Composite door impact beam and method of manufacturing the same

Abstract

The application relates to the field of vehicle body structures, in particular to a composite structure anti-collision rod installed in the interior of a vehicle door and a preparation method thereof. The anti-collision rod comprises an outer steel pipe made of hot-formed steel, the cross section of the outer steel pipe is in a D shape, the D shape is formed by an outwardly convex arc-shaped wall and a straight wall, an inner pipe is a carbon fiber reinforced resin-based composite material pipe, the inner pipe is sleeved in the outer steel pipe, the cross section of the inner pipe is in a D shape and is matched with the cross section shape of the outer steel pipe, so that a gap is formed between the outer wall of the inner pipe and the inner wall of the outer steel pipe. Through the multilayer composite structure of the outer steel pipe, the inner carbon fiber pipe, the first fluid bag and the second fluid bag, multistage loading and energy absorption are realized.

Description

Technical Field

[0001] This application relates to the field of vehicle body structure, specifically a composite structure anti-collision bar installed inside a vehicle door and its manufacturing method. Background Technology

[0002] Door anti-collision bars are key components for side impact protection of automobiles. They are installed between the inner and outer sheet metal of the door to resist side impact intrusion and absorb collision energy.

[0003] The current mainstream solution uses ultra-high strength hot-formed steel pipes, which obtain a fully martensitic structure through rapid quenching in a mold, achieving tensile strengths of up to gigapascals and strong resistance to intrusion. However, when the pipe wall is subjected to bending loads, the pressure side is prone to localized inward buckling. Once buckling occurs, the load-bearing capacity drops rapidly, and the energy absorption process becomes unstable. Increasing the wall thickness can improve buckling, but it significantly increases the weight, which is not conducive to lightweighting.

[0004] To suppress buckling, existing solutions include filling the steel tube with lightweight materials such as aluminum foam or aluminum honeycomb, or coaxially installing a carbon fiber reinforced composite inner liner. The aluminum foam filling solution has limited effectiveness in suppressing buckling of high-strength steel tubes under high loads and adds extra weight. While the carbon fiber inner liner solution can participate in load-bearing and provide circumferential support, the steel-carbon fiber interface is prone to debonding under long-term vibration and temperature changes; furthermore, none of the above solutions possess stiffness self-adaptation capability, maintaining high stiffness in daily use, which may affect the door closing feel and vibration characteristics.

[0005] Shear-thickening fluids among non-Newtonian fluids exhibit rate dependence: they are liquid at low shear rates but instantly transform into a near-solid state upon high-speed impact, resulting in a sharp increase in stiffness. This characteristic can be used to achieve adaptive stiffness in collisions. However, applying this to car door anti-collision bars faces the following practical challenges: the internal temperature of car doors is extremely high under direct sunlight, and water-based or volatile fluids are prone to evaporation and failure at high temperatures; electrochemical corrosion may occur between the fluid and metal pipes, or swelling may occur in the matrix of resin-based composite materials; and ensuring long-term reliable sealing and coping with thermal expansion and contraction when directly injecting fluid into the pipes is extremely difficult.

[0006] Traditional anti-collision bars mostly use a circular cross-section, which makes it impossible to optimize the stiffness differently for the inside and outside of the car door, and there is a lack of effective solutions for fixing and sealing the two ends of the internal multi-layer composite structure.

[0007] In summary, existing technologies lack a composite door anti-collision bar solution that combines adaptive collision stiffness, effective buckling suppression, meets automotive durability requirements, and has a reasonable cross-sectional shape. Summary of the Invention

[0008] The technical problem to be solved by this application is to provide a composite door anti-collision bar with collision adaptive stiffness, effective buckling suppression, meeting vehicle durability requirements, and having a reasonable cross-sectional shape that is conducive to installation and load-bearing, as well as its preparation method.

[0009] To address the aforementioned technical problems, in a first aspect, this application provides a composite door anti-collision bar, comprising: an outer steel tube made of hot-formed steel with a D-shaped cross-section, the D-shape being formed by an outwardly convex arc-shaped wall and a straight wall; an inner tube, a carbon fiber reinforced resin-based composite material tube, sleeved inside the outer steel tube, with a D-shaped cross-section adapted to the cross-sectional shape of the outer steel tube, such that a gap is formed between the outer wall of the inner tube and the inner wall of the outer steel tube; and at least one first fluid bag, provided with... In the gap, the first fluid bag contains a shear-thickening fluid and is sandwiched between the inner wall of the outer steel tube and the outer wall of the inner tube; at least one second fluid bag is disposed in the hollow cavity of the inner tube, and the second fluid bag contains a shear-thickening fluid; the outer steel tube and the inner tube, the inner tube and the first fluid bag, the inner tube and the second fluid bag, and the outer steel tube and the first fluid bag are fixed by adhesive bonding; the two ends of the anti-collision bar are provided with mounting parts for connection with the vehicle door.

