Automotive crash beam based on continuous fiber printing negative Poisson's ratio structure

Abstract

This invention relates to the field of automotive safety component technology, and discloses an automotive crash beam based on a continuous fiber-printed negative Poisson's ratio structure. The beam comprises a core layer with a negative Poisson's ratio effect integrally formed from continuous carbon fibers and thermosetting resin. The manufacturing method utilizes continuous fiber additive manufacturing equipment to simultaneously extrude continuous carbon fibers and a resin matrix, perform in-situ impregnation, and build up layers to form a green crash beam with the core layer, which is then cured. This invention combines the tensile energy absorption mechanism of the negative Poisson's ratio structure with the high load-bearing capacity of continuous fibers, and utilizes integrated additive manufacturing technology to eliminate weak interfaces in traditional assembly. This effectively solves the technical problems of balancing energy absorption efficiency and lightweight design, as well as stress concentration in the structure. The resulting crash beam exhibits higher specific energy absorption, excellent structural integrity, and a lightweight level.

Description

Technical Field

[0001] This invention relates to the field of automotive safety component technology, specifically to an automotive anti-collision beam based on a continuous fiber-printed negative Poisson's ratio structure. Background Technology

[0002] Lightweighting of automobiles is a key technological path to achieving energy conservation, emission reduction, and improved driving range. As a core energy-absorbing component ensuring vehicle passive safety, the design and manufacturing of crash beams must reduce their weight while meeting stringent collision safety standards. Currently, automotive crash beams are mainly made of high-strength steel, aluminum alloys, or traditional composite materials. However, existing technologies have encountered bottlenecks in further improving the overall performance of crash beams. On the one hand, the energy absorption of traditional crash beams mainly relies on the yielding deformation of the material itself or simple crushing of the structure. The unit mass efficiency of this energy absorption mechanism is approaching its limit. To further increase the total energy absorption, it is often necessary to increase the amount of material used or thicken the structure, which contradicts the development trend of automotive lightweighting.

[0003] On the other hand, the traditional manufacturing process for high-performance composite material anti-collision beams is usually quite complex. To construct an inner core with a buffering effect, a split manufacturing and reassembly technique is typically used. This involves combining pre-prepared surface panels with internal core materials (such as foam or honeycomb structures) through bonding and other secondary processes. This introduces adhesive interfaces into the structure, which are prone to becoming stress concentration points when subjected to impact loads, leading to initial damage such as delamination or detachment, thereby affecting the overall structural integrity and final load-bearing capacity of the component.

[0004] Furthermore, traditional composite material molding processes, such as autoclave curing and resin transfer molding, rely on molds, which present significant challenges when manufacturing optimized structures with complex internal cavities. Mold design and manufacturing are costly, and once finalized, they are difficult to modify, thus limiting the freedom of product design iteration and manufacturing flexibility. For negative Poisson's ratio structures that can improve energy absorption efficiency, traditional processes often struggle to achieve precise and integrated manufacturing, resulting in lengthy production flows that are ill-suited to the demands of rapid response and customization in the market.

[0005] To address the aforementioned problems, this invention provides an automotive crash beam based on a continuous fiber-printed negative Poisson's ratio structure and its manufacturing method. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an automotive crash beam based on a continuous fiber-printed negative Poisson's ratio structure and its manufacturing method, which solves the problems of difficulty in balancing weight and energy absorption performance, complex manufacturing processes, and insufficient structural integrity in existing automotive crash beam technologies.

[0007] To achieve the above objectives, the present invention provides a negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology.

[0008] The negative Poisson's ratio structure automotive carbon fiber anti-collision beam based on continuous fiber printing technology is integrally formed from 3K continuous carbon fiber and thermosetting resin matrix, and includes a core layer and a surface layer.

[0009] In one specific embodiment, the core layer is a star-shaped concave structure or a concave hexagonal structure with a periodic negative Poisson's ratio effect, formed by the 3K continuous carbon fiber and the thermosetting resin matrix. When subjected to axial compressive impact, the microstructure of the star-shaped concave structure or the concave hexagonal structure undergoes lateral contraction rather than expansion; this is the negative Poisson's ratio effect. The negative Poisson's ratio effect can convert some of the impact kinetic energy into rotational and contractile deformation energy of the structural units. Compared to traditional material extrusion deformation, the negative Poisson's ratio structure can maintain a higher plateau stress over a longer displacement stroke, thereby improving the energy absorption efficiency per unit mass.

