A high interlayer strength heavy load composite plate spring and a method of manufacturing the same

Abstract

The application belongs to the technical field of composite material plate spring and preparation, and particularly relates to a high interlayer strength heavy load composite material plate spring and a preparation method. The high interlayer strength heavy load composite material plate spring is obtained by performing glue injection, mold pressing, demolding and post-processing on a composite material plate spring preform. The composite material plate spring preform comprises an upper surface unidirectional layer, a middle woven / knitted layer and a lower surface unidirectional layer which are sequentially arranged from top to bottom. The upper surface unidirectional layer and the lower surface unidirectional layer are obtained by laying a unidirectional fiber fabric. The middle woven / knitted layer comprises a plurality of woven / knitted preforms which are arranged in an array. The woven / knitted preform comprises a warp filling yarn, a binding warp yarn and a weft yarn. The warp filling yarn density, the binding warp yarn density and the weft yarn density decrease in sequence. The application can ensure manufacturing efficiency, improve tensile strength, compression strength and interlayer strength, and improve the bending resistance and fatigue life of the plate spring.

Description

Technical Field

[0001] This invention belongs to the field of composite leaf springs and their preparation technology, specifically relating to a high-strength, heavy-duty composite leaf spring between high-rise buildings and its preparation method. Background Technology

[0002] Fiber-reinforced composite materials possess advantages such as high specific strength, corrosion resistance, and long fatigue life, leading to their increasingly widespread application in lightweight applications in automobiles, rail vehicles, and low-altitude aircraft. Composite leaf springs are an important structural component where composite materials play a primary load-bearing role. Their large load-bearing capacity, large deformation, and complex operating conditions result in high stress, high strain, and high stress levels during operation, particularly high interlaminar shear stress, posing significant challenges to interlaminar strength and fatigue life.

[0003] Traditional composite leaf spring manufacturing processes include prepreg molding, pultrusion, winding, and HP-RTM. They are generally made using unidirectional fiber fabrics or two-dimensional planar fabrics with unidirectional fiber as the main component. Under large bending loads, the interlayer strength of composite leaf springs is relatively weak. For working conditions with small loads, composite leaf springs prepared by the above processes can meet the requirements. However, for working conditions with large loads, delamination defects are prone to occur, which seriously affects the fatigue life of composite leaf springs.

[0004] To improve the interlaminar properties of composite leaf springs, scientists have conducted relevant research.

[0005] Patent application CN110373807A discloses a three-dimensional braided leaf spring preform and its braiding process. It proposes to use three-dimensional braiding technology to achieve the connection between the leaf spring's coil lug and the main body of the leaf spring, and to achieve integrated weaving with varying thickness and cross-section of the main body of the leaf spring. This avoids the damage to the overall material performance caused by processing steps such as cutting and drilling, and reduces the use of connecting parts, thus improving the overall performance. This method can improve the integrity of composite leaf springs. However, three-dimensional braiding has low efficiency and high cost, making it difficult to meet the requirements of mass production and application.

[0006] Patent application CN105134849A discloses a three-dimensional braided composite material automotive leaf spring and its preparation method. It proposes a method that uses a mixture of fibers of various materials to form yarn, then uses the yarn to form a three-dimensional braided fabric structure, and finally uses resin transfer molding technology to prepare the product. The three-dimensional braided fabric structure is divided into four parts, and the parts are connected by seams. This method has a complex manufacturing process and is not conducive to high-efficiency mass production and application.

[0007] Patent application CN116065285A discloses a method for preparing 2.5D woven fabric composite materials, the materials obtained, and their applications. It proposes a method for preparing prepregs using 2.5D structure woven fabrics, and then cutting, laying, and hot-pressing the prepregs to prepare composite leaf springs. This method improves the interlayer strength within a single layer of 2.5D woven prepreg and increases the laying efficiency, but it does not mention improving the interlayer strength between prepreg layers.

