Inner shroud segment of aircraft turbomachine
By using a combination of composite inner layer and expanded material body in the inner shield section of the aircraft turbine, the problem of excessive mass of the inner shield section is solved, mass reduction and mechanical strength improvement are achieved, and the sealing effect is improved.
Patent Information
- Application Number
- CN202480006854.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-01-25
- Filing Date
- 2024-01-22
- Publication Date
- 2025-08-12
AI Technical Summary
The mass of the shield section in the turbine of the existing aircraft is large, resulting in an increase in the weight of the aircraft and an increase in energy consumption. The thickness adjustment of traditional titanium alloy cannot effectively reduce the mass.
The inner and outer layers of the composite material are used, and the expanded material body is sandwiched between them to form a local thickening part. The expansion characteristics of the expanded material under the action of heat are used to compress the composite material to reduce porosity and form an internal groove profile suitable for sealing and fit.
Effectively reduce the quality of the inner shield section, maintain mechanical strength and thermal deformation resistance, and achieve rapid molding and efficient sealing of composite materials.
Smart Images
Figure CN120476246A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of aircraft turbine casings, and more particularly to an inner shroud segment. Background Art
[0002] Known, reference Figure 1 Aircraft turbomachine 500, whose longitudinal axis is X, includes, from upstream to downstream, a fan 200, a low-pressure compressor 220, a high-pressure compressor 230, a combustion chamber 240, a high-pressure turbine 250, and a low-pressure turbine 260. Compressors 220, 230, combustion chamber 240, and turbines 250, 260 collectively define a primary flow channel 400 for air circulation, which is externally bounded by a central casing 270. Aircraft turbomachine 500 also includes a secondary flow channel 410 for air circulation, which extends externally around primary flow channel 400 and is surrounded by a nacelle 300.
[0003] Known as Figure 1 As shown, an aircraft turbine 500 includes an intermediate casing 190 including an inner shroud 100 and an outer shroud 180, which respectively define the interior and exterior of a secondary flow passage 410. The inner shroud 100 is connected upstream to the hub 160 of the intermediate casing 190. The inner shroud 100 and the outer shroud 180 are connected by a support arm 170, which extends radially in the secondary flow passage 410 downstream of a row of outlet guide vanes (OGVs) 330. The outer shroud 180 extends in the downstream extension of the fan casing 210 and in the upstream extension of the outer fan duct 320.
[0004] Known and as Figure 1 and Figure 2 As shown, the inner shroud 100 extends in the upstream extension of the inner fan duct 310, and the inner fan duct 310 and the central casing 270 together define the core module 280 extending radially between the primary flow channel 400 and the secondary flow channel 410. More specifically, referring to Figure 2 The inner shroud 100 includes a stepped downstream end 120 configured so that the upstream end of the inner fan duct 310 can overlap the downstream end and be fixed to the upstream end by fastening screws radially inserted into the through holes 130. This assembly method is called swaging.
[0005] In practice, the inner shroud 100 is assembled from a plurality of angled inner shroud segments 110, which are connected together via connecting plates 140 using fastening screws inserted radially into through-holes 130. The inner shroud segments 110 are typically formed as one-piece titanium alloy components. While titanium alloys advantageously possess high mechanical strength and resistance to thermal deformation, they also possess high density, resulting in a relatively high mass for the inner shroud segments 110. This increases the weight of the aircraft turbine 500 and, consequently, its energy consumption during flight.
[0006] To reduce the mass of the inner shroud segment, it is known to have a titanium alloy inner shroud segment with a variable thickness, where the thickness of the inner shroud segment is reduced in areas subject to less stress and is increased in areas subject to the greatest stress, such as at the connection holes. However, this improvement in mass is insufficient.
[0007] It is known from patent application US2021340881 A1 that a fan casing which externally delimits an air flow channel is formed from a composite material having a honeycomb reinforcement. Summary of the Invention
[0008] The present invention aims to reduce the mass of an inner shroud segment of an aircraft turbomachine while maintaining satisfactory mechanical and thermal deformation resistance.
