Abstract:
A hybrid fastener is provided in combination with a structural insert. The insert is disposed about a shank of the fastener at an unthreaded section. In another aspect, a sleeve surrounds the shank of the fastener and has apertures for receiving the insert therethrough. Methods of using the above-described hybrid fastener for securing workpieces are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. Ser. No. 13/910,266, filed on Jun. 5, 2013; which claims the benefit of U.S. Provisional Application No. 61/658,163, filed on Jun. 11, 2012, both of which are incorporated by reference herein. 
     
    
     BACKGROUND AND SUMMARY 
       [0002]    The present invention generally pertains to fasteners and more particularly to a hybrid fastener having an insert between the fastener and a workpiece being joined. 
         [0003]    It is known to use a fastener to secure a plurality of workpieces. It is also known to employ a ferrule around a shank of the fastener or an adhesive material to the threads of a fastener to strengthen the joint and/or to further secure the fastener to the workpieces. Examples of such traditional devices are disclosed in U.S. Pat. No. 3,472,301 entitled “Self-Sealing Mechanical Fastener;” U.S. Pat. Nos. 4,094,222 and 4,263,832 both entitled “Adhesively Secured Anchor Bolt;” U.S. Pat. Nos. 4,776,738 and 4,990,041 both entitled “Fastening Device;” and U.S. Pat. No. 5,249,899 entitled “Head Bolt and Driver Therefor;” all of which are incorporated by reference herein. Prior disclosed ferrules require precision machining and/or a large inventory of products to accommodate different fastener sizing, while prior adhesive materials are merely thin coatings along the threads of a fastener that provide no additional structure, cannot guarantee a filled gap, and have little to no stress-reducing properties. Furthermore, either design requires workpieces that are carefully machined, matched, and aligned. 
         [0004]    In accordance with the present invention, an apparatus is provided having a fastener and a structural insert. In another aspect, the fastener includes a head and a shank. A further aspect provides at least one thread helically located about a shank. In still another aspect, an insert is disposed about a shank at an unthreaded section and extends at least partially into a head and/or the shank. In another aspect, a sleeve surrounds a shank of the fastener and has apertures extending therethrough. Yet another aspect provides a magnetically, electrically, or chemically attractive coating on the shank for attracting friable or elastomeric particles in a structural insert. In another aspect, electrically conductive particles are contained in the insert to accelerate curing by application of an electric field. In another aspect, the fastener is a self-drilling and self-tapping fastener. In another aspect, the fastener is a rivet. Methods of using the above-described hybrid fastener for securing workpieces are also disclosed. 
         [0005]    The present hybrid fastener is advantageous over prior fastening members. For example, the present apparatus and method advantageously alleviate stress concentrations and contact stresses in workpieces being joined. Notably, the present hybrid fastener also works to seal edges of the apertures in the workpieces so as to preclude invasion by moisture or dirt. Moreover, the present apparatus effectively reduces costs by allowing increased tolerances for the workpiece apertures. Additional advantages and features of the present invention will be found in the following description and accompanying claims, as well as in the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a partially fragmented, side view of workpieces joined by a hybrid fastener according to the present invention; 
           [0007]      FIG. 2  is a partially fragmented, side view of a tool for injecting insert material into the fastener of  FIG. 1 ; 
           [0008]      FIG. 3  is a partially fragmented, side view of an alternate configuration to the tool of  FIG. 2 ; 
           [0009]      FIG. 4  is a partially fragmented, side view of an alternate configuration to the fastener of  FIG. 1 ; 
           [0010]      FIG. 5  is a partially fragmented, side view of an alternate configuration to the workpieces of  FIG. 1 ; 
           [0011]      FIG. 6  is a partially fragmented, side view of an alternate configuration to the workpieces of  FIG. 1 ; 
           [0012]      FIG. 7  is a partially fragmented, side view of an alternate configuration to the fastener of  FIG. 1  including a sleeve member; 
           [0013]      FIG. 8  is an exploded view of the fastener and sleeve member of  FIG. 7 ; 
           [0014]      FIG. 9  is a partially fragmented, side view of an alternate configuration to the fastener of  FIG. 1  including a telescoping sleeve member; 
