Preparation method of 2.5D woven fabric composite material, obtained materials and applications

Abstract

The present invention discloses a preparation method, obtained materials and applications of a 2.5D woven fabric composite material, wherein the preparation method adopts a woven fabric prepreg with a 2.5D interlayer angle interlocking structure as a reinforcing material, and performs cutting, paving and hot pressing. The 2.5-dimensional structured woven fabric has excellent interlayer performance and can solve the requirements for interlayer bonding force of composite materials (composite materials for automobiles, especially leaf springs) under complex driving conditions. At the same time, the thickness of the 2.5-dimensional structured woven fabric is thicker than that of traditional unidirectional or bidirectional fiber-reinforced prepreg materials, which can greatly reduce the number of single-layer prepregs to be laid, reduce the difficulty of laying, and improve preparation efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of 2.5D woven fabric composite materials, and in particular relates to a preparation method of a 2.5D woven fabric composite material, the obtained material and application. Background Art

[0002] Traditional composite material manufacturing processes (such as leaf springs) primarily include winding, pultrusion, and prepreg molding. These methods present the following challenges: The fiber structure is often a single, two-dimensional layer, lacking effective interlayer bonding. This results in low interlayer bonding strength under primary vertical loads, making it prone to delamination during use, significantly impacting the fatigue life of composite leaf springs. Furthermore, when using prepreg as the primary material and molding to manufacture composite materials (such as composite leaf springs for automotive applications), the number of prepreg sheets often exceeds hundreds, requiring high technical and labor-intensive placement techniques, resulting in low production efficiency and unfavorable mass production.

[0003] In order to improve the interlayer performance and production efficiency of composite leaf springs, scientific and technological workers have also conducted a lot of research. Patent CN105134849A discloses a method for preparing a three-dimensional woven composite automotive leaf spring, which is formed by weaving a mixed fiber combination into a three-dimensional fabric structure. The preform weaving equipment of this method is expensive, the weaving efficiency is extremely low, and the production cost is very high. Patent CN105128357A discloses a method for preparing an interlayer reinforced two-dimensional and three-dimensional woven composite automotive leaf spring, which is formed by three-dimensional weaving to form a single layer of fabric of different fiber materials, and then the laminated single layer structure is formed into a whole by longitudinal stitching between layers, and finally cured and formed by a resin vacuum transfer molding process. The biggest drawback of this method is that the process is cumbersome, the product processing takes a long time, the production efficiency is low, and it is difficult to meet the requirements of industrialization. Patent CN109109344A discloses a manufacturing process for a composite short-term leaf spring for automobiles, which uses the HP-RTM molding method to prepare composite leaf springs, which can effectively improve the production efficiency of leaf springs. However, the HP-RTM molding equipment involved in this method is expensive, the leaf spring curing molding time is greatly shortened, the resin gel and solid process requirements used are high, and product performance will also be lost.

[0004] Therefore, how to improve the interlayer bonding strength of fiber-reinforced composite materials (such as leaf springs) under fatigue conditions of vehicles with high load requirements and the preparation efficiency of composite materials (such as leaf springs) has become a key research topic in automotive composite materials (such as leaf springs). Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, the present invention provides a method for preparing a 2.5D woven fabric (2.5-dimensional woven fabric) composite material and the resulting material, wherein the preparation method uses a woven fabric prepreg with a 2.5D interlayer angle interlocking structure as a reinforcing material for cutting, paving, and hot pressing. The 2.5-dimensional structured woven fabric has excellent interlayer performance and can solve the requirements for interlayer bonding force of composite materials (composite materials for automobiles, especially leaf springs) under complex driving conditions. At the same time, the thickness of the 2.5-dimensional structured woven fabric is thicker than that of traditional unidirectional or bidirectional fiber-reinforced prepreg materials, which can greatly reduce the number of single-layer prepregs to be laid, reduce the difficulty of laying, and improve preparation efficiency.