[0010] In one specific embodiment, the surface layer is a 0° / 90° orthogonal layup continuous carbon fiber reinforcement layer, which is composed of the 3K continuous carbon fibers and the thermosetting resin matrix. This 0° / 90° orthogonal layup structure provides the surface layer with high strength and high stiffness in both the longitudinal and transverse directions, enabling it to withstand the main bending and torsional loads during a collision and maintain the macroscopic structural stability of the crash beam, while also constraining and protecting the internal core layer.

[0011] In one specific embodiment, in the anti-collision beam body, the volume fraction of the 3K continuous carbon fiber is 55-65%, and the volume fraction of the thermosetting resin matrix is ​​35-45%. This volume fraction range ensures that the reinforcing fibers are fully impregnated in the matrix, forming a composite material structure with low porosity, while maximizing the load-bearing capacity of the continuous fibers, which is a necessary condition for achieving lightweight and high-strength mechanical properties.

[0012] As a preferred technical solution, the structural unit size of the core layer exhibiting the periodic negative Poisson's ratio effect is 5-10 mm, and the unit wall thickness is 0.5-1 mm. This size range was determined by comprehensively considering energy absorption performance and the feasibility of continuous fiber printing technology. Excessively large unit sizes are detrimental to the uniformity of energy absorption, while excessively small unit sizes place excessively high demands on printing accuracy and efficiency.

[0013] Preferably, the thermosetting resin matrix is ​​composed of bisphenol A type epoxy resin and an imidazole latent curing agent. This resin system has a low viscosity at the printing temperature, which is beneficial for in-situ impregnation of continuous fibers; the imidazole latent curing agent remains stable at room temperature and printing temperature, and is only activated during the subsequent high-temperature stage of autoclave curing, thus providing a wide process window for the printing process.

[0014] Preferably, the 3K continuous carbon fiber has a tensile strength of 3.0-4.0 GPa and a fiber areal density of 250-350 g / m³. ² The 3K continuous carbon fiber with the aforementioned performance parameters can provide the required impact resistance and structural stiffness for the crash beam.

[0015] The present invention also includes a method for manufacturing a negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology.

[0016] The manufacturing method includes the following steps:

[0017] S1. Using dual-nozzle synchronous extrusion technology, 3K continuous carbon fibers are printed along a preset path, and a thermosetting resin matrix composed of bisphenol A epoxy resin and imidazole latent curing agent is extruded simultaneously to complete in-situ impregnation. This step combines fiber placement and resin impregnation into one process, eliminating the need for traditional prepreg preparation or post-impregnation processes, and enabling the direct fabrication of integrated composite material structures with complex internal cavity geometries.

[0018] S2. After printing one layer, the completed printed layer undergoes infrared pre-curing treatment to achieve a partial curing degree of 40-60% for the thermosetting resin matrix. The purpose of this step is to improve the structural stiffness (i.e., green strength) of the printed layer, making it sufficient to support the weight of subsequent printed layers and mechanical disturbances during the printing process, ensuring that complex three-dimensional structures can be accurately formed without collapse or deformation without mold support.

[0019] S3. After all layers are printed, the printed part is cured in a staged autoclave under a vacuum of -0.09 to -0.1 MPa. The staged autoclave curing process includes the following steps:

[0020] The carbon fiber crash beam for automobiles is prepared by holding the material at 50-70℃ for 1.0-1.5 hours, then raising the temperature to 120℃ and applying a pressure of 0.5-1.0 MPa for 1.5-2.5 hours, followed by raising the temperature to 160℃ and holding for 1.0-1.5 hours. After cooling and demolding, the carbon fiber crash beam is obtained. This vacuum environment is used to remove residual air and trace amounts of volatiles generated during resin curing, thus inhibiting pore formation. The staged heating and pressurization process controls the resin flow, gelation, and cross-linking processes to reduce internal stress during curing, ultimately resulting in a dense composite material component with excellent mechanical properties.

[0021] Preferably, prior to step S1, the 3K continuous carbon fiber is subjected to plasma surface treatment with a power of 450-550W. Plasma surface treatment increases the number of oxygen-containing functional groups on the carbon fiber surface, improves its surface energy, thereby improving the interfacial wettability and chemical bonding strength between the fiber and the epoxy resin matrix, ultimately enhancing the interlaminar shear strength and overall mechanical properties of the composite material.

[0022] Preferably, in step S1, the dual-nozzle synchronous extrusion technology is performed using a six-axis linkage dual-nozzle printer, wherein the carbon fiber nozzle temperature is 20-30℃, the resin nozzle temperature is 70-90℃, the printing speed is 150-250mm / min, and the volumetric flow rate ratio of the thermosetting resin matrix to the 3K continuous carbon fiber is 1:0.8. These process parameters together constitute a stable and implementable process window.