           [0015]      FIG. 10  is an exploded view of the fastener and telescoping sleeve member of  FIG. 9 ; 
           [0016]      FIG. 11  is a partially fragmented, side view of an alternate configuration to the fastener of  FIG. 1  including a mesh sleeve member; 
           [0017]      FIG. 12  is an exploded view of the fastener and mesh sleeve member of  FIG. 11 ; 
           [0018]      FIG. 13  is a partially fragmented, side view of unassembled workpieces and a fastener having a capsule; 
           [0019]      FIG. 14  is a partially fragmented, side view of the assembled workpieces and the fastener having the capsule of  FIG. 13 ; 
           [0020]      FIG. 15  is a partially fragmented, side view of an alternate configuration to the workpieces of  FIG. 14 ; 
           [0021]      FIG. 16  is a partially fragmented, side view of an unassembled alternate configuration to the fastener of  FIG. 14  including a telescoping sleeve member; 
           [0022]      FIG. 17  is a partially fragmented, side view of an assembled alternate configuration to the fastener of  FIG. 14  including a telescoping sleeve member; 
           [0023]      FIG. 18  is a partially fragmented, side view of workpieces joined by a hybrid self-drilling fastener according to the present invention; 
           [0024]      FIG. 19  is a partially fragmented, side view of an alternate configuration to the self-drilling fastener of  FIG. 18 ; 
           [0025]      FIG. 20  is a partially fragmented, side view of an alternate configuration to the self-drilling fastener of  FIG. 18 ; 
           [0026]      FIG. 21  is a partially fragmented, side view of an alternate configuration to the self-drilling fastener of  FIG. 18 ; 
           [0027]      FIG. 22  is a partially fragmented, side view of an alternate configuration to the self-drilling fastener of  FIG. 18 ; 
           [0028]      FIG. 23  is a partially fragmented, side view of an alternate configuration to the self-drilling fastener of  FIG. 18 ; 
           [0029]      FIG. 24  is a partially fragmented, side view of an alternate configuration to the self-drilling fastener of  FIG. 18 ; and 
           [0030]      FIG. 25  is a partially fragmented, side view of workpieces joined by a hybrid rivet fastener according to the present invention. 
       
    
    
       [0031]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0032]    Multiple embodiments of a hybrid fastener  10  for joining a first workpiece  12  to a second workpiece  14  are illustrated and described with respect to  FIGS. 1 through 25 . Hybrid fastener  10 , as described herein, allows for increased tolerances for apertures  16 ,  18  in workpieces  12 ,  14 , respectively, while still sealing edges of the apertures  16 ,  18 , and alleviating stress concentrations and contact stresses in the workpieces  12 ,  14  being joined. Workpieces  12 ,  14  may be brittle components that are negatively impacted by high stress concentrations (e.g., composite materials used for aircraft components). Accordingly, reduction in these stress concentrations and contact stresses are particularly important for these types of materials. 
         [0033]    With reference now to  FIG. 1 , hybrid fastener  10  includes a head  20  disposed at a first end  22 , a shank  24  extending from head  20  between first end  22  and a second end  26 , and a helical thread  28  extending about shank  24  adjacent second end  26  and extending towards first end  22 . An underside  30  of head  20  includes an integrally formed spacer  32  for centering fastener  10  within apertures  16 ,  18  of workpieces  12 ,  14 . Alternately, spacer  32  may be a secondary part assembled before fastener  10  is inserted into workpieces  12 ,  14  (e.g., a washer). At least one slot  34  extends from spacer  32  to an outer diameter of head  20  along underside  30  of head  20 . Shank  24  includes a channel  36  extending transversely to a longitudinal axis  38  of fastener  10  through the outer diameter of shank  24  so as to be in communication with a non-threaded portion  40  of shank  24 . A duct  42  extends from a flared portion  44  at second end  26  and along longitudinal axis  38  until terminating at channel  36 . Channel  36  and duct  42  may be produced by any of several different machining processes including, for example, drilling, electrical discharge machining, laser cutting or water-jet cutting. Furthermore, although channel  36  is shown extending fully through the diameter of shank  24  so as to be in a T-shaped configuration with duct  42 , it is contemplated that channel  36  may only extend partially through shank  42  so as to be in an L-shaped configuration with duct  42 . 