[0006] One of the objects of the present invention is to provide a method for preparing a 2.5D woven fabric composite material, comprising: (1) preparing a prepreg of a 2.5D woven fabric, (2) cutting the prepreg, (3) preforming, (4) molding and curing, and (5) demoulding and post-processing.

[0007] In addition to three-dimensional braided integral molding or winding molding, traditional composite leaf springs are all made of Figure 2 The layers are laid in the four directions (in the middle and middle directions) and then molded or RTM formed. The use of three-dimensional braided preforms has low weaving efficiency and high cost, and often requires high-pressure RTM molding, which increases equipment costs.

[0008] 2.5D woven fabrics can be woven using traditional loom equipment with considerable weaving efficiency; the single piece of prepreg is thick, which greatly reduces the number of layers; overall, it can achieve a balance between economy and efficiency.

[0009] In a preferred embodiment, the 2.5D woven fabric in step (1) has an interlayer angle interlocking structure, and the fabric structure diagram is as follows: Figure 1 As shown in the figure, 1 is the binding warp yarn, 2 is the lining warp yarn, and 3 is the weft yarn.

[0010] In a further preferred embodiment, the thickness of the 2.5-dimensional fabric in step (1) can be adjusted by changing the number of weaving layers and the density (roots / cm) and linear density (tex) of the binding warp yarns, the lining warp yarns and the weft yarns.

[0011] In a further preferred embodiment, the number of fabric layers of the 2.5D woven fabric in step (1) is 5-10, the density (roots / cm) of the binding warp yarn, the lining warp yarn and the weft yarn is 3-8, the linear density (tex) is 200-1200, and the thickness of a single piece of 2.5D woven fabric is 5-10 mm.

[0012] In a preferred embodiment, the fibers used in the 2.5D woven fabric are selected from one or more of carbon fiber, aramid fiber, ultra-high molecular weight polyethylene fiber, glass fiber, and basalt fiber.

[0013] In a further preferred embodiment, the fibers used in the 2.5D woven fabric are selected from glass fibers, especially glass fiber rovings.

[0014] In a preferred embodiment, step (1) is performed as follows:

[0015] (1.1) Passing the 2.5D woven fabric through a mold with glue injection holes along the direction of the binding warp yarn (lining warp yarn);

[0016] (1.2) injecting glue into a mold to impregnate the 2.5D woven fabric to obtain a fabric strip;

[0017] (1.3) Release paper is placed on both the upper and lower surfaces of the fabric strip, and the strip is introduced into a drying tunnel for pre-polymerization, and the release paper is pulled out from both the upper and lower surfaces.

[0018] In a preferred embodiment, in step (1.2), the glue is selected from at least one of epoxy prepreg resin, unsaturated polyester, and phenolic prepreg resin, preferably epoxy prepreg resin.

[0019] In a preferred embodiment, in step (1.2), the impregnation injection pressure is 0.5-5 MPa, preferably 1-3 MPa.

[0020] For example, in step (1.2), the impregnation injection pressure is 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa or 5 MPa.

[0021] In a preferred embodiment, in step (1.3), the drying temperature of the drying tunnel is divided into three sections, namely 20-60°C in the first section, 50-90°C in the second section, and 80-120°C in the third section, wherein the temperature of the second section is higher than that of the first section, and the temperature of the third section is higher than that of the second section.

[0022] Among them, through the control of the temperature of multiple drying stages, it is ensured that the resin does not convert from stage A to stage B prematurely, and can transition to stage B evenly; the volatiles in the resin are fully removed; and the polymerization is stopped just when it reaches the outlet, so that the residual heat will not cause the resin to continue to react and fail prematurely.

[0023] In a further preferred embodiment, in step (1.3), the drying temperature of the drying tunnel is divided into three sections, namely 30-50°C in the first section, 60-80°C in the second section, and 90-105°C in the third section.

[0024] For example, the first section is 30°C, 40°C or 50°C, the second section is 60°C, 70°C or 80°C, and the third section is 90°C, 100°C or 105°C.