[0008] Considering the structure and stress characteristics of composite leaf springs, under bending loads, the normal stress on the upper and lower surfaces of the leaf spring is the greatest, while the shear stress on the center surface is the greatest. Increasing the number of fibers penetrating between layers (using braiding / weaving processes) can improve the interlaminar shear strength. However, because braiding / weaving causes warp fiber bending, it reduces the tensile and compressive strength of the composite material. None of the aforementioned patent applications have considered the impact of the loss of warp tensile and compressive strength caused by braiding / weaving on the load-bearing capacity and fatigue life of composite leaf springs. Therefore, how to improve the interlaminar shear strength in the middle while ensuring the tensile and compressive strength of the upper and lower surfaces of the composite leaf spring, and ensuring manufacturing efficiency, has become the key research content of composite leaf springs. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a high-strength, heavy-duty composite leaf spring with interlaminar strength and a preparation method, which improves tensile, compressive and interlaminar strength, and enhances the bending resistance and fatigue life of the leaf spring while ensuring manufacturing efficiency.

[0010] This invention provides a high-strength, heavy-duty composite leaf spring with interlayer strength, comprising a composite leaf spring preform, wherein the composite leaf spring preform is subjected to injection molding, compression molding, demolding and post-processing to obtain a high-strength, heavy-duty composite leaf spring with interlayer strength. The composite material leaf spring preform includes an upper surface unidirectional layer, a middle braided / woven layer and a lower surface unidirectional layer laid out sequentially from top to bottom. The upper surface unidirectional layer and the lower surface unidirectional layer are obtained by laying out unidirectional fiber fabric. The central braided / woven layer comprises multiple braided / woven prefabricated bodies arranged in a row. Each braided / woven prefabricated body includes a backing warp, a knotting warp, and a weft, with the linear density of the backing warp, the knotting warp, and the weft decreasing sequentially.

[0011] Preferably, the warp yarn density is not less than 2400 tex, the knotting warp yarn density is not less than 600 tex, and the weft yarn density is not more than 600 tex. For example, the warp yarn density is 9600 tex, the knotting warp yarn density is 4800 tex, and the weft yarn density is 600 tex; or the warp yarn density is 4800 tex, the knotting warp yarn density is 2400 tex, and the weft yarn density is 600 tex.

[0012] Preferably, the composite material leaf spring preform is a structure of equal thickness or a structure of variable thickness.

[0013] Preferably, the weft yarns in the plurality of woven / woven prefabricated bodies are continuous fibers, that is, the plurality of woven / woven prefabricated bodies are connected into a whole by continuous weft yarns; it can be that each weft yarn is continuous and cut at the outermost edge, or that the weft yarns in all places are the same.

[0014] Preferably, the composite material leaf spring preform is a variable thickness structure, including a straight section in the middle, variable thickness sections at both ends of the straight section in the middle, and straight end sections at both ends of the variable thickness sections.

[0015] Preferably, the variable thickness structure is achieved by using a higher weft yarn linear density and weft yarn density in the middle straight section, and gradually reducing the thickness of the preform by one or more methods, such as decreasing the weft yarn linear density, reducing the weft yarn density, and reducing the number of warp yarn layers, from the middle straight section towards the two ends of the variable thickness section. Weft yarn linear density refers to the fineness of the weft yarn itself, such as 600 tex; it refers to the number of weft yarns woven into a unit length of fabric (usually measured radially), and is a structural parameter of the fabric, depending on the weaving process (such as beat-up density), such as 3 cm / weft yarn. Warp yarns include backing warp yarns and splicing warp yarns.

[0016] Preferably, the middle braided / woven layer is made of 2.5D woven or three-dimensional woven fabric, wherein the 2.5D woven fabric is an interlayer corner interlocking structure, and the three-dimensional woven fabric is an orthogonal three-way woven or Z-direction stitching structure.

[0017] This invention provides a method for preparing a high-strength, heavy-duty composite leaf spring between high layers, wherein the composite leaf spring preform is injected with glue, molded, demolded, and post-treated to obtain the high-strength, heavy-duty composite leaf spring between high layers.