         [0034]    Fastener  10  is arranged in workpieces  12 ,  14  by inserting shank  24  into apertures  16 ,  18  so as to protrude from workpieces  12 ,  14  by a distance such that a majority of shank  24  arranged within workpieces  12 ,  14  is devoid of helical thread  28 . Fastener  10  is secured with a nut  46  over the extending portion of shank  24  for joining first and second workpieces  12 ,  14 , as shown. Similarly to fastener  10 , nut  46  also includes a spacer  48  and at least one slot  50  extending from spacer  48  to an outer diameter of nut  46 . An at least partially liquefied structural insert material  52  is injected through duct  42  at flared portion  44  so as to fill duct  42  and channel  36 , as will be described in more detail below. Insert material  52  is injected completely through duct  42  and channel  36  so as to be disposed about shank  24  at non-threaded portion  40  adjacent first end  22  of fastener  10  within a void area  54  defined between workpieces  12 ,  14  and shank  24  and between head  20  and nut  46 . Void area  54  may be sized appropriately for each application; however, one exemplary void area  54  may provide an insert thickness of at least 2 mm. To assure complete fill of void area  54 , slot  34  in head  20  and slot  50  in nut  46  are designed to allow trapped air to escape. Further, complete filling of void area  54  is signaled when a small amount of insert material  52  is extruded from slots  34 ,  50 . 
         [0035]    Insert material  52  hardens after injection so as to remain in void area  54  and at least partially in channel  36  and duct  42 . In this way, insert material  52  serves to add strength and/or stiffness to the workpiece/fastener joint by eliminating clearance between shank  24  and surrounding apertures  16 ,  18 . Insert material  52  may also reduce or control stress concentrations caused by tilting of fastener  10 , as well as contact of asperities between contacting surfaces, for example, by redistributing the bearing contact stresses between fastener  10  and workpieces  12 ,  14 . This may be achieved by varying thickness or composition of insert material  52 . 
         [0036]    The composition of insert material  52  is selected so as to tailor the material properties to the application. Insert material  52  may be a matrix or carrier material having an additive material suspended therein. The additive material may be a solid particulate or fiber that contributes to the desired properties of the joint. For example, for a joint that is subject to impact loads and propagation of stress waves through the bolted joint, insert materials that create an impedance mismatch between the joint components can be chosen in order to attenuate the stress waves. In other cases, maximum stiffness and/or strength is sought. In some applications, such as when vibrational loads are expected, a balance between strength and compliance must be achieved. Certain electrical, magnetic, and chemical properties can also be controlled by choice of material components. 
         [0037]    The matrix or carrier material may be, for example, a thermosetting resin (e.g., toughened epoxy hybrids, epoxy nylon, epoxy phenolic, polyurethane, phenolic, polyester resin) or a thermoplastic resin (e.g., polyamide, polyester (saturated), nylon, polystyrene, polyethylene). The additive material(s) may be graphene nanoparticles (e.g., foliated graphite nanoplatelets having a particle size range of 0.3 to 100 nanometers thickness by 0.3 to 10 micrometers length, with a preferred size of 5 micrometers), silica (nanosilica) particles (e.g., amorphous silicon dioxide having a size range of 200 to 500 nanometers), graphene coated with an elastomer, nylon particles, chopped graphite fibers, chopped glass fibers, aluminum particles, steel or iron particles, elastomeric (including neoprene) particles, aluminum oxide particles, ceramics (e.g., silicon carbide), and/or chopped cellulose fibers. 
