Preparation method of mixed bistable laminated plate based on continuous natural fiber 3D printing

Abstract

The invention discloses a preparation method of a mixed bistable laminated plate based on continuous natural fiber 3D printing, and a mixed bistable composite laminated plate is formed by combining a bistable laminated plate laid by unidirectional carbon fiber prepreg with a 3D printing natural fiber silk layer. The problems that two steady-state sudden change loads of an existing bistable carbon fiber composite material laminated plate are similar, the curvature is greatly influenced by bending moment and torque, and the second steady-state configuration is unstable are solved. Due to the fact that the natural fiber silk layer is added, the structural rigidity is improved, the critical load value of conversion from the first steady state to the second steady state is increased, the critical load value of conversion from the second steady state to the first steady state is reduced, the stability of the curvature of the second steady state is improved, and the influence of bending moment and torque on the curvature of the second steady state is reduced. Therefore, the method has a wider application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of composite material structure design, and particularly relates to a preparation method of a hybrid bistable laminate based on continuous natural fiber 3D printing. Background Art

[0002] As a natural fiber, silk fiber can be used to manufacture silk fiber-reinforced composite material structures through vacuum injection of epoxy resin and manual layup technology, and endow the structures with properties such as high toughness, ductility, and degradability. However, due to the high limitations and low designability of traditional forming methods such as vacuum injection method and manual layup, and the limited strength and stiffness of silk fiber, these deficiencies limit the application of silk fiber-reinforced composite materials in the field of intelligent materials. As an emerging method, continuous fiber 3D printing technology, combined with unidirectional carbon fiber prepreg, can provide a new way for the preparation and application of silk fiber composite materials.

[0003] Due to excellent mechanical properties, flexible designability, and the excellent characteristic that the stable state configuration does not require external force to maintain, bistable composite materials have broad application prospects in the fields of aerospace, soft robotics, and cushioning energy absorption. In recent years, with the research on bistable composite materials, the hybrid laminate structure of bistable composite materials based on continuous fiber 3D printing has received increasing attention. However, at present, the second stable state configuration of the bistable carbon fiber composite laminate structure has a large torsion at room temperature, and the curvature changes greatly under the influence of bending and torsion, and the critical loads of the two stable states are similar, which limit the application of this structure in the fields of space, soft robotics, etc. Summary of the Invention

[0004] In view of the above problems, the present invention provides a preparation method of a hybrid bistable laminate based on continuous natural fiber 3D printing. The purpose of the present invention is to combine the bistable laminate laid with unidirectional carbon fiber prepreg with the 3D printed natural fiber silk layer, so as to achieve more excellent mechanical properties, improve the stable state characteristics of the overall structure, and make the second stable state configuration of the hybrid bistable laminate have a certain stability in the ambient temperature environment.

[0005] In order to achieve the above object, the technical solutions adopted by the present invention are as follows:

[0006] S1: According to the composition and ratio of the epoxy resin composite material, prepare epoxy resin powder and heat it to 85 °C to make it in a molten state; pass the natural fiber through the molten epoxy resin to prepare continuous natural fiber pre-impregnated filaments.

[0007] S2: Model the natural fiber silk layer through three-dimensional modeling software, import the STL file into the 3D printer slicing software to generate model G-code, and import it into the 3D printer. Based on the fused deposition technology, prepare the natural fiber silk layer through the continuous natural fiber pre-impregnated filaments.

[0008] S3: Use a cutting machine to cut the unidirectional carbon fiber prepreg into the required laying shape, and lay the cut prepreg and the natural fiber silk layer on a metal cylindrical mold according to a certain laying order. The number of layers of the unidirectional carbon fiber prepreg is an even number, and the natural fiber silk layer is used as the intermediate layer. Lay them in a certain order and perform vacuum pumping treatment, and finally put them into a autoclave for high-temperature and high-pressure curing.

[0009] S4: After curing is completed, take the hybrid bistable laminate out of the autoclave to obtain a carbon fiber / natural fiber reinforced composite laminate with an initial curvature, which is in the first stable state.

