Patent Publication Number: US-9896938-B2

Title: Gas turbine engines with internally stretched tie shafts

Description:
TECHNICAL FIELD 
     The following discussion generally relates to gas turbine engine systems and methods, and more particularly, to systems and methods associated with a tie shaft of a gas turbine engine. 
     BACKGROUND 
     A gas turbine engine may be used to power various types of vehicles and systems, including aircraft. A typical gas turbine engine may include, for example, a compressor section, a combustion section, a turbine section, and an exhaust section. During operation, the compressor section raises the pressure of inlet air, and the compressed air is mixed with fuel and ignited in the combustion section. The high-energy combustion gases flow through the turbine section, thereby causing rotationally mounted turbine blades to rotate and generate energy. The air exiting the turbine section is exhausted from the engine via the exhaust section. Energy extracted by the turbine section may drive the fans, compressors, power gearboxes, generators, and other external devices. 
     Many gas turbine engines include multiple stages of compressors and turbines arranged in series. For example, a conventional two-stage gas turbine engine includes, in flow-path order: a fan and/or a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine and/or power turbine. Two or more these components may be considered a rotating group that share a common tie shaft that imparts an axial force to maintain the position and alignment of the rotating components. Generally, however, given the complex structure and function of the various components associated with the tie shaft, it may be challenging or impossible to assemble and disassemble selected components without complete disassembly of the rotating group. 
     This is particularly an issue because certain engine components may require more frequent cleaning, repair, and disassembly than other components. For example, combustors and high pressure turbine vanes and blades often require more frequent maintenance than high pressure compressor vanes and rotors. Service issues may be further complicated by recent advancements in gas turbine engine technology involving reduced physical size and increased speeds and temperatures that make the conventional mechanisms for accessing the components associated with the tie shaft more challenging. 
     Accordingly, it is desirable to provide gas turbine engines that enable a more efficient manner for selective assembly and disassembly of components while meeting the mechanical limitations of current engine requirements. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
     BRIEF SUMMARY 
     In an exemplary embodiment, a tie shaft for a rotating group of an engine core includes a cylindrical body having an internal surface and an external surface and extending between a forward end and an aft end. The tie shaft further includes a first group of internal grooves on the internal surface of the cylindrical body proximate to the forward end and a second group of internal grooves on the internal surface of the cylindrical body proximate to the aft end. 
     In another exemplary embodiment, a rotating assembly for a gas turbine engine includes at least two rotating group components defining a bore and a tie shaft extending through the bore and axially retaining the at least two rotating group components during operation of the gas turbine engine. The tie shaft has a forward end and an aft end and defining an interior surface. The tie shaft includes a first at least one internal groove on the interior surface at the forward end and a second at least one internal groove on the interior surface at the aft end. 
     In a further exemplary embodiment, a method is provided for servicing an engine assembly with a rotating group axially retained by a tie shaft. The method includes inserting a stretch tool assembly through the tie shaft; exerting an outward axial force on the interior surface of the tie shaft at a forward end and at an aft end to stretch the tie shaft to axially decouple the tie shaft from the rotating group; and removing at least one component of the rotating group from the tie shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG. 1  is a simplified cross-sectional side view of a gas turbine engine according to an exemplary embodiment; 
         FIG. 2  is a partial cross-sectional view of high pressure core retained by a tie shaft suitable for use with the engine of  FIG. 1  in accordance with an exemplary embodiment; 
         FIG. 3  is an isometric view of a tool assembly in accordance with an exemplary embodiment; and 
         FIGS. 4-15  are partial isometric and/or cross-sectional views of the tie shaft of  FIG. 2  and the tool assembly of  FIG. 3  during a disassembly procedure in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
     Broadly, exemplary embodiments discussed herein include gas turbine engines with improved modularity. In particular, the tie shaft of a gas turbine engine may have features that enable engagement with a tool assembly such that components retained by the tie shaft may be assembled and disassembled in a more efficient manner. In one exemplary embodiment, the tie shaft includes internal grooves that enable the tie shaft to be internally stretched by the tool assembly. 