         [0038]    In addition, a magnetically, electrically, or chemically attractive material may be coated on shank  24  and/or on inner surfaces of apertures  16 ,  18  of the workpieces  12 ,  14  before arranging fastener  10  in workpieces  12 ,  14  so as to attract friable or elastomeric particles in structural insert material  52 . In this way, migration of an additive friable or elastomeric particle causes a predefined weakened zone for insert  52  to assist in removal of fastener  10 . Furthermore, an electroconductive material may be incorporated into insert material  52 , itself, such that application of an electrical or magnetic field will induce heating and accelerate curing of insert material  52 . Alternately or in addition, a release agent may be applied to shank  24  and/or to inner surfaces of apertures  16 ,  18  of workpieces  12 ,  14  to assist in removal of fastener  10  and/or insert material  52 . 
         [0039]    With reference to  FIG. 2 , a tool  60  for injecting insert material  52  into fastener  10  is described as having a main body  64 , an internal thread  66 , an integral nut-shaped boss  68 , and an inner cavity  70  defining a reservoir for both insert material  52  and a piston  72 . Thread  66  is used to secure tool  60  onto shank  24  of fastener  10  at second end  26 , such that a nose  74  of piston  72  engages and seals against flared portion  44  of duct  42 . As tool  60  advances further along the threads of shank  24 , piston  72  is forced downwardly into cavity  70  where it compresses insert material  52 . Notably, as piston  72  engages shank  24  it ceases rotational movement. However, body  64  continues rotating, which assists in agitating and mixing insert material  52 . This compression of insert material  52  forces its upward movement through a central opening  76  in piston  72  and into duct  42  of fastener  10 . Optionally, a gasket or O-ring  78  may be added to the interface between piston  72  and fastener  10  to assist in preventing leakage of insert material  52  during injection. 
         [0040]    Although not shown, tool  60  may also be applicable to two-part material systems. In such a case, tool  60  may include separate compartments for housing material constituents before combination during insertion. Alternately, tool  60  may include piercing features for opening a capsule containing constituent material products. In any of these cases, tool  60  is designed as a single-use device (e.g., discardable materials) or reusable product. 
         [0041]    Referring now to  FIG. 3 , an alternate tool  80  for injecting insert material  52  into fastener  10  is described as a snap-on grease fitting. Tool  80  is threaded into or machined integral with shank  24  for injecting insert material  52  with a lever or air pressure system (not shown). Tool  80  may resemble a zerk fitting; however, a spring-loaded check valve may or may not be used. Tool  80  allows an insert injection device (not shown), such as a grease gun, a calking gun, a syringe, or a resin-mixing applicator to be attached thereto, so that insert material  52  can be injected under pressure. 
         [0042]    With reference now to  FIG. 4 , an alternate hybrid fastener  100  is described for joining workpieces  12 ,  14 . Hybrid fastener  100  is constructed substantially similarly to hybrid fastener  10 ; however, hybrid fastener  100  omits both channel  36  and duct  42 . Instead, hybrid fastener  100  includes a duct  142  extending downwardly through head  20  to void  54  from an injection port  144 . Duct  142  is arranged parallel and offset from longitudinal axis  38 . Although not shown, it should be understood that duct  142  and injection port  144  may also be arranged to extend through nut  46 , instead of or in addition to head  20 . 
         [0043]    Referring now to  FIG. 5 , fastener  10  can alternately be used to create a hybrid joint  182  between workpieces  184 ,  186 . Hybrid joint  182  combines mechanical joining with adhesive fastening in a single step without the need for additional equipment (e.g., clamps). In particular, edges of surfaces  188 ,  190  of the workpieces  184 ,  186  are tapered or scarfed so as to create a cavity  192  adjacent fastener  10 . Insert material  52  is inserted into duct  42  and channel  36  as previously described. Insert material  52  extends from void  54  into cavity  192 . 
         [0044]    In an alternate hybrid joint configuration  194  shown in  FIG. 6 , workpieces  12 ,  14  are separated by a spacer  196 . Material for spacer  196  is chosen to provide appropriate adhesive film thickness, and may be, for example, paper, cardboard, etc. Spacer  196  is arranged between workpieces  12 ,  14  for providing a gap between workpieces  12 ,  14 . Fastener  10  is then inserted into workpieces  12 ,  14  and insert material  52  is injected therein, as previously described. Insert material  52  extends from void  54  into a cavity  198  defined by spacer  196  and workpieces  12 ,  14 . Spacer  196  remains in between workpieces  12 ,  14  after installation. 
