Method for the production of hybrid bistable laminates based on continuous natural fiber 3d printing

Abstract

The application discloses a kind of preparation methods of mixed bistable laminated plate based on continuous natural fiber 3D printing, by the bistable laminated plate of unidirectional carbon fiber prepreg laying and 3D printing natural fiber silk layer are combined, form mixed bistable composite laminated plate.The application solves the problems that the two stable state mutation load of current bistable carbon fiber composite laminated plate is similar, curvature is greatly influenced by bending moment and torque and the second stable state configuration is unstable and the like.Because natural fiber silk layer is added in the application, the structural stiffness is improved, the first stable state changes critical load value to the second stable state, the conversion critical load of the second stable state to the first stable state is reduced, and the stability of the second stable state curvature is improved, the influence of bending moment and torque on the second stable state curvature is reduced.Therefore, the application has more extensive application prospect.

Description

Technical Field

[0001] This invention belongs to the field of composite material structural design, specifically relating to a method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing. Background Technology

[0002] Silk fiber, as a natural fiber, can be used to create silk fiber-reinforced composite structures with high toughness, ductility, and biodegradability through vacuum injection molding of epoxy resin and manual lay-up techniques. However, the limitations and low designability of traditional molding methods such as vacuum injection molding and manual lay-up, along with the limited strength and stiffness of silk fibers, restrict the application of silk fiber-reinforced composites in the field of smart materials. Continuous fiber 3D printing technology, as an emerging method, combined with unidirectional carbon fiber prepreg, offers a new approach to the preparation and application of silk fiber composites.

[0003] Bistable composite materials, due to their excellent mechanical properties, flexible designability, and the fact that their steady-state configuration does not require external force to maintain, have broad application prospects in aerospace, soft robotics, and energy absorption. In recent years, with the advancement of research on bistable composite materials, hybrid laminated structures based on continuous fiber 3D printing of bistable composite materials have attracted increasing attention. However, current bistable carbon fiber composite laminate structures suffer from large torsion in the second steady-state configuration at room temperature, significant curvature variations due to bending and torsion, and similar critical loads in the two steady states. These shortcomings limit the application of this structure in aerospace, soft robotics, and other fields. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing. The purpose of this invention is to combine a bistable laminate with unidirectional carbon fiber prepreg with a 3D-printed natural fiber silk layer, thereby achieving superior mechanical properties, improving the overall structural stability, and ensuring that the second stable configuration of the hybrid bistable laminate exhibits certain stability in a room temperature environment.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] S1: Based on the composition and proportion of epoxy resin composite materials, prepare epoxy resin powder and heat it to 85°C to make it molten; pass natural fibers through the molten epoxy resin to prepare continuous natural fiber prepreg.

[0007] S2: The natural fiber silk layer is modeled using 3D modeling software. The STL file is imported into the 3D printer slicing software to generate the model G code, which is then imported into the 3D printer. Based on fused deposition modeling technology, the natural fiber silk layer is prepared by continuous natural fiber prepreg.

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

[0009] S4: After curing, the mixed bistable laminate is removed from the autoclave to obtain a carbon fiber / natural fiber reinforced composite laminate with initial curvature, which is in the first stable state.

[0010] S5: By applying an external force to change the shape of the first steady state, the second steady state of the carbon fiber / natural fiber composite laminate is obtained, and its second steady state curvature, steady state critical load, and steady state configuration are measured.

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

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

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

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

[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 iron plate covered with Teflon.

[0016] Furthermore, in step S3, the prepreg is laid in a certain order, specifically: equal amounts of unidirectional carbon fiber prepreg are antisymmetrically distributed on the upper and lower sides of the natural fiber silk layer, and the fiber direction of the unidirectional carbon fiber prepreg on each side is alternately set at 45° and -45°.

[0017] Furthermore, in step S3, the high-temperature and high-pressure curing temperature is 125℃, the holding time is 130min, the pressure is set to 800kpa, and the holding time is 105min.

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

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

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

[0021] Furthermore, a method to increase the critical load of the first steady state is to reduce the critical load value from the second steady state to the first steady state by changing the proportion of the natural fiber silk layer and the continuous fiber 3D printing parameters. Increasing the number of natural fiber silk layers in the hybrid bistable laminate can significantly increase the steady-state critical load value of the bistable laminate. When only one layer of natural fiber silk is added to the hybrid bistable laminate, the first steady-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 steady-state load value can also be increased by 109%. In addition, reducing the linewidth of the continuous fiber 3D printing from 0.7mm to 0.3mm can increase the first steady-state load value from 56N to 102N, an increase of 82%.

