U.S. patent application number 15/605297 was filed with the patent office on 2018-11-29 for crushable spacer and bolted joint for a gas turbine engine.
The applicant listed for this patent is General Electric Company. Invention is credited to Manoj Kumar Jain, Apostolos Pavlos Karafillis, Nagamohan Govinahalli Prabhakar, Thomas Chadwick Waldman.
Application Number | 20180340447 15/605297 |
Document ID | / |
Family ID | 64400623 |
Filed Date | 2018-11-29 |
United States Patent
Application |
20180340447 |
Kind Code |
A1 |
Karafillis; Apostolos Pavlos ;
et al. |
November 29, 2018 |
CRUSHABLE SPACER AND BOLTED JOINT FOR A GAS TURBINE ENGINE
Abstract
A bolted joint apparatus includes: a first component including a
first row of first bolt holes extending therethrough; a second
component including a second row of second bolt holes extending
therethrough wherein the second bolt holes are aligned coaxially
with the first bolt holes, a plurality of fasteners, each of
fasteners disposed through aligned pairs of the first and second
bolt holes to couple together the first and second components, each
of the fasteners including a shank; and crushable spacers disposed
around the shanks of the fasteners, the crushable spacers clamped
in compression between the fasteners and one of the components,
wherein each of the crushable spacers has a tubular body
interconnecting first and second enlarged ends, the tubular body
being defined by a peripheral wall which incorporates at least one
weakening feature.
Inventors: |
Karafillis; Apostolos Pavlos;
(Winchester, MA) ; Jain; Manoj Kumar; (Bangalore,
IN) ; Waldman; Thomas Chadwick; (Boston, MA) ;
Prabhakar; Nagamohan Govinahalli; (Bangalore, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Family ID: |
64400623 |
Appl. No.: |
15/605297 |
Filed: |
May 25, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02C 7/00 20130101; F01D
25/243 20130101; F01D 25/00 20130101; F05D 2260/311 20130101; F01D
21/045 20130101 |
International
Class: |
F01D 25/24 20060101
F01D025/24; F02C 3/04 20060101 F02C003/04 |
Claims
1. A bolted joint apparatus, comprising: a first component
including a first row of first bolt holes extending therethrough; a
second component including a second row of second bolt holes
extending therethrough, wherein the second bolt holes are aligned
coaxially with the first bolt holes, a plurality of fasteners, each
of fasteners disposed through aligned pairs of the first and second
bolt holes to couple together the first and second components, each
of the fasteners including a shank; and crushable spacers disposed
around the shanks of the fasteners, the crushable spacers clamped
in compression between the fasteners and one of the components,
wherein each of the crushable spacers has a tubular body including
a central portion interconnecting first and second enlarged ends,
the tubular body being defined by a peripheral wall which
incorporates at least one weakening feature.
2. The apparatus of claim 1 wherein the fasteners comprise bolts,
each of the bolts including a bolt head, a thread, and a shank
therebetween.
3. The apparatus of claim 2 further comprising a plurality of nuts,
each nut engaging the threads of one of the bolts.
4. The apparatus of claim 1 wherein the at least one weakening
feature is an opening formed in the peripheral wall.
5. The apparatus of claim 4 wherein the opening passes completely
through the peripheral wall.
6. The apparatus of claim 4 wherein the opening is an elongated
slot.
7. The apparatus of claim 1 wherein the at least one weakening
feature is an hourglass shape of the peripheral wall.
8. The apparatus of claim 1 wherein the at least one weakening
feature is a kink in the peripheral wall.
9. The apparatus of claim 1 wherein the at least one weakening
feature is a discrete thin section in the peripheral wall.
10. The apparatus of claim 9 wherein the thin section is configured
as an annular band.
11. A gas turbine engine, comprising: turbomachinery components
including a fan, a compressor, a compressor, a combustor, and a
turbine arranged in serial flow relationship and circumscribed
about an engine centerline axis; and a supporting static structure
circumscribing the turbomachinery components; wherein at least one
of the turbomachinery components and the static structure include a
bolted flange assembly, including: a first component having a first
flange including a first row of first bolt holes extending
therethrough; a second component having a second flange including a
second row of second bolt holes extending therethrough, wherein the
second bolt holes are aligned coaxially with the first bolt holes;
a plurality of fasteners, each of fasteners disposed through
aligned pairs of the first and second bolt holes to couple together
the first and second flanges, each of the fasteners including a
shank; and crushable spacers disposed around the shanks of the
fasteners, the crushable spacers clamped in compression between the
fasteners and one of the flanges, wherein each of the crushable
spacers includes a tubular body extending axially between first and
second enlarged ends, the tubular body being defined by a
peripheral wall that incorporates at least one weakening
feature.