         [0045]    While not shown, alternate hybrid joint configurations are also contemplated. For example, workpieces  12 ,  14  may each have a shallow counterbore formed at mating surfaces adjacent apertures  16 ,  18 . Furthermore, while only one spacer is shown in  FIG. 6 , it is contemplated that multiple spacers may also be used to separate workpieces  12 ,  14 . In these alternate hybrid joint configurations, it may not be necessary to include a channel for air bleed to assure filling of the void  54  and/or cavity  192 ,  198  as workpiece roughness will provide passages for air escapement. 
         [0046]    With reference now to  FIGS. 7 and 8 , an alternate hybrid fastener  200  is described for joining workpieces  12 ,  14 . Hybrid fastener  200  is constructed substantially similarly to hybrid fastener  10 ; however, hybrid fastener  200  incorporates a collar or sleeve  202  surrounding a shank  224  of fastener  200 . Sleeve  202  is a thin-walled, circular cylinder  204  having a plurality of spaced apart apertures  206  (preferably at least 6 apertures) for allowing insert material  52  to pass therethrough. Sleeve  202  may be manufactured as a hollow cylinder of a metallic material, such as a steel or an aluminum alloy, or of a polymer, such as nylon or phenolic. Sleeve  202  has a length L that is slightly less than the combined thickness T of workpieces  12 ,  14 . Furthermore, centering spacers  232 ,  248  on head  220  and nut  246  are shaped to center sleeve  202  along and about shank  224 . As installation of fastener  200  is similar to that described for fastener  10 , a detailed description is foregone. However, sleeve  202  is arranged about shank  224  before insertion of fastener  200  into workpieces  12 ,  14 . Insert material  52  passes through apertures  206  so as to integrally incorporate sleeve  202  after hardening. In this way, insert material  52  preferably encapsulates all sides of sleeve  202  when in the fully installed condition. 
         [0047]    Referring now to  FIGS. 9 and 10 , an alternate sleeve  302  is described for use with hybrid fastener  200  in joining workpieces  12 ,  14 . Sleeve  302  is a telescoping or self-adjusting sleeve having a first thin-walled hollow cylinder  304  with an outer diameter D 1  and a second thin-walled hollow cylinder  306  with an inner diameter D 2 . Outer diameter D 1  is slightly smaller than inner diameter D 2 , such that first cylinder  304  slides within second cylinder  306 . Sleeve  302  is used in situations where thickness T of workpieces  12 ,  14  is unknown, such as in field assembly. In this way, the length of sleeve  302  is adjustable to a broad range of workpiece thicknesses during installation. Both cylinders  304 ,  306  include a plurality of apertures  308  for allowing insert material  52  to pass therethrough. In use, cylinder  304  is slipped into cylinder  306  so as to have a combined length L 2  that is greater than thickness T of workpieces  12 ,  14 . The tightening of nut  246  causes cylinders  304 ,  306  to telescope together to properly accommodate workpiece thickness T. 
         [0048]    In an alternate embodiment shown in  FIGS. 11 and 12 , another alternate sleeve  402  is described for use with hybrid fastener  200  in joining workpieces  12 ,  14 . Sleeve  402  is a woven or stitched tube of graphite fiber, glass fiber, or other fibrous reinforcing material, for resisting effects of shear stresses between and within workpieces  12 ,  14 . Sleeve  402  is manufactured as a length of woven fiber cloth that is stitched into a substantially circular or cylindrically-shaped tube or, alternately, may be cut from a pre-woven tube of the desired fabric. An outer diameter  404  of sleeve  402  is less than the inner diameter of either aperture  16  of workpiece  12  or aperture  18  of workpiece  14 . However, sleeve  402  must be thick enough to meet strength requirements for the joint, be capable of radial expansion during assembly, and be flexible enough to conform to apertures  16 ,  18 . Sleeve  402  has a length  406  that is equal to or slightly greater than the combined thickness T of workpieces  12 ,  14 . In use, sleeve  402  is arranged about shank  224  before insertion of fastener  200  into workpieces  12 ,  14 . As insert material  52  is forced against an interior surface  408  of sleeve  402 , it expands sleeve  402  so that it conforms closely to apertures  16 ,  18 . At the same time, apertures  410  between threads of fabric of sleeve  402  become impregnated with insert material  52 . Accordingly, as insert material  52  solidifies, sleeve  402  and insert material  52  form a tight-fitting monolithic structure between fastener  200  and workpieces  12 ,  14 . 