[0018] Preferably, the method for preparing the composite material leaf spring preform is as follows: a braided / woven preform is prepared, cut and arranged to form a middle braided / woven layer; then unidirectional fiber fabric is cut and laid on the upper and lower surfaces of the middle braided / woven layer, preformed and then cut to obtain the composite material leaf spring preform.

[0019] Preferably, a setting powder is disposed between the woven / machine-woven preform and the unidirectional fiber fabric.

[0020] The beneficial effects of this invention are as follows: Based on the distribution characteristics of bending normal stress and shear stress in leaf springs, this invention employs unidirectional fabric lay-ups on the upper and lower surfaces where normal stress is greatest, ensuring good tensile and compressive strength of the surface layer. In the middle section where shear stress is greater, an interlayer reinforcement layer prepared by weaving / knitting is used to improve interlayer shear strength, forming a fiber-reinforced structure consisting of a surface unidirectional layer, a middle interlayer reinforcement layer, and a surface unidirectional layer. This effectively improves the interlayer shear strength of the composite leaf spring and, being located in the middle layer, enhances the ability of the composite leaf spring to withstand shear stress in the middle section under large bending loads. Laying unidirectional fiber fabric on the surface of the interlayer reinforcement layer ensures the surface tensile and compressive strength of the composite material and avoids the loss of warp tensile and compressive strength due to warp fiber bending caused by weaving / knitting processes, which would affect the load-bearing and fatigue performance of the composite leaf spring.

[0021] This invention sets the yarn density of the lining warp yarn > the yarn density of the bonding warp yarn > the yarn density of the weft yarn, and optimizes the tensile, compression and interlayer shear strength through reasonable fiber linear density design.

[0022] This invention can achieve variable thickness weaving of woven / machine-woven prefabricated structures by adjusting weft yarn density, weft yarn density, warp yarn reduction, etc., which is beneficial for realizing variable thickness composite leaf spring structures and reducing the stress value and weight of composite leaf springs.

[0023] According to the width requirements of composite leaf springs, this invention weaves multiple parallel braided / woven preforms connected by continuous weft yarns, and then cuts them to obtain a single leaf spring braided / woven preform, which can realize the efficient preparation of composite leaf springs.

[0024] This invention improves interlaminar shear performance while ensuring the ability to withstand large bending deformations. Unidirectional plywood composites exhibit good tensile and compressive strength but poor interlaminar properties. While braiding / woven fabrics can improve interlaminar properties by causing warp fiber bending, they reduce the tensile and compressive strength of the composite. Based on the different mechanical properties of composites prepared from unidirectional plywood and braided / woven prefabricated structures, this invention utilizes braided / woven prefabricated fabrics in the central region of the leaf spring, where interlaminar shear stress is highest and bending normal stress is lowest, to enhance the interlaminar strength of the composite. Conversely, unidirectional fiber fabrics are used on the surface of the leaf spring, where interlaminar shear stress is lowest and bending normal stress is highest, to improve the tensile and compressive strength of the surface layer. Through this plywood design, the bending resistance of the composite leaf spring can be significantly improved.

[0025] Based on the roles of the lining warp, knotting yarn, and weft yarn in the preform structure, this invention proposes a weaving process structure with the lining warp yarn linear density > knotting warp yarn linear density > weft yarn linear density. The lining warp yarn provides tensile and compressive strength to the composite leaf spring, the knotting yarn provides improved impact resistance and interlaminar shear strength to the composite leaf spring, and the weft yarn mainly plays a layered skeleton support role. This is the optimal choice to ensure that the woven / machine-woven preform can withstand large deformation bending while improving interlaminar shear performance. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a prefabricated composite leaf spring structure with equal thickness.

[0027] Figure 2 This is a schematic diagram of a variable thickness composite material leaf spring structure.

[0028] Figure 3 This is a schematic diagram of a prefabricated composite leaf spring structure with varying thickness.

[0029] Figure 4 This is a schematic diagram of the precast slab layup structure.

[0030] Figure 5 This is a schematic diagram of the precast slab structure after preforming.

[0031] Figure 6 This diagram illustrates the efficient manufacturing process of composite leaf springs.

