An integrated heterogeneous knitted shape memory composite pod stem, its multicellular structure, and preparation method

Abstract

This invention belongs to the field of intelligent composite materials and spatially deployable structures, and discloses an integrated heterogeneous knitted shape memory composite pod stem, its multicellular structure, and preparation method. The pod stem comprises an integrated knitted pod stem reinforcing preform and a shape memory polymer matrix impregnated and cured therein. The preform, along its cross-section, includes an upper arc-shaped shell segment, a lower arc-shaped shell segment, a connecting segment, and a transition zone between the arc-shaped shell segment and the connecting segment. The arc-shaped shell segment uses a plain weave structure, the connecting segment uses a rib structure, and the transition zone uses a modified plain weave structure with straight floating yarn segments, continuously knitted with adjacent structures to form an integral fiber network structure without adhesive overlap. Multiple cells can be arranged side-by-side along the width direction and integrated through the connecting segment to form a multicellular pod stem structure. This structure can be folded up and unfolded during the processes of heating and softening, flattening and rolling, cooling and fixing, and re-heating. It has advantages such as good integrity, no adhesive interface and low risk of interface failure, high bending stability, large storage ratio and recovery from large deformation. It can be used in aerospace deployable structures, building structures and soft robots.

Description

Technical Field

[0001] This invention relates to an integrated heterogeneous knitted shape memory composite pod stem, its multicellular structure, and its preparation method, belonging to the field of intelligent composite materials and spatial deployable structures technology. Background Technology

[0002] In recent years, the rapid development of my country's aerospace industry has created an increasingly urgent demand for lightweight, highly reliable large-scale deployable space structures, such as large antennas, solar panels, and flexible robotic arms. Shape memory polymer composites, with their advantages of being lightweight, possessing excellent mechanical properties, and offering great design freedom, can be applied in aerospace deployment fields, medical equipment, and soft robotics. Currently, pod-like structures are widely studied as deployment rods in the storage and deployment of large structures due to their high storage ratio and stable deployment performance. Based on these advantages, shape memory composite pod-like structures, with their lightweight, simple structure, high strength, and reliable folding and unfolding capabilities, are expected to become ideal materials for realizing the next generation of large-scale deployable space structures.

[0003] Currently, existing literature has studied the shape memory composite pod rod structure, such as the patent disclosed in CN 112298613A, which describes a composite pod rod based on shape memory composite material for controlling the retraction and unfolding. This patent achieves the unfolding process of the structure by regulating the temperature, resulting in a stable unfolding process and high recovery accuracy. However, the use of adhesive-bonded pod rods poses a risk and problem of interface debonding failure, leading to reduced tolerance to extreme environments and failing to meet the long-term use requirements of spatial unfolding structures.

[0004] Therefore, how to design a heterogeneous knitted deployable structure with high buckling stiffness, large deformation recovery, large storage ratio and integral molding to address the interface distortion problem during large deformation of thin-walled spatial configurations is an industry bottleneck that urgently needs to be solved in the field of spatial deployable mechanisms. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an integrated heterogeneous knitted shape memory pod structure and its preparation method. By introducing a single-sided weft plain knit variation structure at the rigid-flexible interweaving interface, the debonding failure problem caused by stress concentration in traditional glued pods is solved, achieving synergistic optimization of lightweight, high buckling stiffness, large deformation recovery, and large packing ratio.

[0006] To achieve the above objectives, the technical solution of the present invention is:

[0007] This invention provides an integrated heterogeneous knitted shape memory composite pod rod structure, comprising an integrated knitted pod rod reinforcing preform and a shape memory polymer matrix impregnated and cured in the integrated knitted pod rod reinforcing preform; the integrated knitted pod rod reinforcing preform includes an upper arc-shaped shell segment (1), a lower arc-shaped shell segment (2), and a connecting segment (3) located at the edge of adjacent arc-shaped shell segments along the cross-sectional direction; both the upper arc-shaped shell segment (1) and the lower arc-shaped shell segment (2) are composed of a weft plain knit structure (11), and the connecting segment (3) 3) It is composed of double rib structure, that is, it is formed by interweaving the first layer of rib structure (31) and the second layer of rib structure (32); an upper transition area (4) is provided between the upper arc-shaped shell segment (1) and the connecting segment (3), and a lower transition area (5) is provided between the lower arc-shaped shell segment (2) and the connecting segment (3); the upper transition area (4) and the lower transition area (5) are continuously woven with the corresponding arc-shaped shell segment and connecting segment, so that the arc-shaped shell segment, the transition area and the connecting segment form an integral fiber network structure without glued overlap interface.

