Fiber composite profile and its pultrusion process, tow pre-tension calculation method

Abstract

The application provides a fiber composite profile and a pultrusion process and a tow pre-tension calculation method thereof. The pultrusion process comprises: arranging fiber tows in layers and impregnating the fiber tows with epoxy resin; calculating the pre-tension value required to be applied to each fiber tow, individually tensioning each fiber tow according to the pre-tension value, so that a gradient change internal stress is formed between the layers of fiber tows; keeping each fiber tow at the pre-tension value and passing through a planar pultrusion die, and making the epoxy resin solidify and form a planar profile in the planar pultrusion die; and continuously pulling out the solidified planar profile from the planar pultrusion die, and forming a curved profile with a target curvature based on the release of the gradient change internal stress. The pultrusion process provided by the application can naturally form a curved profile with a target curvature based on the release of the gradient change internal stress, and can reduce the processing difficulty and cost of the curved fiber composite profile.

Description

Technical Field

[0001] This invention belongs to the field of fiber composite material processing technology, specifically relating to a fiber composite profile and its pultrusion molding process, and a method for calculating fiber bundle pretension. Background Technology

[0002] Fiber composite profiles possess excellent mechanical properties along their fiber direction and a lower density compared to metallic materials, leading to their widespread application in building reinforcement. Currently, pultrusion molding is the most widely used and efficient process for producing fiber composite profiles. Traditional pultrusion molding processes for flat profiles can only produce straight flat profiles, but curved profiles with a certain curvature are frequently used in practical applications.

[0003] Currently, the main method for producing curved profiles relies on modifying the shape of the pultrusion die, shaping the die cavity into a curved form with a specific curvature. This method uses pultrusion dies that are difficult and costly to manufacture, and the same die can only be used to produce profiles with the same fixed curvature. For the production of profiles with various curvatures, multiple dies with corresponding curvatures need to be pre-fabricated, significantly increasing the production cost. Summary of the Invention

[0004] This invention provides a fiber composite profile and its pultrusion molding process and fiber bundle pretension calculation method, aiming to reduce the processing difficulty and cost of curved fiber composite profiles with curvature.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Firstly, a method for calculating the pretension of a filament bundle is provided, comprising:

[0006] Determine the distance between the center of each fiber bundle and the curved inner surface of the fiber composite profile;

[0007] Based on the radius of curvature of the fiber composite profile and the distance between the center of each fiber bundle and the inner side of the bend, the strain at the position of the center of each fiber bundle is calculated.

[0008] The tensile modulus of the fiber composite profile is calculated based on the fiber bundle content, fiber bundle tensile modulus, and cured resin tensile modulus.

[0009] The stress value at the center of each fiber bundle is determined based on the strain at the center of each fiber bundle and the tensile modulus of the fiber composite profile.

[0010] The required pretension value for each fiber bundle is calculated based on the stress value at the center of each fiber bundle.

[0011] In conjunction with the first aspect, in one possible implementation, calculating the required pretension value for each fiber bundle based on the stress value at the center of each fiber bundle includes:

[0012] Calculate the stress-bearing area of ​​each fiber bundle based on the thickness and width of the fiber composite profile;

[0013] The total tension required for each layer of fiber bundles is calculated based on the stress area of ​​each layer of fiber bundles and the stress value at the center of each layer of fiber bundles.

[0014] Calculate the required pretension for each fiber bundle based on the total tension required for each layer of fiber bundles and the number of fiber bundles in each layer.

[0015] In some embodiments, the stress-bearing area of ​​each fiber bundle is the product of half the center-to-center distance between the two adjacent fiber bundles above and below it and the width of the fiber composite profile.

[0016] For example, the distances from the center of the first and second layer fiber bundles near the inner side of the bend to the inner side of the bend are the first distance and the second distance, respectively; wherein, the force-bearing area of ​​the first layer fiber bundle near the inner side of the bend is half the product of the sum of the first distance and the second distance and the width of the fiber composite profile.

