C / SiC composite material secondary lens barrel body and preparation method thereof and secondary lens barrel

Abstract

The invention relates to a C / SiC composite secondary lens barrel body and a preparation method and secondary lens barrel structure, so as to solve the technical problems that the mechanical analysis results of the existing C / SiC composite lens barrel split structure deviate from the design, and the split redundant connection leads to a large overall structure mass of the lens barrel. The barrel body comprises an inner barrel, a flange and a reinforcing rib, and the inner barrel, the flange and the reinforcing rib are integrally formed and the material is C / SiC composite material. The preparation method of the barrel body comprises: 1. obtaining a barrel mold and a five-sided box body mold; 2. laying a first carbon fiber cloth layer; 3. laying a second carbon fiber cloth layer; 4. sewing the first carbon fiber cloth layer and the second carbon fiber cloth layer into a whole; 5. chemical vapor deposition. The secondary lens barrel structure comprises the above-mentioned barrel body, and a supporting structure fixedly connected to the barrel body; the supporting structure comprises three brackets and a reinforcing ring; the three brackets and the reinforcing ring are all made of SiC / SiC composite material.

Description

Technical Field

[0001] The invention relates to a secondary lens barrel structure and a preparation method of a secondary lens barrel body, and in particular to a C / SiC composite secondary lens barrel body and a preparation method thereof, and a secondary lens barrel structure. Background Art

[0002] With the rapid development of aerospace optical remote sensing technology, higher and higher requirements are put forward for the structural rigidity and dimensional accuracy of space optical systems. The secondary mirror tube is one of the key optical components of optical remote sensors and is also the most important main supporting structure. It is used to support optical detectors and their related circuits, and plays a role in ensuring the mirror surface shape and mirror distance, which directly affects the imaging quality of the optical system and has high thermal stability and mechanical performance requirements. Therefore, for the selection of materials for the secondary mirror tube, in addition to having the characteristics of low density, high rigidity, high strength, and high fracture toughness, it must also meet optical requirements, such as high dimensional accuracy, good dry and wet stability, high thermal stability, and high thermal conductivity.

[0003] Carbon fiber reinforced silicon carbide ceramic matrix composites (C / SiC composites) combine the advantages of C / C composites and SiC ceramics, and have a series of excellent properties such as high specific strength, high specific modulus, good temperature stability, high temperature resistance, low temperature resistance, and low density. They have great application potential in the field of optical remote sensor structural materials. At the same time, carbon fiber reinforced silicon carbide ceramic matrix composites have strong designability and good molding processability. Effectively utilizing these two characteristics to optimize the design of the lens barrel structure can ultimately produce a high-performance C / SiC composite lens barrel suitable for space environments.

[0004] The axial thermal displacement of the lens barrel using C / SiC composite materials is consistent with the thermal displacement of the focal plane, which can minimize the defocus. In order to improve the structural rigidity and strength of the lens barrel, a certain number of longitudinal ribs and annular ribs are often arranged on the outer or inner surface of the lens barrel. The general C / SiC composite lens barrel mostly adopts the method of split molding-assembly connection, that is, the barrel and the reinforcement ribs are formed separately, and then the pins, bolts and other connecting structures are introduced to make them a whole. However, the stiffness and strength loss of the connection part are difficult to simulate accurately, so the mechanical analysis results of the finished product and the design stage have a large deviation; and after the split connection using C / SiC composite connectors (pins, bolts, etc.), CVI needs to be performed multiple times to fill the redundant connection gaps, which makes the mass of the entire lens barrel structure larger and cannot achieve lightweight design. Summary of the invention

[0005] The present invention aims to solve the technical problems that the mechanical analysis results of the existing C / SiC composite material telescope barrel split structure deviate from the design, and the split redundant connection leads to a large overall structure mass of the telescope barrel, and proposes a C / SiC composite material secondary telescope barrel body and a preparation method thereof and a secondary telescope barrel structure.

[0006] The technical solution of the present invention is:

[0007] A C / SiC composite secondary lens barrel, which is special in that it includes an inner barrel, a flange and reinforcing ribs;

[0008] The flange comprises a first flange and a second flange respectively located at two ends of the inner cylinder and protruding outward;

[0009] The reinforcing ribs include at least one circumferential reinforcing rib and a plurality of axial reinforcing ribs; the circumferential reinforcing rib is located outside the inner cylinder and surrounds the inner cylinder in the circumferential direction, and the axial reinforcing rib is located outside the inner cylinder and extends to both ends of the inner cylinder in the axial direction;

[0010] The inner cylinder, flange and reinforcing ribs are integrally formed and made of C / SiC composite material.

