Abstract:
The present disclosure relates a rivet body, including a rivet head and a rivet shank, composed of a different material than a mandrel used for insertion into a workpiece(s), the mandrel including a mandrel shaft and a mandrel cap. The rivet body receives the mandrel shaft, including the mandrel cap, through the rivet shank. The mandrel shaft is received by the installation tool, which rotates the rivet body, and the mandrel cap locally deforms workpieces(s) through friction riveting to install the rivet body. During the friction riveting, the fast-rotating rivet body is pushed into the workpiece(s) causing local deformation/melting where the mandrel cap contacts the workpiece(s). The mandrel cap creates a cavity which progresses through an upper surface and a lower surface of the workpiece(s).

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to joining workpieces similar or dissimilar in material. More specifically, the present disclosure relates to reducing galvanic corrosion caused by electrochemical pathways created between the workpieces by mechanical fasteners. 
       BACKGROUND 
       [0002]    Using rivets as mechanical fasteners to join components (e.g., sheets of material) is widespread in many industries. In recent years, polymer based composite materials have been widely used within applications for purposes such as decreasing weight components and fasteners. 
         [0003]    Fast, easy-to-use rivets allow for relatively speedy assembly, consistent mechanical performance and streamlined installed appearance, making riveting a reliable and economical assembly method in areas such as assembly of bridge components and joining of automotive workpieces. Rivets are regularly used with similar dissimilar metals such as combinations amongst aluminum, stainless steel, and copper, among others. 
         [0004]    Before being installed, a rivet body (e.g., a blind rivet) consists of a rivet head and a smooth cylindrical rivet shank. The rivet body is set using a mandrel, driven through the rivet body. Upon installation, the rivet body is placed into an installation tool and then inserted into a punched or pre-drilled hole within the workpiece. Activating an installation tool pulls the mandrel into the rivet body and securely clamps the workpieces together. When the mandrel reaches a predetermined break-load, the mandrel breaks away and is removed from the set rivet body. A small portion of the mandrel remains in the bottom of the rivet shank to ensure the clamping force is retained in the joint. In final form, the rivet shank is deformed (known as upsetting), so that the rivet shank expands larger than the original rivet shank diameter, thus holding the rivet body in place. 
         [0005]    Using pre-drilled holes for riveting can cause future issues with the integrity of the joint. Problems associated with pre-drilled holes include issues such as, but not limited to, drilling with the wrong size drill bit, drilling of the intended pre-drilled hole center mark, and forgetting to deburr holes in the workpieces, which can create debris within the hole and thus the joint. Additionally, in situations where flush riveting is necessary, forgetting to provide a top and/or bottom dimple or making a machined-countersunk hole too shallow or too deep can cause future problems with the joint. Moreover, the need for pre-drilled holes can add significant cost and time to a manufacturing process. 
         [0006]    Additionally, the use of pre-drilled holes can increase possible galvanic corrosion of the workpieces. When dissimilar workpieces come into contact with one another in the presence of an electrolyte (e.g., water), an electrochemical process known as a galvanic reaction occurs. The galvanic reaction, known as galvanic corrosion, corrodes one metal at a faster rate and the other more slowly. The rate of corrosion depends upon a) the difference in electrical potential of the conductors, b) the conductivity of the electrolyte and c) the relative sizes of the contacting areas. 
         [0007]    Joining composite workpieces, especially an electrically conductive composite workpiece, with rivets require special efforts to minimize or prevent the galvanic corrosion. Often galvanic corrosion can be associated with noise generated by contact and sealing of the joined workpieces. The corrosion on the surface area where the rivet joins the workpieces can cause noise (e.g., a grinding or squeaking) and issues with sealing the workpieces. Additionally, in environments high in moisture content (e.g., air conditioners) galvanic corrosion can cause pre-mature break down at the joined location of the workpieces (i.e., at the rivet), causing possible failure of the joint. 
         [0008]    Previous attempts have been tried to reduce and/or avoid galvanic corrosion, where corrosion becomes a threat to the serviceability of the joint, for example, incorporating a barrier between the workpieces. Barriers may include painted added to one or more portions of the workpieces, or washers and/or gaskets inserted between the workpieces to prevent direct contact. Adding a protective coating (e.g., anodic oxide finish) to the rivet shank has also been used in an effort to prevent galvanic corrosion. 