[0008] The integrated heterogeneous knitted shape memory composite pod structure is characterized in that: the upper transition zone (4) is composed of the upper weft plain knit variation structure (41), and the lower transition zone (5) is composed of the lower weft plain knit variation structure (41); the weft plain knit variation structure is based on the loop (111) and includes straight floating line segments (411) arranged in rows along the length direction of the pod, the straight floating line segments (411) spanning adjacent longitudinal rows or multiple adjacent longitudinal rows to form a continuous transition structure between the weft plain knit structure (11) and the rib structure.

[0009] The pod stalk structure is a multi-cell structure. The integrated heterogeneous knitted shape memory composite pod stalk structure is characterized in that: the multi-cell structure includes at least two single-cell structures arranged side by side along the width direction. Adjacent single-cell structures are integratedly connected by the connecting segment (3) as described in claim 1, thereby forming a heterogeneous multi-cell structure in which multiple upper arc-shaped shell segments (1) and lower arc-shaped shell segments (2) and multiple connecting segments (3) serving as longitudinal rigid reinforcing ribs work together to bear force. A double-cell structure (6) includes two cells and three connecting segments, and a triple-cell structure (7) includes three cells and four connecting segments.

[0010] The integrated heterogeneous knitted shape memory composite pod rod structure is characterized in that: the shape memory polymer resin is one of the following: shape memory epoxy resin, shape memory phenolic resin, shape memory polyamide resin, shape memory styrene, shape memory polyether ether ketone, shape memory cyanate ester, shape memory polynorbornene, shape memory polyimide, shape memory polyphenylene sulfide, and shape memory polyvinyl alcohol.

[0011] The integrated heterogeneous knitted shape memory composite pod stalk structure is characterized in that: the knitted reinforced pod stalk preform is integrally woven from high-performance yarn. The high-performance yarn is a blend of one or two of glass fiber, carbon fiber, aramid fiber, polyimide fiber, basalt fiber, quartz fiber, and alumina fiber, with a yarn fineness of 60-300 tex.

[0012] The integrated heterogeneous knitted shape memory composite pod stalk structure is characterized by the following steps in its preparation method: ① Knitting the pod stalk reinforcement preform: A pattern drawing of the pod stalk structure is created in pattern-making software and then imported into a computerized flat knitting machine. The pod stalk reinforcement preform is knitted using 60-300 tex yarn. ② Pretreatment: A release agent is applied to the surface of the mold, and then the mold is placed in the cavity of the integrated pod stalk fabric. ③ The knitted pod stalk reinforcement preform is impregnated with shape memory resin. ④ Thermosetting treatment is performed, and the preform is demolded after cooling to room temperature to obtain the shape memory composite pod stalk structure.

[0013] The integrated heterogeneous knitted shape memory composite material pod rod structure is characterized in that: the knitted pod rod reinforced preform, the connecting section (3) interval: the command instantly switches to a full needle double needle bed knitting configuration. The front needle bed and the rear needle bed needles participate in the loop formation simultaneously, and the first layer of rib structure (31) and the second layer of rib structure (32) are deeply interlocked and interwoven in the longitudinal and transverse rows of the loops to form a rigid rib structure with doubled thickness and fiber volume content; the knitted pod rod reinforced preform consists of an upper arc-shaped shell section (1), a lower arc-shaped shell section (2), an upper transition zone (4), and a lower transition zone (5): the front needle bed needles are responsible for knitting the upper weft plain knit structure (11) and the upper weft plain knit variation structure (41), and the corresponding needles of the rear needle bed are responsible for knitting the lower weft plain knit structure (11) and the lower weft plain knit variation structure (41). During the reciprocating stroke of the machine head, the front and rear needle beds are independently controlled to de-loop in layers, thereby constructing a completely hollow and independent physical cavity in the plane.