[0023] Preferably, the preset path mentioned in step S1 is determined through simulation analysis using finite element analysis software. This simulation analysis aims to simulate the stress distribution and energy transfer path of the anti-collision beam under impact load. Based on the analysis results, the fiber laying trajectory is planned and optimized to ensure that the direction of the continuous fibers is consistent with the principal stress direction within the structure to the greatest extent possible, thereby achieving optimal mechanical load-bearing and energy absorption performance. Specifically, the preset path can be optimized into a staggered spiral filling path, wherein the interlayer misalignment angle is preferably 20-25°.

[0024] Preferably, in step S1, the printing of the 3K continuous carbon fiber and the extrusion process of the thermosetting resin matrix are controlled by a fiber tension feedback system and a resin pressure closed-loop control system. The fiber tension feedback system monitors and adjusts the fiber tension in real time (with a control accuracy of ±2N) to ensure that the fiber is not over-tensioned or relaxed during the laying process. The resin pressure closed-loop control system (with a control accuracy of ±5kPa) ensures that the resin extrusion flow rate is accurate and stable. The two work together to ensure a uniform and constant fiber volume fraction and avoid internal defects.

[0025] Preferably, after step S3, a post-processing step is included, in which mounting holes and edge chamfering are machined on the cured part using a five-axis machine tool. This is a necessary step to obtain a finished product that meets the final assembly accuracy requirements.

[0026] This invention provides an automotive crash beam based on a continuous fiber-printed negative Poisson's ratio structure. It offers the following advantages:

[0027] 1. This invention combines a core layer with a negative Poisson's ratio effect with high-strength continuous carbon fiber to improve the energy absorption characteristics of the anti-collision beam. When subjected to impact load, the negative Poisson's ratio structure undergoes a unique lateral contraction (expansion) deformation, which can stably absorb and dissipate energy during a long displacement process. Compared with the compression and collapse mode of traditional structures, its energy absorption efficiency per unit mass is higher, thereby achieving lightweight components while effectively enhancing the passive safety of the vehicle.

[0028] 2. This invention uses continuous fiber printing technology to achieve integrated molding of the crash beam, so that the complex negative Poisson's ratio core layer and the outer surface layer form a seamless whole. This eliminates the connection interfaces (such as welds or adhesive layers) that exist in traditional multi-part assembly processes, avoids stress concentration and potential failure risks caused by connection interfaces, and thus improves the overall structural integrity and mechanical performance reliability of the crash beam.

[0029] 3. The manufacturing method of this invention enables highly flexible design of the anti-collision beam structure, allowing for the creation of complex and optimized internal cavity structures that are difficult to achieve using traditional processes, based on different performance requirements. Simultaneously, this method integrates fiber placement, in-situ resin impregnation, and structural molding into a single automated step, simplifying the manufacturing process of composite material components, thereby shortening the production cycle and reducing reliance on complex, specialized molds. Attached Figure Description

[0030] Figure 1 This is a perspective view of the present invention;

[0031] Figure 2 This is a cross-sectional view of the anti-collision beam body of the present invention;

[0032] Figure 3 This is the finite element model of the core layer of this invention.

[0033] The components are: 1. Anti-collision beam body; 2. Energy absorption box; 3. Mounting plate; 4. Surface layer; 5. Core layer. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, preparation examples, embodiments, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Please see the appendix Figure 1 and attached Figure 2 This invention provides a negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology. The entire carbon fiber anti-collision beam consists of an anti-collision beam body 1, which serves as the main load-bearing component, an energy-absorbing box 2 for connecting to the vehicle body and initially absorbing energy, and a mounting plate 3. Its core technology lies in the fact that the entire anti-collision beam body 1 is a seamless integral structure manufactured using 3K continuous carbon fiber and a thermosetting resin matrix through an integrated molding technology. Internally, it includes a core layer 5 that plays a crucial role in energy absorption and a surface layer 4 that provides the main load-bearing capacity. The internal core layer 5 is designed with a periodic negative Poisson's ratio structure featuring a star-shaped concave or concave hexagonal shape, which can undergo unique tensile deformation during a collision to efficiently dissipate energy. The external surface layer 4 effectively resists bending and torsional stresses caused by impact through continuous carbon fiber with 0° / 90° orthogonal layups. By precisely controlling the volume fraction of 3K continuous carbon fiber within a high content range of 55-65%, a lightweight effect is achieved.

[0036] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0037] Raw materials for preparation:

[0038] Bisphenol A type epoxy resin, CAS No.: 25068-38-6;

[0039] Imidazole latent curing agent, CAS No.: 931-36-2.

[0040] Preparation Example 1: Preparation of Printable Thermosetting Resin Matrix

[0041] S1. Place the bisphenol A type epoxy resin in a vacuum drying oven at 100℃ and dry for 2 hours, then set aside.