[0011] Furthermore, it also includes a first flange adjustment plate disposed on the first flange and a second flange adjustment plate disposed on the second flange;

[0012] A plurality of upper metal mounting sheets are evenly arranged along the circumferential direction on the side of the first flange adjustment plate by gluing, and a plurality of lower metal mounting sheets are evenly arranged along the circumferential direction on the side of the first flange by gluing, and the upper metal mounting sheets and the lower metal mounting sheets are correspondingly arranged to clamp the first flange adjustment plate and the first flange in the middle; and first connecting through holes are sequentially arranged along the upper metal mounting sheets, the first flange adjustment plate, the first flange and the lower metal mounting sheets;

[0013] The second flange and the second flange adjustment plate are evenly penetrated with a plurality of metal inserts along the circumferential direction, one end of the metal insert is flush with the surface of the second flange, and the other end is provided with an end cap to form a step on the surface of the second flange adjustment plate; the metal insert has a second connecting through hole penetrated therethrough;

[0014] The first flange adjustment plate is made of C / SiC composite material with a thickness of no more than 4 mm, and the first flange adjustment plate is riveted to the first flange by C / SiC composite material pins;

[0015] The second flange adjustment plate is made of C / SiC composite material with a thickness of no more than 4 mm. The second flange adjustment plate is riveted to the second flange by C / SiC composite material pins.

[0016] Furthermore, the radial wall thickness of the inner cylinder is 2.5 to 4 mm;

[0017] The thickness of the circumferential reinforcing ribs along the axial direction is 2.5 to 4 mm; the thickness of the axial reinforcing ribs along the circumferential direction is 2.5 to 4 mm;

[0018] The thickness of the flange along the axial direction is 1.5 to 2 mm.

[0019] The present invention also provides a method for preparing the C / SiC composite secondary barrel body, which is special in that it comprises the following steps:

[0020] S1. Obtain a mold, wherein the mold includes a cylinder mold and a plurality of five-sided box molds matched with the cylinder mold;

[0021] The cylinder mold has an outer surface for cooperating with the inner surface of the inner cylinder;

[0022] The outer side of the inner cylinder has a plurality of weight-reducing grooves surrounded by the flange and the reinforcing ribs; the outer profiles of the plurality of five-sided box body molds are used to match the weight-reducing grooves one by one;

[0023] S2, laying carbon fiber cloth on the outer surface of the cylinder mold to form a first carbon fiber cloth layer;

[0024] S3, laying carbon fiber cloth on the outer surface of the five-sided box mold to form a second carbon fiber cloth layer;

[0025] S4, sewing the first carbon fiber cloth layer and the second carbon fiber cloth layer, and the adjacent second carbon fiber cloth layers, so that the first carbon fiber cloth layer and the second carbon fiber cloth layer are sewn into a whole, forming a carbon fiber preform;

[0026] S5. Performing chemical vapor deposition on the carbon fiber preform multiple times, and gradually removing the cylinder mold and the five-sided box mold in the intervals between the multiple chemical vapor depositions.

[0027] Further, in step S1, the barrel mold and a plurality of five-sided box molds matched with the barrel mold are all graphite molds;

[0028] In step S2 and step S3, the carbon fiber cloth is a two-dimensional plain weave carbon fiber cloth.

[0029] Meanwhile, the present invention also provides a secondary lens barrel structure, which is special in that it comprises the above-mentioned C / SiC composite secondary lens barrel body, and a supporting structure fixedly connected to the barrel body;

[0030] The support structure comprises three brackets and a reinforcement ring;

[0031] The first ends of the three brackets are evenly and fixedly connected to the second flange along the circumferential direction; the second ends of the three brackets are fixedly connected to the reinforcement ring;

[0032] The three brackets and the reinforcement ring are all made of SiC / SiC composite material.