12. The engine of claim 11 wherein the fasteners comprise bolts,
each of the bolts including a bolt head, a thread, and a shank
therebetween.
13. The engine of claim 12 further comprising a plurality of nuts,
each nut engaging the threads of one of the bolts.
14. The engine of claim 11 wherein the at least one weakening
feature is an opening formed in the peripheral wall.
15. The engine of claim 11 wherein the opening passes completely
through the peripheral wall.
16. The engine of claim 14 wherein the opening is an elongated
slot.
17. The engine of claim 11 wherein the at least one weakening
feature is an hourglass shape of the peripheral wall.
18. The engine of claim 11 wherein the at least one weakening
feature is a kink in the peripheral wall.
19. The engine of claim 11 wherein the at least one weakening
feature is a discrete thin section in the peripheral wall.
20. The engine of claim 11 wherein the thin section is configured
as an annular band.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to bolted joints, and more
specifically to bolted joints within gas turbine engines.
[0002] A gas turbine engine includes a turbomachinery core having a
high-pressure compressor, combustor, and high pressure turbine in
serial flow relationship. The core is operable in a known manner to
generate a primary flow of propulsive gas. A typical turbofan
engine adds a low-pressure turbine driven by the core exhaust gases
which in turn drives a fan rotor through a shaft to generate a
bypass flow of propulsive gas. In the case of a high bypass engine
this provides the majority of the total engine thrust.
[0003] Bolted joints are used in several locations in a gas turbine
engine. Each bolted joint includes abutting flanges which are held
together by bolts or other fasteners through bolt holes provided in
each of the flanges that are aligned with each other. During
operation, the engine can experience unusual events such as the
fracture and release of a fan blade ("FBO"). This can produce
extreme stresses, forces, and deflection all over the engine. Large
radial, tangential, or axial loads with respect to an axial
centerline of the bolted joint can impose bending moments or
tensile forces in the flange that can cause deformation or rupture
of the bolts. It is an FAA certification requirement that during
such an event the engine must retain its structural integrity, so
that components do not strike other portions of an aircraft, or
fall off of the aircraft.
[0004] In order to mitigate the forces on the engine, there are
several locations within the engine which use "fused" connections.
One type of fuse element is a crushable spacer, which is a small
generally cylindrical device placed over the shank of a bolt and
clamped together in a bolted joint. The spacer is able to resist
the bolted joint preload while retaining structural integrity, but
if an excessive load is incurred, the spacer will crush/fail thus
relieving stress in adjoining components. Under the circumstances,
if the crushable spacers fail the connected components will
generally remain connected sufficiently to ensure a safe outcome,
but if they retain their integrity they may transfer extreme forces
to the surrounding components causing them to fail in unpredictable
ways.
[0005] In the prior art, the crushable spacer is sized by selecting
its wall thickness and material, which is typically a metal alloy.
One problem with bolted joints using existing spacers is that is
that the force/deflection characteristics are undesirable.
Specifically, there is a region of elastic deflection, followed by
yielding, followed by eventual tensile failure. In operation, there
can be a large difference in the load required to produce elastic
deflection and the load required to produce failure. The crushable
spacer can experience a very large degree of yielding before spacer
column buckling occurs. The net effect is that the spacer fails in
a drawn-out fashion and that a plurality of spacers subjected to an
overload can often fail inconsistently at different times. This
defeats the purpose of the crushable spacer.
[0006] BRIEF DESCRIPTION OF THE INVENTION
[0007] This problem is addressed by a bolted joint incorporating a
crushable spacer having a peripheral wall incorporating at least
one weakening feature.
[0008] According to one aspect of the technology described herein,
a bolted joint apparatus includes: a first component having a first
flange including a first row of first bolt holes extending
therethrough; a second component having a second flange including a
second row of second bolt holes extending therethrough wherein the
second bolt holes are aligned coaxially with the first bolt holes,
a plurality of fasteners, each of the fasteners disposed through
aligned pairs of the first and second bolt holes to couple together
the first and second flanges, each of the fasteners including a
shank; and crushable spacers disposed around the shanks of the
fasteners, the crushable spacers clamped in compression between the
fasteners and one of the flanges, wherein each of the crushable
spacers has a tubular body including a central portion
interconnecting first and second enlarged ends, the tubular body
being defined by a peripheral wall which incorporates at least one
weakening feature.