         [0009]    Although barriers and coatings provide a corrosion-resistant finish, barriers and coatings increase the surface of the rivet shank because the barrier/coating is placed on the outer surface of the rivet body, which occupies more space than a base metal of the rivet body. An increased surface may create a potential issue of undesirably low machine tolerances or assembly tolerances. As an example, in the case of small holes threaded to accept a fastener (e.g., used when joining surfaces in aircraft or automotive industries), an outer surface coating may cause the rivet shank to bind within the threads of the hole. Moreover, when barriers and coatings are used, it is difficult to ensure that upon the insertion of the rivet the integrity of the barriers and coatings are maintained (e.g., not scratched). Scratches of the barriers and coatings may be created upon rivet insertion and form reactive sites for galvanic corrosion, thereby causing risks for noise and seal issues at the joint and premature failure of the joint. 
       SUMMARY 
       [0010]    Given the aforementioned deficiencies, the need exists for a rivet which can reduce/prevent galvanic corrosion between two joined workpieces. The rivet would also create a cavity within the workpieces as installation occurs, without the use of a pre-drilled hole. 
         [0011]    The present technology relates to a rivet assembly including a rivet body composed of a material and a mandrel composed of a different material than the rivet body. 
         [0012]    The rivet body includes a rivet head and a rivet shank, both composed of a material configured to reduce and/or eliminate galvanic corrosion between the workpiece(s) and the rivet body. In one aspect, when the rivet body and at least one of the workpieces are conductive, the rivet body is composed of a material that reduces electrochemical pathways between the workpieces and the rivet body. However, when the rivet body is composed of a non-conductive material, electrochemical pathways can be eliminated between the rivet body and the conductive workpiece. Furthermore, the non-conductive the rivet body is configured to have a glass transition or melt transition temperature higher than that of the glass transition or melting transition of the workpiece(s). 
         [0013]    The mandrel includes a mandrel shaft and a mandrel cap, each composed of a conductive material such as metal. The mandrel body allows connection of the mandrel body to an installation tool for insertion of the mandrel body and rivet body into one or more workpieces. 
         [0014]    The rivet body receives a mandrel shaft through the rivet shank. The mandrel shaft includes a mandrel cap positioned in connection with the rivet shank. The mandrel shaft is received by the installation tool and the mandrel cap locally deforms the workpieces(s) through friction riveting to install the rivet body. During the friction riveting, the mandrel cap creates a cavity which progresses through an upper surface and a lower surface of the workpiece(s). 
         [0015]    In some embodiments, the rivet shank includes one or more ridges, each having a different size than the rivet shank. The ridge(s) is configured to interlock with one workpiece or multiple workpieces. In some embodiments, the ridge(s) is composed of a material being the same or similar to that of the rivet shank. In alternate embodiments, the ridge(s) comprises a material being different in composition than the material of the rivet shank. 
         [0016]    In some embodiments, rivet body further includes a washer in connection with the rivet head. The washer is configured to contact an upper surface of the workpiece to promote sealing. 
         [0017]    The present technology also relates to a method of using the rivet body to join the workpiece(s) without the need of a pre-drilled hole. The method involves using friction riveting, which induces heat generated from the installation tool applying torque (e.g., a normal rotational force) to the rivet body. The fast-rotating rivet body is pushed into the workpiece(s) due to local deformation/melting where the mandrel cap contacts the workpiece(s). The use of friction riveting reduces and/or eliminates cracking of workpieces, e.g., composite workpiece(s), which can be brittle. 
         [0018]    Other aspects of the present technology will be in part apparent and in part pointed out hereinafter. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  illustrates a schematic side view of an exemplary embodiment of a rivet including a vertical cross-section callout. 