[0010] S5: Apply an external force to change the shape of the first stable state to obtain the second stable state of the carbon fiber / natural fiber composite laminate, and measure its second stable state curvature, stable critical load and stable configuration.

[0011] Furthermore, the area of the natural fiber silk layer is equal to or less than the area of the unidirectional carbon fiber prepreg.

[0012] Furthermore, the natural fiber silk layer is a silk fiber reinforced epoxy resin composite, which is composed of E20 epoxy resin powder, dicyandiamide (DICY) and accelerator 100B, and the ratio of the three is 100:8:1, and the melting temperature is 85°C.

[0013] Furthermore, the laying angle of the natural fiber silk layer described in step S3 can be changed according to 3D printing technology, such as: 0°, 45°, -45°, etc.

[0014] Furthermore, in step S2, the hot bed temperature in 3D printing is set to 85°C, the nozzle temperature is 45°C, the printing speed is 50 - 100 mm / min, the printing line width is 0.3 - 0.7 mm, and the printing layer height is 0.1 - 0.2 mm.

[0015] Furthermore, the cross-sectional radius of the metal cylindrical mold used in step S3 is one of R30, R40 and R50, and the metal mold is an aluminum alloy plate or an iron plate coated with Teflon.

[0016] Furthermore, in step S3, laying is carried out according to a certain laying order, specifically: an equal number of unidirectional carbon fiber prepregs are symmetrically distributed on the upper and lower sides of the natural fiber silk layer, and the fiber directions of the unidirectional carbon fiber prepregs on each side are alternately arranged at 45° and -45°.

[0017] Furthermore, in step S3, the curing temperature of high temperature and high pressure is 125°C, the heat preservation time is 130 min, the pressure is set to 800 kpa, and the pressure holding time is 105 min.

[0018] Furthermore, the unidirectional carbon fiber prepreg described in step S3 is one of T300 unidirectional carbon fiber epoxy prepreg and T700 unidirectional carbon fiber epoxy prepreg, and the thickness is 0.1 mm - 0.15 mm.

[0019] The present invention also discloses a bistable carbon fiber / silk fiber composite laminate based on continuous natural fiber 3D printing prepared by the above method. The method for obtaining excellent mechanical properties is: changing the laying angle, the number of laying layers of the natural fiber silk layer, and the 3D printing parameters.

[0020] Furthermore, the method for reducing the torsional effect of the hybrid bistable laminate and improving its stability is: increasing the number of laying layers of the natural fiber silk layer in the hybrid bistable laminate. Increasing the proportion of the natural fiber silk layer in the composite laminate can significantly reduce the torsional effect of the bistable laminate and reduce the influence of bending moment and torque on the second stable configuration of the laminate. When the total number of layers of the hybrid bistable laminate is 8 layers and the proportion of the natural fiber silk layer is 25%, the torsional effect of the second stable state of the hybrid bistable laminate reaches the minimum, and the overall structural layer thickness is 0.9 mm, with specific characteristics such as high strength, high stiffness, and low mass.

[0021] Furthermore, the method for increasing the critical load of the first stable state is to reduce the critical load value from the second stable state to the first stable state: changing the proportion of the natural fiber silk layer and the continuous fiber 3D printing parameters. Increasing the number of laying layers of the natural fiber silk layer in the hybrid bistable laminate can significantly increase the critical load value of the bistable laminate. When only 1 layer of the natural fiber silk layer is added to the hybrid bistable laminate, the first stable state load value of the hybrid bistable laminate can be increased by 121%; at the same time, when the area of the natural fiber silk layer in the hybrid bistable laminate is increased from 100×40 to 100×100, the first stable state load value can also be increased by 109%. In addition, when the continuous fiber 3D printing line width is reduced from 0.7 mm to 0.3 mm, the first stable state load value can be increased from 56 N to 102 N, with an increase amplitude of 82%.

[0022] The present invention successfully solves the problems such as the similar load of the two stable states of the current bistable carbon fiber composite laminate and the large influence of bending and torsion on the curvature of the second stable state. Since the natural fiber silk layer is added in the present invention, the structural stiffness, toughness, and ductility are improved. Therefore, the present invention has a broader application prospect.

