CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 13/299,914, filed Nov. 18, 2011, which application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/415,737, filed Nov. 19, 2010, the disclosure of each of which is incorporated in this disclosure in its entirety by this reference. 
     
    
     FIELD 
       [0002]    Embodiments of the present disclosure relate generally to earth-boring tools and, more specifically, to earth-boring tools including replaceable cutting structures. 
       BACKGROUND 
       [0003]    Earth-boring tools for forming wellbores in subterranean earth formations may include a plurality of cutting elements secured to a body. For example, fixed-cutter earth-boring rotary drill bits (also referred to as “drag bits”) include a plurality of cutting elements that are fixedly attached to a bit body of the drill bit, conventionally in pockets formed in blades and other exterior portions of the bit body. Rolling cone earth-boring drill bits include a plurality of cutters attached to bearing pins on legs depending from a bit body. The cutters may include cutting elements (sometimes called “teeth”) milled or otherwise formed on the cutters, which may include hardfacing on the outer surfaces of the cutting elements, or the cutters may include cutting elements (sometimes called “inserts”) attached to the cutters, conventionally in pockets formed in the cutters. Other bits might include impregnated bits that typically comprise a body having a face comprising a superabrasive impregnated material, conventionally a natural or synthetic diamond grit or thermally stable diamond elements dispersed in a matrix of surrounding body material or segments of matrix material brazed to the bit body. 
         [0004]    The cutting elements used in such earth-boring tools often include polycrystalline diamond cutters (often referred to as “PDCs”), which are cutting elements that include a polycrystalline diamond (PCD) material. Such polycrystalline diamond cutting elements are formed by sintering and bonding together relatively small diamond grains or crystals under conditions of high temperature and high pressure in the presence of a catalyst (such as, for example, cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high-temperature/high-pressure (or “HTHP”) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) such as, for example, cobalt-cemented tungsten carbide. In such instances, the cobalt (or other catalyst material) in the cutting element substrate may be drawn into the diamond grains or crystals during sintering and serve as a catalyst material for forming a diamond table from the diamond grains or crystals. In other methods, powdered catalyst material may be mixed with the diamond grains or crystals prior to sintering the grains or crystals together in an HTHP process. 
         [0005]    Exposed portions of cutting elements, such as, for example, diamond tables, portions of substrates, hardfacing disposed on the outer surfaces of cutting elements, and exposed surfaces of the earth-boring tool, for example, blade surfaces and fluid courses and junk slot surfaces of a drag bit or the cutters of a rolling cone bit, may be subject to failure modes, such as, for example, erosion, fracture, spalling, and diamond table delamination due to abrasive wear, impact forces, and vibration during drilling operations from contact with the formation being drilled. Some portions of the earth-boring tool may be more susceptible to such failure modes, and localized wear and localized impact damage may cause the earth-boring tool to fail prematurely while leaving other portions of the earth-boring tool in a usable condition. For example, cutting elements and the blades to which they are attached may be more susceptible to failure at the shoulder region of a face of the bit body as compared to the central portion of the face of the bit body or gage region of the bit body. In such instances, an annular shaped groove may wear into the face of the bit body at the shoulder region, a phenomenon sometimes referred to as “ring out” or “pocket damage.” Further, cutting elements and the blades to which they are attached may be susceptible to failure at a central, core region of a drill bit located on the face thereof, resulting in “core out.” Other earth-boring tools may similarly exhibit localized wear in certain portions of the earth-boring tools. 
       BRIEF SUMMARY 
       [0006]    In some embodiments, the present disclosure includes earth-boring tools comprising a body and one or more replaceable cutting structures attached to the body at a face region of the body. Each replaceable cutting structure comprises an attachment member and a cutting portion configured to engage an underlying earth formation. 
         [0007]    In additional embodiments, the present disclosure includes an earth-boring tool, comprising a body and one or more replaceable cutting structures. The body comprises a face comprising a shoulder region adjacent a gage region and a plurality of blades extending over the face through the shoulder region to, and including, the gage region. Each replaceable cutting structure comprises an attachment member, the attachment member comprising at least one blade segment attached to a blade of the plurality of blades at the shoulder region, and one or more cutting elements attached to the at least one blade segment. 