[0022] This invention successfully solves the problems of similar steady-state loads in the two steady-state carbon fiber composite laminates and the significant influence of bending and torsion on the second steady-state curvature. Because a natural fiber silk layer is incorporated into this invention, the structural stiffness, toughness, and ductility are improved; therefore, this invention has broader application prospects.

[0023] The hybrid bistable carbon fiber / silk fiber composite laminate of this invention can achieve the following functions: increasing the critical load of the first steady state, which can be achieved by changing the area and number of natural fiber silk layers to alter the overall steady-state performance of the laminate; furthermore, it can reduce the influence of bending moment and torque on the second steady-state configuration at room temperature. These functional adjustments enhance the functionality of the hybrid bistable carbon fiber / silk fiber composite laminate based on natural fiber silk layers, allowing for flexible adjustments according to actual needs, greater intelligence, and broader application prospects. Attached Figure Description

[0024] Figure 1 A schematic diagram of the layup of a hybrid bistable carbon fiber / silk fiber laminate structure based on continuous natural fibers;

[0025] Figure 2 Loading diagrams and critical load diagrams for hybrid bistable carbon fiber / silk fiber composite laminates with different numbers and layup angles of silk fibers;

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

[0027] To more clearly describe the innovative aspects and technical implementation methods of this invention, it is obvious that the described content is only a part of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0028] like Figure 1 As shown, the method for preparing 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: The natural fiber silk layer is modeled using 3D modeling software. The STL file is imported into the 3D printer slicing software to generate model code, which is then imported into the 3D printer. Based on fused deposition modeling technology, the natural fiber silk layer is prepared by 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 natural fiber silk layer on a metal cylindrical mold in a certain laying order. The number of unidirectional carbon fiber prepreg layers is even. The natural fiber silk layer is used as the middle layer. Lay them in a certain order and perform vacuum treatment. Finally, put them into an autoclave for high temperature and high pressure curing.

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

[0033] S5: By applying an external force to change the shape of the first steady state, the second steady state of the carbon fiber / natural fiber composite laminate is obtained, and its second steady state curvature and critical load are measured.

[0034] Example 1

[0035] In this embodiment, 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 at alternating 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] The total number of layers, including the natural fiber silk layer and the carbon fiber prepreg layer, is set as a variable, ranging from 5 to 8 layers. The hybrid bistable laminate layup is as follows: Figure 1 As shown in (a), a natural fiber silk layer serves as the intermediate layer. The metal mold is an aluminum tube wrapped in high-temperature resistant Teflon, as... Figure 1 As shown in (b).

[0039] For the hybrid bistable composite laminate prepared in Example 1, the method for transitioning from the first stable state to the second stable state of the laminate is as follows: the prepared hybrid bistable composite laminate is transformed into the second stable state by applying an external force, that is, a sudden change from the first stable state to the second stable state is achieved, such as... Figure 2 As shown in (a).

[0040] Five sets of mixed bistable composite material laminates, namely 4-1-45, 4-2-45, 6-1-45, 6-2-45, and 6-2-0, were prepared according to the preparation method of the above embodiments. "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 angle of the natural fiber silk layers, as shown in Table 2.

[0041] Table 2

[0042]

[0043] In groups 4-1-45, 4-2-45, 6-1-45, and 6-2-45, the natural fiber silk layers are of equal thickness and shape, but the number of layers increases sequentially. In groups 6-2-45 and 6-2-0, the natural fiber silk layers are of equal thickness, shape, and number of layers, but the layup angles differ. After preparation, an external load is applied to transition from the first steady state to the second steady state, and the required critical load value is measured using a sensor device. Figure 2 As shown in (b). The test results show that the critical load for the transition from the first steady state to the second steady state in the four groups 4-1-45, 4-2-45, 6-1-45, and 6-2-45 increases sequentially; correspondingly, the different laying angles of the natural fiber silk layer also affect the critical load value of the first steady state of the hybrid bistable composite laminate.

[0044] Example 2

[0045] In this embodiment, the area of ​​the natural fiber silk layer is equal to the area of ​​the unidirectional carbon fiber prepreg; the number of mixed lay-up layers is 5, wherein the lay-up angle of the natural fiber silk layer is 45°, and the lay-up angles of the carbon fiber are alternately arranged at 45° and -45°. The 3D printing process parameters of the natural fiber silk layer are the same as in Embodiment 1. The material of the mixed bistable laminate is set as a variable, and the mixed bistable carbon fiber / silk fiber composite laminate is compared with mixed bistable laminates with different materials, such as copper / carbon fiber bistable composite (Cu-C), aluminum / carbon fiber bistable composite (Al-C), and pure carbon fiber bistable composite (CC).

