductivity through the workpiece, especially at joints of workpieces made of composite materials. The outer member  140  can insulate the workpiece  108  from the inner member  145 . High clamp-up forces ensure that multi-component workpieces are held together during the service life of the workpiece. Various types of substances (e.g., lubricants) can be applied to the fastener assembly  100  to facilitate installation and/or enhance performance. For example, the outer member  140  and inner member  145  can be passivated and dry film lubed. The passivated surfaces can provide electrical insulation between the components of the fastener assembly  100 . The dry film lube can reduce the forces required to install the fastener assembly  100 . 
     Workpieces may comprise a wide range of different materials, including materials (e.g., composite materials), that are susceptible to damage due to high strains. Composite materials may include two or more materials with significantly different properties, such as physical properties (e.g., mechanical properties, electrical properties, etc.), chemical properties, or the like. For example, composite materials may include, without limitation, reinforcing elements (e.g., fibers, particles, and the like), fillers, binders, matrix, and the like. Wood, fiberglass, polymers, plastics, metals, ceramics, glass, or the like can be combined to produce one or both of the illustrated composite panels  110 ,  120  with properties that are different from the properties of its constituents individually. In some embodiments, the workpiece  108  can comprise a fiber-reinforced composite, particle-reinforced composite, laminate (e.g., a stack of laminas), or combinations thereof. The matrix of the reinforced composites can be made of metal, polymers, ceramics, and other suitable materials for encapsulating other reinforcement features. The laminates can be unidirectional laminates, cross-ply laminates, angle-ply laminates, symmetric laminates, and the like. 
     The fastener assembly  100  can be installed in the composite workpiece  108  while maintaining the integrity of the workpiece  108 . The outer member  140 , for example, can be easily inserted into the opening  155 . The inner member  145  can expand the outer member  140  such that the expanded outer member  140  produces an interference fit with the workpiece  108 . To minimize, limit, or substantially prevent damage to the material surrounding the opening  155 , the amount of radial expansion can be below a threshold amount of expansion that would cause unwanted damage, such as micro-cracking, buckling of fibers, and the like, of the workpiece  108 . 
     Composites may have relatively low strain capabilities as compared to metals. The fastener assembly  100  can produce compressive loading in the composite material surrounding the opening  155 . If the compressive loading is too high, fibers in a fiber-reinforced composite material can buckle, which in turn affects the material&#39;s properties. Micro-buckling of fibers may significantly reduce the water resistance of the composite material because buckled fibers may cause micro-cracking of the matrix surrounding the fibers. Splitting due to Poisson&#39;s ratio effect, matrix yielding, fiber splitting, de-bonding (e.g., fiber de-bonding, interlaminate de-bonding, and the like), and other failure modes are often caused by compressive loading or high strains. Advantageously, the fastener assembly  100  can be installed using sufficiently low levels of strain to control the amount of damage, if any, to the workpiece  108 . For example, the outer member  140  in an un-expanded state can be installed with a clearance fit or a slight interference fit, as well as other types of fits, until the inner member  145  expands the outer member  140 . Advantageously, the fastener assembly  100  can be installed using sufficiently low levels of strain to control the amount of damage, if any, to the workpiece  108 . The fastener assembly  100 , for example, can be installed with a slight interference fit or other type of fit that keeps the fastener assembly  100  fixed to the workpiece  108 . Outwardly directed compressive forces can be applied to the workpiece  108  without compromising the structural integrity of the workpiece  108 . 
     By knowing the final dimensions of the installed fastener assembly, a desired amount of radial interference between the expanded outer member  140  and the inner member  145  may be selected. It is understood that the inner member  145 , the outer member  140 , and/or the opening  155  in the workpiece  108  may have generally circular cross-sections or non-circular cross-sections such that the amount of interference may need to be expressed with alternate language. It is generally understood that when components are assembled with an “interference fit,” a contact pressure is present between the components after assembly. 
     Further, the installation can be accomplished with both the inner and outer members  140 ,  145  at substantially the same temperature. In some embodiments, the average temperature of the inner member  140  can be less than about 10 degrees Celsius of the average temperature of outer member  145 . In some embodiments, for example, the average temperature of the inner member  140  can be less than 5 degrees Celsius of the average temperature of outer member  145 . This eliminates the need to freeze or heat one of the respective members, which reduces manufacturing time and costs. Thermal processes can often lead to the formation of a condensate, which in turn leads to corrosion of the workpiece  108 . 
     Other types of swaging assemblies can be used to install expandable fastener assemblies.  FIG. 23-25  show a swaging assembly  510  that includes a multi-piece outer housing  512 , a restraint  514 , and a biasing member  576  between the outer housing  512  and the restraint  514 . A gripping mechanism  520  has a jaw  522  for gripping an inner member. The inner member can be inserted into a bore  524  of the gripping mechanism  522 . An actuation assembly  530  includes coupling features  540 , illustrated as internal threads, for coupling to a puller unit. 
       FIG. 26  shows the swaging assembly  510  with a jaw assembly  545 . The jaw assembly  545  includes interior engagement region  546  configured to engage the engagement region of an inner member, such as the engagement region  342  discussed in connection with  FIGS. 7-9 . The illustrated engagement region  546  has a complementary shape to the engagement region  342  of the inner member  145 . The jaw assembly  545  is moveable between an open configuration for receiving the inner member  145  and an open configuration for releasing the detachable section  340  after breaking if off. 
     The various embodiments described above can be combined to provide further embodiments. All of the above U.S. patents, patent applications and publications referred to in this specification, as well U.S. Provisional Patent Application No. 60/999,517, filed Oct. 16, 2007, U.S. application Ser. No. 12/253,141; U.S. Pat. Nos. 3,566,662; 3,892,121; 4,187,708; 4,423,619; 4,425,780; 4,471,643; 4,524,600; 4,557,033; 4,809,420; 4,885,829; 4,934,170; 5,083,363; 5,096,349; 5,103,548; 5,127,254; 5,245,743; 5,305,627; 5,341,559; 5,380,136; 5,405,228; 5,433,100; 7,024,908; 7,100,264; and 7,375,277; U.S. Patent Publication Nos. 2005/0025601; 2007/0110541; 2007/0289351; 2007/0295050; 2008/0005887; 2008/0034831; and 2008/0066518; and International Application No. WO 2007/082077 are incorporated herein by reference. Aspects can be modified, if necessary or desired, to employ devices, features, elements (e.g., fasteners, bushings, nut plates, and other types of expandable members), and concepts of the various patents, applications, and publications to provide yet further embodiments. The fastener assemblies disclosed herein can be made, in whole or in part, of the materials (e.g., materials, coatings, liners, etc.) disclosed in the concepts of the various patents, applications, and publications to provide yet further embodiments 
     From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the disclosed embodiments and the appended claims.