Organic fiber reinforced resin-based ductile Z-pin composite material and method

Abstract

The invention discloses an organic fiber reinforced resin-based ductile Z-pin composite material and a method, and belongs to the technical field of composite material reinforcement. The method comprises the following steps: winding a first organic fiber on a pretreatment net rack, and performing oxygen plasma treatment on the surface of the first organic fiber in a vacuum environment to obtain a second organic fiber of which the surface is physically etched and which has a polar group; and fully and uniformly coating the surface of the second organic fiber with resin through a pultrusion process to obtain an organic fiber and resin preform, and then curing to a preset curing degree to obtain the organic fiber reinforced resin-based ductile Z-pin composite material. According to the obtained organic fiber reinforced resin-based ductile Z-pin composite material, the problem that organic fibers and resin are difficult to combine can be effectively avoided, meanwhile, the failure mode of Z-pin is adjusted according to different requirements of actual application scenes for Z-pin bridging force and bridging energy, and practicability is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material reinforcement, and specifically relates to an organic fiber reinforced resin-based ductile Z-pin composite material, a method and its application in a laminate structure, which is particularly suitable for improving the out-of-plane performance and resistance to interlaminar damage of composite laminates. Background Art

[0002] Z-pin technology was first proposed in the 1970s as a method to improve the through-thickness properties of fiber-reinforced composites, effectively improving their interlaminar fracture toughness, impact damage resistance, and out-of-plane load-bearing capacity. Traditional Z-pin composites typically use surface-sized carbon fibers as reinforcement and a resin as the matrix. This type of Z-pin reinforced composite laminate can provide stable support under out-of-plane loads, but it is prone to Z-pin shear failure when subjected to shear loads, resulting in a significant reduction in energy dissipation and limiting its application under Mode II crack propagation conditions. After co-curing in the composite laminate, the Z-pin composite forms a microscopic interface structure, including the Z-pin internal fiber / resin interface "I" and the Z-pin external surface / composite laminate interface "II". These two interfaces have a significant impact on the traction load and traction energy of the Z-pin during the propagation of Mode I / II interlaminar cracks in the composite laminate.

[0003] Research has shown that using ductile organic fibers as Z-pin reinforcements can effectively improve the Type II delamination bridging energy of composite laminates. However, due to the low surface energy of organic fibers and their poor resin impregnation, the Z-pin internal fiber / resin interface and the Z-pin external surface / composite laminate interface become weak links in the load transfer process, preventing the material's inherent performance advantages from being fully utilized. Currently, traditional Z-pin processes typically use a one-shot curing molding process, which cannot fully optimize and customize the interface properties of organic fiber-reinforced resin-based Z-pin composites, thus limiting their further application. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects in the prior art and provide an organic fiber reinforced resin-based ductile Z-pin composite material and method to improve the interfacial bonding performance between the organic fiber reinforcement and the resin matrix, regulate the failure mode of Z-pin under different stratification forms, and thus give full play to its advantages in interlayer reinforcement and crack propagation inhibition of composite laminates.

[0005] The specific technical solutions adopted in the present invention are as follows:

[0006] In a first aspect, the present invention provides a method for preparing an organic fiber reinforced resin-based ductile Z-pin composite material, as follows:

[0007] S1: Winding the first organic fiber on a pretreated grid, and subjecting the surface of the first organic fiber to oxygen plasma treatment in a vacuum environment to obtain a second organic fiber with a physically etched surface and polar groups;

[0008] S2: The surface of the second organic fiber is fully and evenly coated with resin through a pultrusion process to obtain an organic fiber and resin preform, which is then cured to a preset degree of cure to obtain an organic fiber reinforced resin-based ductile Z-pin composite material.

[0009] Preferably, in S1, a plurality of first organic fibers are wound in parallel and at intervals on the pretreatment grid; the first organic fiber is one of polyimide fiber, Kevlar fiber or PBO fiber.

[0010] Preferably, the polar group is an oxygen-containing functional group including a carbonyl group, a carboxyl group and a hydroxyl group.