[0032] Figure 7 This is a schematic diagram of a woven / machine-woven prefabricated structure.

[0033] In the diagram, 1 is the upper unidirectional layer, 2 is the middle woven / machine-woven layer, 3 is the lower unidirectional layer, 21 is the middle straight section, 22 is the variable thickness section, 23 is the end straight section, 4 is the lining warp yarn, 5 is the splicing warp yarn, and 6 is the weft yarn. Detailed Implementation

[0034] Example 1 like Figure 1 As shown, a high-strength, heavy-duty composite leaf spring (of uniform thickness) has a prefabricated structure comprising an upper unidirectional layer 1, a middle braided / woven layer 2, and a lower unidirectional layer 3. The upper unidirectional layer 1 and the lower unidirectional layer 3 are respectively disposed on the upper and lower sides of the middle braided / woven layer 2.

[0035] The preparation method of the composite material leaf spring preform includes the following steps: 1) Manufacturing of Woven / Machine-Woven Prefabricated Panels. Woven / machine-woven prefabricated panels can utilize 2.5D and three-dimensional woven fabrics, such as interlayer corner interlocking, orthogonal three-dimensional woven structures, and Z-direction stitching. The prefabricated panels have a uniform thickness and can be continuously manufactured using equipment. The width of the prefabricated panel is determined based on the width of the leaf spring and the quantity produced at one time. In the woven / machine-woven prefabricated body, the warp yarn density is > the bonding warp yarn density > the weft yarn density. The warp yarn density is 9600 tex, the bonding warp yarn density is 4800 tex, and the weft yarn density is 600 tex. The structure is as follows: Figure 7 As shown.

[0036] 2) Cutting of braided / woven prefabricated panels. Cut the prefabricated panels to the required length of the leaf springs. The length of the cut prefabricated panels is the required flattened length of the leaf springs, and the width is the total width of the multiple leaf springs produced at one time.

[0037] 3) Unidirectional fiber fabric cutting. The unidirectional fiber fabric is cut to the dimensions of the precast panel, with its fiber direction along the length of the leaf spring. A setting powder is sprinkled on the side of the unidirectional fiber fabric that will be bonded to the woven / machine-woven precast panel.

[0038] 4) Lay-up. Lay a unidirectional fabric layer on the two surfaces perpendicular to the cut surface of the woven / machine-woven prefabricated panel obtained after cutting. The number of lay-up layers is as designed, and not less than one layer. The fiber direction is along the length of the leaf spring.

[0039] 5) Preforming. The precast slab after layup is placed in a preforming mold, and pressure is applied to bend the precast slab into the designed shape. The shaping powder is melted by heating and then cooled to obtain the bent precast slab.

[0040] 6) Cutting. Cut the preformed plate according to the design width of the leaf spring to obtain the composite material leaf spring preform.

[0041] Finally, through high-pressure injection molding, compression molding, demolding, and post-processing, a high-strength, heavy-duty composite leaf spring with interlayer strength is obtained.

[0042] Example 2 like Figure 2-4 As shown, a high-strength, heavy-duty composite leaf spring (variable thickness) has a prefabricated structure comprising an upper unidirectional layer 1, a middle braided / woven layer 2, and a lower unidirectional layer 3. The upper unidirectional layer 1 and the lower unidirectional layer 3 are respectively disposed on the upper and lower sides of the middle braided / woven layer 2.

[0043] The middle woven / woven layer 2 includes a middle straight section 21, a variable thickness section 22, and an end straight section 23.

[0044] The preparation method of composite leaf spring preforms includes the following steps: 1) Manufacturing of Woven / Machine-Woven Prefabricated Panels. Woven / machine-woven prefabricated panels can utilize 2.5D and three-dimensional woven fabrics, such as interlayer corner interlocking, orthogonal three-dimensional woven structures, Z-direction stitching, and Z-direction needle punching. The prefabricated panels have a variable thickness structure, which can be achieved by adjusting the weft yarn density, warp yarn density, and warp yarn reduction. Continuous manufacturing can be achieved through equipment. The width of the prefabricated panel is determined based on the width of the leaf spring and the quantity produced at one time. In the woven / machine-woven prefabricated body, the warp yarn density is > the bonding warp yarn density > the weft yarn density. The warp yarn density is 4800 tex, the bonding warp yarn density is 2400 tex, and the weft yarn density is 600 tex. The structure is as follows: Figure 7 As shown.