[0010] Compared with the prior art, this application has at least one of the following beneficial effects: First, this application employs a D-shaped cross-section design, with the curved wall facing outwards from the door, providing a larger collision contact area and effectively dispersing impact loads; the straight wall faces inwards, with a small protrusion height, saving space in the passenger compartment and facilitating adaptation to the internal structure of the door. The longitudinal reinforcing ribs on the outer steel tube wall improve the tube's bending stiffness and guide collision buckling deformation within the straight wall area between the ribs, making the crushing process more orderly and controllable.

[0011] Secondly, this application achieves multi-level load-bearing and energy absorption through a multi-layered composite structure consisting of an outer steel tube, an inner carbon fiber tube, a first fluid bag, and a second fluid bag. In daily use, the shear-thickened fluid remains liquid at low shear rates, resulting in moderate overall stiffness of the anti-collision bar and not affecting the normal use of the door. During a high-speed collision, the fluid bag is subjected to severe compression and shearing, causing the shear-thickened fluid to instantly transform into a near-solid state, tightly locking the outer steel tube and inner carbon fiber tube, thus significantly increasing the overall bending stiffness. Simultaneously, the thickened fluid strongly supports the tube wall from the inside, suppressing local buckling and making crush deformation more stable.

[0012] Third, by encapsulating the shear-thickening fluid in an independent flexible film bag, the problem of long-term fluid sealing is fundamentally solved, and the corrosion or swelling problems that may be caused by direct contact between the fluid and steel or carbon fiber tubes are completely avoided, ensuring the long-term durability and reliability of the product. The fluid bag is directly inserted and glued in place during assembly, avoiding complex online filling and sealing processes, making it suitable for industrial mass production.

[0013] Fourth, the installation part adopts a plug welded to the end of the outer steel tube. The plug is provided with a socket to fix the end of the inner tube, realizing reliable positioning and fixation of the inner and outer tubes at the end. At the same time, the mounting ear provides a connection interface with the inner panel of the door.

[0014] In a preferred embodiment, the outer steel pipe has at least one longitudinal reinforcing rib along its length on its arc-shaped wall and / or straight wall; in the installed state, the arc-shaped wall faces outward toward the door and the straight wall faces inward toward the vehicle interior.

[0015] In a preferred embodiment, the base fluid of the shear-thickening fluid is polyethylene glycol or silicone oil, and the dispersed phase is at least one selected from nano-silica, nano-calcium carbonate, and nano-alumina. The aforementioned base fluid has a high boiling point, a low freezing point, and good temperature resistance, meeting the operating conditions of car doors under extreme conditions of exposure to high temperatures and cold winters.

[0016] In a preferred embodiment, the first fluid bag and the second fluid bag are made of a flexible polymer film, which is a polyurethane film, an aluminum foil composite film, or a fluoroplastic film; the first fluid bag is an integral D-shaped annular bag, fitted over the outside of the inner tube; or, the first fluid bag is a plurality of segmented bags, respectively attached to the arc-shaped wall region and / or the straight wall region; the shape of the second fluid bag matches the inner cavity shape of the inner tube and fills the entire core space.

[0017] In a preferred embodiment, the fiber layup of the inner tube includes circumferential layup, ±45 degree layup and axial layup, and the inner wall and / or outer wall of the inner tube are provided with longitudinally extending grooves or textures; the inner surface of the inner tube is provided with an insulating liner made of metal foil or polymer coating.

[0018] In a preferred embodiment, the mounting part includes a plug, which is welded to the end of the outer steel pipe. The plug has a socket, into which the end of the inner pipe is inserted and fixed. The plug also extends a mounting ear for connecting to the inner door panel.

[0019] Secondly, this application also provides a method for preparing the above-mentioned composite door anti-collision bar, comprising the following steps: Step 1: Preparation of outer steel pipe: The steel plate is rolled into a D-shaped pipe, and longitudinal reinforcing ribs are pressed into the pipe wall during the rolling process. After welding the joint, a pipe blank is obtained; then the pipe blank is subjected to hot stamping and quenching treatment to obtain the outer steel pipe. Step 2: Preparation of inner tube: A carbon fiber reinforced resin matrix composite tube with a D-shaped cross-section is prepared by filament winding or pultrusion molding process, and an isolation liner is set on the inner wall of the tube to obtain the inner tube; Step 3: Preparation of fluid bags: A shear-thickening fluid, with polyethylene glycol or silicone oil as the base liquid and at least one of nano-silica, nano-calcium carbonate, and nano-alumina as the dispersed phase, is filled into a bag made of a flexible polymer film and heat-sealed to make a first fluid bag and a second fluid bag. Step 4: Assemble the inner core: Place the second fluid bag into the inner cavity of the inner tube, making it fit against the inner wall; then put the first fluid bag onto the outside of the inner tube; Step 5, Overall Assembly: Push the inner tube assembly obtained in Step 4 into the outer steel tube, so that the first fluid bag is located in the gap between the outer steel tube and the inner tube; Step 6: Bonding and fixing: The outer steel pipe, inner pipe, first fluid bag and second fluid bag are fixed together by bonding. Step 7, Welding and Installation: Weld plugs with sockets to both ends of the assembled parts that have been bonded and fixed, and insert the end of the inner tube into the socket. The mounting ears extending from the plugs are used to connect with the inner door panel.