       FIG. 1  is a simplified, cross-sectional view of a gas turbine engine  100  according to an embodiment. The engine  100  may be disposed in an engine case  110  and may include a compressor section  130 , a combustion section  140 , a turbine section  150 , and an exhaust section  160  mounted on a shaft assembly  170 . The compressor section  130  may include a series of compressors that raise the pressure of the air entering the engine  100 . The compressors then direct the compressed air into the combustion section  140 . In the combustion section  140 , the high pressure air is mixed with fuel and combusted. The combusted air is then directed into the turbine section  150 . 
     The turbine section  150  may include a series of turbines disposed in axial flow series. The combusted air from the combustion section  140  expands through and rotates the turbines prior to being exhausted through the exhaust section  160 . In one embodiment, the turbines rotate to drive equipment in the engine  100  via concentrically disposed shafts or spools within the shaft assembly  170 . Specifically, the turbines may drive the compressors via one or more rotors.  FIG. 1  depicts one exemplary configuration, and other embodiments may have alternate arrangements. The exemplary embodiments discussed herein are not limited to use in conjunction with a particular type of turbine engine. 
       FIG. 2  is a more detailed partial cross-sectional view of the shaft assembly  170  and portions of the compressor section  130 , the combustion section  140 , and the turbine section  150  of the engine  100  of  FIG. 1  in accordance with an exemplary embodiment. In  FIG. 2 , only half the cross-sectional view of the shaft assembly  170  is shown; the other half would be substantially rotationally symmetric about a centerline and axis of rotation  200 . Additionally, certain aspects of the engine  100  may not be shown in  FIG. 2 , or only schematically shown, for clarity in the relevant description of exemplary embodiments. As noted above, the compressor and turbine sections  130 ,  150  may have multiple stages. In the view of  FIG. 2 , the compressor section  130  may include a high pressure compressor  132  immediately upstream of the combustion section  140 , and the turbine section  150  may include a high pressure turbine  152  immediately downstream of the combustion section  140 . As described in greater detail below, the high pressure compressor  132 , the combustion section  140 , and the high pressure turbine  152  may collectively be referred to as a high pressure core  202 . 
     Generally, the high pressure compressor  132  defines a flow path  230  and includes one or more stator assemblies  232 ,  236 ,  239  and rotor assemblies  234 ,  237 . The stator assemblies  232 ,  236 ,  239 ,  241  are stationary and function to direct the air through the flow path  230 . Typically, the compressor rotor assemblies  234 ,  237  include one or more rotor disks  238 ,  242 , each with a circumferential series of rotor blades  240 ,  244  extending into the flow path  230 . As the rotor blades  240 ,  244  rotate, air flowing through the flow path  230  is compressed. As noted above, the compressor rotor assemblies  234 ,  237  may be driven by the turbine section  150  via the shaft assembly  170 . 
     As also noted above, the compressed air from the compressor section  130  is mixed with fuel and ignited in a combustor  142  of the combustion section  140  to generate high energy combustion gases that are directed into the turbine section  150 , particularly the high pressure turbine  152 . The high pressure turbine  152  generally includes one or more turbine stator assemblies (or nozzles)  254  and one or more turbine rotor assemblies  256 . Each turbine rotor assembly  256  includes a turbine rotor disk  258  with a circumferential series of turbine rotor blades  260  extending from the turbine rotor disk  258 . As the combustion gases flow through the high pressure turbine  152 , the rotor blades  260  rotate to drive the rotor disk  258 , which in turn, is coupled to the shaft assembly  170  to drive various components, such as the high pressure compressor  132 . 