[0025] In a preferred embodiment, in step (1.3), the pultrusion pulling rate is 2-20 mm / min, preferably 5-15 mm / min.

[0026] For example, the pultrusion pulling rate is 5 mm / min, 8 mm / min, 10 mm / min, 12 mm / min or 15 mm / min.

[0027] In a preferred embodiment, the mass content of glue in the prepreg prepared in step (1) is 20-50%, preferably 30-38%.

[0028] For example, the mass content of glue in the prepreg prepared in step (1) is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37% or 38%.

[0029] In a preferred embodiment, the prepreg is cut according to the designed size. Preferably, when the composite material is a leaf spring, it is cut into long strips according to the designed size of the prepared leaf spring.

[0030] In a further preferred embodiment, the 2.5D woven fabric is cut along the weft direction, and the length of the weft cutting is the design length value of the composite material (such as a leaf spring); the length of the cutting along the binding warp (lining warp) direction is the thickness value of the composite material (such as a leaf spring).

[0031] The number of prepreg sheets is the ratio of the leaf spring width to the thickness of the 2.5-dimensional single prepreg.

[0032] In a preferred embodiment, in step (3), the preforming includes laying, preheating and forming.

[0033] In a further preferred embodiment, the laying is preferably performed as follows: the cut prepreg is laid along the width direction of the composite material (eg Figure 3 6) and lay them neatly layer by layer.

[0034] In addition to three-dimensional braided integral molding or winding molding, traditional composite leaf springs are all made of Figure 2 The composite leaf spring is laminated in the middle (4 directions) and formed by winding or thickness direction lamination. Under the action of the vertical main load of the leaf spring, it is often easy to cause interlayer cracking in the thickness direction of the composite leaf spring.

[0035] The present invention utilizes 2.5D fabrics which inherently have relatively good interlayer performance, combined with a special laying method of laying the layers along the width direction of the leaf spring, thereby greatly enhancing the interlayer performance of the leaf spring in the thickness direction.

[0036] In a further preferred embodiment, the preheating temperature is 60-100°C, preferably 70-90°C.

[0037] For example, the preheating temperature is 60°C, 70°C, 80°C, 90°C or 100°C.

[0038] If the preheat temperature is below 60°C, the prepreg will have poor adhesion and flexibility, especially for thicker prepregs, which will have poor draping properties. The poor adhesion between layers can easily lead to defects such as voids. If the temperature is higher, such as above 100°C, the viscosity is too high, and if the paving fails, the two pieces of tape cannot be separated without damage for re-paving. Furthermore, excessively high temperatures can trigger polymerization reactions, causing composite molding failure.

[0039] In a further preferred embodiment, the molding refers to kneading the preheated prepreg into the shape of the composite material and then placing it into a mold; for example, when the composite material is a leaf spring, the preheated prepreg is bent along its thickness direction and then placed into a mold.

[0040] In a preferred embodiment, in step (4), the molding curing is carried out in two stages, wherein the temperature of the first stage is 70-100°C, the pressure is 2-12 MPa, and the time is 2-12 min; the temperature of the second stage is 90-120°C, the pressure is 8-18 MPa, and the time is 8-18 min; and the temperature of the second stage is higher than or equal to (preferably higher than) that of the first stage, the pressure of the second stage is higher than (preferably higher than) that of the first stage, and the time of the second stage is higher than or equal to (preferably higher than) that of the first stage.

[0041] Among them, the first stage of molding temperature is mainly to reduce the viscosity of the resin so that the resin can fully infiltrate the fiber and reduce defects. If the temperature is low, the viscosity is high and it is not easy for the resin to flow. If the temperature is high, the reaction will occur prematurely, affecting the performance of the composite material. At the same time, the second stage of temperature is also to make the resin fully infiltrate the fiber before the reaction as much as possible, so as to improve the overall performance of the product. This process method is for leaf spring products, and the material properties are not compared. If a comparison is really necessary, the performance of the leaf spring products is evaluated based on the vertical fatigue performance. Since composite leaf springs are not mass-produced in China and the materials and process methods are not unified, there is no complete unified standard for the vertical performance test of composite leaf springs. Basically, they are based on the vertical fatigue test method and fatigue life value of steel leaf springs. The specific fatigue life value cannot be unified. After analysis and research, the inventor uses a vertical fatigue life of more than 800,000 times and no obvious stress whitening, cracks, delamination and other defects on the appearance of the leaf spring as the evaluation standard for the performance of composite leaf springs.