[0020] In a preferred method, the bonding in step six includes applying structural adhesive to both ends of the inner tube, which cures to form a rigid fixing ring; and / or achieving bonding by activating the hot melt adhesive on the surface of the fluid bag through heating.

[0021] The beneficial effects listed above are not exhaustive of all advantages. Other potential beneficial effects and detailed technical implementation methods will be further disclosed in the embodiments or other descriptive sections of this application. Attached Figure Description

[0022] A better understanding of various aspects of this disclosure will be achieved by reading the following detailed description in conjunction with the accompanying drawings. The positions, dimensions, and extents of the structures shown in the drawings, etc., do not always represent actual positions, dimensions, and extents. In the drawings: Figure 1 This is a schematic diagram of the overall structure of one embodiment disclosed in this application.

[0023] Figure 2 This is a cross-sectional structural diagram of one embodiment disclosed in this application.

[0024] Figure 3 This is a three-dimensional structural diagram of a partial segment of an embodiment disclosed in this application, in which the first fluid bag and the second fluid bag have been removed.

[0025] Figure 4 This is a flowchart of a method according to an embodiment of this application. Detailed Implementation

[0026] The present application will now be described in detail with reference to the accompanying drawings and embodiments. The following embodiments are merely illustrative of the technical solutions of the present application and are not intended to limit it. Those skilled in the art should understand that various modifications and variations can be made to these embodiments without departing from the concept of the present application, and all such modifications and variations fall within the protection scope of the present application. Example 1

[0027] like Figures 1 to 3 As shown, this embodiment provides a composite door anti-collision bar, including an outer steel tube 1, an inner tube 2, a first fluid bag 3, a second fluid bag 4, and a mounting part 5.

[0028] The outer steel pipe 1 is made of hardenable boron-containing steel plate, roll-formed and high-frequency welded into a D-shaped pipe. The D-shaped cross-section consists of an outwardly protruding arc-shaped wall 11 and a roughly straight wall 12. The radius of curvature of the arc-shaped wall is greater than the width of the straight wall, and the connection between the two is a rounded transition. During roll forming, a longitudinal reinforcing rib 13 protruding outward is pressed into the central area of ​​the arc-shaped wall 11, and an outward reinforcing rib 13 is also pressed into the central area of ​​the straight wall 12. A reinforcing rib is also pressed into the rounded transition corner between the arc-shaped wall and the straight wall, for a total of 6 reinforcing ribs evenly distributed circumferentially. After welding, the pipe is heated to approximately 950°C in a protective atmosphere furnace and held at that temperature. Subsequently, it is hot-stamped and rapidly cooled in a mold with cooling channels to obtain a fully martensitic structure, significantly improving hardness. The inner wall of the steel pipe is phosphated and coated with an epoxy anti-corrosion primer to prevent corrosion that may occur during subsequent use.

[0029] The inner tube 2 is a thin-walled D-shaped tube made of high-strength carbon fiber and epoxy resin through a winding process. Its cross-sectional shape matches the D-shaped contour of the outer steel tube's inner cavity, but the overall size is reduced, resulting in a uniform gap between the outer wall of the inner tube and the inner wall of the outer steel tube after assembly. This gap is defined by the dimensional differences between the corresponding wall surfaces of the D-shaped cross-sections of the inner and outer tubes, and is basically uniformly distributed along the entire circumference. The inner tube's layup design, from the inside out, includes: 1 circumferential layup (fiber direction along the tube's circumference), 2 alternating ±45 degree layups, 3 axial layups (fiber direction along the tube's longitudinal direction), and the outermost ±45 degree layup. Before winding, the inner wall is pre-laid with a layer of aluminum foil approximately 0.05 mm thick as an isolation liner, and the aluminum foil seams are sealed with epoxy adhesive to prevent internal substances from penetrating into the carbon fiber resin matrix. After demolding, the inner wall has multiple micro-axial grooves formed by the surface texture of the mold. The outer wall uses a woven release fabric to form a micro-texture during the final winding of the outer layer, in order to increase the mechanical engagement with the fluid bag. The outer wall of the inner tube is lightly sandblasted to increase roughness and improve adhesion strength.