           [0020]      FIG. 2  shows the arrangement of  FIG. 1  as used to join two workpieces together. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    As required, detailed embodiments of the present disclosure are disclosed herein. The disclosed embodiments are merely examples that may be embodied in various and alternative forms, and combinations thereof. As used herein, for example, exemplary, and similar terms, refer expansively to embodiments that serve as an illustration, specimen, model or pattern. 
         [0022]    The figures are not necessarily to scale and some features may be exaggerated or minimized, such as to show details of particular components. In some instances, well-known components, systems, materials or methods have not been described in detail in order to avoid obscuring the present disclosure. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure. 
         [0023]    In some instances, well-known components, systems, materials or methods have not been described in detail in order to avoid obscuring the present disclosure. Specific structural and functional details disclosed herein are therefore not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present disclosure. 
         [0024]    Phrasing such as ‘configured to’ perform a function, including in the claims, can include any or all of being sized, shaped, positioned in the arrangement, and comprising material to perform the function. 
       I. GENERAL OVERVIEW OF HYBRID RIVET—FIG.  1   
       [0025]    Turning to the figures, and more specifically the first figure,  FIG. 1  illustrates a hybrid rivet assembly  100  (hereinafter rivet assembly  100 ), including a rivet body made of a material different than a mandrel body. 
         [0026]    The rivet body includes a rivet head  140  connected to a rivet shank  150 . The rivet head  140  is configured such that a tool (e.g., an installation tool like that shown in  FIG. 2 ) can engage the hybrid rivet assembly  100  at or near an upper surface  142  of the rivet head  140  and apply torque to the rivet head  140  and the rivet shank  150 , causing the hybrid rivet assembly  100  to push through workpieces to form a joint. 
         [0027]    The rivet head  140  can have any of a number of shapes, depending on a particular use. The rivet head  140  can include a countersunk head, a large flange, or a dome head (low-profile or otherwise), among others. For example, the rivet head  140  can be dome-shaped with a diameter sized to create a desired retention strength of the joint, which is a function of an overhang distance between an outer diameter of the rivet shank  150  and an outer diameter of the rivet head  140 . 
         [0028]    The rivet shank  150  is attached to a lower surface  144  of the rivet head  140 , opposite the upper surface  142  of the rivet head  140 . 
         [0029]    The rivet shank  150  includes a diameter smaller than that of the rivet head  140 . Specifically, the rivet shank  150  has a diameter that promotes relatively easy puncturing of a surface and passing through the surface of the workpieces. 
         [0030]    In some embodiments, the rivet head  140  and/or the rivet shank  150  may include a non-conductive material. Using a non-conductive material eliminates electrochemical pathways that lead to galvanic corrosion. 
         [0031]    The material of the rivet head  140  and/or the rivet shank  150  should be such that a phase transformation (e.g., glass transition of a polymer composite) of the hybrid rivet assembly  100  occurs at a temperature higher than a phase transformation (e.g., glass transition or melting transition) of the workpieces (e.g., polymer or metal). Stated another way, the rivet head  140  and/or the rivet shank  150  have a glass transition or melt transition temperature higher than that of the glass transition or melting transition of the workpieces. For example, the rivet head  140  and/or the rivet shank  150  may include polymers such as polyvinyl chloride (PVC), polyethylene, silicone, polyamide, polyether ether ketone (PEEK), polyetherimide (PEI), or the like, having phase transformation temperatures higher than the workpieces that the hybrid rivet assembly  100  would be used to join. 
         [0032]    Where the rivet head  140  and/or the rivet shank  150  comprise a non-conductive material, the rivet head  140  and/or the rivet shank  150  may include reinforced fibres (e.g., fibre-reinforced polymer). The fibres are of a material that can be incorporated into the material of the rivet head  140  and/or the rivet shank  150  in a two-dimensional or three-dimensional matrix using known textile processing techniques such as weaving, knitting, braiding, and stitching, among others. For example, the fibres can include materials such as, but not limited to, glass, carbon, basalt, aramid, paper, and wood. 
         [0033]    In other embodiments, the rivet head  140  and/or the rivet shank  150  include a conductive material that reduces electrochemical pathways between the workpieces and the rivet head  140  and/or rivet shank  150 . For example, the rivet head  140  and/or the rivet shank  150  may include a material that has a similar electrode potential as at least one of the workpieces. 