[0017] For example, the distances from the center of the first and second layer fiber bundles near the curved outer side of the fiber composite profile to the curved outer side are the third distance and the fourth distance, respectively; wherein, the force-bearing area of ​​the first layer fiber bundle near the curved outer side is half the product of the sum of the third and fourth distances and the width of the fiber composite profile.

[0018] The beneficial effects of the fiber bundle pretension calculation method provided by this invention are as follows: Compared with the prior art, the fiber bundle pretension calculation method of this invention, by calculating the pretension value required to be applied to each fiber bundle inside the fiber composite profile, can achieve the following when processing curved profiles with a target curvature: simply maintain the pretension value applied to each fiber bundle during the epoxy resin curing process to form a gradient internal stress inside the fiber composite profile. This allows the fiber composite profile to naturally bend to obtain the target curvature after extrusion into a planar pultrusion die and removal of the tensioning force, based on the release of the gradient internal stress. This enables curved fiber composite profiles with curvature to be processed using a planar pultrusion die, thereby reducing the processing difficulty and cost of fiber composite profiles.

[0019] Secondly, embodiments of the present invention also provide a pultrusion molding process for fiber composite profiles, comprising the following steps:

[0020] The fiber bundles are arranged in layers and then impregnated with epoxy resin.

[0021] Calculate the required pretension value for each fiber bundle, and tension each fiber bundle individually according to the pretension value to create a gradient of internal stress between the fiber bundles in each layer;

[0022] Each fiber bundle is kept under pretension and passed through a planar pultrusion die, and the epoxy resin is cured and molded in the planar pultrusion die to obtain a planar profile;

[0023] The solidified planar profile is continuously drawn out from the planar pultrusion die and forms a curved profile with a target curvature based on the release of gradient-varying internal stress.

[0024] The required pretension value for each fiber bundle is calculated using the aforementioned fiber bundle pretension calculation method.

[0025] In conjunction with the second aspect, in one possible implementation, individually tensioning each fiber bundle according to the pretension value includes:

[0026] Each fiber bundle is equipped with a separate force controller, which adjusts the tension of the fiber bundle to the pre-tension value.

[0027] In some embodiments, each tension controller automatically adjusts the pretension value of the fiber bundles based on the entered control program, so as to form a continuously varying gradient internal stress between the fiber bundles in each layer, and the planar profile forms a curved profile with variable curvature based on the release of the continuously varying gradient internal stress.

[0028] For example, the distribution density of the fiber bundles in each layer gradually increases from the outer side of the curved profile to the inner side of the curved profile; the fiber bundles near the inner side of the curved profile pass through the planar pultrusion die in a flattened state.

[0029] The beneficial effects of the fiber composite profile pultrusion molding process provided by this invention are as follows: Compared with the prior art, the fiber composite profile pultrusion molding process of this invention can calculate the required pretension value of each fiber bundle inside the fiber composite profile through the above-mentioned fiber bundle pretension calculation method. When processing curved profiles with target curvature, it is only necessary to maintain the pretension value applied to each fiber bundle during the epoxy resin curing process to form a gradient internal stress inside the fiber composite profile. This allows the fiber composite profile to naturally bend to obtain the target curvature based on the release of gradient internal stress after being pultruded into a planar pultrusion die and the tensioning force is removed. The processing can be carried out using a planar pultrusion die, which meets the needs of processing fiber composite profiles with multiple curvatures using a single planar pultrusion die, thereby reducing the processing difficulty and cost of fiber composite profiles.

[0030] Thirdly, embodiments of the present invention also provide a fiber composite profile, which is obtained by the above-mentioned fiber composite profile pultrusion molding process; the fiber composite profile has multiple layers of fiber bundles distributed inside, and the fiber composite profile forms a curved profile with fixed curvature or variable curvature based on the release of internal stress by the gradient change between the fiber bundles.