[0009] The present invention relates to an inner shroud segment installed in an aircraft turbomachine, the inner shroud being a rotating member rotating about a longitudinal axis extending from upstream to downstream and configured to internally delimit a secondary flow passage of the aircraft turbomachine, the inner shroud segment comprising a downstream end, the downstream end comprising:
[0010] an upstream longitudinal portion located at a first radial distance from the longitudinal axis and configured to extend in an upstream extension of the inner fan duct;
[0011] a downstream longitudinal portion located at a second radial distance from the longitudinal axis that is less than the first radial distance and configured to extend inside the inner fan duct; and
[0012] - an intermediate portion connecting the upstream longitudinal portion and the downstream longitudinal portion.
[0013] The present invention is notable in that the inner shroud segment comprises at least one inner layer of composite material and at least one outer layer of composite material, the composite material being in the form of a plurality of reinforcing fibers in a matrix, and the intermediate portion at the downstream end comprising at least one body of expanded material sandwiched between the inner layer of composite material and the outer layer of composite material so as to form a local thickening in the longitudinal direction.
[0014] The use of composite materials advantageously reduces the mass of the inner shroud segment. The expansion material reduces the porosity of the composite material in the middle section, thereby obtaining an inner shroud segment with very good mechanical strength. The composite material layers, which are initially plastic, need to be hardened together by radial compression at a heated temperature. However, radial compression cannot effectively compress the middle section, especially when the distance the middle section extends in the radial direction is greater than twice the thickness of the longitudinal section. Therefore, the expansion material body, due to its expansion characteristics under the action of heat, makes it possible to further compress the composite material in the middle section to locally reduce the porosity. Compared with the use of pre-cut composite material layers, the expansion material also makes it easier and faster to form local thickening sections. This arrangement with the expansion membrane makes it possible to achieve a local variation in thickness at the downstream end of the composite sector, thereby obtaining an internal groove profile that is different from the external stepped profile - usually an angled (steep) external profile and a regular, flat internal profile that is very suitable for sealing with a gasket.
[0015] According to a preferred aspect of the invention, the inner shroud segment comprises a plurality of composite material layers, each composite material layer extending uniformly across the downstream end.Using expanded material avoids the time-consuming task of cutting and locally stacking composite material layers to form the thickened portion.
[0016] According to one aspect of the present invention, the expanded material body of the middle portion has a longitudinal thickness parallel to the longitudinal axis, with the longitudinal thickness decreasing radially from the outside to the inside, preferably decreasing from a maximum value to a minimum value that is no more than half of the maximum value. Preferably, the maximum longitudinal thickness is at least four times the minimum value. Preferably, the maximum longitudinal thickness is at most ten times the minimum value. The expanded material is advantageously positioned in the middle portion so as to increase the longitudinal component of the middle portion and reduce its radial component. The resulting middle portion has a more gradual radial slope, which results in a better compression effect on the composite material.
[0017] According to one aspect of the invention, the intermediate portion comprises an outer wall perpendicular to the longitudinal axis. This ensures its abutment and engagement with the upstream end of the inner fan duct.
[0018] According to one aspect of the invention, the intermediate portion comprises at least a first and a second angular piece arranged side by side, the body of expanded material extending only in the first angular piece. This preferably forms a longitudinal connecting strip at the corner edge of the inner shroud segment to ensure its connection to the adjacent inner shroud segment.
[0019] According to one aspect of the present invention, the central portion includes an inner surface that projects from the first corner piece relative to the second corner piece to form a longitudinal projection. This longitudinal projection increases the longitudinal component of the central portion and reduces its radial component. This creates a central portion with a gentler radial slope, resulting in better compression of the composite material. Advantageously, the outer surface is free of projections to facilitate compatibility with the inner fan duct.
[0020] According to one aspect of the invention, the body of expanded material extends radially throughout the intermediate portion so as to connect the upstream longitudinal portion and the downstream longitudinal portion, thereby forming a gentle radial slope to ensure good radial compression.