         [0034]    In some embodiments, it is desirable to increase interlock of the hybrid rivet assembly  100  with the workpieces. 
         [0035]    In some embodiments, increased interlock with workpieces is accomplished through the rivet shank  150  including one or more ridges or threads  160 . In some implementations, the ridge(s) is separate from and connected to the rivet shank  150 , and in some implementations they are unitary. The ridge(s)  160  facilitates and assists with the rivet shank  150  interlocking with the workpieces during entry. The interlocking of the rivet shank  150  secures the positioning of the hybrid rivet assembly  100  within the workpieces. Secure positioning of the hybrid rivet assembly  100  can reduce unnecessary movement thus reducing air and/or moisture that is introduced into the joint, which may contribute to galvanic corrosion. Additionally, secure positioning of the hybrid rivet assembly  100  can reduce noise caused by damage to the surface area where galvanic corrosion has occurred. Moreover, the workpieces exhibit different thermo-mechanical properties because of their dissimilar composition. In particular, the coefficient of thermal expansion and deformation (creep) properties correlate to dimensional changes based on exposure temperature and forces of the workpieces. Interlocking the workpieces may provide a method for counteracting these dimensional changes and property differences, thereby insuring longer life to the joint. 
         [0036]    The ridge(s)  160  can have a size slightly larger diameter than a primary, or shaft, diameter of the rivet shank  150 . Alternately, one or more of the ridge(s)  160  can have a smaller diameter or a different shape than the shaft of the rivet shank  150 . A difference in diameter between the rivet shank  150  and the ridge(s)  160  allows the ridge(s)  160  to interlock with the workpieces, as described in association with  FIG. 2 . 
         [0037]    The material of the ridge(s)  160  can be manufactured as part of the rivet shank  150 , creating a single unit shank and ridge combination. For example, the material of the ridge(s)  160  can be the same or similar material as that of the rivet shank  150 . Specifically, the material of the ridge(s)  160  may be the same polymer materials used within the rivet shank  150 . Additionally, the ridge(s) may have other similar characteristics as the rivet shank  150  including, a similar melting point, a similar rigidness, among others. 
         [0038]    Alternately, the ridges(s)  160  can be attached to the rivet shank  150  in a subsequent process (e.g., attached as a sleeve pulled over the rivet shank  150 ) prior to inserting the hybrid rivet assembly  100  into the workpieces. Stated another way, the material of the ridge(s)  160  may be a different material than the material used within the rivet shank  150 . However, where the material of the ridge(s)  160  and the rivet shank  150  differ, the material of the ridge(s)  160  should have similar material properties (e.g., hardness, thermal conductivity, and the like) as the material of the rivet shank  150 . 
         [0039]    Although the ridge(s)  160  are described as having a diameter and a circumference, implying a circular cross-section, rivet head  140 , the rivet shank  150 , and/or the ridge(s)  160  may include other shapes such as, but not limited to, triangular, oval, hexagonal, and the like. For example, using shaped ridge(s)  160  may be beneficial in applications, for example, where interlock between the hybrid rivet assembly  100  and joined workpieces are desired or the hybrid rivet assembly  100  is inserted without the use of a rotational installation tool. When a shaped cross section is not approximately circular, a hole formed by the mandrel cap  130 /mandrel shaft  120  will likely be larger than the shank creating a risk for joint failure, tolerance issues, noise, seal, among others. In situations where the rivet shank  150 , and/or the ridge(s)  160  are non-circular, the mandrel cap  130  may be oversized to ensure, upon removal for the mandrel shaft  120  during upsetting (mushrooming) of the rivet shank  150 , the mandrel cap  130  is larger than the formed hole. 
         [0040]    In some embodiments, increased interlock with workpieces is accomplished through one or more washer(s)  170  in contact with the lower surface  144  of the rivet head  140 . The washer  170  is positioned such that one side of the washer  170  is in contact with the lower surface  144  of the rivet head  140  and the other side of the washer  170  is in contact with a surface of a workpiece, upon installation, as seen in  FIG. 2 . 