         [0008]    In further embodiments, the present disclosure includes methods of forming an earth-boring tool comprising attaching one or more cutting elements to a replaceable cutting structure; positioning the replaceable cutting structure proximate a region of a body of an earth-boring tool that is susceptible to at least one of localized wear and localized impact damage; and attaching the replaceable cutting structure to the body. 
         [0009]    In additional embodiments, the present disclosure includes methods of forming an earth-boring tool comprising attaching one or more cutting elements to a replaceable cutting structure; positioning the replaceable cutting structure proximate a region of a body of an earth-boring tool that is susceptible to at least one of localized wear and impact damage; and attaching the replaceable cutting structure to the body at the region that is susceptible to localized wear. 
         [0010]    In still further embodiments, the present disclosure includes methods of forming an earth-boring tool comprising positioning a replaceable cutting structure in a mold configured to form a body of an earth-boring tool at a portion of the mold configured to form a region of the body that is susceptible to localized wear; and forming the body around the replaceable cutting structure within the mold. 
         [0011]    In additional embodiments, the present disclosure includes methods of repairing an earth-boring tool comprising bringing a replaceable cutting structure proximate at least one portion of a body of an earth-boring tool exhibiting at least one of localized wear and localized impact damage, the replaceable cutting structure comprising an attachment member exhibiting a geometry cooperative with the at least one portion and a cutting portion configured to engage an underlying earth formation; and attaching the replaceable cutting structure to the earth-boring tool at the at least one portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present disclosure, various features and advantages of embodiments of this disclosure may be more readily ascertained from the following description of embodiments of the disclosure when read in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  illustrates an overhead view of an earth-boring tool including a replaceable cutting structure in accordance with an embodiment of the present disclosure; 
           [0014]      FIG. 2  illustrates a perspective view of the earth-boring tool including the replaceable cutting structure shown in  FIG. 1 ; 
           [0015]      FIG. 3  illustrates a perspective view of a replaceable cutting structure in accordance with an embodiment of the present disclosure; 
           [0016]      FIG. 4  illustrates a perspective view of an earth-boring tool to which a replaceable cutting structure in accordance with one or more embodiments of the disclosure may be attached; 
           [0017]      FIG. 5  illustrates a perspective view of a plurality of replaceable cutting structures in accordance with an embodiment of the disclosure; 
           [0018]      FIG. 6  illustrates a perspective view of an earth-boring tool to which a plurality of replaceable cutting structures in accordance with one or more embodiments of the disclosure may be attached; 
           [0019]      FIG. 7  illustrates a perspective view of an earth-boring tool including a replaceable cutting structure in accordance with an embodiment of the present disclosure; 
           [0020]      FIG. 8  illustrates a perspective view of an earth-boring tool including a replaceable cutting structure in accordance with an embodiment of the present disclosure; and 
           [0021]      FIG. 9  illustrates a partial perspective view of an earth-boring tool including a replaceable cutting structure in accordance with an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Some of the illustrations presented herein are not meant to be actual views of any particular earth-boring tool, cutting element, or replaceable cutting structure, but are merely idealized representations that are employed to describe embodiments of the present disclosure. Additionally, elements common between figures may retain the same or similar numerical designation. 
         [0023]    Although some embodiments of the present disclosure are depicted as being used and employed in earth-boring rotary drill bits, such as fixed-cutter rotary drill bits, persons of ordinary skill in the art will understand that replaceable cutting structures in accordance with the present disclosure may be employed with any earth-boring tool. Accordingly, the terms “earth-boring tool” and “earth-boring drill bit,” as used herein, mean and include any type of bit or tool used for drilling during the formation or enlargement of a wellbore in a subterranean formation and include, for example, rolling cone bits, core bits, eccentric bits, bicenter bits, reamers, expandable reamers, mills, drag bits, hybrid bits, impregnated bits, and other drilling bits and tools known in the art. 