[0042] S2. Based on a mass ratio of 100:4, accurately weigh 1000g of bisphenol A type epoxy resin and 40g of 2-ethyl-4-methylimidazolium that have undergone drying treatment in step S1.

[0043] S3. Place the weighed epoxy resin in a 2L three-necked flask equipped with a mechanical stirrer and a heating mantle, and heat it under nitrogen protection while maintaining the temperature at 60°C.

[0044] S4. Start the mechanical stirrer, set the speed to 300 rpm, and slowly add the weighed 2-ethyl-4-methylimidazolium powder while stirring.

[0045] S5. Stir continuously for 60 minutes at 60℃ and 300rpm until the curing agent powder is completely dissolved and the system becomes a homogeneous, clear and transparent liquid.

[0046] S6. Transfer the mixture obtained in step S5 to a vacuum drying oven and perform vacuum degassing treatment at 60°C and -0.09MPa for 30 minutes to remove air bubbles introduced during stirring.

[0047] S7. After processing, a colorless, transparent, viscous printable thermosetting resin matrix is ​​obtained. It is sealed and stored at 4°C for later use.

[0048] Examples 1-3:

[0049] Example 1:

[0050] Please see the appendix Figure 3 This embodiment provides a method for manufacturing a negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology. The specific steps are as follows:

[0051] S1. Structural Simulation and Printing Path Planning: Before physical printing, an accurate 3D digital model of the crash beam was constructed using Abaqus finite element analysis software. The core layer 4 of the model has a star-shaped concave structure with a unit size of 5mm and a wall thickness of 0.5mm. The surface layer 5 is a 0° / 90° orthogonal layup. A dynamic impact analysis was performed on the 3D digital model using simulated frontal collision loads. Based on the obtained stress distribution results, a preset path was planned and generated to guide physical printing. This path was optimized to be an interlaced spiral filling path with an interlayer misalignment angle of 20° to ensure that the continuous fiber layup direction is aligned with the principal stress path.

[0052] S2. Fiber pretreatment: 3K type continuous carbon fiber is treated in a plasma surface treatment device with a treatment power of 450W and a treatment speed of 5m / min.

[0053] S3, 3D Printing and In-situ Impregnation: The continuous carbon fiber treated in step S1 and the printable thermosetting resin matrix prepared in Example 1 are respectively loaded into a six-axis linkage dual-nozzle additive manufacturing equipment. Based on the three-dimensional model and printing path determined in step S1, the following process parameters are set for printing:

[0054] Carbon fiber nozzle temperature: 20℃;

[0055] Resin nozzle temperature: 70℃;

[0056] Printing speed: 150mm / min;

[0057] The volumetric flow rate ratio of thermosetting resin matrix to 3K continuous carbon fiber is 1:0.7.

[0058] The printing path parameters are executed according to the plan in step S1. During the printing process, the fiber tension feedback system and the resin pressure closed-loop control system operate throughout.

[0059] S4. Infrared pre-curing: After each printed layer is laid, the infrared heating module integrated into the equipment heats the layer to achieve a partial curing degree of 40% for the resin matrix.

[0060] S5. Autoclave Curing: After all layers are printed, the obtained anti-collision beam preform is transferred into the autoclave, the door is closed, the vacuum is drawn to -0.09MPa, and the following staged curing procedure is started:

[0061] First stage: Heat to 50°C at a rate of 5°C / min and hold at this temperature for 1.0 hour.

[0062] Second stage: Heat to 110°C at a rate of 3°C / min, while applying a pressure of 0.5MPa inside the tank, and hold at this temperature and pressure for 1.5 hours.

[0063] The third stage involves heating to 150°C at a rate of 3°C / min, maintaining a pressure of 0.5 MPa, and holding at this temperature and pressure for 1.0 hour. After the process is complete, allow the furnace to cool naturally to room temperature, depressurize, open the can, and remove the cured and molded parts.

[0064] S6. Post-processing: Fix the cured and molded parts onto the worktable of the five-axis machining center, and drill the mounting holes and chamfer the edges according to the three-dimensional digital model of the product.

[0065] Finally, the automotive carbon fiber anti-collision beam sample of Example 1 was obtained.

[0066] Example 2:

[0067] This embodiment provides a method for manufacturing a negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology. The specific steps are as follows:

[0068] S1. Structural Simulation and Printing Path Planning: Before physical printing, an accurate 3D digital model of the crash beam was constructed using Abaqus finite element analysis software. The core layer 4 of the model is a concave hexagonal structure with a unit size of 7.5mm and a wall thickness of 0.75mm. The surface layer 5 is a 0° / 90° orthogonal layup. A dynamic impact analysis was performed on the 3D digital model, simulating a frontal collision load. Based on the obtained stress distribution results, a preset path was planned and generated to guide the physical printing. This path was optimized to be an interlaced spiral filling path with an interlayer misalignment angle of 22.5° to ensure that the continuous fiber layup direction is aligned with the principal stress path.