         [0041]    The washer  170  can be used to secure the bond between the rivet head  140  and a workpiece, thus preventing a gap from forming between the rivet head  140  and the workpiece. In addition to filling the gap between the rivet head  140  and the workpiece, the washer  170  may also function as a buffer to prevent electromechanical contact between the rivet head  140  material, typically metal, and the workpiece, which may cause galvanic corrosion over time. 
         [0042]    The washer  170  may comprise an adhesive (fully or partially cured) or other adhering material used to bond the washer  170  to bottom side of the rivet head  140 . The washer  170  can include, for example, fully cured or partially cured epoxy, urethane, acrylate resins, foamed tape, sprayed on pressure sensitive adhesive layers, and the like. 
         [0043]    The mandrel includes a mandrel shaft  120  connected to a mandrel cap  130 . The mandrel shaft  120  may pass through the center of the rivet body. As seen in the callout of  FIG. 1 , the mandrel shaft  120  extends through the length of the rivet body and connects to the mandrel cap  130 , located on a bottom surface of the mandrel shaft  120 . In practice, the mandrel shaft  120  and the mandrel cap  130  can be formed as one piece. 
         [0044]    The mandrel shaft  120  is a length longer than the rivet body, thus allowing the mandrel shaft  120  to slide up and down the length of the rivet body (denoted by the two-way arrow). As described below, when the rivet body is ready for use, the mandrel shaft  120  is pulled drawing the mandrel cap  130  to the bottom of the rivet shank  150 . Specifically, the mandrel cap  130  is in contact with a bottom surface of the rivet shank  150 , opposite the rivet head  140  (seen in step  200  of  FIG. 2 ). 
         [0045]    In further embodiments, a portion of the mandrel shaft  120  may break away from mandrel cap  130  at a pre-determined break load. The break load is designed to prevent too much force being developed, which may damage the workpieces being joined. Typically, the break load is greater than a force used to join workpieces (e.g., a clamping force). A break load less than the clamping force may compromise joint integrity. 
         [0046]    The mandrel shaft  120  is of a diameter that allows passage through the rivet head  140  and the rivet shank  150 . Specifically, the diameter of the mandrel shaft  120  is smaller than the diameter of the rivet head  140  and the rivet shank  150 . 
         [0047]    The mandrel cap  130  is shaped to attach to the mandrel shaft  120 . As stated above, the mandrel shaft  120  and the mandrel cap can be formed as one piece. Additionally, the mandrel cap  130  is of a diameter that it does not fully pass through the rivet shank  150  upon installation of the rivet body. Said another way, the mandrel cap  130  has a diameter larger than that of the mandrel shaft  120  and larger than that of the rivet shank  150 , so as to allow upsetting (mushrooming) of the rivet body. 
         [0048]    The material of the mandrel shaft  120  and/or the mandrel cap  130  should ensure workpieces are secured during clamping and constrained during servicing of the joint. Additionally, the mandrel shaft  120  and/or the mandrel cap  130  may be made of a material that is stronger than the material of the workpieces to be joined. Strength of the mandrel shaft  120  and the mandrel cap  130  can be evaluated using any number of material mechanics, such as but not limited to yield strength and ultimate strength. A stronger material allows the mandrel shaft  120  and the mandrel cap  130  to maintain their geometric integrity while fully penetrating the workpieces during a joining process, described below. For example, the mandrel can comprise materials including, but not limited to, steel, stainless steel, carbon steel, copper, aluminum, brass, and the like. 
       II. PROCESS FOR FRICTION RIVETING—FIG.  2   
       [0049]      FIG. 2  illustrates the process of joining a first workpiece  210  and a second workpiece  220  using the hybrid rivet assembly  100 . The first workpiece  210  and the second workpiece  220  may be similar in material structure. In one embodiment, the first workpiece  210  and the second workpiece  220  both comprise a polymer composite material. In another embodiment, the first workpiece  210  has a different material than the second workpiece  220 . For example, the first workpiece  210  may be a composite material, while the second workpiece  220  may be an aluminium alloy. 