[0045] 2) Cutting of braided / woven prefabricated panels. Cut the prefabricated panels to the required length of the leaf springs. The length of the cut prefabricated panels is the required flattened length of the leaf springs, and the width is the total width of the multiple leaf springs produced at one time.

[0046] 3) Unidirectional fiber fabric cutting. The unidirectional fiber fabric is cut to the dimensions of the precast panel, with its fiber direction along the length of the leaf spring. A setting powder is sprinkled on the side of the unidirectional fiber fabric that will be bonded to the woven / machine-woven precast panel.

[0047] 4) Lay-up. Lay a unidirectional fabric layer on the two surfaces perpendicular to the cut surface of the woven / machine-woven prefabricated panel obtained after cutting. The number of lay-up layers is as designed, and not less than one layer. The fiber direction is along the length of the leaf spring.

[0048] 5) Preforming. The precast slab after layup is placed in a preforming mold, and pressure is applied to bend the precast slab into the designed shape. The shaping powder is melted by heating and then cooled to obtain the bent precast slab.

[0049] 6) Cutting. Cut the preformed plate according to the design width of the leaf spring to obtain the composite material leaf spring preform.

[0050] Finally, through high-pressure injection molding, compression molding, demolding, and post-processing, a high-strength, heavy-duty composite leaf spring with interlayer strength is obtained.

[0051] Based on the different mechanical properties of composite materials prepared by unidirectional plywood structure and braided / woven preform structure, this invention uses braided / woven preform in the middle of the leaf spring where the interlayer shear stress is the largest and the bending normal stress is small to improve the interlayer strength of the composite material. In the area on the surface of the leaf spring where the interlayer shear stress is small and the bending normal stress is the largest, unidirectional fiber fabric is used to improve the tensile and compressive strength of the surface layer of the composite material. Through the above plywood structure design, the bending resistance of the composite leaf spring can be greatly improved.

[0052] Unidirectional plywood composites have good tensile and compressive strength but poor interlaminar properties; braiding / woven fabrics can cause warp fiber bending, which can improve interlaminar properties but will reduce the tensile and compressive strength of the composites.

[0053] The performance of ply structures and woven / woven prefabricated structures is compared in the table below.

[0054]

[0055] The term "layout structure" refers to a composite material sample prepared using only unidirectional fiber fabric layup, and "woven / woven preform" refers to a composite material sample prepared using only woven / woven preform.

[0056] The magnitude of the shear stress of a leaf spring is inversely proportional to its distance from the neutral axis. The closer it is to the neutral plane of the leaf spring, the greater its shear stress. The shear stress on the upper and lower surfaces of the leaf spring is equal to zero.

[0057] Therefore, considering the mechanical properties of composite materials prepared by unidirectional lay-up and braided / woven preforms, as well as the distribution characteristics of normal stress and shear stress during bending of composite leaf springs, the leaf spring structure proposed in this invention uses braided / woven preforms in the middle of the leaf spring where the interlayer shear stress is the greatest and the bending normal stress is the smallest, thereby improving the interlayer strength of the composite material. In the area on the surface of the leaf spring where the interlayer shear stress is the smallest and the bending normal stress is the greatest, unidirectional fiber fabrics are used to improve the tensile and compressive strength of the surface layer of the composite material. Through the above lay-up structure design, the bending resistance of composite leaf springs can be significantly improved.

[0058] Comparative Example 1 Compared with Example 1, the difference is that the warp yarn density is equal to the knotting warp yarn density and the weft yarn density. The warp yarn density is 2400 tex, the knotting warp yarn density is 2400 tex, and the weft yarn density is 2400 tex. Everything else is the same as in Example 1.