[0014] The integrated heterogeneous knitted shape memory composite pod rod structure is characterized in that: at the junction of the upper weft plain knitting structure (11) and the first layer rib knitting structure (31), and the lower weft plain knitting structure (11) and the second layer rib knitting structure (32), in order to eliminate edge looping and geometric abrupt changes caused by inconsistent shrinkage rates at both ends, four horizontal rows of weft plain knitting variation structures (41) are constructed in the pattern-making software. This structural design, consisting of 1×1 "coil-float" spatial misalignment and interlocking, ensures that high-density longitudinal straight tension ribs are embedded inside the variation structure area after the machine is removed from the machine.

[0015] The integrated heterogeneous knitted shape memory composite pod rod structure is characterized in that: the knitted pod rod reinforcing preform is knitted into loops using high-performance inorganic / organic yarns with a fineness in the range of 60-300 tex. Because these fibers lack the softness of clothing fibers, they are prone to fuzzing or yarn accumulation during mechanical bending, which can also damage the needle latch. Therefore, the following adjustments must be made to the flat knitting machine parameters: In the machine head operation program, highly discontinuous yarn bending depth values ​​are assigned to different areas; in the single-sided weft plain knit cell area, the yarn bending depth value is 330-355; in the double rib connection section, due to the congestion of the double-layer loops, a larger yarn bending depth value is set than that of the single-sided structure, i.e., 360-370; appropriately reducing the yarn feeding tension and machine speed, setting the machine speed to 0.3-0.5 m / s, can reduce the friction during yarn knitting, thereby reducing loop fuzzing and loop slippage.

[0016] The method for gathering and unfolding the integrated heterogeneous knitted shape memory composite pod stalk structure is characterized in that the gathering method includes the following steps: Step 1, heating and softening: heating the entire pod stalk to a high temperature (the glass transition temperature T of the shape memory resin). g ~T g +40℃), at which point the resin matrix changes from a glassy state to a highly elastic rubbery state, making the entire composite material structure easily deformable; Step 2, flattening deformation: applying external force to flatten the single-cell or multi-cell pod stalks with an arc-shaped cross-section; Step 3, curling and storage: in the flattened state, the pod stalks are curled and deformed around a cylindrical mold; Step 4, cooling and fixing: maintaining the constraint force in the curled state, the structure is cooled to room temperature. At this point, the resin returns to the glassy phase and hardens. Even after the external force is removed, it can still maintain the folded state; the unfolding process includes the following steps: Step 1, thermal drive: placing the folded pod stalks under a thermal external field, causing the structure temperature to rise again and exceed T g Step 2, Cooperative Stable Deployment: Through the mechanism of "active recovery of connecting segments and follow-up recovery of shell segments", the pod stalk gradually extends from the curled state and recovers from the flattened state to the initial arc-shaped cross-sectional configuration; Step 3, Cooling and Fixing: After the deployment is completed, if the ambient temperature decreases or the heat source is removed, the structure restores its rigidity and enters the working state by relying on the geometry of the pod stalk to provide high bending stiffness and structural stability.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. In the integrated heterogeneous knitted shape memory composite pod stalk, its multicellular structure, and preparation method of the present invention, the heterogeneous knitted reinforcing skeleton comprises two symmetrical upper and lower layers, mainly composed of weft plain knit and double rib knit. The double rib knit is formed by the interweaving of a first layer of rib knit and a second layer of rib knit. The upper layer consists of an upper layer of weft plain knit, an upper layer of weft plain knit variation, and a first layer of rib knit connected sequentially; the lower layer consists of a lower layer of weft plain knit, a lower layer of weft plain knit variation, and a second layer of rib knit connected sequentially. A 1×1 "coil × float" weft plain knit variation transition is used between the double rib and the weft plain knit. The float acts as a transverse microscopic unidirectional tension rib perpendicular to the heterogeneous boundary in the circumferential direction, providing stable connection and support for the structure. Therefore, the heterogeneous knitted integrated pod stalk knitting skeleton designed in this invention has high reliability and stability.