         [0049]    Referring now to  FIGS. 13 and 14 , an alternate hybrid fastener  500  is described for joining workpieces  12 ,  14 . Fastener  500  includes a head  520  disposed at a first end  522 , a shank  524  extending from head  520  between first end  522  and a second end  526 , and a helical thread  528  extending about shank  524  adjacent second end  526  and extending towards first end  522 . 
         [0050]    An underside  530  of head  520  includes an integrally formed spacer  532  for centering fastener  500  within apertures  16 ,  18  of workpieces  12 ,  14 . Alternately, spacer  532  may be a secondary part assembled before fastener  500  is inserted into workpieces  12 ,  14  (e.g., a washer). At least one slot  534  extends from spacer  532  to an outer diameter of head  520  along underside  530  of head  520 . Underside  530  of head  520  also includes a plurality of sharp projections  536  extending from spacer  532 . A substantially toroidal capsule  538  containing an insert material  552  is arranged about shank  524 . Alternately, capsule  538  may be a flat envelope or an assembly of hollow tubes (e.g., nanotubes) wrapped about shank  524 . Capsule  538  is made of a material that will fragment, tear, or burst when sufficiently compressed and/or pressed against projections  536 . As such, capsule  538  is sized to house enough insert material  552  to fill a void area  554  between shank  524  and apertures  16 ,  18  and yet be long enough to reach projections  536 , as will be described in more detail below. When insert material  552  consists of two or more components (e.g., an epoxy), capsule  538  may be subdivided into two or more compartments. 
         [0051]    Fastener  500  is arranged in workpieces  12 ,  14  by inserting shank  524  into apertures  16 ,  18  so as to protrude from workpieces  12 ,  14  by a distance such that a majority of shank  524  arranged within workpieces  12 ,  14  is devoid of devoid of helical thread  528 . Fastener  500  is secured with a nut  546  over the extending portion of shank  524  for joining first and second workpieces  12 ,  14 , as shown. Similarly to fastener  500 , nut  546  also includes a spacer  548  and at least one slot  550  extending from spacer  548  to an outer diameter of nut  546 . During installation and tightening of nut  546 , projections  536  perforate capsule  538  and dislodge insert material  552  therefrom. Insert material  552  is injected completely into void area  554  so as to be disposed about shank  524  at a non-threaded portion  540  adjacent first end  522  of fastener  500 . To assure complete fill of void area  554 , slot  534  in head  520  and slot  550  in nut  546  are designed to allow trapped air to escape. Further, complete filling of void area  554  is signaled when a small amount of insert material  552  is extruded from slots  534 ,  550 . Insert material  552  hardens after injection so as to remain in void area  554  and at least partially encompass capsule  538 . 
         [0052]    With reference now to  FIG. 15 , fastener  500  can alternately be used to create a hybrid joint  582  between workpieces  12 ,  14 . Workpieces  12 ,  14  are separated by a spacer  584 . Spacer  584  can be made of paper, cardboard, or a number of other materials, chosen to provide appropriate adhesive film thickness. Spacer  584  is arranged between workpieces  12 ,  14  for providing a gap between workpieces  12 ,  14 . Fastener  500  is then inserted into workpieces  12 ,  14  and insert material  552  is rejected from capsule  538 , as previously described. Insert material  552  extends from void  554  into a cavity  586  defined by spacer  584  and workpieces  12 ,  14  so as to form a patch of insert that will act as an adhesive between workpieces  12 ,  14 . Spacer  584  remains between workpieces  12 ,  14  after installation. It should be noted that any of the aforementioned hybrid joints may be used in place of spacers  584  (e.g., scarfing workpieces, counterbores on workpieces, etc.). 