         [0050]    In some embodiments, one or more of the workpieces  210 ,  220  may include but are not limited to polymers such as (functionalized) polycarbonate, polyolefin (e.g., polyethylene and polypropylene), polyamide (e.g., nylons), polyacrylate, and acrylonitrile butadiene styrene. 
         [0051]    In other embodiments, one or more of the workpieces  210 ,  220  may include, but are not limited, to composites such as reinforced plastics where the plastics may include any of the exemplary polymers listed above, and the reinforcement may include one or more of the following clay, glass, carbon, polymer in the form of particulate, (nano, short, or long) fibres, (nano-sized or micron-sized) platelets, whiskers, among others. 
         [0052]    At least one of the workpieces  210 ,  220  can include synthetic, or inorganic, molecules. While use of so-called biopolymers (or, green polymers) is increasing, petroleum based polymers are still much more common. Material of one or both of the workpieces  210 ,  220  may also include recycled material, such as a polybutylene terephthalate (PBT) polymer, which is about eighty-five percent post-consumer polyethylene terephthalate (PET). In one embodiment one or both of the workpieces  210 ,  220  includes some sort of plastic. In one embodiment, the material includes a thermo-plastic. 
         [0053]    In one embodiment one or both of the workpieces  210 ,  220  includes a composite. For example, in one embodiment one or both of the workpieces  210 ,  220  includes a fibre-reinforced polymer (FRP) composite, such as a carbon-fibre-reinforced polymer (CFRP), or a glass-fibre-reinforced polymer (GFRP). The composite may be a fibreglass composite, for instance. In one embodiment, the FRP composite is a hybrid plastic-metal composite. The material in some implementations includes a polyamide-grade polymer, which can be referred to generally as a polyamide. Material of one or both of the workpieces  210 ,  220  may also include includes polyvinyl chloride (PVC). In one embodiment, the material of one or both of the workpieces  210 ,  220  includes acrylonitrile-butadiene-styrene (ABS). In one embodiment, the material of one or both of the workpieces  210 ,  220  includes a polycarbonate (PC). Material of one or both of the workpieces may also comprise a type of resin. Example resins include a fibreglass polypropylene (PP) resin, a PC/PBT resin, and a PC/ABS resin. 
         [0054]    The first workpiece  210  includes an upper surface  212  and a lower surface  214 , and the second workpiece  220  includes an upper surface  222  and a lower surface  224 . The lower surface  214  of the first workpiece  210  and the upper surface  222  of the second workpiece contact upon joining of the workpieces  210 ,  220  and are securely held with the hybrid rivet assembly  100 . 
         [0055]    As seen at step  200  in  FIG. 2 , to join the workpieces  210 ,  220 , the hybrid rivet assembly  100  is first placed into an installation tool  230 . Activating the installation tool  230  pulls the mandrel shaft  120 , drawing the mandrel cap  130  into the rivet shank  150  of the hybrid rivet assembly  100 . Specifically, the mandrel cap  130  is in contact with a bottom surface of the rivet shank  150 . When properly positioned, the mandrel cap  130  has one end attached to the mandrel shaft  120  and another end approximately near the upper surface  212  of the first workpiece  210 . 
         [0056]    At step  200 , the installation tool  230  provides torque that causes the mandrel cap  130  and the rivet shank  150  to penetrate the workpieces  210 ,  220 , creating a cavity  240 . The cavity  240  is formed by the mandrel shaft  120 , including the mandrel cap  130 , which penetrates each workpiece  210 ,  220  to allow entry of the rivet shank  150 . As seen, the cavity  240  becomes the same shape and size as the rivet shank  150 . As stated above, to allow penetration of the workpieces  210 ,  220 , the mandrel shaft  120  and the mandrel cap  130  should be a material that is stronger than each workpieces  210 ,  220  at any temperature reached during the insertion process. 