[0019] 2. In the integrated heterogeneous knitted shape memory composite pod stalk, its multicellular structure, and preparation method of the present invention, the knitted integrated heterogeneous knitted pod stalk skeleton is impregnated with a shape memory epoxy resin system, then heated and cured, and cooled to room temperature to form a three-dimensional material with shape memory. Because a weft plain knit variation structure is introduced into the knitted reinforcing skeleton, the float yarns are not looped, thus forming a groove-shaped flexible folded hinge with a physical thickness lower than that of the structures on both sides, and constituting a micro-mesh. This reduces the formation of a local resin-rich matrix layer or brittle defects at the heterogeneous interface edge during the resin impregnation and curing process. This shape memory composite material utilizes the excellent ductility and deformation recovery of the weft plain knit structure, and the stable structure, lateral resistance to curling, and good tensile recovery of the double rib knit structure, which can meet the requirements of large deformation, recovery, and structural stability of the pod stalk during flattening and curling. Because the composite material of the integrated heterogeneous knitted shape memory pod stalk structure designed in this way achieves a glue-free interface, it not only has high integrity but also excellent recovery rate.

[0020] 3. In the integrated heterogeneous knitted shape memory composite pod rod of the present invention, its multicellular structure, and preparation method, multiple cell structures are arranged side-by-side along the width direction. Compared with a single rod, the multicellular structure significantly enhances the bending stiffness and stability of the pod rod structure due to the synergistic force distribution of multiple cells. Furthermore, the multicellular structure design also has high functional redundancy; damage to local cells does not affect the overall functional failure. Therefore, this design can adapt to different application scenarios, further expanding the application of shape memory composite materials in aerospace.

[0021] 4. During the folding process of the integrated heterogeneous knitted shape memory composite pod rod of this invention, the structure maintains its integrity and remains crack-free even when the memory material is rolled on a mold with a very small radius. During the unfolding process of the adhesive-free interface integrated heterogeneous knitted shape memory pod rod structure of this invention, a collaborative mechanism of "active recovery of the connecting segment and follow-up recovery of the shell segment" is achieved. Under thermal drive, the connecting segment preferentially generates a restoring force to drive the structure back to its original shape, which in turn drives the softened shell segment to move synchronously, ensuring the path controllability of the pod rod in the folding-unfolding cycle. Even after multiple folding-unfolding cycles, the shape memory pod rod of this invention still exhibits excellent shape recovery rate. Therefore, the shape memory pod rod composite material of this design not only has a high packing ratio but also achieves large deformation and recoverability, meeting the long-term use requirements of deployable structures in aerospace. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the shape memory pod stem unit cell structure of the present invention.

[0023] Figure 2 This is a schematic cross-sectional view of the shape memory pod stem unit cell structure of the present invention.

[0024] Figure 3 This is a schematic diagram of the shape memory bean pod stem twin-cell structure of the present invention.

[0025] Figure 4 This is a schematic diagram of the three-cell structure of the shape memory bean pod stem of the present invention.

[0026] Figure 5 This is a schematic diagram of the weft needle structure.

[0027] Figure 6 This is a schematic diagram of a double ribbed weave structure.

[0028] Figure 7 This is a schematic diagram of the weft-needle weave structure.