[0069] S2. Fiber pretreatment: The 3K type continuous carbon fiber is treated in a plasma surface treatment device with a treatment power of 500W and a treatment speed of 5m / min.

[0070] S3, 3D Printing and In-situ Impregnation: The continuous carbon fiber treated in step S1 and the printable thermosetting resin matrix prepared in Example 1 are respectively loaded into a six-axis linkage dual-nozzle additive manufacturing equipment. Based on the three-dimensional model and printing path determined in step S1, the following process parameters are set for printing:

[0071] Carbon fiber nozzle temperature: 25℃;

[0072] Resin nozzle temperature: 80℃;

[0073] Printing speed: 200mm / min;

[0074] The volumetric flow rate ratio of thermosetting resin matrix to 3K continuous carbon fiber is 1:0.8.

[0075] The printing path parameters are executed according to the plan in step S1. During the printing process, the fiber tension feedback system and the resin pressure closed-loop control system operate throughout.

[0076] S4. Infrared pre-curing: After each printed layer is laid, the infrared heating module integrated into the equipment heats the layer to achieve a partial curing degree of 50% for the resin matrix.

[0077] S5. Autoclave Curing: After all layers are printed, the obtained anti-collision beam preform is transferred into the autoclave, the door is closed, the vacuum is drawn to -0.095MPa, and the following staged curing procedure is started:

[0078] First stage: Heat to 60°C at a rate of 5°C / min and hold at this temperature for 1.25 hours.

[0079] Second stage: Heat to 120°C at a rate of 3°C / min, while applying a pressure of 0.75MPa inside the tank, and hold at this temperature and pressure for 2 hours.

[0080] The third stage involves heating to 160°C at a rate of 3°C / min, maintaining a pressure of 0.5 MPa, and holding at this temperature and pressure for 1.25 hours. After the process is complete, allow the furnace to cool naturally to room temperature, depressurize, open the can, and remove the cured and molded parts.

[0081] S6. Post-processing: Fix the cured and molded parts onto the worktable of the five-axis machining center, and drill the mounting holes and chamfer the edges according to the three-dimensional digital model of the product.

[0082] Finally, the automotive carbon fiber anti-collision beam sample of Example 2 was obtained.

[0083] Example 3:

[0084] Please see the appendix Figure 3 This embodiment provides a method for manufacturing a negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology. The specific steps are as follows:

[0085] S1. Structural Simulation and Printing Path Planning: Before physical printing, an accurate 3D digital model of the crash beam was constructed using Abaqus finite element analysis software. The core layer 4 of the model has a star-shaped concave structure with a unit size of 10mm and a wall thickness of 1.0mm. The surface layer 5 is a 0° / 90° orthogonal layup. A dynamic impact analysis was performed on the 3D digital model using simulated frontal collision loads. Based on the obtained stress distribution results, a preset path was planned and generated to guide physical printing. This path was optimized to be an interlaced spiral filling path with an interlayer misalignment angle of 25° to ensure that the continuous fiber layup direction is aligned with the principal stress path.

[0086] S2. Fiber pretreatment: The 3K type continuous carbon fiber is treated in a plasma surface treatment device with a treatment power of 550W and a treatment speed of 5m / min.

[0087] S3, 3D Printing and In-situ Impregnation: The continuous carbon fiber treated in step S1 and the printable thermosetting resin matrix prepared in Example 1 are respectively loaded into a six-axis linkage dual-nozzle additive manufacturing equipment. Based on the three-dimensional model and printing path determined in step S1, the following process parameters are set for printing:

[0088] Carbon fiber nozzle temperature: 30℃;

[0089] Resin nozzle temperature: 90℃;

[0090] Printing speed: 250mm / min;

[0091] The volumetric flow rate ratio of thermosetting resin matrix to 3K continuous carbon fiber is 1:0.9.

[0092] The printing path parameters are executed according to the plan in step S1. During the printing process, the fiber tension feedback system and the resin pressure closed-loop control system operate throughout.

[0093] S4. Infrared pre-curing: After each printed layer is laid, the infrared heating module integrated into the equipment heats the layer to achieve a partial curing degree of 60% for the resin matrix.