[0042] In a further preferred embodiment, in step (4), the molding curing is carried out in two stages, wherein the temperature of the first stage is 80-90°C, the pressure is 5-10 MPa, and the time is 5-10 min, and the temperature of the second stage is 100-110°C, the pressure is 10-15 MPa, and the time is 10-15 min. Preferably, the temperature of the second stage is higher than that of the first stage, the pressure of the second stage is higher than that of the first stage, and the time of the second stage is higher than that of the first stage.

[0043] In a preferred embodiment, in step (5), the demoulding is performed at 70-100°C, preferably at 80-100°C.

[0044] For example, the demolding is performed at 70°C, 80°C, 90°C, or 100°C.

[0045] In a further preferred embodiment, in step (5), the post-processing includes trimming, grinding and polishing.

[0046] A second object of the present invention is to provide a composite material obtained by the preparation method described in one of the objects of the present invention.

[0047] The third object of the present invention is to provide an application of the preparation method described in the first object of the present invention in the preparation of leaf springs for automobiles, especially in the preparation of leaf springs for heavy-duty automobiles with a thickness range of 50 mm or more.

[0048] Leaf springs are a crucial component of the automotive suspension system, primarily supporting the vehicle body, carrying loads, and providing cushioning. Traditional steel leaf springs are inexpensive and easy to maintain, but their relatively high mass increases fuel consumption and defies energy conservation and environmental protection requirements. Replacing traditional steel leaf springs with fiber-reinforced composite leaf springs offers numerous advantages: low density, high specific strength, and significant weight reduction; an integrated, flexible design; fatigue life 2-10 times that of steel leaf springs, resulting in reasonable lifecycle costs; a safe fracture mode; and excellent vehicle performance. Internationally, research on composite leaf springs has been underway since the early 1970s, and large-scale application has been achieved. In recent years, a surge in research and application development of composite leaf springs has also taken place in China.

[0049] The endpoints and any values of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and a separate point value, and the separate point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be considered as specifically disclosed in this article.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) Compared with the existing winding, pultrusion, and prepreg molding processes, the present invention has a reinforcing material with an interlayer angle interlocking structure. After being molded by the cutting and laying method of the present invention, the interlayer strength of the composite leaf spring during use can be greatly improved, especially the interlayer strength under the action of the main bearing vertical load, thereby improving the dimensional stability and service life.

[0052] (2) Compared with three-dimensional weaving, two-dimensional longitudinal stitching three-dimensional braided bodies and HP-RTM molding methods, the 2.5-dimensional weaving equipment has a simple structure and is similar to traditional weaving equipment. After a slight modification, 2.5D fabrics can be woven, and the weaving efficiency is high, which is suitable for mass production.

[0053] (3) The present invention is more suitable for preparing heavy-duty vehicle leaf springs with a thickness range of more than 50 mm, which can effectively reduce the number of layers, improve production efficiency, and enhance the reliability of heavy-duty vehicle leaf springs. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Shown are schematic diagrams of the structures of 2.5D woven fabrics in Examples 1 to 3;

[0055] exist Figure 1In the diagram, 1 represents the binding warp yarn, 2 represents the lining warp yarn, and 3 represents the weft yarn.

[0056] Figure 2 Schematic diagram of the cross section of the leaf spring prepreg after preforming in Examples 1 to 3;

[0057] exist Figure 2 In the figure, 4 represents thickness and 5 represents length.