[0029] In the diagram: 1 is the upper arc-shaped shell segment of the pod stalk; 2 is the lower arc-shaped shell segment; 3 is the connecting segment; 4 is the upper transition zone; 5 is the lower transition zone; 6 is the double-cell structure; 7 is the triple-cell structure; 11 is the weft plain knit fabric; 31 is the first layer rib knit; 32 is the second layer rib knit; 111 is the loop; 41 is the weft plain knit variation structure; and 411 is the float. The same reference numerals are used for similar structural elements. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] See Figures 1-7The present invention discloses a shape memory composite material pod stalk structure, which is a symmetrical structure both vertically and horizontally. Along the cross-sectional direction, it includes an upper arc-shaped shell segment (1), a lower arc-shaped shell segment (2), and a connecting segment (3) located at the edge of adjacent arc-shaped shell segments. The upper arc-shaped shell segment (1) and the lower arc-shaped shell segment (2) are both composed of a weft plain knit weave (11), and the connecting segment (3) is composed of a double rib weave, i.e., a first rib weave (31) and a second rib weave (32) interwoven. An upper transition zone (4) is provided between the upper arc-shaped shell segment (1) and the connecting segment (3), and a lower transition zone (5) is provided between the lower arc-shaped shell segment (2) and the connecting segment (3). Both the upper transition zone (4) and the lower transition zone (5) are continuously woven with the corresponding arc-shaped shell segment and connecting segment. The upper transition zone (4) is composed of an upper layer of plain weft knitting variation (41), and the lower transition zone (5) is composed of a lower layer of plain weft knitting variation (41). This plain weft knitting variation uses coils (111) as the base structure and is equipped with straight floating line segments (411) arranged in rows along the length of the pod stalk. The straight floating line segments (411) span adjacent longitudinal rows or multiple adjacent longitudinal rows. Therefore, this structure forms a continuous transition structure between the plain weft knitting and double rib knitting, enabling the arc-shaped shell segment, transition zone, and connecting segment to form an integral fiber network structure without adhesive overlap. Furthermore, the shape memory composite material pod stalk multicellular structure of the present invention includes at least two single-cell structures arranged side-by-side along the width direction, and adjacent single-cell structures are integrated through connecting segments, improving the overall integrity and stability of the structure.

[0032] In embodiments 1-5 of the present invention, the preparation of shape memory composite material pod stems follows the general process described below:

[0033] 1. Knitting the Prefabricated Structure: Draw the machine drawing of the pod stalk structure in the constant force pattern, then import it into the computerized flat knitting machine and knit using 200tex glass fiber yarn. Proceed to step 2.

[0034] II. Pretreatment: Coat the mold with a release agent, then place it inside the cavity of the integrated pod stalk fabric. Proceed to step three.

[0035] 3. Impregnation: The fabric preform is impregnated with shape memory epoxy resin. A shape memory epoxy resin mixture of epoxy resin / aniline / p-phenylenediamine is used to impregnate the reinforced preform. After completion, proceed to step 4.

[0036] IV. Heat Treatment: The impregnated bean pod stem preform is placed in an oven. First, it is cured at 70℃ for 1 hour, then at 120℃ for 2 hours. After cooling to room temperature, it is demolded to obtain the shape memory composite bean pod stem structure.

[0037] The glass transition temperature T of the shape memory epoxy resin is mentioned.g At 80℃, under external heat drive, the resin will undergo a phase transition from a glassy state to a rubbery state, promoting shape recovery.

[0038] Example 1:

[0039] This example demonstrates the shape memory properties and bending stiffness of a basic unit cell structure.

[0040] The flattened width of the single-cell arc-shaped shell segment is 60mm, the width of each side of the edge is 10mm, and the length is 160mm.

[0041] The shape memory performance test procedure involves heating the sample to 110°C, flattening it, and then winding it 360° around a mold with a radius of 30mm. The sample is then fixed and cooled to a temporary shape. Upon reheating to 110°C, the structure recovers due to the active recovery of the connecting sections, which in turn causes the shell sections to follow suit. After the curling test, the sample surface showed no cracks or whitening.

[0042] The bending stiffness test was conducted using a universal testing machine, and the bending stiffness of the single-cell pod stalk was measured through a three-point bending test, with a span of 110 mm.

[0043] Example 2:

[0044] Unlike Example 1, during the curling process, the single-cell pod stalk composite material was wound onto a mold with a radius of 20 mm, while the structural parameters and testing methods remained the same as in Example 1.

[0045] Example 3:

[0046] Unlike Example 1, during the curling process, the single-cell pod stalk composite material was wound onto a mold with a radius of 10 mm, while the structural parameters and testing methods remained the same as in Example 1.

[0047] Example 4:

[0048] This example demonstrates the shape memory properties and bending stiffness of a twin-cell structure. (See...) Figure 3 .

[0049] The twin-cell structure comprises two shell segments and three double-ribbed connecting segments. The flattened width of the arc-shaped shell segment is 27.5 mm, the width of each side of the edge is 10 mm, the connecting segment between adjacent cells is 5 mm, and the length is 160 mm.