[0011] Preferably, in S1, the parameters of the oxygen plasma treatment are: vacuum degree 20-60 Pa, radio frequency power 100-300 W, oxygen flow rate 100-400 sccm, and treatment time 0-15 minutes.

[0012] Preferably, in S2, the fiber pulling speed of the pultrusion process is constant and is 0.5-1.8 mm / s.

[0013] Preferably, the resin is epoxy resin, and the preset degree of curing is 0.6-1.0.

[0014] Preferably, the organic fiber reinforced resin-based ductile Z-pin composite material has a diameter of 0.1-0.8 mm and a circular cross-section.

[0015] Preferably, the organic fiber reinforced resin-based ductile Z-pin composite material is stored at -20 to -10°C.

[0016] In a second aspect, the present invention provides an organic fiber reinforced resin-based ductile Z-pin composite material obtained by using any preparation method described in the first aspect.

[0017] In a third aspect, the present invention provides a Z-pin reinforced composite laminate, in which the organic fiber reinforced resin-based ductile Z-pin composite material as described in the second aspect is pre-punched into a composite laminate preform and co-cured to form a reinforced interface.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Through oxygen plasma pretreatment (i.e., step S1), the organic fiber surface is etched to increase the roughness and introduce oxygen-containing polar groups, which enhances the mechanical intercalation and chemical bonding ability of the fiber-resin interface and regulates the fiber-resin interface strength within the Z-pin.

[0020] 2. By controlling the pre-curing degree of the organic fiber-reinforced Z-pin composite material (i.e., step S2), the strength of the co-cured interface between the Z-pin surface and the composite laminate is regulated, thereby improving the anti-delamination ability of the composite laminate;

[0021] 3. The successive use of two processes (i.e., a method for adjusting the interface between the Z-pin internal fiber and resin, and a method for adjusting the interface between the Z-pin external resin layer and the composite laminate) can synergistically enhance the bridging performance of the Z-pin composite material, forming a process model for organic fiber-reinforced resin-based ductile Z-pin composite materials with customizable interface strength, which can be used in various Z-pin reinforcement scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of the preparation process of the Z-pin composite material in a preferred embodiment of the present invention;

[0023] Figure 2 Schematic diagram of the internal interface structure and reinforcement of the Z-pin composite material prepared in a preferred embodiment of the present invention;

[0024] Figure 3 The tensile strength-displacement curve of the Z-pin composite material obtained in the embodiment of the present invention;

[0025] Figure 4 The bridge load-displacement curve of the Z-pin reinforced composite laminate obtained in the embodiment of the present invention;

[0026] Figure 5 Surface morphologies of two Z-pin composite materials obtained in the examples of the present invention: fully cured (curing degree of 1.0) and pre-cured (curing degree of 0.6). DETAILED DESCRIPTION

[0027] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0028] The present invention provides a method for preparing an organic fiber reinforced resin-based ductile Z-pin composite material, which is specifically as follows:

[0029] S1, Method for adjusting the interface between fiber and resin inside Z-pin composite material:

[0030] The first organic fiber is wound around a pretreated mesh, and the exposed surface of the pretreated mesh, which is not wrapped with the fiber, becomes the plasma treatment area. Under a vacuum environment, the entire surface of the mesh wrapped with the first organic fiber is treated with oxygen plasma to produce a second organic fiber with a physically etched surface and polar groups.

[0031] As a preferred embodiment of the present invention, a plurality of first organic fibers are wound on the pretreatment grid in parallel with each other and at a certain interval.

[0032] As a preferred embodiment of the present invention, the first organic fiber is one of polyimide fiber, Kevlar fiber, PBO fiber and the like.

[0033] As a preferred embodiment of the present invention, the polar group is an oxygen-containing functional group, such as a carbonyl group, a carboxyl group, a hydroxyl group, and the like.