     The shaft assembly  170  includes a tie shaft  300  that functions to axially retain the rotating components of the high pressure core  202 , particularly the compressor rotor assemblies  234 ,  237  of the high pressure compressor  132  and the turbine rotor assembly  256  of the high pressure turbine  152 . The tie shaft  300  may also retain various other components, such as bearings  354 ; seals  352 ,  356 ; shaft components  282 ,  286 ; shims  358 ; and/or other components as needed. Collectively, the retained components associated with the tie shaft  300  may be referred to as a component group or rotating component group. The components of the component group are maintained radially concentric to one another, while in one exemplary embodiment, the tie shaft  300  provides only the axial load necessary to retain the relative positions. 
     In addition to the tie shaft  300 , the shaft assembly  170  may include one or more components that facilitate the transfer of torque within the rotating group. These components may be generally referred to as a power shaft assembly (portions of which are shown in  FIG. 2 ) and are typically positioned concentric to the tie shaft  300 . In particular, a forward shaft component  282  functions to couple the tie shaft  300  to other components of the power shaft assembly and rotating group components for common rotation during operation, as described below. However, during an assembly or disassembly operation, the tie shaft  300  may be decoupled from the forward shaft component  282  to enable independent rotation, as also described below. 
     As further described below, the tie shaft  300  is typically “stretched” upon installation or service by a tension force on the tie shaft  300  to result in the decoupling of the tie shaft  300  and rotating group components to enable assembly and/or disassembly. Additionally, upon release of this tension force, the tie shaft  300  exerts the above-referenced inward axial force on the components to maintain the relative positions and alignments during operation. The discussion below particularly details the structure of tie shaft  300  and systems and methods for stretching the tie shaft  300  such that, during the stretching operation, portions of the high pressure core  202  may be assembled and disassembled, and upon completion of the stretching operation, the inward axial retention force is applied in preparation for engine operation. In particular, the high pressure turbine rotor assembly  256  portion may be more easily removed for maintenance, thereby also providing access to the high pressure turbine nozzle  254  and combustor  142 , as needed. In the discussion below, the “stretching” operation refers to the preparation, installation and/or application of the tension force resulting in the inward axial retention force and/or assembly or disassembly for servicing. 
     As shown, the tie shaft  300  has a cylindrical body  302  extending from a first (or forward) end  310  to a second (or aft) end  312  through a collective bore  206  generally defined by the annular nature of the high pressure core  202 . In one exemplary embodiment, the first and second ends  310 ,  312  are arranged and positioned such that the entire tie shaft  300  is considered to be completely internal to the rotating component group of the high pressure core  202 . In other words, the first end  310  of the tie shaft  300  is aft of the forward end of the most forward rotating component, which in the depicted exemplary embodiment is shaft component  282 . On the other side, the second end  312  is forward of the aft end of the most aft rotating component, which in the depicted exemplary embodiment is turbine rotor assembly  256  of the high pressure turbine  152 . As a result of this arrangement, no axial face of the tie shaft  300  may be accessible by tooling for the stretching operation. In other exemplary embodiments, the tie shaft  300  may extend beyond the ends of the rotating components. 
     The first end  310  of the tie shaft  300  has a protrusion  320  that forms an axial face  322  facing the aft direction. The axial face  322 , in the position shown, is pressed against a collar  280 , which in turn is coupled to shaft component  282 , introduced above. When the tie shaft  300  is in the position shown in  FIG. 2 , the tie shaft  300  axially retains the rotating group components via the interface formed by the axial face  322  and collar  280 . 
     The shaft component  282  and/or collar  280  may define a recess  284  to accommodate the protrusion  320  and first end  310  of the tie shaft  300 . The recess  284  may be sized to additionally accommodate some amount of axial movement of the first end  310  of the tie shaft  300 . As described below, during the stretching operation, the tie shaft  300  is stretched such that the first end  310  moves in an axial forward direction, and as a result of this movement, the axial face  322  may separate from the collar  280 . Upon separation, the tie shaft  300  is rotationally decoupled from the compressor rotor assembly  234  and may rotate separately from other components of the shaft assembly  170 . In other words, upon separation of the axial face  322  and collar  280 , there is no feature that restricts rotation of tie shaft  300  relative to shaft component  282 . 