[0033] Furthermore, each of the brackets includes two symmetrically arranged sub-brackets, and the two sub-brackets are connected by SiC / SiC pins;

[0034] The bracket also includes a three-claw connecting plate, which includes a three-claw inner connecting plate, a three-claw outer connecting plate and a three-claw adjusting plate;

[0035] The first ends of the two corresponding sub-brackets are respectively formed with connection grooves in opposite directions, and the connection grooves have a sub-bracket inner connection plate, a sub-bracket outer connection plate and a sub-bracket bottom connection plate;

[0036] The inner connecting plates of the sub-brackets corresponding to the two sub-brackets are connected to the three-claw inner connecting plates through SiC / SiC pins, the outer connecting plates of the sub-brackets corresponding to the two sub-brackets are connected to the three-claw outer connecting plates through SiC / SiC pins, and the sub-bracket bottom connecting plates corresponding to the two sub-brackets are fixedly connected to the three-claw adjustment plate and the second flange through C / SiC pins.

[0037] Furthermore, the second ends of the two corresponding sub-brackets form an arc-shaped connecting section that matches the curvature of the outer side surface of the reinforcement ring, and the arc-shaped connecting sections of two adjacent sub-brackets of adjacent brackets are stacked and fixed on the reinforcement ring through SiC / SiC pins;

[0038] The two arc-shaped connecting sections formed by the two sub-brackets of the bracket form a gap with the reinforcement ring, and a metal mounting block is arranged in the gap. The metal mounting block includes a leveling end cap and a connector. The connector matches the gap and is used to be inserted into the gap to achieve connection. The lower end surface of the convex edge of the leveling end cap abuts against the arc-shaped connecting section and the reinforcement ring, so as to adjust the flatness of the connecting end of the supporting structure by leveling the upper surface of the leveling end cap.

[0039] Furthermore, it also includes a three-claw reinforcement plate, which is arranged on the outer side of the arc connecting section after the arc connecting sections of two adjacent sub-supports are stacked, and the three-claw reinforcement plate is connected to the arc connecting section through SiC / SiC composite material pins.

[0040] Furthermore, the thickness of the sub-bracket is 1.5 to 2 mm;

[0041] The thickness of the three-claw inner connecting plate, the three-claw outer connecting plate and the three-claw adjusting plate is 2-4 mm.

[0042] Beneficial effects of the present invention:

[0043] 1. The secondary barrel structure provided by the present invention is made of C / SiC composite material, which makes up for the defects of the traditional metal support structure that is too heavy and has a large expansion coefficient, so that the barrel has a smaller temperature linear expansion coefficient, its structural size changes little when the temperature changes, and the thermal stress generated is small, which greatly reduces the requirements for the thermal control system and is conducive to the installation and stability of the system.

[0044] 2. The secondary telescope barrel structure provided by the present invention is processed in one piece, which avoids the processing of connecting holes and complicated mechanical connectors, reduces the difficulty of processing the composite barrel in the later stage, and realizes lightweight design, so that the prepared C / SiC composite material telescope barrel has a higher fundamental frequency, dynamic and static stiffness and strength, stable size, low cost, and meets the use requirements of the space environment.

[0045] 3. The barrel preparation method of the present invention realizes integrated processing and overall shaping process through laying, sewing and depositing of carbon fiber cloth, thereby avoiding the existence of installation gap between the inner barrel and the outer ring frame in the original connection method. At the same time, a five-sided box mold is used to prepare a matching five-sided box (weight reduction groove), so that the barrel is supported by reinforcing ribs in both axial and circumferential directions, thereby improving the structural rigidity and strength of the barrel.

[0046] 4. The barrel preparation method of the present invention sews the first carbon fiber cloth layer and the second carbon fiber cloth layer and then deposits the whole body, which reduces the use of connectors and does not require additional CVI deposition to fill the connection gap to increase the overall weight, so that the barrel structure achieves overall weight reduction.

[0047] 5. In the secondary mirror tube structure of the present invention, the supporting structure adopts SiC / SiC composite material with higher modulus. The secondary mirror support tube is subjected to characteristic level knocking modal test. The first-order frequency of the structural constraint state with 1 kg counterweight is greater than 170 Hz, and it has higher rigidity, meeting the requirements for use in space environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a schematic diagram of the structure of a C / SiC composite material secondary barrel embodiment of the present invention;

[0049] Figure 2 It is a schematic structural diagram of an embodiment of the secondary barrel structure of the present invention;

[0050] Figure 3 This is a schematic diagram of the sub-bracket structure in an embodiment of the present invention;

[0051] Figure 4 Schematic diagram of the metal mounting block structure in an embodiment of the present invention.