         [0053]    Referring now to  FIGS. 16 and 17 , an alternate hybrid fastener  600  is described for joining workpieces  12 ,  14 . Hybrid fastener  600  is constructed substantially similarly to hybrid fastener  500 ; however, hybrid fastener  600  incorporates a self-adjusting or telescoping sleeve  602  surrounding a capsule  636  about a shank  624  of fastener  600 . Sleeve  602  has a first thin-walled hollow cylinder  604  and a second thin-walled hollow cylinder  606 , with cylinder  604  being slightly smaller than cylinder  606  so that cylinder  604  slides within cylinder  606 , as previously described. Both cylinders  604 ,  606  have a plurality of apertures  608  for allowing insert material  552  to pass therethrough. As installation of fastener  600  is similar to that described for fastener  500 , a detailed description is foregone. However, sleeve  602  is arranged about capsule  636  before insertion of fastener  600  into workpieces  12 ,  14 . Cylinder  604  is slipped into cylinder  606  so as to have a combined length that is greater than thickness T of workpieces  12 ,  14 . The tightening of nut  646  causes cylinders  604 ,  606  to telescope together to properly accommodate workpiece thickness T. Insert material  552  passes through apertures  608  so as to integrally incorporate sleeve  602  after hardening. It should be understood that any of the aforementioned sleeves (e.g., single sleeve, fabric sleeve, etc.) may be used in place of sleeve  602 . Notably, sleeve  602  may also incorporate a plurality of projections (not shown) to facilitate perforation and tearing of capsule  636 . 
         [0054]    With reference now to  FIG. 18 , a fastener  700  is substantially similar to that described with respect to fastener  10 ; however, fastener  700  is shown as a self-drilling/self-tapping fastener. Fastener  700  includes a head  720  disposed at a first end  722 , a shank  724  extending from head  720  between first end  722  and a second end  726 , and a fluted or drilling/tapping portion  728  extending about shank  724  adjacent second end  726  and extending towards first end  722 . Notably, flute  728  has a minor thread diameter greater than the diameter of shank  724 . An underside  730  of head  720  includes at least one slot  734  extending from shank  724  to an outer diameter of head  720 . Shank  724  includes a channel  736  extending transversely to a longitudinal axis  738  of fastener  700  through the outer diameter of shank  724  so as to be in communication with a non-threaded portion  740  of shank  724 . A duct  742  extends from a flared portion  744  at head  720  and along longitudinal axis  738  until terminating at channel  736 . Channel  736  and duct  742  may be produced by any of several different machining processes including, for example, drilling, electrical discharge machining, laser cutting or water-jet cutting. 
         [0055]    Fastener  700  is arranged in a plurality of workpieces  712 ,  714  by driving flute  728  so as to protrude from workpieces  712 ,  714  by a distance such that only a portion of second end  722  (e.g., portion of shank  724  having flute  728 ) is arranged within workpieces  712 ,  714 . An at least partially liquefied structural insert material  752  is injected through duct  742  at flared portion  744  so as to fill duct  742  and channel  736 , as previously described. Insert material  752  is injected completely through duct  742  and channel  736  so as to be disposed about shank  724  at non-threaded portion  740  adjacent first end  722  of fastener  700  within a void area  754  defined between workpieces  712 ,  714  and shank  724  and between head  720  and an uppermost thread  756  arranged within workpiece  714 . To assure complete fill of void area  754 , slot  734  in head  720  is designed to allow trapped air and excess insert material  752  to escape. Complete filling of void area  754  is signaled when a small amount of insert material  752  is extruded from slot  734 . Notably, insert material  752  fills the threads that have been cut by flute  728  thereby reducing or eliminating stress concentrations present at the roots and tips of screw threads. 