     The cylindrical body  302  of the tie shaft  300  defines an external (or outer) surface  304  and an internal (or inner) surface  306  that forms an internal bore  308 . The external surface  304  of the tie shaft  300  includes external threads  324  at the second end  312  upon which the turbine rotor assembly  256  is mounted with corresponding threads. As described below, the turbine rotor assembly  256  may be removed from the tie shaft  300  by counter-rotating the tie shaft  300  and turbine rotor assembly  256  to uncouple the threaded engagement. A retaining ring  382  may also be positioned on the external surface  304  to assist disassembly. 
     The internal surface  306  of the tie shaft  300  defines a first set of internal grooves (or rings)  330  proximate to the first end  310  and a second set of internal grooves  332  proximate to the second end  312 . As described in greater detail below, the internal grooves  330 ,  332  enable engagement with a tool assembly that may be used to stretch the tie shaft  300  and assemble and/or disassemble the high pressure core  202  relative to the tie shaft  300 . One or both sets of the grooves  330 ,  332  may be concentric, e.g. separate circumferential grooves, such that control of the angular position of the tool assembly is not required. Furthermore, each of the grooves  330 ,  332  may be shaped such that the load capability is increased in the desired direction consistent with the application of stretch tool load. In other words, the wall of the respective groove on the side of the desired direction (e.g., the forward side wall of grooves  330  and the aft side wall of grooves  332 ) may be angled inward or perpendicular to a radial plane to enhance load bearing characteristics, although other configurations and groove shapes are possible. In one exemplary embodiment, the shape of the grooves  330 ,  332  may closely resemble the shape of buttress threads, albeit formed as separate, concentric circumferential grooves, rather than the typical, helical, threaded form. As such, in some embodiments, the grooves  330 ,  332  may be referred to as buttress rings. In alternate embodiments, the grooves  330 ,  332  may have such a helical or threaded form. In the depicted embodiment, the grooves  330 ,  332  are formed within the internal surface  306 , although in other embodiments, the grooves  330 ,  332  may be formed by lands extending from the internal surface  306 . 
     The tie shaft  300  may further include one or more internal slots  340 ,  342  extending from the internal surface  306  into or through the body  302 . In one exemplary embodiment, the tie shaft  300  may have a first circumferential series or row of slots  340  proximate to the first set of internal grooves  330  and a second circumferential series or row of slots  342  proximate to the second set of internal grooves  332 . As described in greater detail below, the slots  340 ,  342  enable rotatable coupling of the tie shaft  300  to the tool assembly as needed to assemble and/or disassemble the high pressure core  202  relative to the tie shaft  300 . An exemplary tool assembly will be introduced prior to a description of the engagement and function with respect to the tie shaft  300 . 
     Reference is made to  FIG. 3 , which is a perspective view of a tool assembly  400  for engagement with a tie shaft (e.g., tie shaft  300  of  FIG. 2 ) in accordance with an exemplary embodiment. The tool assembly  400  includes a forward tool portion  410  and an aft tool portion  420 . As shown, each of the tool portions  410 ,  420  has a cylindrical configuration, and the forward and aft tool portions  410 ,  420  may have a telescoping, sliding engagement relative to one another. 
     In this exemplary embodiment, the forward tool portion  410  has a forward expander  470  and a main body  414 . Generally, the main body  414  extends the entire length of tool assembly  400  and includes segments or portions that are sized to accommodate concentric, axial movement relative to the aft tool portion  420  and the aft expander  480 . As described below, the aft tool portion  420  includes an aft tool body  459  and an aft expander  480 . The aft tool body  459  and aft expander  480  are sized such that the aft tool body  459  slides over a portion of the main body  414  and the aft expander  480  slides over the aft tool body  459 . 