[0094] S5. Autoclave Curing: After all layers are printed, the obtained anti-collision beam preform is transferred into the autoclave, the door is closed, the vacuum is drawn to -0.1MPa, and the following staged curing procedure is started:

[0095] First stage: Heat to 70°C at a rate of 5°C / min and hold at this temperature for 1.5 hours.

[0096] Second stage: Heat to 130°C at a rate of 3°C / min, while applying a pressure of 1.0MPa inside the tank, and maintain this temperature and pressure for 2.5 hours.

[0097] The third stage involves heating to 170°C at a rate of 3°C / min, maintaining a pressure of 0.5 MPa, and holding at this temperature and pressure for 1.5 hours. After the process is complete, allow the furnace to cool naturally to room temperature, depressurize, open the can, and remove the cured and molded parts.

[0098] S6. Post-processing: Fix the cured and molded parts onto the worktable of the five-axis machining center, and drill the mounting holes and chamfer the edges according to the three-dimensional digital model of the product.

[0099] Finally, the carbon fiber anti-collision beam sample for automobiles in Example 3 was obtained.

[0100] Comparative Examples 1-3:

[0101] Comparative Example 1:

[0102] Compared with Example 2, the difference lies in the following: In step S2, the core layer 4 of the three-dimensional model is replaced with a conventional hexagonal honeycomb structure that does not have a negative Poisson's ratio effect, and its unit size and wall thickness are the same as those of the core layer 4 in Example 2. All other raw materials, equipment, and process parameters are exactly the same as those in Example 2.

[0103] Comparative Example 2:

[0104] The difference from Example 2 is that, instead of continuous fiber printing technology, a fused deposition modeling 3D printer was used, employing chopped carbon fiber reinforced nylon material to print a three-dimensional solid with the exact same external dimensions and internal negative Poisson's ratio structure as the sample in Example 2. This process does not involve fiber pretreatment, infrared pre-curing, or autoclave curing steps.

[0105] Comparative Example 3:

[0106] Compared to Example 2, the difference lies in the fact that instead of a single-piece printing process, a traditional step-by-step manufacturing and bonding process for composite materials is used. Specifically, the upper layer, lower layer, and core material with a negative Poisson's ratio structure are first prepared using the same raw materials and processes as in Example 2. Then, epoxy structural adhesive is used to bond and assemble the three components, which are then cured under specified conditions to ultimately form a crash beam with the same external dimensions and internal structure as the sample in Example 2. This method introduces an adhesive interface.

[0107] Test Example 1-2:

[0108] Test Example 1: Physical Performance Test

[0109] 1-A: Curb weight test

[0110] The testing method is as follows:

[0111] S1. The final anti-collision beam samples prepared in Examples 1-3 and Comparative Examples 1-3 were left to stand for 24 hours at room temperature of 25°C and relative humidity of 50%.

[0112] S2. Weigh each sample using an electronic balance (accuracy 0.0001g) and record its total mass.

[0113] S3. Weigh each sample three times and calculate the arithmetic mean as its final ready mass.

[0114] Test Example 1-B: Fiber Volume Fraction Test

[0115] This test is conducted according to ASTM D3171-15, "Standard Test Method for Component Content in Composite Materials," using the acid digestion method specified therein.

[0116] The testing method is as follows:

[0117] S1. Cut three specimens with dimensions of 20mm×20mm×3mm from the center of each specimen.

[0118] S2. Weigh the initial mass of each dried sample using an electronic balance, and record it as follows: .

[0119] S3. Place the sample in a beaker and add a digestion solution made of concentrated sulfuric acid and 30% hydrogen peroxide solution in a volume ratio of 7:3, ensuring that the sample is completely submerged.

[0120] S4. Place the beaker in a constant temperature water bath at 80℃ and heat until the resin matrix is ​​completely decomposed.

[0121] S5. Filter the residue in the beaker and rinse it repeatedly with deionized water until the washing solution is neutral.

[0122] S6. Dry the washed fibers in an oven at 120℃ for 4 hours until constant weight, weigh them, and record the mass as follows. .

[0123] S7. Based on the known carbon fiber density ( =1.80g / cm 3 ) and the density of the cured resin matrix ( =1.21g / cm 3 The fiber volume fraction is calculated using the following formula. The average value of the three samples is taken as the final result.

[0124] ;

[0125] in:

[0126] The fiber volume fraction is usually expressed as a percentage (%).

[0127] The initial total mass of the composite material sample is expressed in grams (g).

[0128] This represents the mass of the remaining dry carbon fiber after the resin matrix has been digested and removed, expressed in grams (g).

[0129] The density of carbon fiber material is expressed in grams per cubic centimeter (g / cm³). 3 );

[0130] This represents the density of the cured resin matrix, expressed in grams per cubic centimeter (g / cm³). 3 ).