[0021] In one aspect of the present invention, the intermediate portion includes at least one membrane that separates the expanded material body from the inner and outer composite material layers. Preferably, the membrane is waterproof. This prevents deformation of the material during compression and heating, thereby increasing the mechanical strength of the final component.
[0022] According to one aspect of the invention, the intermediate portion extends radially for a distance at least twice, preferably at least four times, the radial thickness of the upstream longitudinal portion. According to a preferred aspect, the intermediate portion extends radially for a distance greater than the radial thickness of the downstream longitudinal portion, preferably at least three times. Such an intermediate portion makes it particularly important to enhance compression by expanding the material.
[0023] According to one aspect of the present invention, the porosity of the composite material inner layer and the composite material outer layer at the middle portion is less than 2%, preferably less than 1%, and more preferably less than 0.7%.This porosity level ensures good mechanical strength.
[0024] According to one aspect of the present invention, the expanded material body of the intermediate portion is designated as a first expanded material body, and the downstream longitudinal portion includes at least one second expanded material body sandwiched between the inner and outer composite material layers to form a localized thickening in the radial direction, the second expanded material body extending in the longitudinal extension of the first expanded material body. The first and second expanded material bodies together form a longitudinal connecting band having high mechanical strength.
[0025] According to a preferred aspect, the upstream longitudinal portion includes at least one third expanded material body sandwiched between the inner and outer composite material layers to form a localized thickening in the radial direction, the third expanded material body extending within the longitudinal extension of the first expanded material body. The first and third expanded material bodies together form a longitudinal connecting band having high mechanical strength.
[0026] The present invention relates to an inner shroud segment as described above before compression and heating, wherein the expansion material is adapted to expand under the action of heat, preferably at a predetermined temperature greater than 115° C. and less than 180° C. Before compression and heating, the composite material and the expansion material are in a ductile state.
[0027] The present invention also relates to an inner shroud segment after compression and heating as described above, wherein the expansion material is in an expanded state. After compression and heating, the composite material and the expansion material are in a hardened state.
[0028] The invention also relates to an inner shroud for an aircraft turbine, comprising a plurality of inner shroud segments as described above, the inner shroud being a rotating element rotating about a longitudinal axis extending from upstream to downstream, the rotating element being configured to internally delimit a secondary flow channel of the aircraft turbine.
[0029] The present invention also relates to an intermediate casing for an aircraft turbine, comprising an inner shroud and an outer shroud as described above. The intermediate casing includes a hub, the inner shroud being connected to the hub, and the outer shroud extending opposite the inner shroud and configured to externally delimit a secondary flow channel of the aircraft turbine. The intermediate casing preferably includes at least one arm connecting the inner shroud and the outer shroud.
[0030] The present invention also relates to an aircraft turbomachine comprising a primary flow channel and a secondary flow channel extending externally around the primary flow channel, the aircraft turbomachine comprising an intermediate case as described above, wherein an inner shroud and an outer shroud delimit the secondary flow channel externally and internally, respectively. Preferably, the outer shroud extends in a downstream extension of the fan case. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The invention will be better understood on reading the following description, given by way of example, and with reference to the following drawings, given by way of non-limiting example, in which like references indicate similar objects.
[0032] Figure 1 is a longitudinal half-section view of an aircraft turbine according to the prior art.
[0033] Figure 2 It is a schematic diagram of the inner shroud section of the prior art viewed from downstream.
[0034] Figure 3 is a longitudinal half-section view of an aircraft turbine including an inner shroud segment according to one embodiment of the present invention.
[0035] Figure 4 FIG. 1 is a schematic diagram of an inner shroud segment according to an embodiment of the present invention as viewed from downstream.
[0036] Figure 5 yes Figure 4 Schematic perspective view of the downstream end of the inner shroud section as viewed from downstream.
[0037] Figure 6 yes Figure 5 A radial cross-sectional view of the first corner piece at the downstream end.
[0038] Figure 7 yes Figure 5 Schematic perspective view of the downstream end of the reactor as seen from upstream.