         [0024]    As used herein, the teen “cutting element” means and includes any structure configured to engage an earth formation including, by way of example and without limitation, tungsten carbide inserts, polycrystalline diamond compact (PDC) cutting elements and inserts, thermally stable polycrystalline (TSP) diamond compact cutting elements, natural diamonds, superabrasive-impregnated elements, and other cutting element materials and structures as known in the art. In addition, cutting elements and cutting faces thereof may include any geometric shape or configuration, such as, for example, cylindrical, dome-shaped, tombstone, chisel-shaped, pyramids, and other shapes and configurations as known in the art. 
         [0025]    Referring to  FIGS. 1 and 2 , an earth-boring tool  10  including a replaceable cutting structure  12  in accordance with the present disclosure is shown. The earth-boring tool  10  includes a body  13  comprising a face  14 , a gage region  16 , and a shoulder region  18  at a radially outer portion of the face  14  proximate the gage region  16 . A plurality of circumferentially spaced blades  20  extends longitudinally from the face  14  over the shoulder region  18  and along the gage region  16 . A plurality of junk slots  22  also extends longitudinally from the face  14  over the shoulder region  18  and along the gage region  16  in the circumferential spaces between adjacent blades  20 . A plurality of cutting elements  24  is attached to the body  13  on the blades  20  thereof. The cutting elements  24  may be at least partially disposed in recesses, which may also be characterized as “pockets,” formed in the blades  20 . 
         [0026]    A replaceable cutting structure  12  may be attached to the earth-boring tool  10  at the shoulder region  18 . In other embodiments, a replaceable cutting structure may be attached to an earth-boring tool at other locations such as, for example, on the face of a rotary drag bit, on the face of an impregnated bit, on a supporting ring of cutting elements of a roller cone on a rolling cone drill bit. In further embodiments, a replaceable cutting structure may be attached to an earth-boring tool on a formation-engaging portion of a reamer tool, on a region of a hybrid bit susceptible to at least one of localized wear and localized impact damage, or on any other portion of an earth-boring tool that is susceptible to at least one of localized wear and localized impact damage as a result of drilling. 
         [0027]    As shown in  FIG. 3 , a replaceable cutting structure  12  may comprise an attachment member  26  in the form of a plurality of blade segments  23  and a cutting portion configured to engage an underlying earth formation. The cutting portion may comprise, for example, a plurality of cutting elements  24 , as shown in  FIG. 3 , or a superabrasive material disposed in a matrix material, such as, for example, a diamond material in a metal matrix. The blade segments  23  may comprise interconnected portions of an annular member generally conforming to an exterior shape of a body  13  of an earth-boring tool  10  at a shoulder region  18  (see  FIG. 4 ). Thus, portions of blades  20  in the form of blade segments  23  and of intervening junk slots  22  may be formed in the attachment member  26 , enabling the attachment member  26  to provide an at least substantially smooth transition between adjacent exterior surfaces of the earth-boring tool  10  and the replaceable cutting structure  12 . The replaceable cutting structure  12  may be configured to attach to a body  13  of an earth-boring tool  10 , for example, on the face  14  thereof. The attachment member  26  may comprise planar surfaces at right angles to one another at the inner and lower surfaces of the attachment member  26 , the planar surfaces being configured to abut against and attach to cooperative surfaces on the body  13  of an earth-boring tool  10 . In other embodiments, the inner and lower surfaces of attachment member  26 , and the cooperative surfaces of the body  13  may not be planes at right angles to one another, but may be curved, angled, notched, or may have other cooperative interface features, such as, for example, recesses or protrusions, disposed thereon. In broad terms, the attachment member  26  may be said to be configured for disposition in one or more cooperatively configured seats on the body  13 . The cutting elements  24  are attached to the blade segments  23  of the attachment member  26 . The cutting elements  24  may be disposed in multiple rows along the blade segments  23  of the attachment member  26 . In other embodiments, the cutting elements  24  may be disposed in a single row at the rotationally leading end of the blade segments  23  or, alternatively, a single cutting element  24  may be disposed on each blade segment  23  of the attachment member  26 . 