[0050] The difference between this example and examples 1-3 is that the number of parallel cells is increased, while the bending stiffness and shape memory tests are the same as in example 3.

[0051] Example 5:

[0052] This example demonstrates the shape memory properties and bending stiffness of a tripartite structure. (See...) Figure 4 .

[0053] The described three-cell structure comprises three shell segments and four double-ribbed connecting segments. The flattened width of the arc-shaped shell segments is 16.7 mm, the width of each side of the edge is 10 mm, and the connecting segment between adjacent cells is 5 mm.

[0054] The difference between this example and examples 1-3 is that the number of parallel cells is increased, while the bending stiffness and shape memory tests are the same as in example 3.

[0055] Test data analysis:

[0056] By conducting shape memory tests on this implementation case at high temperatures and performing three-point bending tests in a universal testing machine, the data shown in the table were obtained.

[0057] Final response rate 99.2% 98.5% 98% 97.8% 97.2% Response time 118s 134s 145s 162s 175s Response rate after 10 "crowd-expand" cycles ＞95% ＞95% ＞95% ＞95% ＞95%

[0058] The results show that for single-cell structures, as the curl radius decreases from 30 mm to 10 mm, the recovery time increases and the final recovery rate decreases slightly, but it can still remain above 98%. For multi-cell structures, as the number of cells increases, the structural constraint strengthens, the recovery time increases, and the final recovery rate decreases slightly. After 10 coiling-unfolding cycles, the pod stem of this invention can still maintain a shape recovery rate of over 95%, meeting the long-term reliability requirements of aerospace deployment mechanisms.

[0059] The data in the table are obtained by performing a three-point bending test on the universal testing machine at room temperature for this implementation case.

[0060] Bending failure load 161.1N 271.5N 340.9N fracture displacement 17mm 22mm 29mm

[0061] The test results show that as the number of cells increases, the slope of the elastic segment of the load-displacement curve increases, i.e., the flexural modulus increases; at the same time, the flexural failure load and fracture displacement of the specimen increase. This indicates that multicellular structures exhibit higher flexural load-bearing capacity and better post-peak stability.

[0062] Example 6:

[0063] A method for preparing a shape memory pod stem structure composed of a mixture of two types of yarn.

[0064] I. Knitting the Prefabricated Structure: Draw the machine layout diagram of the pod stalk structure in the constant force pattern making system. Arrange two yarn feeders in the pattern making system, namely yarn feeder No. 3 and yarn feeder No. 4. The upper layer plain weft knit, the upper layer plain weft knit variation, and the first layer rib knit are controlled by yarn feeder No. 3. The lower layer plain weft knit, the lower layer plain weft knit variation, and the second layer rib knit are controlled by yarn feeder No. 4. Then, import it into the computerized flat knitting machine. Use yarn feeder No. 3 to thread carbon fiber and yarn feeder No. 4 to thread aramid fiber. Then, weave. During weaving, yarn feeder No. 3, guided by the machine head, completes the upper layer knitting of the pod stalk, and yarn feeder No. 4, guided by the machine head, completes the lower layer knitting of the pod stalk. Proceed to step two.

[0065] II. Pretreatment: Coat the mold with a release agent, then place it inside the cavity of the integrated pod stalk fabric. Proceed to step three.

[0066] 3. Impregnation: The fabric preform is impregnated with shape memory epoxy resin. A shape memory epoxy resin mixture of epoxy resin / aniline / p-phenylenediamine is used to impregnate the reinforced preform. After completion, proceed to step 4.

[0067] IV. Heat Treatment: The impregnated bean pod stem preform is placed in an oven. First, it is cured at 70℃ for 1 hour, then at 120℃ for 2 hours. After cooling to room temperature, it is demolded to obtain the shape memory composite bean pod stem structure.

[0068] The glass transition temperature T of the shape memory epoxy resin is mentioned. g At 80℃, under external heat drive, the resin will undergo a phase transition from a glassy state to a rubbery state, promoting shape recovery.

[0069] The shape memory pod stalk composite material, reinforced by a hybrid weaving of carbon fiber and aramid fiber, exhibits high stiffness on the carbon fiber side and high toughness on the aramid fiber side. Therefore, the hybrid shape memory pod stalk prepared in this example possesses excellent shape memory properties while also achieving a balance between high stiffness and high fracture toughness.