[0039] Figure 8is a radial cross-sectional view of a first gusset at the downstream end of another embodiment including a diaphragm.
[0040] It should be noted that the accompanying drawings illustrate the invention in detail in order to implement the invention and that said drawings can of course serve to better define the invention if necessary. DETAILED DESCRIPTION
[0041] refer to Figure 3 As mentioned above, the aircraft turbine 50 generally extends along a longitudinal axis X extending from upstream to downstream. Hereinafter, the terms "upstream" and "downstream" are defined relative to the orientation of the longitudinal axis X. The terms "inner" and "outer" are defined relative to a radial axis perpendicular to the longitudinal axis X.
[0042] Still refer to Figure 3 The aircraft turbine 50 generally includes, from upstream to downstream, a fan 20, a low-pressure compressor 22, a high-pressure compressor 23, a combustion chamber 24, a high-pressure turbine 25, and a low-pressure turbine 26. The compressors 22, 23, the combustion chamber 24, and the turbines 25, 26 together define a primary flow channel 40 for air circulation, which is externally bounded by a central casing 27. The aircraft turbine 50 also includes a secondary flow channel 41 for air circulation, which extends externally around the primary flow channel 40 and is surrounded by the nacelle 30.
[0043] refer to Figure 3 , an aircraft turbine 50 comprises an intermediate casing 19 comprising an inner shroud 15 and an outer shroud 18, which delimit a secondary flow channel 41 on the outside and inside, respectively. The inner shroud 15 is connected upstream to the hub 16 of the intermediate casing 19. In this example, the inner shroud 15 and the outer shroud 18 are connected by arms 17, which extend radially in the secondary flow channel 41 downstream of a row of outlet guide vanes (OGV) 33. The outer shroud 18 extends in the downstream extension of the fan casing 21 and in the upstream extension of the outer fan duct 32. The inner shroud 15 extends in the upstream extension of the inner fan duct 31, which together with the central casing 27 defines a core compartment 28 extending radially between the primary flow channel 40 and the secondary flow channel 41.
[0044] like Figure 3 and Figure 4 As shown, the inner shroud 15 is a rotating element that rotates about a longitudinal axis X in an aircraft turbine 50. Hereinafter, the longitudinal axis X refers indiscriminately to both the axis of the turbine 50 and the axis of the inner shroud 15, which axes coincide. The inner shroud 15 is assembled from a set of interconnected inner shroud segments 1 distributed circumferentially about the longitudinal axis X. Preferably, the inner shroud segments 1 have a variable angular width.
[0045] According to the present invention and Figure 4As shown, each inner shroud segment 1 includes a downstream end 2, which includes an upstream longitudinal portion 3 and a downstream longitudinal portion 4 connected by an intermediate portion 5. The upstream longitudinal portion 3 and the longitudinal portion 4 are respectively located at a first radial distance R3 and a second radial distance R4 from the longitudinal axis X and satisfy: R4>R3( Figure 6 ). The upstream longitudinal portion 3 extends in the upstream extension of the inner fan duct 31. The downstream longitudinal portion 4 extends inside the inner fan duct 31. Preferably, the radial extension distance H of the intermediate portion 5 is between 24-32 mm.
[0046] According to the present invention and Figure 4 and Figure 6 As shown, the inner shroud segment 1 includes at least one inner composite material layer 9a and at least one outer composite material layer 9b. The composite material is in the form of a plurality of reinforcing fibers in a matrix. The intermediate portion 5 of the downstream end 2 includes at least one expanded material body 10-1 sandwiched between the inner composite material layer 9a and the outer composite material layer 9b to form a localized thickening in the longitudinal direction. Preferably, each composite material layer 9a, 9b has a constant thickness.
[0047] Advantageously, the composite material has a lower density than conventional titanium alloys, reducing the mass of the inner shroud segment 1. Composite materials are generally suitable for aircraft parts with uniform thickness and minimal mechanical stress and thermal deformation, but their use in the inner shroud segment 1 is unprecedented.