[0034] As a preferred embodiment of the present invention, the oxygen plasma treatment process is specifically as follows:

[0035] In a vacuum environment, the processing ambient gas is extracted to a vacuum degree of 20-60 Pa, and an oxygen flow is introduced until the vacuum degree is stable; the first organic fiber is subjected to plasma treatment for 0-15 minutes under the conditions of a radio frequency power of 100-300 W and an oxygen flow rate of 100-400 sccm, so that the surface of the first organic fiber is physically etched and polar groups are introduced.

[0036] After the S1 step is completed, the prepared second organic fiber should be quickly taken out for subsequent Z-pin composite material preparation to avoid flipping of the surface groups of the second organic fiber.

[0037] S2, adjustment method of the interface between the external resin layer of the Z-pin composite material and the composite laminate:

[0038] Through a pultrusion process, the second organic fiber prepared in step S1 is uniformly coated with resin to form an organic fiber and resin preform. This is then cured to a predetermined degree of cure to produce an organic fiber-reinforced resin-based ductile Z-pin composite material. The resulting Z-pin composite material can then be pre-perforated and implanted into a composite laminate preform and co-cured to form a reinforced interface, thereby increasing the Z-pin composite material's peak bridging load and modifying its failure mode.

[0039] As a preferred embodiment of the present invention, the steps are as follows:

[0040] The second organic fiber is passed through a resin impregnation tank at a constant fiber pulling speed (e.g., 0.5-1.8 mm / s) to ensure that the second organic fiber surface is fully coated with resin. Excess resin is then scraped off through a specifically shaped mold to ensure even resin distribution. Based on the selected resin curing mechanism, the resin is slowly cured at a specific temperature to a specified pre-cure degree. Finally, the pre-cured Z-pin is stored in a cold storage facility at -20 to -10°C to maintain stable performance.

[0041] In actual use, the resin is epoxy resin, which is slowly cured to a specified pre-curing degree of 0.6 (partially cured) -1.0 (fully cured) under a temperature environment of 90-130°C.

[0042] As a preferred embodiment of the present invention, the shape and size of the resulting Z-pin composite material can be changed by adjusting the mold shape in S2. For example, in this embodiment, the cross-sectional shape of the resulting Z-pin composite material is circular with a diameter of 0.1-0.8 mm.

[0043] The Z-pin composite material obtained by the present invention exhibits enhanced interfacial bonding strength between the fiber and the resin, as evidenced by the Z-pin's tensile strength increasing with appropriate increases in plasma treatment time. The present invention can test and analyze samples with different process parameters, establishing a relationship between Z-pin process parameters and interfacial strength. This allows for the selection of the optimal preparation process based on specific structural reinforcement requirements, enabling customized adjustment of interfacial strength.

[0044] The preparation method and effects of the present invention will be further illustrated by way of examples below.

[0045] Example

[0046] This embodiment prepares an organic fiber reinforced resin-based ductile Z-pin composite material, and the flow chart of its preparation method is as follows: Figure 1 As shown, the specific steps include:

[0047] Step 1: Oxygen plasma pretreatment of polyimide fiber.

[0048] 1. Select S35 polyimide fiber and evenly wind it on the pre-treated grid;

[0049] 2. Place the fiber in the processing chamber, evacuate to 60 Pa, adjust the oxygen flow rate to 1-2 L / min, maintain for 1 minute or more, then adjust the gas flow rate to 0.4-0.6 L / min and keep it stable;

[0050] 3. Turn on the RF power supply and perform plasma treatment at a power of 150 W for a treatment time range of 0-8 minutes.

[0051] 4. After the treatment is completed, remove the fiber immediately to avoid surface group flipping and ensure the strengthening effect.

[0052] Step 2: Rapid pultrusion of polyimide fiber reinforced epoxy resin-based Z-pin.

[0053] 1. Winding the organic fiber obtained in step 1 into a pultrusion device;

[0054] 2. Fully impregnate the surface-treated polyimide fiber with epoxy resin AF-4900 to ensure that the resin fully impregnates the fiber;

[0055] 3. The motor is used to adjust the pultrusion speed to a constant 1mm / s, optimizing the pultrusion process to improve production efficiency;

[0056] 4. Use a circular mold to scrape off excess resin on the surface and ensure molding accuracy.