[0031] The beneficial effects of the fiber composite profile provided by the present invention are as follows: Compared with the prior art, the fiber composite profile of the present invention forms a gradient internal stress by applying pretension to each fiber bundle during the epoxy resin curing process, thereby naturally forming a curved plate with a target curvature based on the release of the gradient internal stress, which is easy to process and low in cost. Attached Figure Description

[0032] Figure 1 A flowchart illustrating the pultrusion process for fiber composite profiles provided in an embodiment of the present invention;

[0033] Figure 2 A flowchart illustrating the method for calculating the pretension of the filament bundle provided in an embodiment of the present invention;

[0034] Figure 3 for Figure 2 A flowchart illustrating the specific calculation steps for step S105.

[0035] Figure 4 A schematic diagram of the cross-sectional structure of the fiber composite profile provided in an embodiment of the present invention;

[0036] Figure 5 This is a structural block diagram of the pultrusion equipment used in the pultrusion molding process of fiber composite profiles provided in the embodiments of the present invention.

[0037] In the diagram: 10. Fiber composite profile; 11. Fiber bundle; 12. Inner curved surface; 13. Outer curved surface. Detailed Implementation

[0038] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0039] It should be understood that the terms "length," "width," "thickness," "upper," "lower," "front," "rear," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of the invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0040] Please refer to the following: Figure 1 and Figure 2 The method for calculating the pretension of the filament bundle provided by this invention will now be described. The method for calculating the pretension of the filament bundle includes the following steps:

[0041] Step S101: Determine the distance between the center of each layer of fiber bundle 11 and the curved inner surface 12 of the fiber composite profile 10.

[0042] Specifically, the aforementioned inner curved surface 12 refers to the side of the fiber composite profile 10 facing its center of curvature, while the side away from the center of curvature is called the outer curved surface 13. Assuming the thickness of the fiber composite profile 10 to be processed is h, and the total number of fiber bundles 11 layers inside the fiber composite profile 10 is a, then the distance between the first layer of fiber bundles 11 near the inner curved surface 12 and the inner curved surface 12 is y1, the distance between the second layer of fiber bundles 11 and the inner curved surface 12 is y2, and so on, with the last layer of fiber bundles 11 near the outer curved surface 13, and its distance from the inner curved surface 12 is y1. a .

[0043] Step S102: Based on the radius of curvature of the fiber composite profile 10 and the distance between the center of each layer of fiber bundle 11 and the inner curved surface 12, calculate the strain at the position of the center of each layer of fiber bundle 11.

[0044] In this embodiment, under ideal conditions, the fiber composite profile 10 can be considered as a uniform material, and its inner curved surface 12 does not deform (normally, the position where no deformation occurs is at the thickness center of the fiber composite profile 10, but since the tension of the fiber bundle 11 is controlled to be at least zero and cannot be negative, it is assumed that the inner curved surface 12 does not deform). Based on the radius of curvature R of the fiber composite profile 10 to be produced and the various distance values ​​y determined above, the strain ε at the center position of each layer of fiber bundle 11 can be calculated. y =y / R.

[0045] Step S103: Calculate the tensile modulus of the fiber composite profile 10 based on the fiber bundle 11 content, the tensile modulus of the fiber bundle 11, and the tensile modulus of the cured resin.

[0046] In this embodiment, the number of fiber bundles 11 designed within the fiber composite profile 10 (total number of bundles) is η, and the tensile modulus of each fiber bundle 11 is E. t The tensile modulus of the cured resin, also known as the tensile modulus of the cured resin, is E. s Then the tensile modulus E of the fiber composite profile 10 is ηE. t +(1-η)E s .

[0047] Step S104: Determine the stress value at the center of each layer of fiber bundle 11 based on the strain at the center of each fiber bundle 11 and the tensile modulus of the fiber composite profile 10.