[0030] The first fluid bag 3 is a single D-shaped annular bag, made of multiple layers of composite film (including a polyester layer, an aluminum foil layer, and a cast polypropylene heat-sealing layer) through heat sealing. The shape of the bag body matches the shape of the gap between the inner and outer tubes, and the thickness of the bag body is adapted to the width of the gap. The bag contains a shear-thickening fluid. The specific preparation method of the shear-thickening fluid is as follows: the base liquid is dimethyl silicone oil (viscosity approximately 100 cSt), the dispersed phase is nano-silica particles (average particle size approximately 200 nm, specific surface area 200 m² / g) modified with a silane coupling agent, and the target solid volume fraction is 52%. Under room temperature conditions, the metered nano-silica powder is added in batches to the continuously stirred silicone oil. After the addition is completed, a high-speed disperser is used to continuously stir at 3000 rpm for 30 min to initially disperse the particles; then the mixture is placed in an ultrasonic disperser and ultrasonically dispersed at a frequency of 20 kHz and a power of 500 W for 60 min to obtain a uniform and stable suspension. Rheometer testing verified that the viscosity of the suspension is below 100 Pa·s at low shear rates (≤10 s⁻¹), exhibiting a liquid state; when the shear rate reaches approximately 600 s⁻¹, the viscosity rises sharply to over 1000 Pa·s, exhibiting a near-solid state, demonstrating a significant shear thickening effect, thus meeting the functional requirements of this application. The prepared shear thickening fluid was filled into bags using a quantitative filling machine, degassed under vacuum for 10 minutes, and then sealed with a heat sealer to ensure no air bubbles remain inside the bag. The outer surface of the bag is pre-coated with a layer of hot melt adhesive film (EVA-based hot melt adhesive), and release paper is applied to the outside of the adhesive layer for easy removal before assembly.

[0031] The second fluid bag 4 is also made of a multi-layer composite film, and its cross-sectional shape matches the inner cavity D-shape of the inner tube 2. It is encapsulated with a shear-thickening fluid of the same formulation as the first fluid bag, and the filling and sealing methods are the same. The surface of the bag is also pre-coated with a hot melt adhesive film.

[0032] During assembly, first insert the second fluid bag 4 into the inner cavity of the inner tube from end 1, and gently press it to make its outer surface adhere to the inner wall of the inner tube; then, fit the first fluid bag 3 onto the outside of the inner tube, allowing it to naturally cover the inner tube. Next, apply a ring-shaped epoxy structural adhesive strip, approximately 10mm wide, circumferentially to the outer walls of both ends of the inner tube. Push the entire inner tube assembly, including the fluid bag, axially into the outer steel tube, so that the first fluid bag is clamped between the inner wall of the outer steel tube and the outer wall of the inner tube, with the structural adhesive strips at both ends contacting and adhering to the inner wall of the outer steel tube. Place the assembly in an oven and heat to 120℃ and hold for 60 minutes to cure the end structural adhesive into a rigid fixing ring, simultaneously activating the hot melt adhesive on the surface of the fluid bag, ensuring a firm bond between the fluid bag and the adjacent tube wall.

[0033] Mounting part 5 uses a steel plate stamped into a D-shaped ring plug with weldability matching that of the steel pipe. A D-shaped socket is opened in the center of the plug, the size of which matches the shape of the inner tube, with a gap of approximately 0.2mm. The outer ring of the plug matches the inner hole at the end of the steel pipe, and mounting ears extend from the outside of the plug, with bolt mounting holes drilled on the ears. After the above-mentioned bonded and cured assembly is assembled, the plug is fitted onto the ends of the inner tube, allowing the inner tube end to insert into the socket. Then, the outer ring of the plug is laser-welded to the end of the steel pipe to achieve a secure connection. Low-power, short-pulse laser welding parameters are used during welding to control the heat input and prevent welding heat from being conducted to the interior, damaging the fluid bag and adhesive layer. After welding, the end of the inner tube is reliably positioned and fixed by the socket, and the mounting ears are used for bolt connection to the inner door panel.

[0034] During installation, the curved wall 11 of the bumper bar faces outward from the door, and the straight wall 12 faces inward from the vehicle. Example 2

[0035] This embodiment is basically the same as Example 1 in terms of structure and preparation method, except that the base liquid of the shear-thickening fluid is changed to polyethylene glycol (PEG400), and the dispersed phase is still nano-silica (surface treated with silane coupling agent, with an average particle size of about 300 nm), with a solid volume fraction of about 50%. During preparation, measured nano-silica is added in batches to continuously stirred polyethylene glycol, stirred at high speed for 40 min, and then ultrasonically dispersed for 60 min to obtain a uniform suspension. Rheological tests show that its critical shear rate is about 800 s⁻¹, and the viscosity after thickening is greater than 800 Pa·s, also exhibiting good shear-thickening characteristics. To reduce the impact of polyethylene glycol's hygroscopicity on long-term stability, 0.5% by mass of an antioxidant corrosion inhibitor is added during preparation. The fluid bag film is made of fluoroplastic film (FEP, thickness 0.15 mm) to better adapt to the chemical properties of polyethylene glycol. The remaining structure and preparation process are consistent with Example 1.

[0036] Comparative Example 1 A conventional hot-formed steel pipe anti-collision bar was prepared. A D-shaped steel pipe with the same cross-sectional shape and dimensions as in Example 1 was used. It was also rolled to produce six longitudinal reinforcing ribs and subjected to hot stamping and quenching treatment. The material and heat treatment process were the same as in Example 1, but the pipe contained no inner tube or fluid bag. Mounting ears of the same type as in Example 1 were directly welded to both ends.