[0057] Step 3: Curing process and final preparation.

[0058] 1. The epoxy resin is mixed with Huibai New Materials AF-4900A resin, AF-4900B curing agent and 21# release agent in a weight ratio of 100:120:1; therefore, the DSC isothermal process is used to determine the process curve of its curing degree changing with time, and the curing plan is set.

[0059] 2. According to the set curing plan, cure the materials to a pre-curing degree of 0.6, 0.8 and a full curing degree of 1.0 respectively, and store them in a cold storage at -17°C;

[0060] 4. Finally, three Z-pin composite materials with different curing degrees were obtained. The microstructures of the Z-pin composite materials with curing degrees of 0.6 and 1.0 are shown in the figure below. Figure 5 As shown in the figure, the fully cured Z-pin surface (i.e., degree of cure of 1.0) shows a tight bond between the fibers and the resin, indicating that the resin has fully solidified. The partially cured Z-pin surface (i.e., degree of cure of 0.6) exhibits a glossy appearance, indicating that the resin is still in a liquid or gel state. Subsequently, Z-pin composites with three different degrees of cure were implanted into T800 fiber composite laminate preforms and co-cured to produce the corresponding Z-pin-reinforced composite laminates.

[0061] The process can be used to obtain Z-pin composite materials with different Z-pin internal fiber / resin interface strength and Z-pin surface / composite laminate interface strength. The structure is as follows: Figure 2As shown in the figure, it can be seen that the oxygen plasma pretreatment method can adjust the interface strength between the internal fiber and the resin of the Z-pin, and the co-curing method of pre-curing the Z-pin can adjust the interface strength between the Z-pin surface resin layer and the laminate.

[0062] In order to verify the mechanical properties of the organic fiber reinforced resin-based ductile Z-pin composite material prepared by the method of this embodiment, a tensile test of the polyimide fiber reinforced epoxy resin-based ductile Z-pin composite material was designed with reference to the GBT3362 multifilament tensile performance test standard. The experimental steps are as follows:

[0063] Step 1: Cut the Z-pin tow (cured to a degree of cure of 1) obtained in the example into 250 mm segments and attach reinforcement sheets 50 mm above and below. The Z-pins were divided into five groups based on the oxygen plasma pretreatment time (PI: 0, 2, 4, 6, and 8 min) and tested for tensile strength. The Z-pins treated for 0 min served as the control group.

[0064] Step 2: Test in strict accordance with the requirements of GBT3362 multifilament tensile performance test standard to ensure the rationality of sample failure and the confidence of data. At least 5 tests were performed for each treatment time group.

[0065] The tensile strength-displacement curve after the test is as follows Figure 3 As shown in the figure, the Z-pin tensile strength increases with increasing oxygen plasma pretreatment time, indicating that the interfacial bonding strength between the fiber and resin within the Z-pin composite is enhanced, promoting load transfer. The Z-pin tensile properties reach their optimum at treatment times of 4-6 minutes, but show a slight decrease after 8 minutes, likely due to defects caused by excessive etching of the fiber surface.

[0066] At the same time, the delamination bridging performance of the Z-pin composite reinforced laminate was tested. The test steps are as follows:

[0067] Step 1: The Z-pin composite reinforced laminate prepared in Example 1 is divided into three groups of 1, 0.8, and 0.6 according to the different Z-pin pre-curing degrees, and is pasted on the upper and lower planes of the shear fixture respectively to obtain its bridging curve.

[0068] Step 2: Ensure the rationality of sample failure and the confidence of the data, and perform at least 3 tests on each treatment time group.

[0069] The typical bridge force-displacement curve after the test is as follows: Figure 4The results show that regulating the Z-pin pre-cure can effectively increase the Z-pin surface / composite laminate strength, thereby enhancing the Z-pin bridging load. Furthermore, experiments show that regulating the Z-pin pre-cure reduces the strength of the fiber / resin interface within the Z-pin, shifting interfacial failure to the weaker interface. Therefore, pre-treatment of the organic fiber surface can help reduce Z-pin splitting during the bridging process, further synergistically improving the Z-pin bridging load and energy.