[0058] Figure 3 Schematic diagrams showing the structures of the leaf springs after molding and curing in Examples 1 to 3;

[0059] exist Figure 3 In the example, 6 indicates the width. DETAILED DESCRIPTION

[0060] The present invention will be described in detail below with reference to specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0061] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0062] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the scope of protection of the present invention.

[0063] [Example 1]

[0064] Taking the preparation process of an automobile leaf spring with a length of 1.5m, a width of 75mm and a thickness of 50mm as an example, the specific implementation method is as follows:

[0065] a. 2.5D woven fabric. The structure of 2.5D woven fabric is an interlayer angle interlocking structure. The fabric structure diagram is shown in Figure 1 The corresponding 2.5D fabric structural parameters are shown in Table 1.

[0066] Table 1 2.5-dimensional fabric structural parameters (Example 1)

[0067]

[0068] b. Preparation of prepreg for 2.5D woven fabric. The woven 2.5D woven fabric is passed through a mold with glue injection holes along the direction of the connecting warp yarns (lining warp yarns). Epoxy prepreg resin is injected into the mold to impregnate the fabric. The fabric strip is then introduced into a drying tunnel for prepolymerization. After pultrusion and traction, release paper is attached to both sides for use. The impregnation injection pressure is 1 MPa, and the drying temperature of the drying tunnel is divided into three sections: 30°C for the first section, 60°C for the second section, and 90°C for the third section. The pultrusion traction rate is 15 mm / min. The prepreg contains 33% glue by mass.

[0069] c. Cut the prepreg. Cut the prepreg into long strips according to the designed dimensions of the leaf spring. Cut along the weft direction of the 2.5D prepreg, with the weft length equal to the leaf spring length of 1.5m. Cut along the binding warp (lining warp) length equal to the leaf spring thickness of 50mm. The number of prepreg sheets should be 15, with a leaf spring width of 75mm and a 2.5D prepreg thickness of 5mm.

[0070] d. Lay out and preform the prepreg. Tear off the release paper from the cut prepreg and lay it out layer by layer along the width direction of the leaf spring. Place the laid out prepreg in an oven and preheat for 5 minutes. The preforming temperature is 70°C. Then bend the prepreg into the following shape along the thickness direction. Figure 2 The shape shown is then placed into the mold to complete the preforming stage.

[0071] e. Heat and mold to solidify. The upper mold of the mold is along the width direction of the leaf spring. Figure 3 The mold is closed and pressurized, and the pressurization curing is carried out in two stages. The first stage is at a temperature of 80°C, a pressure of 10 MPa, and a time of 10 minutes. The second stage is at a temperature of 100°C, a pressure of 15 MPa, and a time of 15 minutes.

[0072] f. Demolding and trimming. After hot molding and curing, the mold is cooled and demolded. The cooling temperature is 100°C. The molded parts need to be trimmed, ground, and polished after removal.

[0073] The vertical fatigue life of the composite leaf spring produced reaches 800,000 times, and the leaf spring has no obvious stress whitening, cracks or delamination defects on its appearance.

[0074] [Example 2]

[0075] Taking the preparation process of an automobile leaf spring with a length of 1.8m, a width of 90mm and a thickness of 80mm as an example, the specific implementation method is as follows:

[0076] a. 2.5D woven fabric. The structure of 2.5D woven fabric is an interlayer angle interlocking structure. The fabric structure diagram is as follows: Figure 1 The corresponding 2.5D fabric structural parameters are shown in Table 2.

[0077] Table 2 2.5-dimensional fabric structural parameters (Example 2)

[0078]

[0079] b. Preparation of 2.5D woven fabric prepreg. The woven 2.5D woven fabric is passed through a mold with glue injection holes along the direction of the connecting warp yarns (lining warp yarns). Epoxy prepreg resin is injected into the mold to impregnate the fabric. The fabric strip is then introduced into a drying tunnel for prepolymerization. After pultrusion and traction, release paper is attached to both sides for use. The impregnation injection pressure is 3MPa, and the drying temperature of the drying tunnel is divided into three sections: 50°C for the first section, 80°C for the second section, and 105°C for the third section. The pultrusion traction rate is 5mm / min. The prepreg contains 35% glue by mass.