[0037] Comparative Example 2 A composite steel tube and carbon fiber tube bumper without a fluid bag was prepared. The specifications and preparation method of the outer steel tube and inner carbon fiber tube were the same as in Example 1, but the gap between the inner and outer tubes was completely filled with structural adhesive and the two were bonded together as a whole without any fluid bag; the hollow cavity of the inner tube was left empty and unfilled. Ears were welded to both ends.

[0038] Comparative test In order to objectively and comprehensively evaluate the technical effects of this application, the following test methods were set up to compare the performance of four schemes: Example 1, Example 2, Comparative Example 1, and Comparative Example 2.

[0039] The two ends of each crash bar specimen were installed on rigid supports, with a span of 600 mm between the supports. A hemispherical steel indenter with a radius of 150 mm was used, and the loading position was selected as the midpoint of the crash bar span.

[0040] The quasi-static three-point bending test was conducted on an electronic universal testing machine. The indenter was loaded downwards at a constant rate of 10 mm / min, and force and displacement data were collected in real time to plot the force-displacement curve. The test was stopped when the indenter displacement reached 50 mm. The integral area of ​​the force-displacement curve from the zero displacement point to 50 mm was taken as the energy absorption value of this scheme, and the maximum load occurring during the entire loading process was recorded as the peak force.

[0041] The dynamic impact test was conducted using a drop hammer impact testing system to simulate a side impact with a pole-shaped object. The total mass of the drop hammer was set to 120 kg, and the impact contact surface was a cylindrical surface with a radius of 150 mm. The drop hammer was released from a preset height, achieving an impact velocity of 6.5 m / s upon contact with the bumper. Accelerometers and high-speed displacement measuring devices mounted on the drop hammer simultaneously recorded force and displacement data during the impact process, plotting a dynamic force-displacement curve. The integral area within a 50 mm displacement was taken as the dynamic energy absorption value, and the dynamic peak force was recorded.

[0042] The low-speed compression test uses the same support and indenter configuration as the quasi-static test, but the loading speed is reduced to 1 mm / min to simulate low strain rate load conditions such as daily car door closing, in order to evaluate the differences in bending stiffness of each scheme under normal use scenarios.

[0043] Long-term durability testing was conducted in accordance with relevant standards for environmental reliability testing of automotive components. Due to the extremely long cumulative high-temperature and high-humidity exposure time of the car doors within their actual service life, direct real-time verification was not feasible. Therefore, this test employed an accelerated aging test method for equivalent simulation. Each group of samples was placed in a constant temperature and humidity test chamber, with the chamber temperature set at 85℃ and relative humidity at 85%, for continuous exposure for 240 hours. The basis for the accelerated aging equivalent conversion is as follows: the average annual operating temperature of the car door under typical climatic conditions is approximately 30℃. The 85℃ used in this test is approximately 55℃ higher than the average annual temperature. According to the Arrhenius equation, which describes the exponential relationship between chemical reaction rate and temperature, the activation energy for the wet heat aging reaction of general polymer materials is approximately 50kJ / mol to 70kJ / mol. Estimating at 60kJ / mol, the reaction rate approximately doubles for every 10℃ increase in temperature. The temperature difference between 85℃ and 30℃ is 55℃, resulting in an acceleration factor of approximately 2 to the power of 5.5, or about 45 times. Furthermore, the high humidity environment of 85%RH has an additional accelerating effect on the penetration of water molecules into the sealing material and interface. The comprehensive acceleration factor is conservatively estimated to be about 365 times, meaning that 240 hours of accelerated testing is roughly equivalent to 10 years of cumulative damp heat aging under natural conditions. After the test, the samples were removed for visual inspection and the quasi-static three-point bending performance was retested. The strength attenuation rate was calculated by comparing the results with the original performance data.

[0044] Experimental Results and Analysis The performance of each scheme in various tests is compared in detail below. To facilitate a clear presentation of the performance differences between the schemes, the quasi-static peak force and quasi-static energy absorption of Example 1 are used as the baseline, and the corresponding data of other schemes are expressed as a percentage relative to this baseline. Dynamic test data are also compared with the dynamic peak force and dynamic energy absorption of Example 1 as their respective baselines.

[0045] In the quasi-static three-point bending test, the performance of the pure steel pipe scheme in Comparative Example 1 was significantly inferior to that in Example 1. Its quasi-static peak force only reached about 82% of the baseline value in Example 1, and its quasi-static energy absorption was only about 65% of the baseline value. During the test, it was clearly observed that when the indenter was applied to a certain critical load, the pipe wall on the pressure side of Comparative Example 1 suddenly buckled inward at the mid-span, forming a single plastic hinge. Accompanied by a crisp sound, the load dropped sharply and instantly, and the force-displacement curve exhibited typical instability characteristics of a sharp peak followed by a rapid decline. During subsequent loading, the deformation was almost entirely concentrated at this hinge location, while the rest of the pipe remained essentially unchanged, not participating in plastic deformation or energy absorption, resulting in extremely low material utilization efficiency.