     As also shown in  FIG. 3 , the tool assembly  400  further includes two or more jaw members  432  that form a forward jaw set  430  on the outer periphery of the main body  414 . In one exemplary embodiment, the forward jaw set  430  includes three jaw members  432 , although any suitable number may be provided. Each jaw member  432  of the forward jaw set  430  has a first end  434  mounted to the main body  414  at a hinge  438  and a second end  436  with outer circumferential grooves  440 . At each hinge  438 , the respective jaw member  432  is mounted to pivot between expanded and collapsed positions. 
     As described below, the outer circumferential grooves  440  of the forward jaw set  430  are configured to match and mate with the forward internal grooves  330  of the tie shaft  300  ( FIG. 2 ) when the jaw members  432  are in the expanded position. In some embodiments, one or more of the forward jaw members  432  may include pins that engage, in the expanded position, with corresponding slots  340  in the tie shaft  300  ( FIG. 2 ), as discussed below. Moreover, in some exemplary embodiments, the jaw members  432  may have a ring groove and a retaining ring (or o-ring) arranged within the ring groove, as more clearly shown in subsequent views. Such a retaining ring functions to bias the jaw members  432  of the forward jaw set  430  into the collapsed position. 
     The tool assembly  400  further includes one or more jaw members  452  that form an aft jaw set  450  on the outer periphery of the aft tool portion  459 . In one exemplary embodiment, the aft jaw set  450  includes three jaw members  452 , although any suitable number may be provided. Each jaw member  452  of the aft jaw set  450  has a first end  454  mounted to the aft tool portion  420  at a hinge  458  and a second end  456  with outer circumferential grooves  460 . Similar to the forward jaw set  430 , each respective jaw member  452  is mounted to pivot at the respective jaw hinge  458  between expanded and collapsed positions. 
     As described below, the outer circumferential grooves  460  of the aft jaw set  450  are configured to match and mate with the aft internal grooves  332  of the tie shaft  300  ( FIG. 2 ) when the jaw members  452  are in the expanded position. In some embodiments, one or more of the aft jaw members  452  may include pins that engage, in the expanded position, with corresponding slots  342  in the tie shaft  300  ( FIG. 2 ), as discussed below. Moreover, in some exemplary embodiments, the jaw members  452  may have a ring groove and a retaining ring (or o-ring) arranged within the ring groove, as more clearly shown in subsequent views. Such a retaining ring functions to bias the jaw members  452  of the aft jaw set  450  into the collapsed position. In some exemplary embodiments, the grooves  440 ,  460  may be considered buttress rings, and in further exemplary embodiments, the grooves  440 ,  460  may be threaded or helical. Generally, as used herein with respect to grooves  330 ,  332 ,  440 ,  460 , the term “grooves” may refer to both threaded or helical arrangements and concentric arrangements. 
     As introduced above, the tool assembly  400  further includes forward and aft expanders  470 ,  480 . The forward expander  470  is generally cylindrical with a slightly larger diameter than the main body  414  of the forward tool portion  410 . During the stretching operation, as described in greater detail below, the forward expander  470  slides over the forward end of the main body  414  and the leading edge slips between the jaw set  430  and the outer surface of the main body  414 . As a result of this movement, the jaw members  432  are pivoted from the collapsed position to the expanded position. 
     The aft expander  480  functions in a similar manner as the forward expander  470 . The aft expander  480  is generally cylindrical with a slightly larger diameter than the aft tool body  459 . During the stretching operation, as described in greater detail below, the aft expander  480  slides over the aft end of the aft tool body  459  and the leading edge slips between the aft jaw set  450  and the outer surface of the aft tool body  459 . As a result of this movement, the jaw members  452  are pivoted from the collapsed position to the expanded position. 
     The tool assembly  400  further includes forward and aft retention members  490 ,  492 . The forward and aft retention members  490 ,  492  are internally threaded nut-type members. In one exemplary embodiment, the forward retention member  490  engages the forward end of the main body  414  of the forward tool portion  410  to retain the axial position of the forward expander  470 . Similarly, the aft retention member  492  engages the aft end of the aft tool portion  459  to retain the axial position of the aft expander  480 . 