[0070] Through multiple tests, the pretreatment conditions with different Z-pin internal fiber / resin and surface resin / laminate interface strengths were recorded to provide a reference for customized Z-pin composite materials.

[0071] During the preparation of a Z-pin composite material, the present invention utilizes two internal and external interface control methods (including two core steps: oxygen plasma pretreatment and Z-pin pultrusion curing). The relationship between process parameters and interface strength is determined based on evaluation methods for the Z-pin internal interface and the Z-pin / composite laminate interface. Specifically, the oxygen plasma pretreatment aims to etch the organic fiber surface, increasing its roughness and introducing polar groups, thereby enhancing the interfacial bonding between the Z-pin internal fibers and the resin. During Z-pin pultrusion curing, the treated organic fibers are fully impregnated with resin, and further cross-linking between the Z-pin external resin and the laminate is promoted by controlling the curing degree of the formed Z-pin, thereby improving the interface strength of the Z-pin / composite laminate. The organic fiber-reinforced resin-based ductile Z-pin composite material obtained using this method effectively avoids the difficulty of organic fiber-resin bonding. It also adjusts the Z-pin failure mode to meet the varying requirements of Z-pin bridging force and bridging energy in practical applications, demonstrating its high practicality.

[0072] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A method for preparing an organic fiber reinforced resin-based ductile Z-pin composite material, characterized in that: The details are as follows: S1: Winding the first organic fiber on a pretreated grid, and subjecting the surface of the first organic fiber to oxygen plasma treatment in a vacuum environment to obtain a second organic fiber with a physically etched surface and polar groups; S2: The surface of the second organic fiber is fully and evenly coated with resin through a pultrusion process to obtain an organic fiber and resin preform, which is then cured to a preset degree of cure to obtain an organic fiber reinforced resin-based ductile Z-pin composite material.

2. The method for preparing the organic fiber reinforced resin-based ductile Z-pin composite material according to claim 1, characterized in that: In the above-mentioned S1, a plurality of first organic fibers are wound in parallel and at intervals on the pretreatment grid; the first organic fiber is one of polyimide fiber, Kevlar fiber or PBO fiber.

3. The method for preparing the organic fiber reinforced resin-based ductile Z-pin composite material according to claim 1, characterized in that: The polar groups are oxygen-containing functional groups including carbonyl, carboxyl and hydroxyl groups.

4. The method for preparing the organic fiber reinforced resin-based ductile Z-pin composite material according to claim 1, characterized in that: In S1, the parameters of the oxygen plasma treatment are: vacuum degree 20-60 Pa, radio frequency power 100-300 W, oxygen flow rate 100-400 sccm, and treatment time 0-15 minutes.

5. The method for preparing the organic fiber reinforced resin-based ductile Z-pin composite material according to claim 1, characterized in that: In the S2, the fiber pulling speed of the pultrusion process is constant and is 0.5-1.8 mm / s.

6. The method for preparing an organic fiber reinforced resin-based ductile Z-pin composite material according to claim 1, characterized in that: The resin is epoxy resin, and the preset curing degree is 0.6-1.

0.

7. The method for preparing an organic fiber reinforced resin-based ductile Z-pin composite material according to claim 1, characterized in that: The organic fiber reinforced resin-based ductile Z-pin composite material has a diameter of 0.1-0.8 mm and a circular cross-section.

8. The method for preparing an organic fiber reinforced resin-based ductile Z-pin composite material according to claim 1, characterized in that: The organic fiber reinforced resin-based ductile Z-pin composite material is stored at -20 to -10°C.

9. An organic fiber reinforced resin-based ductile Z-pin composite material obtained by the preparation method according to any one of claims 1 to 8.

10. A Z-pin reinforced composite laminate, characterized in that: The organic fiber reinforced resin-based ductile Z-pin composite material as claimed in claim 9 is implanted into a composite laminate preform in a pre-punched manner and co-cured to form a reinforced interface.

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