[0023] The functions that can be achieved by the hybrid bistable carbon fiber / silk fiber composite laminate of the present invention include increasing the critical load of the first stable state, and the stable state performance of the overall laminate can be changed by varying the area and number of plies of the natural fiber silk layer. In addition, at room temperature, the influence of bending moment and torque on the second stable state configuration can be reduced. The above functional adjustments make the hybrid bistable carbon fiber / silk fiber composite laminate based on the natural fiber silk layer more functional, can be flexibly adjusted according to actual needs, is more intelligent, and has a broader application prospect. Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the laying of a hybrid bistable carbon fiber / silk fiber laminated structure based on continuous natural fibers;

[0025] Figure 2 It is a loading schematic diagram and a critical load diagram of a hybrid bistable carbon fiber / silk fiber composite laminate under different numbers of silk fiber plies and laying angles;

[0026] Figure 3 It is a schematic diagram of the stable state configuration of a hybrid bistable carbon fiber / silk fiber composite laminate based on continuous natural fibers. Detailed Embodiments

[0027] In order to describe the innovative points and technical implementation solutions of the present invention more clearly, it is obvious that the described content is only a part of the creation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0028] As Figure 1 shown, the preparation method of a hybrid bistable laminate based on continuous natural fiber 3D printing includes the following steps:

[0029] S1: Prepare continuous natural fiber prepreg by passing natural fibers through molten epoxy resin.

[0030] S2: Model the natural fiber silk layer using 3D modeling software, import the STL file into the 3D printer slicing software to generate model code, and import it into the 3D printer. Based on the fused deposition technology, prepare the natural fiber silk layer with the continuous natural fiber prepreg.

[0031] S3: Use a cutting machine to cut the unidirectional carbon fiber prepreg into the required laying shape, lay the cut prepreg and the natural fiber silk layer on a metal cylindrical mold in a certain laying order, where the number of layers of the unidirectional carbon fiber prepreg is an even number, and the natural fiber silk layer is used as the middle layer, lay it in a certain order and perform vacuum pumping, and finally put it into a autoclave for high-temperature and high-pressure curing.

[0032] S4: After curing is completed, take out the hybrid bistable laminate from the autoclave to obtain a carbon fiber / natural fiber reinforced composite laminate with an initial curvature, which is in the first stable state.

[0033] S5: By applying an external force to change the shape of the first stable state, obtain the second stable state of the carbon fiber / natural fiber composite laminate, and measure its second stable state curvature and critical load.

[0034] Example 1

[0035] In this example, the area of the natural fiber silk layer is equal to the area of the unidirectional carbon fiber prepreg; the natural fiber silk layer and the unidirectional carbon fiber prepreg have equal areas, are laid alternately at angles of 45° and -45°, and have a thickness of 0.1 mm. The 3D printing parameters of the natural fiber silk layer and the process parameters of the hybrid bistable laminate are shown in Table 1.

[0036] Table 1

[0037]

[0038] Set the total number of layers of the natural fiber silk layer and the carbon fiber prepreg layer as a variable, with a range of 5 - 8 layers. The layup of the hybrid bistable laminate is as shown in Figure 1 (a), where the natural fiber silk layer is used as the middle layer. The metal mold is an aluminum tube wrapped with high-temperature Teflon, as shown in Figure 1 (b).

[0039] For the hybrid bistable composite laminate prepared in Example 1, the method for changing from the first stable state to the second stable state of the laminate is as follows: For the prepared hybrid bistable composite laminate, apply an external force to it to change it to the second stable state, that is, achieve a sudden change from the first stable state to the second stable state, as shown in Figure 2 (a).

[0040] Prepare five groups of hybrid bistable composite laminates of 4-1-45, 4-2-45, 6-1-45, 6-2-45, and 6-2-0 according to the preparation method of the above example. "4" and "6" represent the number of unidirectional carbon fiber layers, "1" and "2" represent the number of natural fiber silk layers, and "45" and "0" represent the layup angles of the natural fiber silk layers, as shown in Table 2.