[0048] Specifically, in this embodiment, the stress value σ at the center of each layer of fiber bundle 11 is... y =ε y ×E.

[0049] Step S105: Calculate the required pretension value for each fiber bundle 11 based on the stress value at the center of each fiber bundle 11.

[0050] Specifically, the stress value σ at the center of each fiber bundle 11 can be used as a reference. y The total pretension required to be applied to each layer of fiber bundle 11 is calculated based on the force-bearing area of ​​each layer of fiber bundle 11. Then, the total pretension is evenly distributed based on the number of fiber bundles 11 in each layer to obtain the pretension value required to be applied to each fiber bundle 11.

[0051] It is important to understand that during the pultrusion molding process, each layer of fiber bundle 11 can be tensioned separately using a tension controller based on the total pretension to obtain the gradient internal stress between layers; alternatively, each fiber bundle 11 can be tensioned individually based on the required pretension value to create a gradient internal stress within the fiber composite profile 10. The advantage of tensioning each fiber bundle 11 individually is that it can minimize the deviation between idealized calculation results and actual conditions. Specifically, this includes situations such as non-uniform arrangement of fiber bundles 11 within the fiber composite profile 10 and the inability to precisely control each layer of fiber bundles 11 to be on the same plane. Furthermore, when defects such as local bulges or waves occur during production, the tension of the fiber bundles 11 at the corresponding positions can be adjusted to correct them, thereby ensuring the quality of the product molding.

[0052] Compared with the prior art, the fiber bundle pretension calculation method provided in this embodiment calculates the pretension value required for each fiber bundle 11 inside the fiber composite profile 10. When processing curved profiles with a target curvature, it is only necessary to maintain the pretension value applied to each fiber bundle 11 during the epoxy resin curing process to form a gradient internal stress inside the fiber composite profile 10. This allows the fiber composite profile 10 to naturally bend to obtain the target curvature after extrusion into a planar pultrusion die and removal of the tensioning force, based on the release of the gradient internal stress. This enables all curved fiber composite profiles 10 with curvature to be processed using a planar pultrusion die, thereby reducing the processing difficulty and cost of the fiber composite profile 10.

[0053] In some embodiments, see Figure 2 The calculation of the required pretension value for each fiber bundle 11 based on the stress value at the center of each fiber bundle 11 in step S105 above includes:

[0054] Step S1051: Calculate the stress-bearing area of ​​each layer of fiber bundle 11 based on the thickness and width of the fiber composite profile 10. In this embodiment, the thickness of the fiber composite profile 10 is h, and the width is b.

[0055] It should be noted that, since the spacing between each layer of fiber bundles 11 in the fiber composite profile 10 is small, the stress in the area between adjacent layers of fiber bundles 11 is averaged in this embodiment, so that the area between two adjacent layers of fiber bundles 11 is evenly distributed and used as the stress area of ​​each layer of fiber bundles 11.

[0056] Specifically, for the middle layers, namely the 2nd to the (a-1)th fiber bundles 11, each fiber bundle 11 has adjacent layers on both its upper and lower sides, therefore its force-bearing area S n S is the product of half the center distance between the two adjacent fiber bundles 11 and the width of the fiber composite profile 10. n =b×(y n+1 -y n-1 ) / 2.

[0057] For the first layer of fiber bundles 11 near the inner curved surface 12, unlike the middle layer where each layer of fiber bundles 11 has adjacent layers of fiber bundles 11 on both its upper and lower sides, only the second layer of fiber bundles 11 is adjacent to one side of it. However, the other side of it has a region between itself and the inner curved surface 12 that experiences force. Therefore, the force-bearing area S1 of the first layer of fiber bundles 11 near the inner curved surface 12 is calculated as follows:

[0058] The distances from the center of the first and second layer fiber bundles 11 near the inner side of the bend 12 to the inner side of the bend 12 are the first distance y1 and the second distance y2, respectively; wherein, the force-bearing area of ​​the first layer fiber bundles 11 near the inner side of the bend 12 is half the product of the sum of the first distance and the second distance and the width of the fiber composite profile 10, i.e., S1=b×(y1+y2) / 2.