     Now that the tie shaft  300  and tool assembly  400  have been introduced in  FIGS. 2 and 3 , additional details about stretching operation, including disassembling and assembling the high pressure core  202 , will now be provided with reference to  FIGS. 4-15 . Generally, the views of  FIGS. 4-15  and the associated discussion below are presented in the sequence of a disassembly operation, while the sequence of an assembly operation is reversed. 
       FIG. 4  is a partial perspective view of the tool assembly  400 . Generally,  FIG. 4  depicts portions of the tool assembly  400  as the tool assembly itself is assembled and deployed relative to the tie shaft  300  ( FIG. 3 ). In  FIG. 4 , the surrounding tie shaft  300  and other engine components are omitted for clarity. Initially, during deployment for the stretching operation, the main body  414  of the forward tool portion  410  is inserted through the bore  308  of the tie shaft  300  ( FIG. 2 ) with the forward jaw set  430  in the collapsed position. Although the tie shaft  300  is omitted in  FIG. 4 , the main body  414  is generally positioned within the tie shaft  300  such that the circumferential grooves  440  of the forward jaw set  430  are approximately radially aligned with the internal grooves  330 , as more clearly shown and described with reference to  FIGS. 5 and 6 . 
       FIG. 5  is a further view depicting a partial perspective view of the tool assembly  400  during deployment subsequent to the view of  FIG. 4 . Like  FIG. 4 , the surrounding tie shaft  300  and other engine components are omitted for clarity in  FIG. 5 . In  FIG. 5 , the forward expander  470  is inserted onto the main body  414  from the forward side.  FIG. 6  is a more detailed cross-sectional view of the forward expander  470  being inserted along the main body  414  of the tool assembly  400 , and additionally shows aspects of the engine  100 , particularly portions of the tie shaft  300  and shaft component  282 . As shown in  FIG. 6 , the forward expander  470  has a beveled and angled leading edge  472 , and the jaw members  432  of the forward jaw set  430  have corresponding beveled and angled leading edges  442  such that the forward expander  470  passes between the jaw members  432  and the main body  414  as the forward expander  470  advances along the forward end of main body  414 . 
       FIG. 7  is a further view depicting a partial perspective view of the tool assembly  400  during deployment subsequent to the view of  FIGS. 5 and 6 . In  FIG. 7 , the surrounding tie shaft  300  and other engine components are omitted for clarity. As shown, the forward expander  470  has been advanced such that forward expander  470  positioned between the jaw members  432  and the main body  414 . As a result of this position, the jaw members  432  have been urged into the expanded position. Upon reaching the appropriate axial position, the forward expander  470  may be secured by the forward retention member  490 , which is screwed onto the forward end of the main body  414 .  FIG. 8  is a more detailed cross-sectional view of the main body  414  and the forward retention member  490  in these positions relative to the tie shaft  300 . As shown in  FIG. 8 , in the expanded position, the circumferential grooves  440  engage with the forward internal grooves  330  on the internal surface  306  of the tie shaft  300 . Additionally,  FIG. 8  more clearly depicts the pins  444  on the jaw members  432  that engage the slots  340  on the forward end  310  of the tie shaft  300 . In this position, the forward end  310  of the tie shaft  300  is rotationally coupled to the tool assembly  400  as a result of the engagement between the pins  444  on the jaw members  432  and the slots  340  of the tie shaft  300  and additionally axially coupled to the tool assembly  400  as a result of the engagement between the circumferential grooves  440  of the jaw members  432  and the forward internal grooves  330  on the tie shaft  300 . 
       FIG. 8  additionally depicts the ring groove  446  on the jaw members  432  and the retaining ring  448  extending within the ring groove  446 . As noted above, the retaining ring  448  functions to bias the jaw members  432  into the collapsed position until being forced into the expanded position by the forward expander  470 . 