[0046] Four sets of hybrid bistable composite laminates made of different materials were prepared according to the preparation method of the above embodiments. All four sets of hybrid bistable composite laminates had equal thickness, equal number of layups, and equal shape. After preparation, the bistable laminates were subjected to load to transition from the first stable state to the second stable state, and the maximum critical load value was measured. The critical load values ​​of the hybrid bistable composite laminates made of different materials are shown in Table 3.

[0047] Table 3

[0048]

[0049] 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 largest 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] This 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 altering the layup angle and number of natural fiber silk layers; furthermore, at room temperature, the influence of bending moment and torque on the second steady-state configuration can be reduced, maintaining the curvature at the desired value and keeping it stable, thus changing the steady-state curvature of the composite laminate. (Refer to...) Figure 3 .

[0051] Furthermore, since the critical loads of the two steady states of traditional carbon fiber composite laminates are similar, the adjustability of the material is reduced. Therefore, this invention also proposes to increase the critical load of the first steady state and reduce the critical load value from the second steady state to the first steady state: by changing the shape or size of the natural fiber silk layer, the number of layups, and the printing linewidth, the critical load between the first and second steady states can be changed. When the shape or area of ​​the natural fiber silk layer is changed, 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 accordingly.

[0052] In summary, this invention, by incorporating a natural fiber silk layer into a bistable carbon fiber laminate and by altering parameters such as the shape, number of layers, and layup angle of the natural fiber silk layer, enables the adjustment of relevant critical loads and mitigates the influence of bending moment and torque on the second steady-state configuration. Due to the addition of the natural fiber silk layer, the structural stiffness and toughness are improved, the critical load value for the transition from the first to the second steady state is increased, and the critical load for the transition from the second to the first steady state is decreased, thereby improving the stability of the second steady-state curvature and reducing the influence of bending moment and torque on the second steady-state curvature. Furthermore, compared to other materials, the 3D-printed hybrid bistable carbon fiber / silk fiber composite laminate exhibits superior mechanical properties.

[0053] The above detailed description of the present invention is only a preferred embodiment and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing, characterized in that, Includes the following steps: Step S1: Prepare continuous natural fiber prepreg 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 the 3D printer slicing software to generate model code, import it into the 3D printer, and prepare the natural fiber silk layer using continuous natural fiber prepreg based on fused deposition modeling 3D printing technology. Step S3: Use a cutting machine to cut the unidirectional carbon fiber prepreg into the required laying shape. Lay the cut prepreg and natural fiber silk layer on the metal cylindrical mold in the laying order. The number of unidirectional carbon fiber prepreg layers is even. The natural fiber silk layer is used as the middle layer. Lay them in the order and perform vacuum treatment. Finally, put them into the autoclave for high temperature and high pressure curing. Step S4: After curing, the mixed bistable laminate is removed from the autoclave to obtain a carbon fiber / natural fiber reinforced composite laminate with initial curvature, which is in the first stable state; Step S5: By applying external force to change the shape of the first steady state, the second steady state of the carbon fiber / natural fiber composite laminate is obtained, and its second steady state curvature and critical load are measured.

2. The method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, The natural fiber silk layer is a silk-reinforced epoxy resin-based composite material.

3. The method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, The area of ​​the natural fiber silk layer is equal to or smaller than the area of ​​the unidirectional carbon fiber prepreg.

4. The method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, The layup angle of the natural fiber silk layer described in step S3 includes 0°, 45° or -45°.

5. The method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, In step S2, the heated bed temperature for 3D printing is set to 85 ℃, 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 method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, 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 iron plate covered with Teflon.

7. The method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, In step S3, the prepreg is laid in the following order: equal amounts of unidirectional carbon fiber prepreg are antisymmetrically distributed on the upper and lower sides of the natural fiber silk layer. The fiber direction of the unidirectional carbon fiber prepreg on each side is alternately set at 45° and -45°. The fiber direction of the natural fiber silk layer is one of 0°, 45° and -45°.

8. The method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, In step S3, the high-temperature and high-pressure curing temperature is 125 ℃, the holding time is 130 min, the pressure is set to 800 kPa, and the holding time is 105 min.

9. The method for preparing a hybrid bistable laminate based on continuous natural fiber 3D printing according to claim 1, characterized in that, The unidirectional carbon fiber prepreg mentioned in step S3 is T300 unidirectional carbon fiber epoxy resin-based prepreg and T700 unidirectional carbon fiber epoxy resin-based prepreg, and the thickness is 0.1mm-0.15mm.

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

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