[0131] Table 1. Physical performance test results

[0132]

[0133] As shown in Table 1, the test results obtained by the manufacturing methods of Examples 1-3 all yielded composite material parts with a fiber volume fraction in the range of 55-65%. This is because the method employs a simultaneous extrusion and in-situ impregnation technology of continuous fibers and thermosetting resin matrix, combined with a closed-loop control system for fiber tension and resin pressure. This ensures stable delivery of reinforcing fibers and full wetting of the matrix during the molding process, thereby achieving accurate control of the volume ratio of the two-phase components in the final composite material.

[0134] Comparing the data from Example 2 and Comparative Example 3, the total mass of the sample manufactured using a single-piece molding process (Example 2) is lower than that of the sample manufactured using a separate manufacturing and bonding process (Comparative Example 3). This is because the single-piece molding process avoids the need for additional materials (such as structural adhesives) to connect the separate components, thereby reducing the non-load-bearing mass of the components while achieving the same macroscopic geometry. This result demonstrates that single-piece molding technology is an effective way to achieve structural lightweighting.

[0135] Comparing the data from Example 2 and Comparative Example 2, the sample using continuous fibers (Example 2) showed differences compared to the sample using chopped fibers (Comparative Example 2) in both total mass and fiber volume fraction. This technical solution constructs the main load-bearing network through precise path placement of continuous fibers, achieving high reinforcement content and low total structural mass. In contrast, the manufacturing method of chopped fiber reinforced materials, where fiber content is limited by the rheological properties of the matrix material, results in a higher proportion of polymer matrix in the final part's mass and volume, thus increasing the overall mass of the component.

[0136] Test Example 2: Mechanical Property Test

[0137] 2-A: Three-point bending performance test

[0138] This test was conducted in accordance with GB / T 1449-2005 "Test Method for Bending Properties of Fiber Reinforced Plastics".

[0139] The testing method is as follows:

[0140] S1. From the final samples of Examples 1-3 and Comparative Examples 1-3, rectangular specimens with dimensions of 200mm×25mm×10mm are cut along their main axis. Five specimens are prepared for each group of samples.

[0141] S2. Configure the universal mechanical testing machine to three-point bending mode, set the support span to 160mm, and the loading head radius to 5mm.

[0142] S3. Place the specimen on the support and apply a vertical load at a loading rate of 2 mm / min until the specimen fails or the load drops to less than 20% of the peak load.

[0143] S4. Record the maximum load during the test and calculate the bending strength of each specimen according to the standard formula. Take the arithmetic mean of the five specimens in each group as the final result.

[0144] 2-B: Quasi-static compression energy absorption test

[0145] The testing method is as follows:

[0146] S1. Fix the final anti-collision beam samples of Examples 1-3 and Comparative Examples 1-3 onto the rigid base of the universal testing machine, ensuring that its axis is perpendicular to the loading direction of the testing machine.

[0147] S2. Using a flat pressure head with a diameter of 150 mm, axially compress the sample at a constant speed of 10 mm / min, and set the compression displacement to 60% of the initial height of the sample.

[0148] S3. The testing machine synchronously records the load-displacement data throughout the entire process and plots the load-displacement curve.

[0149] S4. Based on the recorded curves, calculate the following performance metrics:

[0150] Peak load: The first load peak on the curve.

[0151] Total absorbed energy: The integral area of ​​the load-displacement curve within the set compressive displacement range.

[0152] Specific energy absorption: Total absorbed energy divided by the total mass of the sample (data from test example 1).

[0153] S5. Perform three repeated tests on each sample group, and take the arithmetic mean of the three test results as the final performance index.

[0154] Table 2. Mechanical property test results

[0155]

[0156] As shown in Table 2, the sample of Example 2, under similar bending strength and peak load conditions, exhibits a higher specific energy absorption value compared to the sample of Comparative Example 1. This is because the core layer 4 of Example 2 exhibits a negative Poisson's ratio effect. During compression, its star-shaped or concave hexagonal structural units undergo lateral contraction and tensile deformation. This deformation mode dissipates more impact energy under a sustained plateau stress. In contrast, the conventional honeycomb structure of Comparative Example 1 primarily absorbs energy through its own buckling and wrinkling, resulting in a lower energy dissipation mechanism efficiency compared to the negative Poisson's ratio structure.

[0157] Comparing the data of Example 2 and Comparative Example 2, the former exhibits higher flexural strength, peak load, and specific energy absorption, among other mechanical properties. This is because the structure of Example 2 is primarily composed of 3K continuous carbon fibers, which effectively distribute stress along the load transfer path. In contrast, the chopped fiber reinforced material used in Comparative Example 2 relies on the interface between the fiber and the resin matrix for internal stress transfer, and stress concentration occurs at the fiber ends, resulting in macroscopic mechanical properties that are significantly lower than those of the continuously fiber reinforced composite material.