         [0028]    The attachment member  26  may comprise at least one cutting element accommodation recess in an underside thereof. At least one cutting element  24  already attached to an earth-boring tool  10  (see  FIG. 4 ) at a location of intended mounting of the attachment member  26  may protrude from a surface of the body  13  of the earth-boring tool  10  in an area of seat  28  and, absent formation of at least one corresponding cutting element accommodation recess, interfere with attachment of the attachment member  26  to the body  13  of the earth-boring tool  10 . Each cutting element accommodation recess may enable a corresponding cutting element  24  already mounted to the body  13  to be partially disposed therein while enabling attachment of the attachment member  26  to the body  13  of the earth-boring tool  10  with minimal cutting element  24  interference. 
         [0029]    The size of the replaceable cutting structure  12  may correspond to a predicted radially and circumferentially extending region of localized wear occurring on a shoulder region  18  or other region of a body  13  of an earth-boring tool  10  as a result of use of the earth-boring tool  10  in a drilling or reaming operation. The region of localized wear may be predicted using computer modeling, such as, for example, finite element analysis, or by observation of localized wear in the field. Thus, the replaceable cutting structure  12  may be sized to enable easy replacement of a region of a body  13  of an earth-boring tool  10  most susceptible to localized wear and, therefore, most likely to cause premature failure of the earth-boring tool  10 . In addition, the replaceable cutting structure  12  may enable replacement of a worn portion of an earth-boring tool with a replaceable cutting structure  12  having increased wear resistance, impact strength, fracture toughness, or any combination of these. 
         [0030]    Referring again to  FIG. 4 , an earth-boring tool  10  to which a replaceable cutting structure  12  (see  FIG. 3 ) may be attached is shown. The earth-boring tool  10  includes a seat  28  formed in the shoulder region  18  of the body  13  of the earth-boring tool  10 . Surfaces defining the seat  28  may be configured correspondingly to abut against and attach to a replaceable cutting structure  12  (see  FIG. 3 ). Thus, the seat  28  may comprise planar surfaces at right angles to one another. In other embodiments, the surfaces defining the seat  28  and the adjacent surfaces of the replaceable cutting structure  12  for mounting thereon may not be planes at right angles to one another, but may be curved, angled, notched, or may have interface features, such as, for example, recesses or protrusions, disposed thereon. The material of the body  13  of the earth-boring tool  10  may be machinable, enabling the surfaces that define the seat  28  to be formed in the body  13 . For example, if the body  13  suffers wear during a drilling operation, such wear may result in uneven surfaces on the body  13 , so the worn area may be machined to relatively precise tolerances to form the seat  28  for placement and attachment of the replaceable cutting structure  12  thereto. 
         [0031]    The earth-boring tool  10 , itself may comprise at least one cutting element accommodation recess. At least one cutting element  24  attached to an attachment member  26  (see  FIG. 3 ) may protrude from a surface of the attachment member  26  of a replaceable cutting structure  12  and, absent formation of at least one corresponding cutting element accommodation recess in body  13 , interfere with attachment of the attachment member  26  to the body  13  of the earth-boring tool  10 . Each cutting element accommodation recess may enable a corresponding cutting element  24  to be partially disposed therein while enabling attachment of the attachment member  26  to the body  13  of the earth-boring tool  10  with minimal cutting element  24  interference. 
         [0032]    As shown in  FIG. 5 , a plurality of replaceable cutting structures  12  may be provided. Each replaceable cutting structure  12  may comprise one or more cutting elements  24  mounted to an attachment member  26  in the form of a single blade segment  23  generally conforming to the shape of adjacent portions of blades  20  on a body  13  of an earth-boring tool  10  (see  FIG. 6 ), enabling the attachment member  26  to provide an at least substantially smooth transition between the adjacent surfaces of the body  13  of the earth-boring tool  10  and the replaceable cutting structure  12 . Each replaceable cutting structure  12  may be configured to attach to the body  13  of the earth-boring tool  10 . Each attachment member  26  may comprise planar surfaces at right angles to one another at the inner and lower surfaces of the attachment member  26 , the planar surfaces being configured to abut against and attach to the body  13  of an earth-boring tool  10 . In other embodiments, the inner and lower surfaces of the attachment member  26  may not be planes at right angles to one another, but may be curved, angled, notched, or may have interface features, such as, for example, recesses or protrusions, disposed thereon. The cutting elements  24  may be disposed in multiple rows along the blade segments  23  formed in the attachment member  26 . In other embodiments, the cutting elements  24  may be disposed in a single row at the rotationally leading end of the blade segments  23  or a single cutting element  24  may be disposed on each blade segment  23  of the attachment member  26 . 