[0080] c. Cut the prepreg. Cut the prepreg into long strips according to the designed dimensions of the leaf spring. Cut along the weft direction of the 2.5D prepreg, with the weft length equal to the leaf spring's length of 1.8m. Cut along the binding warp (lining warp) direction equal to the leaf spring's thickness of 80mm. The number of prepreg sheets should be 18, with a leaf spring width of 90mm and a 2.5D prepreg thickness of 5mm.

[0081] d. Lay out and preform the prepreg. Tear off the release paper from the cut prepreg and lay it out layer by layer along the width direction of the leaf spring. Place the laid out prepreg in an oven and preheat for 3 minutes. The preforming temperature is 90°C. Then bend the prepreg into the following shape along the thickness direction. Figure 2 The shape shown is then placed into the mold to complete the preforming stage.

[0082] e. Heat and mold to solidify. The upper mold of the mold is along the width direction of the leaf spring. Figure 3 The mold is closed and pressurized as shown. The pressurization curing is divided into two stages. The first stage is at a temperature of 90°C, a pressure of 5 MPa, and a time of 5 minutes. The second stage is at a temperature of 110°C, a pressure of 10 MPa, and a time of 10 minutes.

[0083] f. Demolding and trimming. After hot molding and curing, the mold is cooled and demolded. The cooling temperature is 80°C. The molded parts need to be trimmed, ground, and polished after removal.

[0084] The vertical fatigue life of the composite leaf spring produced reaches 800,000 times, and the leaf spring has no obvious stress whitening, cracks or delamination defects on its appearance.

[0085] Example 3

[0086] Taking the preparation process of a 2m long, 90mm wide, and 100mm thick automobile leaf spring as an example, the specific implementation method is as follows:

[0087] a. 2.5D woven fabric. The structure of 2.5D woven fabric is an interlayer angle interlocking structure. The fabric structure diagram is shown in Figure 1 The corresponding 2.5D fabric structural parameters are shown in Table 3.

[0088] Table 3 2.5-dimensional fabric structural parameters (Example 3)

[0089]

[0090] b. Preparation of 2.5D woven fabric prepreg. The woven 2.5D woven fabric is passed through a mold with glue injection holes along the direction of the connecting warp yarns (lining warp yarns). The epoxy prepreg resin is injected into the mold to impregnate the fabric. The fabric strip is then introduced into a drying tunnel for prepolymerization. After pultrusion and traction, release paper is attached to both sides for use. The impregnation injection pressure is 2MPa, and the drying temperature of the drying tunnel is divided into three sections: 50°C for the first section, 80°C for the second section, and 100°C for the third section. The pultrusion traction rate is 10mm / min. The prepreg contains 35% glue by mass.

[0091] c. Cut the prepreg. Cut the prepreg into long strips according to the designed dimensions of the leaf spring. Cut along the weft direction of the 2.5D prepreg, with the weft length equal to the leaf spring length of 2m. Cut along the binding warp (lining warp) direction equal to the leaf spring thickness of 100mm. The number of prepreg sheets should be 9, with a ratio of 90mm leaf spring width to 10mm 2.5D prepreg thickness.

[0092] d. Lay out and preform the prepreg. Tear off the release paper from the cut prepreg and lay it out layer by layer along the width direction of the leaf spring. Place the laid out prepreg in an oven and preheat for 3 minutes. The preforming temperature is 85°C. Then bend the prepreg into the following shape along the thickness direction. Figure 2 The shape shown is then placed into the mold to complete the preforming stage.

[0093] e. Heat and mold to solidify. The upper mold of the mold is along the width direction of the leaf spring. Figure 3 The mold is closed and pressurized as shown. The pressurization curing is carried out in two stages. The first stage is at a temperature of 90°C, a pressure of 8 MPa, and a time of 8 minutes. The second stage is at a temperature of 105°C, a pressure of 10 MPa, and a time of 12 minutes.