[0048] The use of an intumescent material can improve the material strength of the inner shroud segment 1, i.e., ensure that the composite material has a lower porosity. As described later, the inner shroud segment 1 is formed by heating and compressing a set of composite material layers, wherein one or more intumescent material bodies are inserted into the composite material layers. The compression process is carried out between two molds along the stacking axis of the composite material layers (i.e., radially), but this does not ensure that the middle portion 5 can obtain sufficient compression. Since the intumescent material has the property of expanding when heated, the intumescent material helps to compress the composite material in the middle portion 5 to achieve the desired porosity.
[0049] The expanded material body is also advantageously of any size and shape, so that the desired thickening can be easily obtained. This avoids the need to use composite material layers cut to precise dimensions to form the thickening, as these composite material layers may move when heated and compressed.
[0050] according to Figures 5 to 7 In the preferred aspect shown, the inner shroud segment 1 comprises a plurality of expanded material bodies 10-1, 10-2, 10-3, 10-4. In this example, the inner shroud segment 1 comprises:
[0051] - an expanded material body 10 - 1 located in the middle portion 5 , hereinafter referred to as “a first expanded material body 10 - 1 ”;
[0052] a second body of expanded material 10 - 2 located in the downstream longitudinal portion 4 , the second body of expanded material being located in the downstream extension of the first body of expanded material 10 - 1 ; and
[0053] - A third body of expanded material 10 - 3 located in the upstream longitudinal portion 3 , the third body of expanded material being located in the upstream extension of the first body of expanded material 10 - 1 .
[0054] The first expanded material body 10-1 is connected to the second expanded material body 10-2 and the third expanded material body 10-3, thereby forming a thickened longitudinal strip that extends in the first corner piece T1 of the inner shroud segment 1, preferably at the corner edge of the inner shroud segment 1. This thickened longitudinal strip enables the inner shroud segment 1 to be connected to an adjacent inner shroud segment 1 or a support arm 17, preferably via a connecting plate 14 ( Figure 4 For this purpose, the thickened longitudinal strip comprises one or more connecting through-holes 13 into which connecting elements (such as screws, nails or rivets) are radially inserted. Preferably, the inner shroud segment 1 is provided with the thickened longitudinal strip at its two corner edges.
[0055] Also according to Figure 4 In the preferred aspect shown, the inner shroud section 1 includes one or more openings 29 connected to a discharge pipe for discharging the air flow taken upstream from the low-pressure compressor 22 to avoid low-flow pumping. Figure 5 and Figure 7 As shown, the inner shroud segment 1 preferably comprises a fourth body of expanded material 10 - 4 forming thickened transverse strips located upstream and downstream of the opening 29 to enable connection of the discharge pipe.
[0056] refer to Figure 6 , the inner shroud segment 1 comprises a set of radially stacked composite material layers 9a, 9b, which preferably extend over the entire surface of the downstream end 2 and preferably over the entire surface of the inner shroud segment 1. In this example, only two layers 9a, 9b are shown, but in reality the number of layers is more than eight. Each composite material layer 9a, 9b preferably has a uniform thickness over its entire surface. The layers 9a, 9b preferably have the same thickness. The composite material is in the form of a component consisting of reinforcing fibers (preferably carbon fibers) embedded in a matrix (preferably polyepoxide, i.e. epoxy resin). The composite material layers 9a, 9b are superimposed together and have a ductile structure that is configured to harden and fix together after heating and pressurization to obtain the final shape of the inner shroud segment 1.
[0057] Still refer to Figure 6, the first expansion material body 10-1 is inserted between the inner layer 9a and the outer layer 9b of the composite material. Preferably, the first expansion material body 10-1 is located in a central position, that is, the number of layers of the inner shroud segment 1 on both sides of the first expansion material body 10-1 is basically the same. It is also preferred that all expansion material bodies 10-1, 10-2, 10-3, and 10-4 are inserted between the inner layer 9a and the outer layer 9b. The expansion material body is initially plastic and is configured to expand under the action of heat, preferably at a predetermined temperature greater than 115°C and less than 180°C. After heating, the expansion material remains in a hardened and expanded state. The expansion material preferably includes polyepoxide, such as in the form of a metal-free epoxy adhesive foam (such as FM410-1) or an epoxy adhesive film (such as AF3074FST).