[0059] For the first layer of fiber bundles 11 near the outer curved surface 13, it is the a-th layer relative to the inner curved surface 12. Similarly, only the second layer of fiber bundles 11 near the outer curved surface 13 (which is the a-1-th layer relative to the inner curved surface 12) is adjacent to it, and there is a force in the area between itself and the outer curved surface 13. Therefore, the force-bearing area S of the first layer of fiber bundles 11 near the outer curved surface 13 is... a The calculation method is as follows:

[0060] The distances from the center of the first and second layer fiber bundles 11 near the curved outer surface 13 of the fiber composite profile 10 to the curved outer surface 13 are respectively the third distance y. a and the fourth distance y a-1 Among them, the stress-bearing area of ​​the first layer of fiber bundles 11 near the outer curved surface 13 is half the product of the sum of the third and fourth distances and the width of the fiber composite profile 10, i.e., S a =b×(2h-y) a -y a-1 ) / 2.

[0061] Step S1052: Calculate the total tension required for each layer of fiber bundle 11 based on the force-bearing area of ​​each layer of fiber bundle 11 and the stress value at the center of each layer of fiber bundle 11.

[0062] Specifically, in this embodiment, the total tension F required for each layer of fiber bundle 11 is... n =S n ×σ yn Where n is a positive integer between 1 and a, σ yn This refers to the stress value σ at the center of the nth layer fiber bundle 11. y .

[0063] Step S1053: Calculate the pretension required for each fiber bundle 11 based on the total tension required for each layer of fiber bundle 11 and the number of fiber bundles in each layer of fiber bundle 11.

[0064] In this embodiment, the number of fibers in the nth layer 11 is c. n Therefore, the required pretension for each fiber bundle 11 is evenly distributed, i.e., f n =F n / c n .

[0065] In summary, taking the fiber bundle 11 closest to the inner curved surface 12 as the first layer, the single bundle pretension f on the fiber bundles 11 from the second layer to the (a-1)th layer is... n =b×(y1-y n-1 )×y n ×(ηE t +(1-η)E s ) / 2Rc n The pretension of a single bundle on the first layer of fiber bundle 11 is f1 = b × (y1 + y2) × y1 × (ηE) t +(1-η)E s ) / 2Rc1; Single bundle pretension f on the a-th layer fiber bundle 11 a =b×(2h-y) a -y a-1 )×y a ×(ηE t +(1-η)E s ) / 2Rc a .

[0066] In one possible implementation, to improve the accuracy of calculating the total tension required for each layer of fiber bundle 11, the total tension can be calculated using an integral solution method, specifically as follows:

[0067] Based on the same inventive concept, this application also provides a pultrusion molding process for fiber composite profiles, including the following steps:

[0068] Step S201: Arrange the fiber bundles 11 in layers and impregnate the fiber bundles 11 with epoxy resin.

[0069] Step S202: Calculate the pretension value required for each fiber bundle 11, and tension each fiber bundle 11 individually according to the pretension value to form a gradient internal stress between the fiber bundles 11 in each layer.

[0070] It should be explained that the calculation of the required pretension value of the fiber bundle 11 can be performed before or after step S201. Considering the issue of production efficiency, the pretension value of each fiber bundle 11 can be calculated in advance based on the distribution of the fiber bundle 11 matched with the tensioning process before production construction, i.e., during the production preparation stage, to avoid calculating during the production process and thus avoiding production waiting time.

[0071] In step S203, each fiber bundle 11 is kept under pretension and passed through a planar pultrusion die, and the epoxy resin is cured and formed in the planar pultrusion die to obtain a planar profile.

[0072] In step S204, the solidified planar profile is pulled out from the planar pultrusion die and formed into a curved profile with a target curvature based on the release of gradient-varying internal stress.