[0046] Comparative Example 2, with its fluidless bag composite design, showed a significant improvement over Comparative Example 1 under quasi-static conditions, but still lagged behind Example 1. Its quasi-static peak force reached approximately 95% of the baseline value in Example 1, and its quasi-static energy absorption reached approximately 90% of the baseline value. Because the carbon fiber inner tube provided circumferential support within the outer steel tube, it delayed and suppressed buckling of the inner wall of the steel tube to some extent, maintaining the load-bearing capacity in the initial loading stage. However, as the bending deformation further increased, the inherent differences in elastic modulus and plastic deformation behavior between the steel and carbon fiber materials resulted in significant shear stress and peel stress at the bonding interface. After the test, the specimen was sectioned and examined. Local debonding areas were observed at the bonding interface between the inner and outer tubes near the mid-span, indicating that under high load and large deformation conditions, relying solely on interfacial adhesive was insufficient to maintain the structural integrity.

[0047] In the dynamic impact test, the performance differences between the various schemes were even more significant. The dynamic peak force of the pure steel pipe scheme in Comparative Example 1 was only about 78% of the baseline value of Example 1, and the dynamic energy absorption was only about 58% of the baseline value. Under high-speed impact, the local buckling instability problem of the pure steel pipe was more prominent. The buckling hinge formed and developed in a very short time, with almost no gradual deformation process. The force-displacement curve showed a sharp load peak followed by a rapid decay to a low level, and the effective energy absorption stroke was far less than 50 mm.

[0048] The dynamic peak force of Comparative Example 2 was approximately 92% of the baseline value of Example 1, and the dynamic energy absorption was approximately 85% of the baseline value. Although the supporting effect of the carbon fiber inner tube was improved compared to Comparative Example 1, the interface debonding problem was more severe under the high strain rate conditions of high-speed impact. Cross-sectional inspection revealed that the debonding area was larger than the quasi-static test results, and the carbon fiber tube showed local brittle fracture, with fragments scattered inside the tube cavity, losing its supporting function for the steel tube. The energy absorption curve still had large fluctuations, failing to achieve the ideal smooth and gradual folding.

[0049] Example 2 maintains a high degree of consistency with Example 1 in all indicators. Its quasi-static and dynamic peak forces both reach 97% to 99% of Example 1, and its quasi-static and dynamic energy absorption both reach 98% to 99% of Example 1. This result indicates that, while keeping other structural features unchanged, replacing the base fluid of the shear thickening fluid from silicone oil to polyethylene glycol does not lead to a substantial deterioration in protective performance. The technical solution of this application has a certain range of adaptability to the selection of fluid base fluid types, facilitating flexible adjustments based on cost and environmental requirements of different application scenarios.

[0050] In low-speed compression tests, the initial bending stiffness of Example 1 was found to be approximately 15% lower than that of Comparative Example 2. The physical mechanism behind this phenomenon is that under low-speed loading, the shear rate of the shear-thickening fluid is far below its critical shear-thickening threshold, maintaining its low-viscosity liquid properties. The first and second fluid bags possess a certain degree of flexible deformation capability within their respective gaps and cavities, effectively introducing a small buffer medium between rigid layers, thus reducing the overall stiffness of the structure. This reduction in stiffness helps improve the vehicle's noise, vibration, and acoustic roughness performance, resulting in a smoother feel when the doors close, avoiding harsh collision feedback caused by overly stiff anti-collision bars. Under high-speed collision conditions, the shear-thickening fluid is instantly activated and transforms into a near-solid state. The fluid bag can then firmly lock the inner and outer tubes, causing the dynamic peak force to increase rather than decrease. This bidirectional adaptive characteristic of low-speed low stiffness and high-speed high stiffness is a unique advantage that traditional pure steel pipe solutions and simple composite solutions completely lack.

[0051] The results of long-term durability tests fully validated the design effectiveness of this application in terms of reliability. In Example 1, after completing the accelerated damp heat aging equivalent test at 85°C, 85%RH, and 240 hours, no fluid leakage was found during visual inspection. The aluminum foil composite film bag remained intact, and there was no loosening or cracking at the welds and connectors of the end caps. The quasi-static three-point bending peak force was retested, and the attenuation was less than 3% compared to the original data, meeting the durability life requirements for automotive parts. Disassembly further confirmed that the shear-thickening fluid properties inside the fluid bag did not undergo any perceptible changes, and the anti-corrosion coating on the inner wall of the outer steel pipe remained intact, showing no signs of corrosion or rust. In Example 2, after the same durability test, the performance degradation was slightly higher than in Example 1, approximately 5%, presumably related to the slight hygroscopicity of the polyethylene glycol-based liquid, but still within an acceptable range. Furthermore, the fluoroplastic film encapsulation of the fluid bag effectively blocked the main channels for moisture penetration.