[0041] Table 2

[0042]

[0043] Among them, in the four groups of 4-1-45, 4-2-45, 6-1-45, and 6-2-45, the natural fiber silk layers are of equal thickness and equal shape, but the number of plies increases sequentially. For 6-2-45 and 6-2-0, the natural fiber silk layers are of equal thickness and equal shape and the same number of plies, but the ply angles are different. After preparation, the first steady state is transformed into the second steady state by applying an external force load, and the required critical load value is measured by a sensor device, as Figure 2 (b) shows. The test results show that the critical loads for the transformation from the first steady state to the second steady state in the four groups of 4-1-45, 4-2-45, 6-1-45, and 6-2-45 increase sequentially; correspondingly, different ply angles of the natural fiber silk layers also affect the critical load value of the first steady state of the hybrid bistable composite laminate.

[0044] Example 2

[0045] In this example, the area of the natural fiber silk layer is equal to the area of the unidirectional carbon fiber prepreg; the number of hybrid plies is 5. Among them, the ply angle of the natural fiber silk layer is 45°, and the ply angles of the carbon fiber are arranged alternately at 45° and -45°. The 3D printing process parameters of the natural fiber silk layer are the same as those in Example 1. The material of the hybrid bistable laminate is set as a variable, and the hybrid bistable carbon fiber / silk fiber composite laminate is compared with the hybrid bistable laminate under different materials, such as copper / carbon fiber bistable composite (Cu-C), aluminum / carbon fiber bistable composite (Al-C), and pure carbon fiber bistable composite (C-C), etc.

[0046] Four groups of hybrid bistable composite laminates under different materials are prepared according to the preparation method of the above example. Among them, the four groups of hybrid bistable composite laminates are all of equal thickness, equal number of plies, and equal shape. After preparation, the bistable laminate is transformed from the first steady state to the second steady state by applying a load, and the maximum critical load value is measured. The critical load values of the hybrid bistable composite laminates under different materials are shown in Table 3.

[0047] Table 3

[0048]

[0049] The test results show that: compared with pure carbon fiber, copper / carbon fiber, and aluminum / carbon fiber bistable composites, the hybrid bistable carbon fiber / silk fiber composite laminate has the maximum steady-state critical load and steady-state curvature, indicating that the hybrid bistable carbon fiber / silk fiber composite laminate prepared by 3D printing has better mechanical properties.

[0050] The present invention also proposes a method for changing the second steady-state curvature at room temperature: the second steady-state curvature of the overall laminate can be changed by changing the laying angle and the number of plies of the natural fiber silk layer; in addition, at room temperature, the influence curvature of the bending moment and torque on the second steady-state configuration can be reduced, and the state maintained at the expected value can be stabilized, that is, the steady-state curvature of the composite laminate is changed, for reference Figure 3 .

[0051] In addition, since the critical loads of the two steady states of the traditional carbon fiber composite laminate are similar, the adjustability of the material is reduced. Therefore, the present invention also proposes to increase the critical load of the first steady state and reduce the critical load value of the second steady state to the first steady state: by changing the shape or size, the number of plies and the printing line width of the natural fiber silk layer, the critical load between the first steady state and the second steady state can be changed. When the shape or area of the natural fiber silk layer changes, the proportion of the natural fiber silk layer in the composite laminate increases, the critical load for the transition from the first steady state to the second steady state increases, and the stiffness of the material also increases in turn.

[0052] In summary, the present invention can realize the adjustment of the relevant critical loads by adding a natural fiber silk layer to the bistable carbon fiber laminate and by changing parameters such as the shape, the number of plies and the laying angle of the natural fiber silk layer, and slows down the influence of the bending moment and torque on the second steady-state configuration. Since the natural fiber silk layer is added in the present invention, the structural stiffness and toughness are improved, the critical load value for the transition from the first steady state to the second steady state increases, the conversion critical load from the second steady state to the first steady state decreases, the stability of the second steady-state curvature is improved, and the influence of the bending moment and torque on the second steady-state curvature is reduced. At the same time, compared with other materials, the 3D printed hybrid bistable carbon fiber / silk fiber composite laminate has better mechanical properties.