[0058] according to Figure 8 In the preferred aspect shown, the inner shroud segment 1 further includes a diaphragm 12, preferably a sealing membrane extending on both sides of the expanded material body 10-1 to separate the expanded material body 10-1 from the composite material layers 9a, 9b. The diaphragm 12 prevents mixing of the expanded material and the composite material at the interface during curing and compression. The diaphragm 12 preferably comprises a composite material arranged in one or two layers. This ensures better compression of the composite material and helps reduce the composite material's porosity.
[0059] Preferably, the inner shroud segment 1 is composed solely of the composite material, the expanded material, and preferably the diaphragm 12. The inner shroud segment 1 is also preferably a one-piece structure to improve mechanical strength. Also preferably, the composite material in the shroud segment 1, after curing and compression, has a porosity of less than 2%, preferably less than 1%, and more preferably less than 0.7%.
[0060] like Figures 5 to 7 As shown and described above, the downstream end 2 includes a longitudinal upstream portion 3 and a longitudinal downstream portion 4 connected by an intermediate portion 5, the three of which together form a groove. The intermediate portion 5 includes two continuous bends, namely a first bend 7 and a second bend 8 located radially inward of the first bend 7. In fact, the downstream end 2 forms a step, which allows the upstream end of the inner fan duct 31 to overlap the step and be swaged to the inner fan duct by a connecting element (such as a screw, nail or rivet) radially inserted into the through hole 13 ( Figure 4 ).
[0061] refer to Figure 6The radial thickness e3 of the upstream longitudinal portion 3 is preferably constant throughout its entire length. Similarly, the radial thickness e4 of the downstream longitudinal portion 4 is preferably constant throughout its entire length, preferably equal to the thickness e3 of the upstream longitudinal portion 3. The intermediate portion 5 extends radially over a distance H that satisfies H=R4-R3, and this distance H is preferably at least twice, more preferably at least four times, and even more preferably at most ten times, the thickness e3 of the upstream longitudinal portion 3.
[0062] refer to Figure 5 and Figure 6 The intermediate portion 5 includes a transverse outer wall Pext1 defined between a first bend 7 and a second bend 8, and a longitudinal outer wall Pext2 defined upstream of the first bend 7 and extending in the extension of the upstream longitudinal portion 3. The first bend 7 preferably forms an angle at the outer surface Sext, in this example, a right angle. Similarly, the second bend 8 preferably forms an angle at the outer surface Sext, in this example, a right angle. The transverse outer wall Pext1 extends in a plane perpendicular to the longitudinal axis X to form an abutment for the inner fan duct 31.
[0063] refer to Figures 5 to 7 The longitudinal thickness e of the expanded material body 10-1 in a direction parallel to the longitudinal axis X decreases radially from the outside to the inside. The longitudinal thickness e has a maximum value emax defined at a first radial distance R3 and a minimum value emin defined at a second radial distance R4, and the minimum value emin is at most one-half of the maximum value emax, preferably less than one-quarter, and at least one-tenth thereof.
[0064] refer to Figure 6 and Figure 7 , the first expanded material body 10-1 extends only into the first corner piece T1 of the inner shroud segment 1, and the inner surface Sint forms a longitudinal protrusion 11-1 relative to the adjacent second corner piece T2. In other words, the thickening formed by the first expanded material body 10-1 is only visible on the inner surface Sint. Advantageously, the outer surface Sext has no protrusion at the first corner piece T1. According to a preferred aspect, the first bend 7 and the second bend 8 are preferably gradually curved at the inner surface Sint. According to Figure 7 In the preferred aspect shown, the second, third and fourth expanded material bodies 10-2, 10-3, 10-4 form radial protrusions 11-2, 11-3, 11-4 only on the inner surface Sint.