       FIG. 9  is a further view depicting a partial perspective view of the tool assembly  400  during deployment subsequent to the view of  FIGS. 7 and 8 . In  FIG. 9 , the surrounding tie shaft  300  and other engine components are omitted for clarity. As shown, the aft tool portion  420  is inserted into the bore  308  of the tie shaft  300  (not shown in  FIG. 9 ) from the aft side. As shown, the aft tool body  459  is inserted around and along the aft end of the main body  414 . The aft tool body  459  is inserted with the aft jaw set  450  in a collapsed portion. The main body  414  may have an expanded diameter stop member  449  to provide an indication of the proper position of the aft tool body  459  relative to the forward tool portion  410 . Although the tie shaft  300  is omitted in  FIG. 9  for clarity, the aft tool body  459  is generally positioned within the tie shaft  300  such that the circumferential grooves  460  of the aft jaw set  450  are approximately radially aligned with the internal grooves  332 , as more clearly shown and described below with reference to  FIG. 11 . 
       FIG. 10  is a further view depicting a partial perspective view of the tool assembly  400  during deployment subsequent to the view of  FIG. 9 . In  FIG. 10 , the surrounding tie shaft  300  and other engine components are omitted for clarity. The aft expander  480  is inserted into the bore  308  of the tie shaft  300  ( FIG. 11 ) from the aft side onto the aft tool body  459 .  FIG. 11  is a more detailed cross-sectional view of the aft expander  480  being inserted along the aft tool body  459 . As shown in  FIG. 11 , the aft expander  480  has a beveled and angled leading edge  482 , and the jaw members  452  of the aft jaw set  450  have corresponding beveled and angled leading edges  462  such that the aft expander  480  passes between the jaw members  452  and the aft tool body  459  as the aft expander  480  advances along the aft tool body  459 . 
       FIG. 12  is a further view depicting a partial perspective view of the tool assembly  400  during deployment subsequent to the view of  FIGS. 10 and 11 . In  FIG. 12 , the surrounding tie shaft  300  and other engine components are omitted for clarity. As shown, the aft expander  480  has been advanced such that aft expander  480  is positioned between the jaw members  452  and the aft tool portion  459 . As a result of this position, the jaw members  452  have been urged into the expanded position. Upon reaching the appropriate axial position, the aft expander  480  is secured in this position by the aft retention member  492 , which is screwed onto the aft tool body  459 .  FIG. 13  is a partial, more detailed cross-sectional view of the aft tool portion  420  and the aft retention member  492  in these positions relative to the tie shaft  300 . As shown in  FIG. 13 , in the expanded position, the circumferential grooves  460  on the aft jaw set  450  engage with the aft internal grooves  332  on the internal surface  306  of the tie shaft  300 . 
     Additionally,  FIG. 13  more clearly depicts the pins  464  on the jaw members  452  that engage the slots  342  on the aft end  312  of the tie shaft  300 . In this position, the aft end  312  of the tie shaft  300  is rotationally coupled to the tool assembly  400  as a result of the engagement between the pins  464  of the jaw members  452  and the slots  342  of the tie shaft  300  and additionally axially coupled to the tool assembly  400  as a result of the engagement between the circumferential grooves  460  of the jaw members  452  and the aft internal buttress rings  332  on the tie shaft  300 . 
       FIG. 13  additionally depicts the ring groove  466  on the jaw members  452  and the retaining ring  468  extending within the ring groove  466 . As noted above, the retaining ring  468  functions to bias the jaw members  452  into the collapsed position until being forced into the expanded position by the aft expander  480 . 