[0053] The above detailed description of the present invention is only a preferred embodiment and is not used to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Preparation method of hybrid bistable laminated plate based on continuous natural fiber 3D printing, characterized in that, It includes the following steps: Step S1: Prepare continuous natural fiber prepreg filaments by passing natural fibers through molten epoxy resin; Step S2: Model the natural fiber silk layer using 3D modeling software, import the STL file into 3D printer slicing software to generate model code, import it into the 3D printer, and prepare the natural fiber silk layer based on the fused deposition 3D printing technology using the continuous natural fiber prepreg filaments; Step S3: Use a cutting machine to cut the unidirectional carbon fiber prepreg into the required laying shape, lay the cut prepreg and the natural fiber silk layer on a metal cylindrical mold in the laying order, where the number of layers of the unidirectional carbon fiber prepreg is an even number, and the natural fiber silk layer is used as the intermediate layer, lay them in order and perform vacuum pumping, and finally put them into an autoclave for high-temperature and high-pressure curing; Step S4: After curing is completed, take out the hybrid bistable laminate from the autoclave to obtain a carbon fiber / natural fiber reinforced composite laminate with an initial curvature, in the first stable state; Step S5: Change the shape of the first stable state by applying an external force to obtain the second stable state of the carbon fiber / natural fiber composite laminate, and measure its second stable state curvature and critical load.

2. The preparation method of the hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, wherein The natural fiber silk layer is a silk fiber reinforced epoxy resin matrix composite.

3. The preparation method of the hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, wherein, The area of the natural fiber silk layer is equal to or less than the area of the unidirectional carbon fiber prepreg.

4. The preparation method of the hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, The laying angles of the natural fiber silk layer described in Step S3 include 0°, 45°, or -45°.

5. The preparation method of the hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, wherein In Step S2, the hot bed temperature for 3D printing is set to 85°C, the nozzle temperature is 45°C, the printing speed is 50 - 100 mm / min, the printing line width is 0.3 - 0.7 mm, and the printing layer height is 0.1 - 0.2 mm.

6. The preparation method of the hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, wherein, The cross-sectional radius of the metal cylindrical mold used in Step S3 is one of R30, R40, and R50, and the metal mold is an aluminum alloy plate or an iron plate coated with Teflon.

7. The preparation method of the hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, wherein, In Step S3, laying is carried out in the laying order. Specifically, an equal number of unidirectional carbon fiber prepregs are symmetrically distributed on the upper and lower sides of the natural fiber silk layer, and the fiber directions of the unidirectional carbon fiber prepregs on each side are alternately set at 45° and -45° in turn, where the fiber direction of the natural fiber silk layer is one of 0°, 45°, and -45°.

8. The preparation method of the hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, In Step S3, the curing temperature for high-temperature and high-pressure is 125°C, the heat preservation time is 130 min, the pressure is set to 800 kPa, and the pressure holding time is 105 min.

9. The preparation method of the hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, wherein, The unidirectional carbon fiber prepreg described in Step S3 is a T300 unidirectional carbon fiber epoxy resin prepreg and a T700 unidirectional carbon fiber epoxy resin prepreg, and the thickness is 0.1 mm - 0.15 mm.

10. The preparation method of the hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, wherein, By increasing the number of laying layers of the natural fiber silk layer in the hybrid bistable laminate, the proportion of the natural fiber silk layer in the composite laminate can be increased, the torsional effect of the bistable laminate can be reduced, the influence of bending moment and torque on the second stable state configuration of the laminate can be minimized, and its stability can be improved; By reducing the critical load value from the second steady state to the first steady state, the critical load of the first steady state is increased; specifically: 1) increasing the proportion of the natural fiber silk layer, including increasing the number and area of the natural fiber silk layer; 2) changing the continuous fiber 3D printing parameters.

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