[0073] It should be noted that the traction device configured in the planar pultrusion molding equipment of this embodiment for pulling the planar profile through the planar pultrusion die is an alternating traction method. That is, the traction device has two traction ends that act alternately on the planar profile. When one traction end pulls the planar profile a certain distance, the other traction end approaches the planar pultrusion die to pull the planar profile. At this time, the first traction end releases the planar profile (thus obtaining a section of planar profile in a free state, which bends based on the release of gradient change internal stress) and returns to the discharge end of the planar pultrusion die to wait for the next traction. This is repeated so that the two traction ends work alternately to realize the continuous pulling out of the planar profile.

[0074] In step S202, the pretension value required to be applied to each fiber bundle 11 is calculated according to the above-mentioned fiber bundle pretension calculation method.

[0075] It should be noted that in this embodiment, the fiber composite profile 10 can be processed using conventional planar pultrusion molding equipment in conjunction with tension control equipment. The planar pultrusion molding equipment includes, for example, […]. Figure 5 The yarn frame, yarn collecting plate, impregnation device, flat pultrusion die, traction device, and winding device shown are mature existing technologies, and their specific structures and working principles will not be described in detail here. The tension control device itself is also a mature existing device. Specifically, in this embodiment, the individual tensioning of each fiber bundle 11 according to the pretension value in step S202 above includes: configuring a separate force controller for each fiber bundle 11, and adjusting the tension force on the fiber bundle 11 to the pretension value through the tension controller. That is to say, each fiber bundle 11 is configured with a separate force controller. Each tension controller can be manually controlled to adjust the tension, or it can be automatically controlled to adjust the tension based on the control program entered into the device.

[0076] In this embodiment, the tension control device is located between the yarn frame and the planar pultrusion die. Specifically, the tension controller can be set for each fiber bundle 11 as follows: Figure 5The impregnation device and the flat pultrusion die shown can be located between the yarn collecting plate and the impregnation device, or directly on the yarn frame or between the yarn frame and the yarn collecting plate. The calculated pretension is achieved on each fiber bundle 11 through the cooperation of the traction device and each tension controller. In order to avoid the significant friction caused by the large included angle when the fiber bundle 11 enters the hole of the yarn collecting plate, which would affect the accuracy of the tension application of the fiber bundle 11, a positioning pulley is set in front of the yarn collecting plate to guide and direct the fiber bundle 11, so that the fiber bundle 11 can pass through the yarn collecting plate in a straight line or at a small included angle.

[0077] It is important to understand that, as a basic function, when processing planar composite profiles, i.e. products with zero curvature, it is only necessary to keep the pretension value of each filament bundle consistent. At the same time, due to the presence of the tension controller, when problems such as bending, wavy, or bulging occur during the production of planar composite profiles, the tension of the fiber bundle 11 corresponding to the problem location can be adjusted to obtain a flat and straight planar composite profile, thus ensuring product quality.

[0078] For the production of curved profiles, the tension force can be gradually increased or decreased in each layer of fiber bundles 11 inside the fiber composite profile 10 by applying the pretension required on each fiber bundle 11 according to the calculation. As the fiber bundles 11 and epoxy resin are cured and formed in the planar pultrusion mold, the tension difference between each layer of fiber bundles 11 is transformed into gradient internal stress in the planar profile formed by the planar pultrusion mold. When the planar profile is removed from the planar pultrusion mold and the traction force of the traction device is removed, the gradient internal stress is released, causing the planar profile to bend naturally according to the target curvature, thereby obtaining a curved profile with the target curvature.

[0079] It should be noted that for curved profiles produced using this process, if the product's radius of curvature is less than one meter, a winding device is no longer required for winding. The flat sheet material can be naturally bent into a coil under gradient internal stress after exiting the flat pultrusion die, thus simplifying the production process. However, for products with a radius of curvature exceeding one meter, a winding mechanism is still required to ensure that the product packaging size requirements are met.