[0009] According to another aspect of the technology described
herein, a gas turbine engine includes: turbomachinery components
including a fan, a compressor, a compressor, a combustor, and a
turbine arranged in serial flow relationship and circumscribed
about an engine centerline axis; and a supporting static structure
circumscribing the turbomachinery components; wherein at least one
of the turbomachinery components and the static structure include a
bolted flange assembly, including: a first component having a first
flange including a first row of first bolt holes extending
therethrough; a second component having a second flange including a
second row of second bolt holes extending therethrough, wherein the
second bolt holes are aligned coaxially with the first bolt holes;
a plurality of fasteners, each of the fasteners disposed through
aligned pairs of the first and second bolt holes to couple together
the first and second flanges, each of the fasteners including a
shank; and crushable spacers disposed around the shanks of the
fasteners, the crushable spacers clamped in compression between the
fasteners and one of the flanges, wherein each of the crushable
spacers has a tubular body including a central portion
interconnecting first and second enlarged ends, the tubular body
being defined by a peripheral wall which incorporates at least one
weakening feature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention may be best understood by reference to the
following description taken in conjunction with the accompanying
drawing figures in which:
[0011] FIG. 1 is a schematic half-sectional view of a gas turbine
engine;
[0012] FIG. 2 is a schematic cross-sectional view of a bolted joint
of the engine of FIG. 1;
[0013] FIG. 3 is a side elevation view of a crushable spacer of the
bolted joint;
[0014] FIG. 4 is an end view of the crushable spacer of FIG. 3;
[0015] FIG. 5. is a cross-sectional view of the crushable spacer of
FIG. 3;
[0016] FIG. 6 is a side elevation view of an alternative crushable
spacer;
[0017] FIG. 7 is an end view of the crushable spacer of FIG. 7;
[0018] FIG. 8 is a cross-sectional view of the crushable spacer of
FIG. 7;
[0019] FIG. 9 is a side elevation view of another alternative
crushable spacer;
[0020] FIG. 10 is an end view of the crushable spacer of FIG.
9;
[0021] FIG. 11 is a cross-sectional view of the crushable spacer of
FIG. 10;
[0022] FIG. 12 is a side elevation view of another alternative
crushable spacer;
[0023] FIG. 13 is an end view of the crushable spacer of FIG. 12;
and
[0024] FIG. 14 is a cross-sectional view of the crushable spacer of
FIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Referring to the drawings wherein identical reference
numerals denote the same elements throughout the various views,
FIG. 1 depicts an exemplary gas turbine engine 10. While the
illustrated example is a high-bypass turbofan engine, the
principles of the present invention are also applicable to other
types of engines, such as low-bypass turbofans, turbojets,
turboprops, etc. The engine 10 has a longitudinal center line or
axis 11 and an outer stationary annular core casing disposed
concentrically about and coaxially along the axis 11.
[0026] It is noted that, as used herein, the terms "axial" and
"longitudinal" both refer to a direction parallel to the centerline
axis 11, while "radial" refers to a direction perpendicular to the
axial direction, and "tangential" or "circumferential" refers to a
direction mutually perpendicular to the axial and radial
directions. As used herein, the terms "forward" or "front" refer to
a location relatively upstream in an air flow passing through or
around a component, and the terms "aft" or "rear" refer to a
location relatively downstream in an air flow passing through or
around a component. The direction of this flow is shown by the
arrow "F" in FIG. 1. These directional terms are used merely for
convenience in description and do not require a particular
orientation of the structures described thereby.
[0027] The engine 10 has a fan 14, booster 16, compressor 18,
combustor 20, high pressure turbine 22, and low pressure turbine 24
arranged in serial flow relationship. In operation, pressurized air
from the compressor 18 is mixed with fuel in the combustor 20 and
ignited, thereby generating combustion gases. Some work is
extracted from these gases by the high-pressure turbine 22 which
drives the compressor 18 via an outer shaft 26. The combustion
gases then flow into the low-pressure turbine 24, which drives the
fan 14 and booster 16 via an inner shaft 28. The engine 10
incorporates numerous bolted joints at several locations. Examples
of potential bolted joints are in the circled areas in FIG. 1,
labeled "B".
[0028] Some non-limiting examples of locations where fused bolted
joints would be used are as follows: In a fan load reduction device
("LRD"); In a "backbone" joint between two annular portions of an
engine casing (e.g. compressor case to combustor case); In a joint
between a composite and metal components, for example between a fan
case and a fan inlet; In future applications, it is desirable to
use this type of joint and other locations such as between a fan
hub frame and a core cowl, where one of the components may be
composite such as ceramic matrix composite or polymeric matrix
composite.