         [0056]    Fastener  700  also incorporates an adapter  760  for ease in inserting insert material  752 , as shown in  FIG. 19 . Adapter  760  includes a narrow neck  762  that is threaded into or machined integral with head  720 . Adapter  760  has a duct  764  in communication with duct  742  of head  720  for injecting insert material  752 , such as with the aforementioned tool  60  or with a lever or air pressure system. As can be seen, the injecting device is secured to a threaded portion  766  of adapter  760  during injection. After creation of the joint, adapter  760  can remain attached to head  720  or can be removed (e.g., either by a hammer blow or nipped with cutting pliers). 
         [0057]    Fastener  700  also incorporates a backing plate  770 , as shown in  FIG. 20 . With the incorporation of backing plate  770 , shank  724  is made longer so as to allow flute  728  to extend beyond workpieces  712 ,  714  and lie within backing plate  770  so as to eliminate stress concentration present at the roots of screw threads, create additional joint clamping force, and yield a greater strength. 
         [0058]    With reference now to  FIGS. 21-24 , the concepts developed in the aforementioned embodiments can be applied in combination with fastener  700 . For example, fastener  700  may incorporate an insert material  752  contained within a capsule  772  ( FIG. 21 ) or incorporate both backing plate  770  and capsule  772  ( FIG. 22 ). 
         [0059]    Fastener  700  is also used in applications with workpieces  12 ,  14  having at least one pre-drilled aperture  16 ,  18  ( FIGS. 23 and 24 ). In these applications, a spacer  784  is included for self-centering fastener  700  and at least one sharp projection  786  is included for assisting in cutting open capsule  772 . It is contemplated that other optional features may be combined to obtain optimal results by application (e.g., “scarfed” surfaces; spacers between workpieces; sleeves). 
         [0060]    Referring now to  FIG. 25 , a fastener  800  is substantially similar to that described with respect to fastener  10 ; however, fastener  800  is shown as a rivet. Fastener  800  is shown assembled to workpieces  12 ,  14  through apertures  16 ,  18 . Fastener  800  includes a head  820  disposed at a first end  822 , a shank  824  extending from head  820  between first end  822  and a second end  826 , and a buck-tail  828  formed from shank  824  at second end  826  adjacent workpiece  14 . An underside  830  of head  820  includes at least one slot  834  extending from shank  824  to an outer diameter of head  820 . Shank  824  includes a channel  836  extending transversely to a longitudinal axis  838  of fastener  800  through the outer diameter of shank  824 . A duct  842  extends from a flared portion  844  at head  820  and along longitudinal axis  838  until terminating at channel  836 . Channel  836  and duct  842  may be produced by any of several different machining processes including, for example, drilling, electrical discharge machining, laser cutting or water-jet cutting. 
         [0061]    Fastener  800  is arranged in workpieces  12 ,  14  and shank  824  is compressed to form buck-tail  828 . An at least partially liquefied structural insert material  852  is injected through duct  842  at flared portion  844  so as to fill duct  842  and channel  836 , as previously described. Insert material  852  is injected completely through duct  842  and channel  836  so as to be disposed about shank  824  within a void area  854  defined between workpieces  12 ,  14  and shank  824  and between head  820  and buck-tail  828 . To assure complete fill of void area  854 , slot  834  in head  820  is designed to allow trapped air to escape. Complete filling of void area  854  is signaled when a small amount of insert material  852  is extruded from slot  834 . 
         [0062]    It is envisioned that other styles of fasteners, not specifically described herein, may successfully utilize many of the features described herein. For example, any workpiece needing fastening may benefit from the hybrid fastener having an insert material including a suspended, solid additive as described herein. In particular, the aforementioned inserts allow a workpiece to have a rougher or increased tolerance aperture for receiving the hybrid fastener, as the insert material effectively prevents twisting stresses and fractures. As such, various machining steps may be omitted, leading to reduced production costs and timing. Accordingly, the examples and embodiments described herein are exemplary and are not intended to be limiting in describing the full scope of apparatus, systems, compositions, materials, and methods of this invention. Features of each embodiment can be interchanged with other embodiments disclosed herein. Equivalent changes, modifications, variations in specific embodiments, apparatus, systems, compositions, materials and methods may be made within the scope of the present invention with substantially similar results. Such changes, modifications or variations are not to be regarded as a departure from the spirit and scope of the invention.