[0080] Compared with the prior art, the fiber composite profile pultrusion molding process provided in this embodiment can calculate the required pretension value of each fiber bundle 11 inside the fiber composite profile 10 by using the above-mentioned fiber bundle pretension calculation method. When processing a curved profile with a target curvature, it is only necessary to maintain the pretension value applied to each fiber bundle 11 during the epoxy resin curing process to form a gradient internal stress inside the fiber composite profile 10. This allows the fiber composite profile 10 to naturally bend to obtain the target curvature after being extruded from a planar pultrusion die and the tensioning force is removed, based on the release of the gradient internal stress. The processing can be done using a planar pultrusion die, which meets the need to process fiber composite profiles 10 with multiple curvatures using a single planar pultrusion die, thereby reducing the processing difficulty and cost of the fiber composite profile 10.

[0081] It should be noted that, in this embodiment, each tension controller automatically adjusts the pretension value of the fiber bundle 11 based on the input control program, so that a continuously changing gradient internal stress is formed between the fiber bundles 11 in each layer. The planar profile forms a curved profile with variable curvature based on the release of the continuously changing gradient internal stress. Since the fiber composite profile 10, whether planar or curved, is a long wire product, especially for curved products, it may need to have different radii of curvature in the length direction. Therefore, the required pretension value of each fiber bundle 11 in the region is calculated for the radius of curvature at different length positions of the product. Then, based on the calculated pretension value data, a control program is compiled and input into the tension control device, so that the tension controller can automatically adjust the size of the pretension value during the continuous pultrusion process, so that the planar profile forms a continuously changing gradient internal stress in the length direction, and then a curved profile with different curvature along the length direction, i.e., variable curvature, is obtained by releasing the gradient internal stress.

[0082] In some embodiments, the distribution density of each layer of fiber bundles 11 gradually increases from the outer curved side 13 of the curved profile to the inner curved side 12; the fiber bundles 11 near the inner curved side 12 pass through the planar pultrusion die in a flattened state.

[0083] It should be understood that during the stress release process of the gradient change inside the planar profile, the pretension of the fiber bundles 11 near the inner bending surface 12 is high, and the pretension of the fiber bundles 11 near the outer bending surface 13 is low. This allows the planar profile to bend towards the inner bending surface 12 to release stress. Therefore, this embodiment increases the fiber bundles 11 with a larger tension near the inner bending surface 12. The number of fiber bundles 11 can be increased by 1 to 5% based on the actual situation. This can reduce the uneven distribution of fiber bundles 11 caused by tension differences (when the number of each layer is the same, the different tensions of each layer will lead to uneven distribution of fiber bundles 11 inside the profile after stress release bending), thereby improving the performance of the bent profile after stress release.

[0084] It should be noted that the fiber bundle 11 is normally a round or nearly round bundle. In this embodiment, the fiber bundle can be flattened by adding a fiber spreading device before the tension controller, so that the fiber bundle 11 can be evenly distributed in the epoxy resin in a flattened state, which helps to improve product performance.

[0085] Based on the same inventive concept, this application embodiment also provides a fiber composite profile obtained by the above-mentioned fiber composite profile pultrusion molding process; the fiber composite profile 10 has multiple layers of fiber bundles 11 distributed inside, and the fiber composite profile 10 forms a curved profile with fixed curvature or variable curvature based on the stress release of the gradient change between each layer of fiber bundles 11.