[0029] FIG. 2 illustrates a bolted joint 30 which is generally
representative of any of the bolted joints described above. A first
component 32 (a portion of which is shown) includes a first flange
34. A second component 36 (a portion of which is shown) includes a
second flange 38. In the illustrated example, each of the first and
second components 32, 36 is a body of revolution about the
centerline axis 11; however, this need not be the case.
[0030] The first flange 34 incorporates at least one first bolt
hole 40; for example, a ring or row 42 of first bolt holes 40 may
be provided. The second flange 38 includes at least one second bolt
hole 44; for example, a ring or row 46 of second bolt holes 44 may
be provided. The first flange 34 abuts the second flange 38 such
that the first bolt holes 40 are aligned coaxially with the second
bolt holes 44.
[0031] Bolts 48 are disposed through the first bolt holes 40 and
the second bolt holes 44. Each of the bolts 48 includes a bolt head
50, a shank 52, and a thread 54.
[0032] Crushable spacers 56, described in more detail below, are
disposed around the shanks 50 of the bolts 48. The crushable
spacers 56 contact and axially extend between the bolt heads 50 and
a first annular surface 58, preferably flat, of the first flange
34. Nuts 60 are provided having internal threads which engage the
threads 54 of the bolt 48 and are tightened to provide a desired
clamping load on the bolted joint 30, clamping the crushable
spacers 56 in compression. It will be understood that the crushable
spacers 56 could alternatively be placed on the other side of the
bolted joint 30, that is, between the second flange 38 and the nuts
60.
[0033] It will be understood that the bolts 48 could be replaced
with any fastener capable of clamping together the first flange 34,
the second flange 38, and the crushable spacer 56 with a
predetermined clamping load.
[0034] For example, instead of using the bolts 48 with nuts 60, one
of the flanges 34, 38 could be provided with internal threads (not
shown) to engage the threads 54 of the bolt 48. These could be
formed, for example by a thread-cutting operation or by the
installation of a threaded insert into one of the flanges 34,
38.
[0035] As another example, instead of using the illustrated bolts
48 and nuts 60, a threaded stud with nuts secured to both ends (not
shown) could be used.
[0036] As yet another example, instead of using the illustrated
bolts 48 and nuts 60, a fastener such as a conventional rivet or
blind rivet (not shown) could be used.
[0037] FIGS. 3-5 show one of the crushable spacers 56 in more
detail. The crushable spacer 56 has a body including a central
portion 62 extending axially between and interconnecting first and
second enlarged or flanged ends 64, 66. The first and second ends
64, 66, define first and second end faces 68, 70 respectively,
which may be planar.
[0038] The crushable spacer 56 has a peripheral wall 72 defining a
hollow interior or through-bore 74. The body of the crushable
spacer 56 may thus be generally described as a "tubular" form. In
the illustrated example the peripheral wall 72 is cylindrical or a
body of revolution. Other cross-sectional shapes, such as regular
or irregular polygons, could be used as well.
[0039] The peripheral wall 72 has a basic thickness "T" selected to
have particular strength characteristics as described in more
detail below. The peripheral wall 72 further includes at least one
weakening feature. As used herein, the term "weakening feature"
refers to a feature which reduces the buckling strength or critical
load of the crushable space 56, as compared to a cylindrical wall
of uniform basic thickness T.
[0040] The peripheral wall 72 includes a weakening feature embodied
as at least one opening formed therein. This opening may take
numerous forms. In the example illustrated in FIGS. 3-5, the
opening takes the form of one or more elongated slots 76 passing
completely through the thickness of the peripheral wall 72 and
having parallel sides 78 joined by rounded ends 80.
[0041] The characteristics of the openings, including their number,
shape, location, and dimensions, may be varied to suit a particular
application. For example, the openings could take the form of
singular or plural circular holes, or spiral slots (not shown).
Optionally, the openings could be "blind" openings which do not
pass all the way through the thickness of the peripheral wall 72.
In general, it is preferable that the cross-sectional area
remaining in the peripheral wall 72 be suitable to withstand the
desired compressive force due to bolt preload forces as well as
expected forces during normal operation, but that the buckling
strength be reduced.
[0042] The material selected for the crushable spacer 56 should
have a generally high tensile strength and a ratio of ultimate
tensile strength ("UTS") to yield strength ("YS") strength as low
as possible. The crushable spacer 56 should be sized for yield
strength YS at assembly clamp load, and the buckling is based on an
ultimate tensile strength UTS for the load expected at an event
such as blade out. The lower the ratio of UTS/YS, the lower the
flange load (past flange separation) needed to crush the crushable
spacer 56 in a manner such that rapid predictable failure will
occur when loads exceed a predetermined stress, without a
significant amount of yielding. The presence of a weakening feature
as described herein further contributes to buckling and rapid
predictable failure.