[0158] Comparing the data from Example 2 and Comparative Example 3, the bending strength and peak load values ​​of the sample in Example 2 are both higher than those of the sample in Comparative Example 3. This is because Example 2 is a monolithic structure manufactured using integrated printing technology, with a continuous internal fiber network and no physically weak interfaces. In contrast, the sample in Comparative Example 3 is bonded using structural adhesive, and the adhesive interfaces become stress concentration areas under stress, representing potential locations for initial structural failure. Therefore, components prepared using the integrated molding method have higher structural integrity and load-bearing capacity.

Claims

1. A negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology, characterized in that, include: The anti-collision beam body (1) includes a core layer (5) and a surface layer (4). The core layer (5) is located inside the surface layer (4). Two energy-absorbing boxes (2) are fixedly connected to the outside of the anti-collision beam body (1). An installation plate (3) is fixedly connected to the other side of each of the two energy-absorbing boxes (2). The anti-collision beam body (1) is integrally formed from 3K continuous carbon fiber and thermosetting resin matrix. The core layer (5) has a star-shaped concave structure or a concave hexagonal structure with a periodic negative Poisson's ratio effect. The surface layer (4) is a continuous carbon fiber reinforcement layer with 0° / 90° orthogonal layup. The continuous carbon fiber reinforcement layer is composed of the 3K continuous carbon fiber and the thermosetting resin matrix. In the anti-collision beam body (1), the volume fraction of the 3K continuous carbon fiber is 55-65%, and the volume fraction of the thermosetting resin matrix is ​​35-45%. The manufacturing method of the negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology includes the following steps: S1. Using dual-nozzle synchronous extrusion technology, the 3K continuous carbon fiber is printed along a preset path, and a thermosetting resin matrix composed of bisphenol A type epoxy resin and imidazole latent curing agent is extruded simultaneously to complete in-situ impregnation. S2. After printing one layer, the printed layer is subjected to infrared pre-curing treatment to make the thermosetting resin matrix reach 40-60% partial curing degree. S3. After all layers are printed, the printed parts are cured in a staged autoclave under a vacuum of -0.09 to -0.1 MPa. The staged autoclave curing process includes the following steps: The carbon fiber anti-collision beam for automobiles is prepared by holding the material at 50-70℃ for 1.0-1.5 hours, raising the temperature to 120℃ and applying a pressure of 0.5-1.0MPa for 1.5-2.5 hours, raising the temperature to 160℃ and holding for 1.0-1.5 hours, and then cooling and demolding.

2. The negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology according to claim 1, characterized in that, The structural unit size of the core layer (5) with periodic negative Poisson's ratio effect is 5-10 mm, and the unit wall thickness is 0.5-1 mm.

3. The negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology according to claim 1, characterized in that, The thermosetting resin matrix is ​​composed of bisphenol A type epoxy resin and imidazole latent curing agent.

4. The negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology according to claim 1, characterized in that, The 3K continuous carbon fiber has a tensile strength of 3.0-4.0 GPa and a fiber areal density of 250-350 g / m³. 2 .

5. The negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology according to claim 1, characterized in that, Before step S1, the 3K continuous carbon fiber is subjected to plasma surface treatment with a power of 450-550W.

6. The negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology according to claim 1, characterized in that, In step S1, the dual-nozzle synchronous extrusion technology is performed using a six-axis linkage dual-nozzle printer, wherein the carbon fiber nozzle temperature is 20-30℃, the resin nozzle temperature is 70-90℃, the printing speed is 150-250mm / min, and the volume flow ratio of the thermosetting resin matrix to the 3K continuous carbon fiber is 1:0.

8.

7. The negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology according to claim 1, characterized in that, In step S1, the preset path is determined by simulation using finite element analysis software, and the preset path is an interlaced spiral filling path with an interlayer misalignment angle of 20-25°.

8. The negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology according to claim 1, characterized in that, In step S1, the printing of the 3K continuous carbon fiber and the extrusion process of the thermosetting resin matrix adopt a fiber tension feedback system and a resin pressure closed-loop control system. The control accuracy of the fiber tension feedback system is ±2N, and the control accuracy of the resin pressure closed-loop control system is ±5kPa.

9. The negative Poisson's ratio structure carbon fiber anti-collision beam for automobiles based on continuous fiber printing technology according to claim 1, characterized in that, After step S3, a post-processing step is also included, in which mounting holes and edge chamfering are machined on the cured molded part using a five-axis machine tool.

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