[0086] Compared with the prior art, the fiber composite profile provided in this embodiment forms a gradient internal stress by applying pretension to each fiber bundle during the epoxy resin curing process. Based on the release of the gradient internal stress, a curved plate with a target curvature is naturally formed, which is easier to process and has a lower cost.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for calculating the pretension of a filament bundle, characterized in that, include: Determine the distance between the center of each fiber bundle and the curved inner surface of the fiber composite profile; Based on the radius of curvature of the fiber composite profile and the distance between the center of each layer of fiber bundle and the inner side of the bend, the strain at the position of the center of each layer of fiber bundle is calculated respectively. The tensile modulus of the fiber composite profile is calculated based on the fiber bundle content, fiber bundle tensile modulus, and cured resin tensile modulus. The stress value at the center of each layer of fiber bundle is determined based on the strain at the center location of each layer of fiber bundle and the tensile modulus of the fiber composite profile. The required pretension value for each fiber bundle is calculated based on the stress value at the center of each layer of fiber bundles. The calculation of the required pretension value for each fiber bundle based on the stress value at the center of each layer of fiber bundles includes: The stress-bearing area of ​​each layer of fiber bundles is calculated based on the thickness and width of the fiber composite profile. The total tension required for each layer of fiber bundles is calculated based on the stress area of ​​each layer of fiber bundles and the stress value at the center of each layer of fiber bundles. The required pretension for each fiber bundle is calculated based on the total tension required for each layer of fiber bundles and the number of fiber bundles in each layer; For each of the middle layers, the force-bearing area of ​​each fiber bundle is the product of half the center distance between the fiber bundles of the two adjacent layers above and below it and the width of the fiber composite profile. The distances from the center of the first and second layer of fiber bundles near the inner side of the bend to the inner side of the bend are the first distance and the second distance, respectively; wherein, the force-bearing area of ​​the first layer of fiber bundles near the inner side of the bend is half the product of the sum of the first distance and the second distance and the width of the fiber composite profile; The distances from the center of the first and second layer of fiber bundles near the curved outer side of the fiber composite profile to the curved outer side are the third distance and the fourth distance, respectively; wherein, the force-bearing area of ​​the first layer of fiber bundles near the curved outer side is half the product of the sum of the third distance and the fourth distance and the width of the fiber composite profile.

2. A pultrusion molding process for fiber composite profiles, characterized in that, Includes the following steps: The fiber bundles are arranged in layers and then impregnated with epoxy resin. Calculate the required pretension value for each fiber bundle, and tension each fiber bundle individually according to the pretension value to create a gradient of internal stress between the fiber bundles in each layer; Each fiber bundle is held at the pretension value and passed through a planar pultrusion die, and the epoxy resin is cured and formed in the planar pultrusion die to obtain a planar profile. The solidified planar profile is continuously pulled out from the planar pultrusion die and forms a curved profile with a target curvature based on the release of the gradient-varying internal stress. The required pretension value for each fiber bundle is calculated according to the fiber bundle pretension calculation method as described in claim 1.

3. The pultrusion molding process for fiber composite profiles as described in claim 2, characterized in that, The step of individually tensioning each fiber bundle according to the pretension value includes: Each fiber bundle is individually equipped with a tension controller, which adjusts the tension of the fiber bundle to the pre-tension value.

4. The pultrusion molding process for fiber composite profiles as described in claim 3, characterized in that, Each tension controller automatically adjusts the pretension value of the fiber bundle based on the input control program, so as to form a continuously changing gradient internal stress between the fiber bundles in each layer, and the planar profile forms a curved profile with variable curvature based on the release of the continuously changing gradient internal stress.

5. The pultrusion molding process for fiber composite profiles as described in any one of claims 2-4, characterized in that, The distribution density of the fiber bundles in each layer gradually increases from the outer side of the curved profile to the inner side of the curved profile; the fiber bundles near the inner side of the curved profile pass through the planar pultrusion die in a flattened state.

6. A fiber composite profile, characterized in that, The fiber composite profile is obtained by the pultrusion molding process as described in any one of claims 2-5; the fiber composite profile has multiple layers of fiber bundles distributed inside, and the fiber composite profile forms a curved profile with fixed curvature or variable curvature based on the release of internal stress by the gradient change between the fiber bundles in each layer.

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