[0052] The reference numerals are as follows:

[0053] 1-barrel, 101-axial reinforcement rib, 102-circumferential reinforcement rib, 103-inner cylinder, 104-first flange, 105-second flange adjustment plate, 106-C / SiC composite material pin, 107-lower metal mounting plate, 108-metal sleeve, 109-first flange adjustment plate, 110-second flange, 2-support structure, 201-bracket, 202-reinforcement ring, 203-three-claw reinforcement plate, 204-SiC / SiC pin, 205-three-claw outer connecting plate, 206-metal mounting block, 2061-leveling end cap, 2062-connector, 207-three-claw inner connecting plate, 208-sub-bracket outer connecting plate, 209-sub-bracket inner connecting plate, 210-sub-bracket bottom connecting plate, 211-sub-bracket. DETAILED DESCRIPTION

[0054] In this embodiment, the central axis of the secondary lens barrel 1 is taken as the center, the area close to the central axis is considered as the inside, and the area far from the central axis is considered as the outside.

[0055] See also Figure 1 This embodiment provides a C / SiC composite secondary barrel body, which includes an inner barrel 103, a flange, reinforcing ribs, a first flange adjustment plate 109 and a second flange adjustment plate 105; wherein the radial wall thickness of the inner barrel 103 is 3 mm, and the thickness of the flange along the axial direction is 1.5 mm.

[0056] The flange includes a first flange 104 and a second flange 110 respectively located at both ends of the inner cylinder 103 and protruding outward; the first flange adjustment plate 109 is riveted to the first flange 104 by double-row staggered C / SiC composite material pins 106, the first flange adjustment plate 109 is made of C / SiC composite material, and has the same shape as the first flange 104, and has a thickness of 3.5 mm; the second flange adjustment plate 105 is riveted to the second flange 110 by C / SiC composite material pins 106, the second flange adjustment plate 105 is made of double-row staggered C / SiC composite material The inner cylinder 103 is made of composite material and has the same shape as the second flange 110, with a thickness of 3.5 mm; when the axial dimension of the processed inner cylinder 103 does not meet the design dimension, for example, when the axial dimension of the inner cylinder 103 is larger than the design dimension, the axial dimension of the cylinder body 1 can be adjusted as a whole by reducing the thickness of the first flange adjustment plate 109 and / or the second flange adjustment plate 105; when the axial dimension of the inner cylinder 103 is smaller than the design dimension, the axial dimension of the cylinder body 1 can be adjusted as a whole by increasing the thickness of the first flange adjustment plate 109 and / or the second flange adjustment plate 105.

[0057] The connection method of the C / SiC composite secondary lens barrel 1 and other components in the optical remote sensor is as follows: after the first flange adjustment plate 109 and the first flange 104 are riveted together by the C / SiC composite pins 106, a plurality of upper metal mounting plates are evenly arranged along the circumference on the side surface of the first flange adjustment plate 109 by gluing, and a first overflow groove is provided on the gluing surface of the upper metal mounting plate and the first flange adjustment plate 109 to ensure the firmness of the bonding; a plurality of lower metal mounting plates 107 are evenly arranged along the circumference on the side surface of the first flange 104 by gluing, and the lower metal mounting plates 107 and the first flange adjustment plate 109 are connected to the first flange adjustment plate 109 by gluing. A second overflow groove is provided on the bonding surface of a flange 104; the upper metal mounting plate and the lower metal mounting plate 107 are correspondingly arranged to clamp the first flange adjustment plate 109 and the first flange 104 in the middle; a first connecting through hole is sequentially arranged along the upper metal mounting plate, the first flange adjustment plate 109, the first flange 104 and the lower metal mounting plate 107; the upper metal mounting plate and the lower metal mounting plate 107 can protect the first flange adjustment plate 109 and the first flange 104 of the C / SiC composite material, and are also convenient for connection with other components through the first connecting through hole. A plurality of metal sleeves 108 are uniformly arranged through the second flange 110 and the second flange adjustment plate 105 along the circumferential direction. One end of the metal sleeve 108 is flush with the surface of the second flange 110, and an end cap is arranged at the other end to form a step on the surface of the second flange adjustment plate 105. A groove is arranged along the end surface of the end cap for accommodating a connector. The metal sleeve 108 has a second connecting through hole arranged through it for connecting with other components, and the connection occurs between the metal sleeve 108 and the other components to prevent damage to the C / SiC composite secondary barrel.