[0094] f. Demolding and trimming. After hot molding and curing, the mold is cooled and demolded. The cooling temperature should be between 80-100°C. The molded parts need to be trimmed, ground, and polished after removal.

[0095] The vertical fatigue life of the composite leaf spring produced reaches 800,000 times, and the leaf spring has no obvious stress whitening, cracks or delamination defects on its appearance.

[0096] [Comparative Example 1]

[0097] Repeat the process of Example 1, except that: along the thickness direction of the leaf spring ( Figure 2 The layers are laid in the middle 4 directions, and other conditions remain unchanged.

[0098] The vertical fatigue life of the composite leaf spring produced reached 800,000 times, but the composite leaf spring showed obvious cracks and delamination, and the delamination mainly occurred between the two prepreg layers in the thickness direction of the leaf spring.

[0099] [Comparative Example 2]

[0100] The process of Example 1 was repeated, with the only difference being that the drying temperature in the drying tunnel was not segmented but was performed in one segment at 90°C.

[0101] The resin prematurely and unevenly transitions from stage A to stage B, preventing the volatiles from being fully expelled. Polymerization fails to fully cease by the time it reaches the outlet, trapping the residual heat and causing the resin to continue reacting, leading to premature partial failure. The resulting composite leaf spring has a vertical fatigue life of less than 500,000 cycles, and exhibits stress whitening, cracks, and delamination defects.

[0102] [Comparative Example 3]

[0103] The process of Example 1 was repeated, except that the preheating temperature was 50°C.

[0104] Prepregs have poor adhesion and flexibility, especially thicker prepregs, which have poor drapeability. Poor adhesion between layers also creates defects such as voids. This results in a vertical fatigue life of less than 300,000 cycles for the resulting composite leaf springs, and noticeable stress whitening, cracks, and delamination.

[0105] [Comparative Example 4]

[0106] The process of Example 1 was repeated, except that the preheating temperature was 120°C.

[0107] High temperatures and excessive viscosity make it impossible to separate the two sheets of tape without damage for re-applying if the tape fails. Excessive temperatures also trigger premature polymerization. The resulting composite leaf spring has a vertical fatigue life of less than 300,000 cycles, and exhibits noticeable stress whitening, cracks, and delamination.

[0108] [Comparative Example 5]

[0109] The process of Example 1 was repeated, except that the compression curing was not performed in stages but was performed at a temperature of 95° C., a pressure of 10 MPa, and a time of 10 min.

[0110] The resin cannot fully impregnate the fibers, easily creating defects such as gaps between the layers. The resulting composite leaf springs have a vertical fatigue life of less than 500,000 cycles, and exhibit obvious stress whitening, cracks, and delamination defects.

[0111] [Comparative Example 6]

[0112] The process of Example 1 was repeated, with the only difference being that during the segmented molding, the temperature of the first segment was 50°C and the temperature of the second segment was 130°C.

[0113] The primary molding temperature is primarily designed to reduce resin viscosity, allowing it to fully impregnate the fibers and reduce defects. Lower temperatures, coupled with higher viscosity, hinder resin flow. Higher temperatures can cause premature reactions, impacting composite material performance. Furthermore, the secondary temperature is designed to ensure that the resin fully impregnates the fibers before reacting, improving the overall performance of the product. The resulting composite leaf spring exhibited a vertical fatigue life of less than 500,000 cycles, and exhibited noticeable stress whitening, cracks, and delamination defects.

[0114] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a 2.5D woven fabric composite material, comprising: (1) preparing a prepreg of a 2.5D woven fabric, (2) cutting the prepreg, (3) preforming, (4) molding and curing, (5) demolding and post-processing; in step (3), the preforming includes laying, preheating and molding, and the laying is carried out as follows: laying the cut prepreg layer by layer in a straight line along the width direction of the composite material; step (1) is carried out as follows: (1.1) passing the 2.5D woven fabric through a mold with a glue injection hole along the direction of the binding warp yarn; ( 1.2) injecting glue into a mold to impregnate the 2.5D woven fabric to obtain a fabric strip; (1.3) placing release paper on both the upper and lower surfaces of the fabric strip, introducing it into a drying tunnel for prepolymerization, and pultruding to pull out the release paper on the upper and lower surfaces; in step (1.3), the drying temperature of the drying tunnel is divided into three sections, namely 20-60°C in the first section, 50-90°C in the second section, and 80-120°C in the third section, wherein the temperature of the second section is higher than that of the first section, and the temperature of the third section is higher than that of the second section.