         [0057]    During friction riveting, the hybrid rivet assembly  100  is brought into contact with the upper surface  212  of the first workpiece  210  by the installation tool  230 , which applies an amount of torque, to the hybrid rivet assembly  100 , which is dependent on the composition of the workpieces  210 ,  220 . Specifically a normal force (e.g., a feed rate of approximately 120 to 900 millimeters per minute) and/or rotational force (e.g., a spindle speed of approximately 9,000 revolutions per minute) are applied to the hybrid rivet assembly  100 . Frictional heating of the material in the first workpiece  210  is generated when the hybrid rivet assembly  100  rotates when being inserted into the first workpiece  210  by the installation tool  230 . When the amount of heat generated becomes equal or greater than the softening (e.g., glass or melting transition temperature) of the first workpiece  210 , the material of the first workpiece  210  soften and further deforms. Local softening and/or melting allows the hybrid rivet assembly  100  to penetrate into the first workpiece  210  under the torque applied by the installation tool  230 , without the need for a pre-drilled hole. A similar friction riveting process occurs with the second workpiece  220 . The material of the second workpiece  220  is locally melted and/or deformed allowing the hybrid rivet assembly  100  to penetrate into the second workpiece  220 , thus continuing the cavity  240 . In some embodiments, the rivet shank  150  may interlock with the second workpiece  220  to insure that the hybrid rivet assembly  100  maintains compression on both of the workpiece  210 ,  220 . Interlocking with the second workpiece  220  would provide a result similar to when working with a screw (e.g., a drywall anchor). 
         [0058]    Friction riveting allows secure positioning of the hybrid rivet assembly  100 , within the workpieces  210 ,  220 , which can reduce unnecessary movement of the hybrid rivet assembly  100 , as seen with pre-drilled holes. When unnecessary movement is reduced, the effects of galvanic corrosion is also reduced, because air and/or electrolytes (e.g., water) are not introduced into the joint. Specifically, the hybrid rivet assembly  100  can reduce unnecessary moisture that is introduced when joining workpieces  210 ,  220 . 
         [0059]    Finally, as seen in step  400 , the mandrel shaft  120  reaches a predetermined break-load, with a portion of the mandrel shaft  120  breaking away and being removed from the set rivet assembly  100 . In some embodiments, the mandrel cap  130  remains encapsulated at or near the lower surface  224  of the second workpiece  220 . 
         [0060]    It is understood by one of skill in the art that the above process can be used to install the hybrid rivet assembly  100  into one workpieces (e.g., the first workpiece  210 ) or multiple workpieces (e.g., the first workpiece  210 , the second workpiece  220 , and/or a third workpiece). The hybrid rivet assembly  100  can be used to sure the multiple workpieces together. 
       III. SELECTED FEATURES 
       [0061]    Many features of the present technology are described herein above. The present section presents in summary some selected features of the present technology. It is to be understood that the present section highlights only a few of the many features of the technology and the following paragraphs are not meant to be limiting. 
         [0062]    The technology reduces galvanic corrosion formed between workpieces and the rivet. Reduction of galvanic corrosion increases long-term performance of the joined materials, and reduces audible sounds associated with material affected by galvanic corrosion. 
         [0063]    The technology also eliminates the need for pre-drilled holes within composite material workpieces, specifically carbon fibre composite workpieces. Within the technology, a cavity is formed within the workpieces as the rivet is inserted, thus eliminating the need for pre-drilled holes to receive the rivet. The elimination of pre-drilled holes can prevent problems such as reworking to re-tap a pre-drilled hole to receive the original rivet or reworking a workpiece to fabricate a larger hole to receive a larger rivet. 
         [0064]    The technology also reduces the weight of the rivet. Within the technology, the rivet shank is manufactured from a polymer, or similar material, which has a lower weight than traditional metal-based shanks. Reducing the weight of the rivet can allow use of the rivet in situations of particular weight requirement (e.g., aircraft and automotive industries). 
       IV. CONCLUSION 
       [0065]    Various embodiments of the present disclosure are disclosed herein. The disclosed embodiments are merely examples that may be embodied in various and alternative forms, and combinations thereof. 
         [0066]    The above-described embodiments are merely exemplary illustrations of implementations set forth for a clear understanding of the principles of the disclosure. 
         [0067]    Variations, modifications, and combinations may be made to the above-described embodiments without departing from the scope of the claims. All such variations, modifications, and combinations are included herein by the scope of this disclosure and the following claims.