[0058] The reinforcing ribs include at least one circumferential reinforcing rib 102 and a plurality of axial reinforcing ribs 101; the circumferential reinforcing rib 102 is located outside the inner cylinder 103 and surrounds the inner cylinder 103 circumferentially, and the axial reinforcing rib 101 is located outside the inner cylinder 103 and extends axially to both ends of the inner cylinder 103; the thickness of the circumferential reinforcing rib 102 in the axial direction is 2.5 to 4 mm; the thickness of the axial reinforcing rib 101 in the circumferential direction is 2.5 to 4 mm.

[0059] The inner cylinder 103, the flange and the reinforcing ribs are integrally formed and made of C / SiC composite material.

[0060] The method for preparing the C / SiC composite secondary barrel body comprises the following steps:

[0061] S1. Obtain a mold, which includes a cylinder mold and a plurality of five-sided box molds that cooperate with the cylinder mold, both of which are graphite molds; the cylinder mold has an outer surface for cooperating with the inner surface of the inner cylinder 103; the outer side of the inner cylinder 103 has a plurality of weight-reducing grooves surrounded by flanges and reinforcing ribs; the outer surfaces of the plurality of five-sided box molds are used to cooperate with each weight-reducing groove in a one-to-one correspondence, specifically, the five-sided box mold includes four side surfaces and a bottom surface, with an empty groove inside, the four side surfaces respectively matching the side surfaces of the corresponding weight-reducing grooves, and a bottom surface matching the bottom surface of the corresponding weight-reducing groove.

[0062] S2. Laying a two-dimensional plain carbon fiber cloth on the outer surface of the cylinder mold to form a first carbon fiber cloth layer.

[0063] S3. Laying a two-dimensional plain-weave carbon fiber cloth on the outer surface of the five-sided box mold to form a second carbon fiber cloth layer.

[0064] S4, sewing the first carbon fiber cloth layer and the second carbon fiber cloth layer, and the adjacent second carbon fiber cloth layers, so that the first carbon fiber cloth layer and the second carbon fiber cloth layer are sewn into a whole, forming a carbon fiber preform.

[0065] S5. Performing chemical vapor deposition on the carbon fiber preform multiple times, and gradually removing the cylinder mold and the five-sided box mold in the intervals between the multiple chemical vapor depositions.

[0066] See also Figure 2 This embodiment also provides a secondary lens barrel structure, which includes a barrel body 1 prepared by the above-mentioned preparation method, and a support structure 2 fixedly connected to the barrel body 1; the support structure 2 includes three brackets 201, a reinforcement ring 202, and a three-claw reinforcement plate 203, and the three brackets 201, the reinforcement ring 202 and the three-claw reinforcement plate 203 are all made of SiC / SiC composite materials.

[0067] The first ends of the three brackets 201 are evenly fixedly connected to the second flange 110 along the circumferential direction, and the second ends of the three brackets 201 are fixedly connected to the reinforcement ring 202 to form a three-claw support structure; specifically, each bracket 201 includes two symmetrically arranged sub-brackets 211, and the thickness of the sub-bracket 211 is 1.5 to 2 mm; the two sub-brackets 211 are connected by SiC / SiC pins 204; the bracket 201 also includes a three-claw connecting plate, and the three-claw connecting plate includes a three-claw inner connecting plate 207, a three-claw outer connecting plate 205 and a three-claw adjustment plate.

[0068] See also Figure 3, the first ends of the corresponding two sub-brackets 211 form connecting grooves in opposite directions, and the connecting grooves have a sub-bracket inner connecting plate 209, a sub-bracket outer connecting plate 208 and a sub-bracket bottom connecting plate 210; the sub-bracket inner connecting plate 209 corresponding to the two sub-brackets 211 is connected to the three-claw inner connecting plate 207 through a SiC / SiC pin 204, the sub-bracket outer connecting plate 208 corresponding to the two sub-brackets 211 is connected to the three-claw outer connecting plate 205 through a SiC / SiC pin 204, and the sub-bracket bottom connecting plate 210 corresponding to the two sub-brackets 211 is fixedly connected to the three-claw adjustment plate and the second flange 110 through a C / SiC pin; the thickness of the three-claw inner connecting plate 207, the three-claw outer connecting plate 205 and the three-claw adjustment plate is 2 to 4 mm.