         [0033]    The attachment member  26  may comprise at least one cutting element accommodation recess. At least one cutting element  24  attached to a body  13  of an earth-boring tool  10  (see  FIG. 4 ) may protrude from a surface of the body  13  of the earth-boring tool  10  in the area of seat  28  and, absent formation of at least one corresponding cutting element accommodation recess, interfere with attachment of the attachment member  26  to the body  13  of the earth-boring tool  10 . Each cutting element accommodation recess may enable a corresponding cutting element  24  on body  13  to be partially disposed in the underside of attachment member  26  while enabling attachment of the attachment member  26  to the body  13  of the earth-boring tool  10  with minimal cutting element  24  interference. 
         [0034]    As previously noted, size of the replaceable cutting structure  12  may correspond to a predicted region of localized wear on a shoulder region  18  or other region of an earth-boring tool  10 . The region of localized wear may be predicted using computer modeling, such as, for example, finite element analysis, or by observation of localized wear in the field. Thus, the replaceable cutting structure  12  may be sized to enable easy replacement of a region of an earth-boring tool  10  most susceptible to localized wear and, therefore, most likely to cause premature failure of the earth-boring tool  10 . 
         [0035]    Referring to  FIG. 6 , an earth-boring tool  10  to which a plurality of replaceable cutting structures  12  (see  FIG. 5 ) may be attached is shown. The earth-boring tool  10  includes a plurality of seats  28  formed in blades  20  at the shoulder region  18  of a body  13  of the earth-boring tool  10 . Surfaces defining the seats  28  may be configured correspondingly to abut against and attach to a like plurality of replaceable cutting structures  12  in the form of blade segments  23  (see  FIG. 5 ). Thus, the seats  28  may comprise planar surfaces at right angles to one another. In other embodiments, the surfaces defining the seats  28  and cooperative surfaces of blade segments  23  may not be planes at right angles to one another, but may be curved, angled, notched, or may have interface features, such as, for example, recesses or protrusions, disposed thereon. The material of the body  13  of the earth-boring tool  10  may be machinable, enabling the surfaces that define the seat  28  to be formed in the body  13 . 
         [0036]    The earth-boring tool  10  may comprise at least one cutting element accommodation recess. At least one cutting element  24  attached to an attachment member  26  of a replaceable cutting structure  12  (see  FIG. 3 ) may protrude from a surface of the attachment member  26  and, absent formation of at least one corresponding cutting element accommodation recess, interfere with attachment of the attachment member  26  to the body  13  of the earth-boring tool  10 . Each cutting element accommodation recess may enable a corresponding cutting element  24  to be partially disposed therein while enabling attachment of the attachment member  26  to the body  13  of the earth-boring tool  10  with minimal cutting element  24  interference. 
         [0037]    Attachment members  26  of replaceable cutting structures  12 , such as blade segments  23 , may comprise strong, tough, and impact- and abrasion-resistant materials suitable for use in earth-boring applications. For example, an attachment member  26  may comprise a metal or metal alloy, such as, for example, steel, or may comprise a cermet material, such as, for example, sintered tungsten carbide in a matrix material. A hardfacing material may, optionally, be disposed on an exterior portion of the attachment member  26 . 