[0059] Comparative Example 2 Compared to Example 1, Comparative Example 2 differs in that the composite material leaf spring prefabricated structure includes an upper braided / woven layer, a middle unidirectional layer, and a lower braided / woven layer. The upper and lower braided / woven layers are respectively located on the upper and lower sides of the middle unidirectional layer, and the unidirectional layer is obtained by laying unidirectional fiber fabric. The specific steps are adjusted accordingly based on Example 1.

[0060] The performance of the leaf springs (of the same size) of Examples 1-2 and Comparative Examples 1-2 was measured, as shown in the table below.

[0061]

[0062] It can be seen that the leaf spring obtained by adopting the structure and preparation method of this application can ensure that it has both large bending performance and large interlaminar strength.

[0063] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0064] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A high-strength, heavy-duty composite leaf spring for high-rise buildings, characterized in that, The composite material leaf spring preform is subjected to injection molding, compression molding, demolding and post-processing to obtain a high-strength heavy-duty composite material leaf spring between layers. The composite material leaf spring preform includes an upper surface unidirectional layer (1), a middle braided / woven layer (2) and a lower surface unidirectional layer (3) laid out sequentially from top to bottom. The upper surface unidirectional layer (1) and the lower surface unidirectional layer (3) are obtained by laying out unidirectional fiber fabric. The middle braided / woven layer (2) is formed by arranging multiple braided / woven preforms. The braided / woven preforms include backing warp yarns (4), knotting warp yarns (5), and weft yarns (6), with the linear density of the backing warp yarns, knotting warp yarns, and weft yarns decreasing sequentially.

2. The high-strength, heavy-duty composite leaf spring with interlayer structure as described in claim 1, characterized in that, The warp yarn density is not less than 2400 tex, the knotting warp yarn density is not less than 600 tex, and the weft yarn density is not higher than 600 tex.

3. The high-strength, heavy-duty composite leaf spring with interlayer structure as described in claim 1, characterized in that, The composite material leaf spring preform is a structure of equal thickness or a structure of variable thickness.

4. The high-strength, heavy-duty composite leaf spring with interlayer structure as described in claim 1, characterized in that, The weft yarns (6) in the plurality of woven / woven prefabricated bodies are continuous fibers.

5. The high-strength, heavy-duty composite leaf spring with interlayer structure as described in claim 3, characterized in that, The composite material leaf spring preform is a variable thickness structure, including a central straight section (21), variable thickness sections (22) located at both ends of the central straight section (21), and end straight sections (23) located at both ends of the variable thickness sections (22).

6. The high-strength, heavy-duty composite leaf spring with interlayer structure as described in claim 5, characterized in that, The variable thickness structure is achieved by using a larger weft yarn density and weft yarn density in the middle straight section (21), and gradually reducing the thickness of the preform by using one or more of the following methods: reducing the weft yarn density, reducing the weft yarn density, and reducing the number of warp yarn layers from the middle straight section (21) to the variable thickness sections (22) at both ends.

7. The high-strength, heavy-duty composite leaf spring with interlayer structure as described in claim 1, characterized in that, The middle braided / woven layer (2) adopts a 2.5D woven or three-dimensional woven fabric, wherein the 2.5D woven fabric is an interlayer corner interlocking structure, and the three-dimensional woven fabric is an orthogonal three-way woven or Z-direction stitching structure.

8. A method for preparing a high-strength, heavy-duty composite leaf spring as described in any one of claims 1-7, characterized in that, The composite leaf spring preform is injected with glue, molded, demolded and post-processed to obtain a high-strength heavy-duty composite leaf spring between high layers.

9. The preparation method according to claim 8, characterized in that, The preparation method of the composite material leaf spring preform is as follows: prepare a braided / woven preform, cut and arrange it to form a middle braided / woven layer (2); then cut the unidirectional fiber fabric and lay it on the upper and lower surfaces of the middle braided / woven layer (2), preform it and then cut it to obtain the composite material leaf spring preform.

10. The preparation method according to claim 9, characterized in that, A setting powder is placed between the woven / machine-woven preform and the unidirectional fiber fabric.

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