Claims

1. An integrated heterogeneous knitted shape memory composite pod rod structure, characterized in that: An integrated heterogeneous knitted shape memory composite pod rod structure includes an integrated knitted pod rod reinforcing preform and a shape memory polymer matrix impregnated and cured in the integrated knitted pod rod reinforcing preform; The integrated knitted pod stalk reinforced preform includes an upper arc-shaped shell segment (1), a lower arc-shaped shell segment (2), and a connecting segment (3) located at the edge of adjacent arc-shaped shell segments along the cross-sectional direction. The upper arc-shaped shell segment (1) and the lower arc-shaped shell segment (2) are both composed of weft plain knitting (11), and the connecting segment (3) is composed of double rib knitting, that is, it is formed by interlacing the first layer of rib knitting (31) and the second layer of rib knitting (32). An upper transition zone (4) is provided between the upper arc-shaped shell segment (1) and the connecting segment (3), and a lower transition zone (5) is provided between the lower arc-shaped shell segment (2) and the connecting segment (3). The upper transition zone (4) and the lower transition zone (5) are continuously knitted with the corresponding arc-shaped shell segment and the connecting segment, so that the arc-shaped shell segment, the transition zone and the connecting segment form an integral fiber network structure without glued overlap interface.

2. The integrated heterogeneous knitted shape memory composite pod rod structure according to claim 1, characterized in that: The upper transition zone (4) is composed of the upper weft plain knit variation structure (41), and the lower transition zone (5) is composed of the lower weft plain knit variation structure (41). The weft plain knit variation structure uses coils (111) as the ground structure and includes straight floating line segments (411) arranged in rows along the length of the pod stalk. The straight floating line segments (411) span adjacent longitudinal rows or multiple adjacent longitudinal rows to form a continuous transition structure between the weft plain knit structure (11) and the rib structure.

3. The integrated heterogeneous knitted shape memory composite pod rod structure according to claim 1, characterized in that: The pod stalk structure is a multicellular structure, which comprises at least two single-cell structures arranged side by side along the width direction. Adjacent single-cell structures are integrated and connected by the connecting segments (3) as described in claim 1, thereby forming a heterogeneous multicellular structure in which multiple upper arcuate shell segments (1) and lower arcuate shell segments (2) and multiple connecting segments (3) acting as longitudinal rigid reinforcing ribs work together to bear force. A two-cell structure (6) comprises two cells and three connecting segments, and a three-cell structure (7) comprises three cells and four connecting segments.

4. The integrated heterogeneous knitted shape memory composite pod rod structure according to claim 1, characterized in that: The shape memory polymer resin is one of the following: shape memory epoxy resin, shape memory phenolic resin, shape memory polyamide resin, shape memory styrene, shape memory polyether ether ketone, shape memory cyanate ester, shape memory polynorbornene, shape memory polyimide, shape memory polyphenylene sulfide, and shape memory polyvinyl alcohol.

5. The integrated heterogeneous knitted shape memory composite pod rod structure according to claim 1, characterized in that: The knitted reinforced bean pod stalk preform is integrally woven from high-performance yarn. The high-performance yarn is one or two of glass fiber, carbon fiber, aramid fiber, polyimide fiber, basalt fiber, quartz fiber, and alumina fiber, and its yarn fineness is 60-300 tex.

6. An integrated heterogeneous knitted shape memory composite pod rod structure as described in claim 1, characterized in that: The preparation method includes the following steps: Knitted pod stalk reinforced preform: The pod stalk structure is drawn in pattern-making software and then imported into a computerized flat knitting machine. The pod stalk reinforced preform is knitted using 60-300 tex yarn. Pretreatment: A release agent is applied to the mold surface, and then the mold is placed in the cavity of the integrated pod stalk fabric. The knitted pod stalk reinforced preform is impregnated with shape memory resin. After thermosetting and cooling to room temperature, it is demolded to obtain a shape memory composite material pod stalk structure.