         [0038]    Attachment members  26  may be formed by casting a metal part and subsequently machining desired features, such as, for example, attachment surfaces or pockets for receiving cutting elements  24 , into the metal part. Alternatively, attachment members  26  may be formed by distributing a plurality of hard particles, such as, for example, tungsten carbide particles, and a plurality of particles comprising a matrix material, such as, for example, copper, copper-based alloys, cobalt, and cobalt-based alloys, in a mold (not shown). In some cases, the matrix material may be melted and infiltrated into the plurality of hard particles. In other cases, the hard particles and particles comprising a matrix material may then be pressed in the mold to form a green part. The hard particles and particles comprising a matrix material may then be subjected to a densification process. For example, the green part may be subjected to heat and pressure to at least partially sinter the green part. The green part may be partially sintered to form a brown part, or may be sintered to a final density. The green, brown, or fully sintered part may also have desired features, such as, for example, attachment surfaces or cutting element  24  pockets, formed therein. Such desired features may be machined, for example, in a green or brown part, or may be molded into an infiltrated part or a fully sintered part. Cutting elements  24  may be attached to the attachment member  26  in pockets formed therein by welding, brazing, shrink-fit, by being captured due to shrinkage of the attachment member  26  during a densification process, or by other means as known in the art. Cutting elements  24  may be attached to the attachment member  26  before or after the attachment member  26  is, itself attached to a body  13  of an earth-boring tool  10 . 
         [0039]    Replaceable cutting structures  12  may be attached to bodies  13  of earth-boring tools  10 . For example, at least one replaceable cutting structure  12  may be attached to a body  13  of an earth-boring tool  10  by welding, by brazing, by shrink-fit, by press-fit, by screws, by bolts, by pins, by keys, by mutually engaging threads on a replaceable cutting structure  12  and a body  13 , by being captured due to shrinkage of an earth-boring tool  10  during a densification process, or by other means as known in the art. Alternatively, at least one preformed replaceable cutting structure  12  may be placed in a mold. The body  13  of an earth-boring tool  10  may then be cast in the mold around the replaceable cutting structure  12 , thereby attaching it to the body  13  of the earth-boring tool  10 . 
         [0040]    In operation, a replaceable cutting structure  12  may be subjected to greater wear than other regions of an earth-boring tool  10  during a drilling or reaming operation, resulting in localized wear of the replaceable cutting structure  12 . For example, as a rotary drag bit rotates in a borehole and engages the underlying earth formation, the combination of abrasive wear, impact forces, and vibrations may cause the replaceable cutting structure  12  to wear down more quickly than other portions and features of the earth-boring tool  10 , such as, for example, other portions of the face  14 , and the gage region  16 . When an operator determines that the replaceable cutting structure  12  has worn down to a selected extent, or when the bit ceases to drill an underlying earth formation at an acceptable rate in the borehole, the earth-boring tool  10  may be extracted from the borehole. The body  13  of the bit and remaining portions of the replaceable cutting structure  12  may be machined to return a seat  28  at a shoulder region  18  of the body  13  to a geometry it exhibited prior to being deployed in the borehole or to a new, selected geometry. Another replaceable cutting structure  12  may then be attached to the body  13 , and the earth-boring tool  10  redeployed in the borehole or deployed in another borehole. Therefore, replaceable cutting structures  12  may increase the useful life of an earth-boring tool  10  by enabling replacement of the region most susceptible to localized wear and, therefore, most likely to cause premature failure of the earth-boring tool  10 . 
         [0041]    An earth-boring tool  10  may comprise one or more failure detection features. Referring to  FIG. 7 , an earth-boring tool  10  comprising a plurality of outlets  30  exposed at an outer surface of a replaceable cutting structure  12  is shown. The outlets  30  comprise channels formed in the replaceable cutting structure  12  and having openings at the outer surface of the replaceable cutting structure  12  at a rotationally leading end thereof. A plurality of channels  32  is formed internally in a body  13  of the earth-boring tool  10  corresponding to and aligned with the outlets  30 , placing the outlets  30  in fluid communication with an internal plenum  34  formed in the body  13  of the earth-boring tool  10 . As the earth-boring tool  10  engages the underlying earth formation, drilling fluid is pumped down the internal plenum  34 , through the channels  32 , and out the outlets  30 , which may have flow-controlling and directing nozzles (not shown) adjacent the face  14 . The outlets  30  may enable cooling at a region of the earth-boring tool  10  and replaceable cutting structure  12  most susceptible to wear and heat generation. The outlets  30  may also enable drilling fluid to be directed at cutting elements  24 , removing cuttings and carrying them up through junk slots  22  (see  FIGS. 1 and 2 ). When the replaceable cutting structure  12  becomes worn to a point where replacement is desirable or necessary, cuttings from the earth formation may become lodged in the channels  32  or worn outlets  30 , causing a pressure spike in drilling fluid pressure which is detectable at the rig floor (not shown). Therefore, the nozzles  30  may enable an operator to detect when the replaceable cutting structure  12  should or must be replaced. 