Claims
1. An inner shroud segment (1) installed in an aircraft turbomachine (50), the inner shroud being a rotating member rotating about a longitudinal axis (X) extending from upstream to downstream, the rotating member being configured to internally delimit a secondary flow passage (41) of the aircraft turbomachine (50), the inner shroud segment (1) comprising a downstream end (2), the downstream end comprising: an upstream longitudinal portion (3) situated at a first radial distance (R3) from the longitudinal axis (X) and configured to extend in the upstream extension of the inner fan duct (31); a downstream longitudinal portion (4) located at a second radial distance (R4) from the longitudinal axis (X) and configured to extend inside the inner fan duct (31); and - an intermediate portion (5) connecting the upstream longitudinal portion (3) and the downstream longitudinal portion (4); characterized in that - The inner shroud section (1) comprises at least one inner composite material layer (9a) and at least one outer composite material layer (9b), the composite material being in the form of a matrix comprising a plurality of reinforcing fibers, the intermediate portion (5) of the downstream end (2) comprising at least one expanded material body (10-1) sandwiched between the inner composite material layer (9a) and the outer composite material layer (9b) so as to form a local thickening portion in the longitudinal direction, the composite material layers (9a, 9b) and the expanded material body (10-1) having plasticity and being adapted to harden during heating and compression, the expanded material body (10-1) being adapted to expand during heating and compression.
2. The inner shroud segment (1) according to claim 1, characterized in that The longitudinal thickness (e) of the expanded material body (10-1) of the middle portion (5) in a direction parallel to the longitudinal axis (X) decreases radially from the outside to the inside, preferably decreasing from a maximum value (emax) to a minimum value (emin) not exceeding one half thereof.
3. The inner shroud segment (1) according to claim 1 or 2, characterized in that The intermediate portion (5) comprises an outer wall (Pext1) perpendicular to the longitudinal axis (X).
4. The inner shroud segment (1) according to any one of claims 1 to 3, characterized in that The middle portion (5) comprises at least a first corner piece (T1) and a second corner piece (T2) arranged in parallel, and the expanded material body (10-1) extends only in the first corner piece (T1).
5. The inner shroud segment (1) according to claim 4, characterized in that The intermediate portion (5) comprises an inner surface (Sint) which forms a longitudinal protrusion (11-1) at the first corner piece (T1) protruding relative to the second corner piece (T2).
6. The inner shroud segment (1) according to one of claims 1 to 5, characterized in that The expanded material body (10-1) extends radially over the entire middle portion (5).
7. The inner shroud segment (1) according to any one of claims 1 to 6, characterized in that The intermediate portion (5) includes at least one membrane (12) which separates the expanded material body (10-1) from the composite material inner layer (9a) and the composite material outer layer (9b).
8. The inner shroud segment (1) according to any one of claims 1 to 7, characterized in that The radial extension (H) of the intermediate portion (5) is at least twice, preferably at least four times, the radial thickness (e3) of the upstream longitudinal portion (3).
9. The inner shroud segment (1) according to any one of claims 1 to 8, characterized in that The porosity of the composite material inner layer (9a) and the composite material outer layer (9b) at the middle portion (5) is less than 2%, preferably less than 1%, and more preferably less than 0.7%.
10. The inner shroud segment (1) according to any one of claims 1 to 9, characterized in that The expanded material body (10-1) of the intermediate portion (5) is designated as a first expanded material body (10-1), and the downstream longitudinal portion (4) comprises at least one second expanded material body (10-2) sandwiched between the composite material inner layer (9a) and the composite material outer layer (9b) so as to form a local thickening in the radial direction, the second expanded material body (10-2) extending in the longitudinal extension of the first expanded material body (10-1).
11. An inner shroud segment (1) obtained by heating and compressing the inner shroud segment (1) according to any one of claims 1 to 10, characterized in that: The composite material layers (9a, 9b) and the expanded material body (10-1) are cured, and the expanded material body (10-1) is in an expanded state.