[0043] The openings described above are one example of a weakening
feature. the specific mechanical design of the crushable spacer 56
may be varied to suit a particular application, and different types
of weakening features may be implemented.
[0044] For example, FIGS. 6-8 illustrate an alternative crushable
spacer 156 similar in construction to the crushable spacer 56
described above. The crushable spacer 156 has a body including a
central portion 162 extending axially between and interconnecting
first and second enlarged or flanged ends 164 and 166. The
crushable spacer 156 has a peripheral wall 172 defining a hollow
interior or through-bore 174. As noted above, this may be generally
described as a "tubular" form. In the illustrated example the
peripheral wall 172 is cylindrical or body of revolution. Other
cross-sectional shapes, such as regular or irregular polygons,
could be used as well.
[0045] The peripheral wall 172 has a basic thickness "T" selected
as described above. The peripheral wall 172 incorporates an
"hourglass shape" wherein the wall pinches inward such that an
outer diameter "D1" near the center of the peripheral wall 172 is
less than a diameter "D2" near the flanged ends 164, 166. This
hourglass shape contributes to a reduced buckling strength as
described above and may be considered a weakening feature. In
addition to the hourglass shape described above, the crushable
spacer 156 may incorporate one or more openings as described
above.
[0046] FIGS. 9-11 illustrate another alternative crushable spacer
256. The crushable spacer 256 has a body including a central
portion 262 extending axially between and interconnecting first and
second enlarged or flanged ends 264 and 266. The crushable spacer
256 has a peripheral wall 272 defining a hollow interior or
through-bore 274. As noted above, this may be generally described
as a "tubular" form. In the illustrated example the peripheral wall
272 is cylindrical or body of revolution. Other cross-sectional
shapes, such as regular or irregular polygons, could be used as
well.
[0047] The peripheral wall 272 has a basic thickness "T" selected
as described above. The peripheral wall 272 incorporates at least
one "kink" 276, defined herein as a discontinuity in the axial
direction. In the illustrated example, the kink 276 takes the form
of a generally semicircular annular bulge located near the center
of the peripheral wall 272. The presence of the kink 276
contributes to a low buckling strength as described above.
Optionally, in addition to the hourglass shape described above, the
crushable spacer 256 may incorporate at least one opening as
described above (not shown)
[0048] FIGS. 12-14 illustrate another alternative crushable spacer
356. The crushable spacer 356 has a body including a central
portion 362 extending axially between and interconnecting first and
second enlarged or flanged ends 364 and 366. The crushable spacer
356 has a peripheral wall 372 defining a hollow interior or
through-bore 374. As noted above, this may be generally described
as a "tubular" form. In the illustrated example the peripheral wall
372 is cylindrical or body of revolution. Other cross-sectional
shapes, such as regular or irregular polygons, could be used as
well.
[0049] The peripheral wall 372 has a basic thickness "T" selected
as described above. The peripheral wall 372 incorporates at least
one discrete thin section 376 having a thickness "T1" which is less
than the basic thickness T. The presence of the discrete thin
section 376 contributes to a low buckling strength as described
above. In the illustrated example the thin section 376 is
configured as an annular ring, but other orientations such as axial
or oblique are possible as well. Optionally, in addition to the
thin section described above, the crushable spacer 356 may
incorporate at least one opening as described above (not
shown).
[0050] The foregoing has described a crushable spacer and a bolted
joint using a crushable spacer for a gas turbine engine. All of the
features disclosed in this specification (including any
accompanying claims, abstract and drawings), and/or all of the
steps of any method or process so disclosed, may be combined in any
combination, except combinations where at least some of such
features and/or steps are mutually exclusive.
[0051] Each feature disclosed in this specification (including any
accompanying claims, abstract and drawings) may be replaced by
alternative features serving the same, equivalent or similar
purpose, unless expressly stated otherwise. Thus, unless expressly
stated otherwise, each feature disclosed is one example only of a
generic series of equivalent or similar features.
[0052] The invention is not restricted to the details of the
foregoing embodiment(s). The invention extends to any novel one, or
any novel combination, of the features disclosed in this
specification (including any accompanying potential points of
novelty, abstract and drawings), or to any novel one, or any novel
combination, of the steps of any method or process so
disclosed.
* * * * *