[0052] Failure Mode Comparison Analysis The failure morphologies of the three schemes after dynamic impact showed significant differences, and detailed analysis was conducted through macroscopic observation and cross-sectional cutting.

[0053] The failure mode of the pure steel pipe scheme in Comparative Example 1 is a typical single-hinge buckling. Directly below the mid-span loading head, the pipe wall on the pressure side indents inward, forming an extremely narrow crease. The pipe body on both sides of the crease remains almost straight, forming a concentrated plastic hinge. After failure, the pipe body only undergoes plastic deformation in a small area near the hinge line; the material over the vast majority of the pipe's length does not participate in energy absorption, resulting in extremely low material utilization efficiency. This failure mode determines its limited energy absorption capacity and large load fluctuations.

[0054] The failure mode of Comparative Example 2 is somewhat improved compared to Comparative Example 1, but it still exhibits significant concentrated deformation characteristics. After failure, a relatively large buckling zone formed in the mid-span region of the tube. The circumferential restraint of the carbon fiber inner tube played a role in delaying buckling. However, outside the buckling zone, extensive peeling of the adhesive layer between the inner wall of the outer steel tube and the outer wall of the inner tube was observed. Local interlaminar cracking and fiber breakage occurred on the buckling compression side of the carbon fiber tube, with some fiber fragments detaching from the parent tube. This indicates that under high dynamic loads, brittle failure and interfacial debonding of the carbon fiber tube occur almost simultaneously. Once the carbon fiber tube loses its structural integrity, its supporting effect on the inner wall of the steel tube is also lost, thus limiting further performance improvements of this structural design.

[0055] The failure modes of Examples 1 and 2 exhibit distinctly different deformation characteristics. Under the same impact conditions, the deformation in Examples 1 and 2 unfolds in a multi-point distributed manner along the length of the anti-collision bar, forming 3 to 4 progressively folded corrugations with relatively uniform spacing, rather than being concentrated at a single location in the mid-span. The reinforcing ribs of the outer steel pipe divide the pipe wall into several wall plate regions circumferentially, and the buckling waves are confined within the wall plate regions between the reinforcing ribs, where they occur and develop. Simultaneously, upon impact, the shear-thickening fluid in the first fluid bag instantly thickens, generating strong incompressible support on the steel pipe wall from the inside, forcing the steel pipe to gradually wrinkle and yield in multiple pre-designed weak areas. Throughout this process, the inner carbon fiber tube is consistently tightly wrapped and supported by the first and second fluid bags, without localized fragmentation, only developing micro-matrix cracks and a small amount of delamination at locations corresponding to the buckling corrugations. It is noteworthy that in the later stages of deformation, both the first and second fluid bags ruptured under intense deformation and compression. However, this rupture occurred after the fluids had completed shear thickening and locked the inner and outer tubes. Their support and locking functions were fully utilized at this point, and the rupture did not lead to a decrease in protective performance. On the contrary, the fluid leakage and pressure release created additional space, allowing the tube walls to further fold and absorb energy, maintaining a progressive and orderly deformation pattern. The force-displacement curve remained at a high level with minimal fluctuations throughout the entire deformation stroke, exhibiting ideal progressive folding energy absorption characteristics. This multi-point progressive folding failure mode allowed a larger volume of material in the tube to participate in plastic deformation, resulting in more complete energy absorption, a lower peak impact force on the occupant compartment, and significantly better protection than the comparative example.

[0056] Comprehensive Comparison Conclusion Based on the above test results, it can be concluded that the composite door anti-collision bar of this application has achieved the following significant technical advancements compared to existing traditional solutions: First, the dynamic collision protection performance is significantly improved. The dynamic peak force of Example 1 is increased by about 22% to 25% compared with the pure steel tube scheme of Comparative Example 1, and by about 8% to 9% compared with the fluidless bag composite scheme of Comparative Example 2; the dynamic energy absorption is increased by about 65% to 72% compared with Comparative Example 1, and by about 15% to 18% compared with Comparative Example 2.

[0057] Secondly, it possesses unique stiffness adaptive characteristics. Under low strain rate daily use conditions, the stiffness is reduced by about 15% compared to simple composite solutions, improving the user experience of the door; under high-speed collision conditions, the stiffness is significantly improved, surpassing simple composite solutions, achieving a balance between low-speed gentleness and high-speed strength.

[0058] Third, the failure mode has been fundamentally improved. The buckling has shifted from a single hinge to multi-point progressive folding, resulting in more uniform deformation, significantly improved material utilization efficiency, a smoother and more stable impact force curve, and less intrusion into the passenger compartment. Even if the fluid bag ruptures after thickening, its locking and support functions are fully utilized, without affecting the protective effect.