[0069] The second ends of the corresponding two sub-brackets 211 form an arc-shaped connecting section that matches the curvature of the outer side surface of the reinforcement ring 202. The arc-shaped connecting sections of two adjacent sub-brackets 211 of adjacent brackets 201 are stacked, and a three-claw reinforcement plate 203 is arranged on the outer side surface of the arc-shaped connecting section. SiC / SiC pins 204 pass through the three-claw reinforcement plate 203, the arc-shaped connecting sections of the two adjacent sub-brackets 211 and the reinforcement ring 202 in sequence for connection and fixation.

[0070] See also Figure 4 The two arc-shaped connecting sections formed by the two sub-brackets 211 of the bracket 201 form a gap with the reinforcement ring 202, and a metal mounting block 206 matching the gap is arranged in the gap. The metal mounting block 206 is a titanium alloy mounting block. The metal mounting block 206 includes a leveling end cap 2061 and a connector 2062. The connector 2062 is inserted into the gap to achieve connection. The lower end surface of the convex edge of the leveling end cap 2061 is in contact with the arc-shaped connecting section and the reinforcement ring 202, which is used to adjust the flatness of the connecting end of the support structure 2 by leveling the upper surface of the leveling end cap 2061, thereby improving the flatness of the connection with other components in the optical remote sensor.

Claims

1. A C / SiC composite secondary lens barrel, characterized in that: It comprises an inner cylinder (103), a flange and reinforcing ribs; The flange comprises a first flange (104) and a second flange (110) which are respectively located at two ends of the inner cylinder (103) and protrude outward; The reinforcing ribs include at least one circumferential reinforcing rib (102) and a plurality of axial reinforcing ribs (101); the circumferential reinforcing rib (102) is located outside the inner cylinder (103) and surrounds the inner cylinder (103) in the circumferential direction, and the axial reinforcing ribs (101) are located outside the inner cylinder (103) and extend axially to both ends of the inner cylinder (103); The inner cylinder (103), flange and reinforcing ribs are integrally formed and made of C / SiC composite material; It also includes a first flange adjustment plate (109) arranged on the first flange (104) and a second flange adjustment plate (105) arranged on the second flange (110); A plurality of upper metal mounting sheets are evenly arranged along the circumference on the side of the first flange adjustment plate (109) by gluing, and a plurality of lower metal mounting sheets (107) are evenly arranged along the circumference on the side of the first flange (104) by gluing, and the upper metal mounting sheets and the lower metal mounting sheets (107) are correspondingly arranged to clamp the first flange adjustment plate (109) and the first flange (104) in the middle; and a first connecting through hole is sequentially arranged along the upper metal mounting sheet, the first flange adjustment plate (109), the first flange (104) and the lower metal mounting sheet (107); A plurality of metal inserts (108) are evenly arranged through the second flange (110) and the second flange adjustment plate (105) along the circumferential direction, one end of the metal insert (108) is flush with the surface of the second flange (110), and the other end is provided with an end cap to form a step on the surface of the second flange adjustment plate (105); the metal insert (108) has a second connecting through hole arranged through it; The first flange adjustment plate (109) is made of C / SiC composite material with a thickness of no more than 4 mm, and the first flange adjustment plate (109) is riveted to the first flange (104) via C / SiC composite material pins (106); The second flange adjustment plate (105) is made of C / SiC composite material and has a thickness of no more than 4 mm. The second flange adjustment plate (105) and the second flange (110) are riveted together via C / SiC composite material pins (106).

2. The C / SiC composite secondary lens barrel according to claim 1, characterized in that: The radial wall thickness of the inner cylinder (103) is 2.5 to 4 mm; The thickness of the circumferential reinforcing rib (102) in the axial direction is 2.5 to 4 mm; the thickness of the axial reinforcing rib (101) in the circumferential direction is 2.5 to 4 mm; The thickness of the flange along the axial direction is 1.5-2 mm.