2. The preparation method according to claim 1, characterized in that The 2.5D woven fabric in step (1) has an interlayer angle interlocking structure; and / or, The number of fabric layers of the 2.5D woven fabric in step (1) is 5-10, the density of the binding warp yarn, the lining warp yarn and the weft yarn is 3-8, the linear density is 200-1200, and the thickness of a single piece of 2.5D woven fabric is 5-10 mm.

3. The preparation method according to claim 1, characterized in that The fibers used in the 2.5D woven fabric are selected from one or more of carbon fiber, aramid fiber, ultra-high molecular weight polyethylene fiber, glass fiber, and basalt fiber.

4. The preparation method according to claim 1, characterized in that In step (1.2), the glue is selected from at least one of epoxy prepreg resin, unsaturated polyester, and phenolic prepreg resin; and / or, In step (1.2), the impregnation injection pressure is 0.5~5 MPa; and / or, In step (1.3), the pultrusion rate is 2~20 mm / min.

5. The preparation method according to claim 1, characterized in that In step (1.2), the glue is selected from epoxy prepreg resin; and / or, In step (1.2), the impregnation injection pressure is 1-3 MPa; and / or, In step (1.3), the pultrusion pulling rate is 5-15 mm / min.

6. The preparation method according to claim 1, characterized in that The mass content of glue in the prepreg prepared in step (1) is 20-50%.

7. The preparation method according to claim 1, characterized in that The mass content of glue in the prepreg prepared in step (1) is 30-38%.

8. The preparation method according to claim 1, characterized in that The prepreg is cut according to the designed size.

9. The preparation method according to claim 8, characterized in that When the composite material is a leaf spring, it is cut into long strips according to the designed size of the prepared leaf spring.

10. The preparation method according to claim 8, characterized in that The 2.5D woven fabric is cut along the weft direction, and the length of the weft cutting is the design length of the composite material; the length of the cutting along the binding warp direction is the thickness of the composite material.

11. The preparation method according to claim 1, characterized in that The preheating temperature is 60-100° C.; and / or, The molding refers to kneading the preheated prepreg into the shape of the composite material and then placing it into a mold.

12. The preparation method according to claim 1, characterized in that The preheating temperature is 70-90°C; and / or, When the composite material is a leaf spring, the prepreg after preheating is bent along its thickness direction and then placed in a mold.

13. The preparation method according to any one of claims 1 to 12, characterized in that In step (4), the molding curing is carried out in two stages, wherein the temperature of the first stage is 70-100°C, the pressure is 2-12 MPa, and the time is 2-12 min; the temperature of the second stage is 90-120°C, the pressure is 8-18 MPa, and the time is 8-18 min; and the temperature of the second stage is higher than or equal to that of the first stage, the pressure of the second stage is higher than or equal to that of the first stage, and the time of the second stage is higher than or equal to that of the first stage.

14. The preparation method according to claim 13, characterized in that In step (5), the demoulding is performed at 70-100°C; and / or, In step (5), the post-processing includes trimming, grinding and polishing.

15. The preparation method according to claim 14, characterized in that In step (5), the demoulding is performed at 80-100°C.

16. A composite material obtained by the preparation method according to any one of claims 1 to 15.

17. Use of the preparation method according to any one of claims 1 to 15 in the preparation of leaf springs for automobiles.

18. The use according to claim 17, characterized in that Application in the preparation of leaf springs for heavy-duty vehicles with a thickness range of 50 mm and above.

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