[0059] Fourth, long-term durability and reliability meet automotive requirements. Through independent fluid bag packaging, anti-corrosion coating, and multi-layer composite protection, the sealing, corrosion, and aging challenges of non-Newtonian fluids in the harsh environment of automotive door cavities are effectively solved. Under accelerated damp heat aging conditions of 85℃ and 85%RH, a 240-hour test is equivalent to approximately 10 years of natural aging, with performance degradation controlled within 3% after the test.

[0060] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any equivalent substitutions and obvious modifications based on the concept of this application shall fall within the scope of protection of this application.

Claims

1. A composite door anti-collision bar, characterized in that, include: The outer steel pipe is made of hot-formed steel and has a D-shaped cross-section, which is formed by an outwardly convex arc-shaped wall and a straight wall. The inner tube is a carbon fiber reinforced resin-based composite material tube, which is sleeved inside the outer steel tube. Its cross-section is D-shaped and matches the cross-sectional shape of the outer steel tube, so that a gap is formed between the outer wall of the inner tube (2) and the inner wall of the outer steel tube. At least one first fluid bag is disposed in the gap, the first fluid bag being encapsulated with a shear-thickening fluid and being sandwiched between the inner wall of the outer steel pipe and the outer wall of the inner pipe; At least one second fluid bag is disposed in the hollow inner cavity of the inner tube, and the second fluid bag contains a shear-thickening fluid. The outer steel pipe is fixed to the inner pipe, the inner pipe to the first fluid bag, the inner pipe to the second fluid bag, and the outer steel pipe to the first fluid bag by adhesive bonding. The anti-collision bar has mounting parts at both ends for connecting to the vehicle door.

2. The composite door anti-collision bar according to claim 1, wherein, The outer steel pipe has at least one longitudinal reinforcing rib along its length on its arc-shaped wall and / or straight wall; in the installed state, the arc-shaped wall faces outward of the door and the straight wall faces inward of the vehicle.

3. The composite door anti-collision bar according to claim 1, wherein, The base liquid of the shear-thickening fluid is polyethylene glycol or silicone oil, and the dispersed phase is at least one selected from nano-silica, nano-calcium carbonate, and nano-alumina.

4. The composite door anti-collision bar according to claim 1, wherein, The first fluid bag and the second fluid bag are made of a flexible polymer film, which is a polyurethane film, an aluminum foil composite film, or a fluoroplastic film; the first fluid bag is an integral D-shaped annular bag, which is sleeved on the outside of the inner tube; or, the first fluid bag is a plurality of segmented bags, which are respectively attached to the arc-shaped wall area and / or the straight wall area; the shape of the second fluid bag matches the inner cavity shape of the inner tube and fills the entire core space.

5. The composite door anti-collision bar according to claim 1, wherein, The fiber layup of the inner tube includes circumferential layup, ±45 degree layup and axial layup, and the inner wall and / or outer wall of the inner tube are provided with longitudinally extending grooves or textures; the inner surface of the inner tube is provided with an isolation liner made of metal foil or polymer coating.

6. The composite door anti-collision bar according to claim 1, wherein, The mounting part includes a plug, which is welded to the end of the outer steel pipe. The plug has a socket, into which the end of the inner pipe is inserted and fixed. The plug also extends a mounting ear for connecting to the inner door panel.

7. A method for preparing the composite door anti-collision bar according to any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Preparation of outer steel pipe: The steel plate is rolled into a D-shaped pipe, and longitudinal reinforcing ribs are pressed into the pipe wall during the rolling process. After welding the joint, a pipe blank is obtained; then the pipe blank is subjected to hot stamping and quenching treatment to obtain the outer steel pipe. Step 2: Preparation of inner tube: A carbon fiber reinforced resin matrix composite tube with a D-shaped cross-section is prepared by filament winding or pultrusion molding process, and an isolation liner is set on the inner wall of the tube to obtain the inner tube; Step 3: Preparation of fluid bags: A shear-thickening fluid, with polyethylene glycol or silicone oil as the base liquid and at least one of nano-silica, nano-calcium carbonate, and nano-alumina as the dispersed phase, is filled into a bag made of a flexible polymer film and heat-sealed to make a first fluid bag and a second fluid bag. Step 4: Assemble the inner core: Place the second fluid bag into the inner cavity of the inner tube, making it fit against the inner wall; then put the first fluid bag onto the outside of the inner tube; Step 5, Overall Assembly: Push the inner tube assembly obtained in Step 4 into the outer steel tube, so that the first fluid bag is located in the gap between the outer steel tube and the inner tube; Step 6: Bonding and fixing: The outer steel pipe, inner pipe, first fluid bag and second fluid bag are fixed together by bonding. Step 7, Welding and Installation: Weld plugs with sockets to both ends of the assembled parts that have been bonded and fixed, and insert the end of the inner tube into the socket. The mounting ears extending from the plugs are used to connect with the inner door panel.

8. The method according to claim 7, wherein, The bonding in step six includes applying structural adhesive to both ends of the inner tube, which cures to form a rigid fixing ring; and / or activating the hot melt adhesive on the surface of the fluid bag by heating to achieve bonding.

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