         [0042]    As shown in  FIG. 8 , outlets  30  may also be located at an interface  36  between a body  13  of an earth-boring tool  10  and a replaceable cutting structure  12 . The outlets  30  comprise openings formed in the body  13  and are located at the interface  36  between the replaceable cutting structure  12  and the body  13 . A plurality of channels  32  is formed internally in the body  13  of the earth-boring tool  10  leading to the outlets  30 , placing the outlets  30  in fluid communication with an internal plenum  34  formed in the body  13  of the earth-boring tool  10 . As the earth-boring tool  10  engages the underlying earth formation, drilling fluid is pumped down the internal plenum  34 , through the channels  32 , and to the outlets  30 . When the replaceable cutting structure  12  becomes worn to a point where the outlets  30  become exposed, the drilling fluid may begin circulating through the nozzles, causing a pressure drop in drilling fluid pressure, which is detectable at the rig floor. Therefore, the outlets  30  may enable an operator to detect when the replaceable cutting structure  12  should or must be replaced. 
         [0043]    Referring to  FIG. 9 , a self-sharpening replaceable cutting structure  12  attached to a body  13  of an earth-boring tool  10  is shown. The self-sharpening replaceable cutting structure  12  includes a first plurality of cutting elements  24 . The first plurality of cutting elements  24  is attached to an attachment member  26  of the replaceable cutting structure  12 , and at least a portion of each cutting element  24  of the first plurality is exposed. Cutting elements  24  of the first plurality are configured to engage an earth formation directly once the earth-boring tool  10  is deployed. The self-sharpening replaceable cutting structure  12  further comprises at least another plurality of cutting elements  24 . Cutting elements  24  of the at least another plurality are located below cutting elements  24  of the first plurality. In other words, the cutting elements  24  of the at least another plurality are located closer to an axial centerline  38  of the body  13  than the cutting elements  24  of the first plurality. The cutting elements  24  of the at least another plurality may be completely embedded within the attachment member  26 . For example, the attachment member  26  may be formed around the cutting elements  24  of the at least another plurality. In other embodiments, cutting elements  24  of the at least another plurality may be at least partially exposed, being disposed in pockets formed in the attachment member  26 . As the earth-boring tool  10  engages an underlying earth formation, the first plurality of cutting elements  24  and the attachment member  26  may wear down to a point where the cutting elements  24  of the first plurality become so worn as to be dislodged. The at least another plurality of cutting elements  24  may then be exposed and begin engaging the earth formation. Thus, the at least another plurality of cutting elements  24  may enable the replaceable cutting structure  12  to be self-sharpening. 
         [0044]    While the present disclosure has been described herein with respect to certain embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, many additions, deletions, and modifications to the embodiments described herein may be made without departing from the scope of the disclosure as hereinafter claimed, including legal equivalents. In addition, features from one embodiment may be combined with features of another embodiment while still being encompassed within the scope of the disclosure as contemplated by the inventors.
Methods of forming an earth-boring tool may involve attaching one or more cutting elements to a replaceable cutting structure and positioning the replaceable cutting structure proximate a region of a body of an earth-boring tool that is susceptible to at least one of localized wear and localized impact damage. The replaceable cutting structure may be to the body. Methods of repairing an earth-boring tool may involve bringing a replaceable cutting structure proximate at least one portion of a body of an earth-boring tool exhibiting at least one of localized wear and localized impact damage. The replaceable cutting structure may be attached to the earth-boring tool at the at least one portion.