     As such, in the position depicted in  FIGS. 12 and 13 , the tool assembly  400  is engaged with the tie shaft  300  via both sets of internal grooves  330 ,  332 . In this position, as partially shown in  FIG. 13 , the main body  414  extends beyond the aft end of the aft tool portion  420 . In this position, a hydraulic ram (not shown) or other equipment may be used to press the main body  414  in a forward direction from the aft end, as represented by arrow  500 . At the same time, the aft tool body  459  is pulled in an aft direction or maintained in position at the aft retention member  492 , as indicated by arrow  502 . As a result of these forces  500 ,  502 , the main body  414  and aft tool body  459  are translated relative to each other such that the total length of the tool assembly  400  is increased. Since the forward and aft tool portions  410 ,  420  are engaged with the internal grooves  330 ,  332  of the tie shaft  300 , the lengthening of the tool assembly  400  functions to stretch the tie shaft  300  in the axial direction. 
       FIG. 14  is a partial cross-sectional view of the stretched tie shaft  300  at the forward end  310 . As the tie shaft  300  is stretched, the axial face  322  separates from the collar  280 , thereby decoupling the tie shaft  300  from the collar  280  and other portions of the rotating components, including the compressor rotor assembly  234 , such that the tie shaft  300  may rotate independently. 
     Upon separation, a first rotating tool (not shown) may be inserted to counter-rotate the high pressure turbine rotor assembly  256  (e.g.,  FIG. 13 ), and consequently, the power shaft assembly, and a second rotating tool (not shown) may be used to rotate the tool assembly  400 , and consequently, the tie shaft  300 . The first and second rotating tools may be any suitable tooling components, including wrenches or tangs. In one exemplary embodiment, the second rotating tool may be formed by tangs on the reaction tool represented by force  502  ( FIG. 13 ). As noted above, for example, in the description of  FIG. 2 , the high pressure turbine rotor assembly  256  has a threaded or screw engagement with the tie shaft  300 . As a result of the relative rotations, the high pressure turbine rotor assembly  256  is decoupled from the tie shaft  300  and may be removed from the aft end  312 . As noted above, the retaining ring  382  ( FIG. 2 ) may be employed to retain the positions of the rotating group components in this position. 
       FIG. 15  is a partial cross-sectional view of the remaining components of the high pressure core  202  and tie shaft  300  after removal of the high pressure turbine rotor assembly  256  (see, e.g.,  FIG. 13 ). In this position, a rotor group retention member  602  may be installed on the aft end  312  of the tie shaft  300  to secure the remaining portions of the high pressure core  202 , either temporarily or for storage. The rotor group retention member  602  may be a nut-type attachment with threads that engage the threads that previously retained the removed turbine rotor assembly  256 . As a result, the high pressure turbine rotor assembly  256  may be removed and the remainder of the rotating group of the high pressure core  202  may remain intact or subject to further disassembly. In this position, the turbine nozzle  254  and liner of the combustor  142  may also be removed. 
     In one exemplary embodiment and referring to  FIGS. 3-15 , the tool assembly  400  may be removed by decoupling the aft retention member  492 , then removing the aft expander  480 , then removing the aft tool body  459 , then removing forward retention member  490 , then removing the forward expander  470 , and then removing the main body  414 . 
     As a result of the interaction between the tie shaft  300  and tool assembly  400 , assembly and disassembly do not require any design changes in disk bore diameters relative to previous arrangements to enable modular disassembly of more efficient maintenance. Although the tie shaft  300  and tool assembly  400  are described above with respect to a high pressure core, exemplary embodiments discussed above may be implemented with any type of rotating group and/or rotor assembly. For example, exemplary embodiments of the shaft assembly and tool assembly described above may be used in a rotating group with only two members, including only two compressor assemblies or only two turbine rotor assemblies. The exemplary embodiments discussed above provide modularity capability for more efficient assembly and disassembly of selective components, particularly without requiring complete disassembly of the gas turbine engine. Exemplary embodiments are applicable to both commercial and military gas turbine engines and auxiliary power units. Moreover, exemplary embodiments may find beneficial uses in many industries, including aerospace and particularly in high performance aircraft, as well as automotive, marine and power generation. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.