7. The integrated heterogeneous knitted shape memory composite pod rod structure according to claim 6, characterized in that: The knitted pod stalk reinforced preform, in the connecting section (3) section: the command instantly switches to a full needle double needle bed knitting configuration. The front needle bed and the rear needle bed knitting needles participate in loop formation at the same time, and the first layer of rib structure (31) and the second layer of rib structure (32) are deeply interlocked and interpenetrated in the longitudinal and transverse rows of the loops to form a rigid rib structure with doubled thickness and fiber volume content; the knitted pod stalk reinforced preform, in the upper arc shell section (1), the lower arc shell section (2), the upper transition area (4), and the lower transition area (5) section: the front needle bed knitting needles are responsible for knitting the upper weft plain knit structure (11) and the upper weft plain knit variation structure (41), and the corresponding needles of the rear needle bed are responsible for knitting the lower weft plain knit structure (11) and the lower weft plain knit variation structure (41). During the reciprocating stroke of the knitting head, the front and rear needle beds are independently controlled to layer and retract, thereby constructing a completely hollow and independent physical cavity in the plane.

8. The integrated heterogeneous knitted shape memory composite pod rod structure according to claim 6, characterized in that: In order to eliminate edge slippage and geometric abrupt changes caused by inconsistent shrinkage rates at both ends, the aforementioned knitted pod-shaped reinforcing preform has four horizontal rows of weft plain knit variation structures (41) constructed in the pattern-making software at the junction of the upper weft plain knit structure (11) and the first layer of rib knit structure (31), and the lower weft plain knit structure (11) and the second layer of rib knit structure (32). This structural design with 1×1 "coil-float" spatial misalignment and interlocking ensures that high-density longitudinal straight tension ribs are embedded in the variation structure area after the machine is removed.

9. The integrated heterogeneous knitted shape memory composite pod rod structure according to claim 6, characterized in that: The aforementioned knitted pod-stalk reinforced preform is knitted into loops using high-performance inorganic / organic yarns with a fineness ranging from 60-300 tex. Because these fibers lack the softness of clothing fibers, they are prone to fuzzing or yarn accumulation during mechanical bending, which can also damage the needle latch. Therefore, the following adjustments must be made to the flat knitting machine's mechanical parameters: In the machine head operation program, highly discontinuous yarn bending depth values ​​are assigned to different areas; in the single-sided plain knit cell area, the yarn bending depth value is 330-355; in the double rib knit connecting section, due to the congestion of the double-layer loops, a larger yarn bending depth value is set than for the single-sided structure, i.e., 360-370; Appropriately reducing the yarn feeding tension and machine speed, setting the machine speed to 0.3-0.5 m / s, can reduce the friction during yarn knitting, thereby reducing loop fuzzing and loop slippage.

10. The method for gathering and unfolding the integrated heterogeneous knitted shape memory composite pod rod structure according to claim 1, characterized in that: The gathering method includes the following steps: Step 1, heating and softening: Heating the entire bean pod stalk to a high temperature (shape memory resin glass transition temperature T). g ~T g +40℃), at which point the resin matrix changes from a glassy state to a highly elastic rubbery state, making the entire composite material structure easily deformable; Step 2, flattening deformation: applying external force to flatten the single-cell or multi-cell pod stalks with an arc-shaped cross-section; Step 3, curling and storage: in the flattened state, the pod stalks are curled and deformed around a cylindrical mold; Step 4, cooling and fixing: maintaining the constraint force in the curled state, the structure is cooled to room temperature. At this point, the resin returns to the glassy phase and hardens. Even after the external force is removed, it can still maintain the folded state; the unfolding process includes the following steps: Step 1, thermal drive: placing the folded pod stalks under a thermal external field, causing the structure temperature to rise again and exceed T g Step 2, Cooperative Stable Deployment: Through the mechanism of "active recovery of connecting segments and follow-up recovery of shell segments", the pod stalk gradually extends from the curled state and recovers from the flattened state to the initial arc-shaped cross-sectional configuration; Step 3, Cooling and Fixing: After the deployment is completed, if the ambient temperature decreases or the heat source is removed, the structure restores its rigidity and enters the working state by relying on the geometry of the pod stalk to provide high bending stiffness and structural stability.

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