3. A method for preparing the C / SiC composite secondary lens barrel according to claim 1 or 2, characterized in that: The following steps are involved: S1. Obtain a mold, wherein the mold includes a cylinder mold and a plurality of five-sided box molds matched with the cylinder mold; The cylinder mold has an outer surface for cooperating with the inner surface of the inner cylinder (103); The outer side of the inner cylinder (103) is provided with a plurality of weight-reducing grooves surrounded by the flange and the reinforcing ribs; the outer profiles of the plurality of five-sided box body molds are used to correspond one-to-one with each of the weight-reducing grooves; S2, laying carbon fiber cloth on the outer surface of the cylinder mold to form a first carbon fiber cloth layer; S3, laying carbon fiber cloth on the outer surface of the five-sided box mold to form a second carbon fiber cloth layer; S4, sewing the first carbon fiber cloth layer and the second carbon fiber cloth layer, and the adjacent second carbon fiber cloth layers, so that the first carbon fiber cloth layer and the second carbon fiber cloth layer are sewn into a whole, forming a carbon fiber preform; S5. Performing chemical vapor deposition on the carbon fiber preform multiple times, and gradually removing the cylinder mold and the five-sided box mold in the intervals between the multiple chemical vapor depositions.

4. The method for preparing the C / SiC composite secondary lens barrel according to claim 3, characterized in that: In step S1, the cylinder mold and a plurality of five-sided box molds matched with the cylinder mold are all graphite molds; In step S2 and step S3, the carbon fiber cloth is a two-dimensional plain weave carbon fiber cloth.

5. A secondary barrel structure, characterized in that: It comprises a secondary lens barrel body (1) made of the C / SiC composite material as claimed in claim 1 or 2, and a supporting structure (2) fixedly connected to the barrel body (1); The support structure (2) comprises three brackets (201) and a reinforcement ring (202); The first ends of the three brackets (201) are evenly and fixedly connected to the second flange (110) along the circumferential direction; the second ends of the three brackets (201) are fixedly connected to the reinforcement ring (202); The three brackets (201) and the reinforcement ring (202) are all made of SiC / SiC composite material.

6. The secondary barrel structure according to claim 5, characterized in that: The support (201) comprises two symmetrically arranged sub-supports (211), and the two sub-supports (211) are connected by SiC / SiC pins (204); The bracket (201) further comprises a three-claw connecting plate, which comprises a three-claw inner connecting plate (207), a three-claw outer connecting plate (205) and a three-claw adjusting plate; The first ends of the two corresponding sub-supports (211) are respectively formed with connection grooves in opposite directions, and the connection grooves have a sub-support inner connection plate (209), a sub-support outer connection plate (208) and a sub-support bottom connection plate (210); The sub-bracket inner connecting plates (209) corresponding to the two sub-brackets (211) are connected to the three-claw inner connecting plates (207) via SiC / SiC pins (204), the sub-bracket outer connecting plates (208) corresponding to the two sub-brackets (211) are connected to the three-claw outer connecting plates (205) via SiC / SiC pins (204), and the sub-bracket bottom connecting plates (210) corresponding to the two sub-brackets (211) are fixedly connected to the three-claw adjustment plate and the second flange (110) via C / SiC pins.

7. The secondary barrel structure according to claim 6, characterized in that: The second ends of the two corresponding sub-supports (211) form an arc-shaped connecting section that matches the curvature of the outer side surface of the reinforcement ring (202); the arc-shaped connecting sections of two adjacent sub-supports (211) of adjacent supports (201) are stacked and fixed to the reinforcement ring (202) via SiC / SiC pins (204); Two arc-shaped connecting sections formed by two sub-supports (211) of the support (201) form a gap with the reinforcement ring (202), and a metal mounting block (206) is arranged in the gap. The metal mounting block (206) comprises a leveling end cap (2061) and a connector (2062). The connector (2062) matches the gap and is used to be inserted into the gap to achieve connection. The lower end surface of the convex edge of the leveling end cap (2061) abuts against the arc-shaped connecting section and the reinforcement ring (202), so as to achieve flatness adjustment of the connecting end of the support structure (2) by leveling the upper surface of the leveling end cap (2061).

8. The secondary barrel structure according to claim 7, characterized in that: It also includes a three-claw reinforcement plate (203), which is arranged on the outer side of the arc-shaped connecting section after two adjacent sub-supports (211) are stacked, and the three-claw reinforcement plate (203) is connected to the arc-shaped connecting section via a SiC / SiC pin (204).

9. The secondary barrel structure according to claim 8, characterized in that: The thickness of the sub-bracket (211) is 1.5 to 2 mm; The thickness of the three-claw inner connecting plate (207), the three-claw outer connecting plate (205) and the three-claw adjusting plate is 2 to 4 mm.

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