Bionic polylactic acid-based composite material and automobile door cover connecting process

Abstract

This invention belongs to the field of polylactic acid (PLA)-based composite material technology, and discloses a biomimetic PLA-based composite material and a connection process for automotive door panels. The composite material uses PLA as the core substrate and includes a surface panel, a biomimetic lattice core, a bottom panel, and an adhesive layer. The biomimetic lattice core is a porous structure with gradient porosity, divided into an edge impact-resistant zone, a transition buffer zone, and a central lightweight zone from the edge to the center, respectively simulating the dense gradient structure of nacre and the porous lightweight structure of a honeycomb. This invention effectively balances impact resistance and lightweight requirements, making it suitable for automotive door panels and other components. The corresponding connection process achieves stable and efficient assembly of the composite material and the automotive door panel through a dual fixing method of positioning clips and bolts.

Description

Technical Field

[0001] This invention belongs to the field of polylactic acid-based composite material technology, specifically relating to a biomimetic polylactic acid-based composite material and a connection process for automotive door covers. Background Technology

[0002] Polylactic acid (PLA), a typical polyester-based biodegradable plastic, has broad application prospects in the fields of automotive lightweighting and environmentally friendly materials. With the rapid development of the new energy vehicle industry, lightweighting, high strength, and environmental degradability have become core requirements for automotive component design. PLA-based materials, due to their advantages such as biodegradability and adjustable mechanical properties, have become the preferred substrate in this field. However, existing PLA-based automotive components are mostly single-structure designs, failing to incorporate naturally optimized structures such as the impact resistance gradient of nacreous shells and the lightweight honeycomb porous structure, making it difficult to meet the comprehensive needs of automotive components.

[0003] Please refer to the attached instruction manual. Figure 1 Existing automotive door liner materials mostly use single-density foam materials or metal skeleton structures, which have obvious defects: First, foam materials have poor mechanical properties and insufficient impact resistance, making it difficult to meet the high safety requirements of new energy vehicles; Second, although metal skeletons have high strength, they are heavy, which goes against the trend of lightweighting, and their recycling rate is low, which does not conform to the concept of environmental protection; Third, some composite liner structures do not adopt a gradient design, resulting in an inability to balance mechanical properties and lightweight requirements, making them prone to local damage or overall failure when subjected to impact.

[0004] In addition, the existing connection methods between the car door liner and the inner panel of the door cover mostly use a single bolt fastening or snap-fit ​​connection, which has problems such as poor assembly stability, inconvenient disassembly or insufficient connection strength. At the same time, the chemical adhesives commonly used in the adhesive bonding process have defects such as poor environmental performance and low curing efficiency, which are difficult to match the green production requirements of new energy vehicles.

[0005] Therefore, developing a biomimetic lattice structure and adaptive connection method based on polylactic acid (PLA) materials to solve the bottleneck in the application of PLA materials in automotive parts has become the key to the industrialization of environmentally friendly automotive materials. Summary of the Invention

[0006] In view of the shortcomings of the prior art described in the background, this invention uses polylactic acid as the core material and draws on the dual advantages of the "gradient structure impact resistance" of the nacreous layer of seashells and the "porous lattice structure lightweight" of honeycomb to propose a biomimetic polylactic acid-based composite material and automotive door cover connection process. By enhancing the mechanical properties of the material through biomimetic gradient design and combining it with a dedicated connection process, the invention achieves a balance between environmental protection and practicality.

[0007] This invention solves the above-mentioned technical problems by providing a biomimetic polylactic acid-based composite material, comprising a surface panel, a biomimetic lattice core, a bottom panel, and a first adhesive layer and a second adhesive layer; the surface panel is bonded to the upper surface of the biomimetic lattice core via the first adhesive layer, and the bottom panel is bonded to the lower surface of the biomimetic lattice core via the second adhesive layer; both the first and second adhesive layers are made of bio-based epoxy resin adhesive; the surface panel is made of polylactic acid and flax fiber composite; the bottom panel is made of bio-based polyhydroxyalkanoate and sisal fiber composite.

[0008] The biomimetic lattice core is located between the surface panel and the bottom panel. It is a gradient porosity frame-type porous structure, which includes an edge impact-resistant zone, a transition buffer zone, and a central lightweight zone from the edge to the center. The three zones adopt a composite design of gradient materials and gradient structures: the edge impact-resistant zone is made of bio-based epoxy resin and carbon fiber composite, with a porosity of 15% to 20%, using rhombic dodecahedral lattice units with a unit size of 5×5×5mm; the transition buffer zone is made of polylactic acid and glass fiber composite, with a porosity of 25% to 30%, using tetrahedral lattice units with a unit size of 10×10×10mm; the central lightweight zone is made of pure polylactic acid material, with a porosity of 40% to 45%, using octahedral lattice units with a unit size of 12×12×12mm.

[0009] Furthermore, the volume fraction of carbon fiber in the edge impact-resistant zone is 25% to 30%, the unit size of 5×5×5mm is the enclosed size of the unit's outer cube, its node diameter is 2.2mm to 2.5mm, the rib diameter is 1.0mm to 1.2mm, the impact strength is not less than 18kJ / m², and it is prepared by stereolithography (SLA) process, which can simulate the dense structure of the nacreous layer of a shell to improve the load-bearing capacity and meet the requirements of impact resistance performance.

[0010] Furthermore, the glass fiber of the transition buffer zone has a length of 0.2 to 0.5 mm and a volume fraction of 20% to 25%, and is prepared by a dual-nozzle fused deposition modeling (FDM) process; the unit size of 10×10×10 mm is the enclosed size of the unit's outer cube, its node diameter is 1.8 mm to 2.0 mm, and its rib diameter is 0.8 mm to 1.0 mm, serving as an intermediate transition structure to achieve a smooth connection of mechanical properties.

[0011] Furthermore, the central lightweight area is continuously printed with a transition buffer zone using a dual-nozzle fused deposition modeling (FDM) process; the unit size of 12×12×12mm is the enclosed size of the unit's outer cube, with node diameters ranging from 1.4mm to 1.6mm and rib diameters ranging from 0.6mm to 0.8mm, which can simulate a honeycomb porous structure to achieve weight reduction. The central lightweight area and the transition buffer zone are connected by a gradual change in rib diameter, and the transition at the connection point is smooth with no stress concentration.

[0012] Furthermore, the overall bio-based content of the biomimetic polylactic acid-based composite material is not less than 85%.

[0013] Furthermore, the thickness of the surface panel is 0.6 mm to 0.8 mm, and the volume fraction of flax fiber is 30% to 40%.

[0014] Furthermore, the surface of the surface panel is treated with plasma and then sprayed with a polytetrafluoroethylene wear-resistant coating with a coating thickness of 5μm to 10μm.

[0015] Furthermore, the thickness of the bottom panel is 0.4mm to 0.6mm, and the volume fraction of sisal fiber is 25% to 35%; the bottom panel has an anti-slip texture on the side that is in contact with the automotive parts, and the texture depth is 0.3mm to 0.5mm.

[0016] Furthermore, the thickness of both the first adhesive layer and the second adhesive layer is 0.1 mm to 0.2 mm; in the first adhesive layer and the second adhesive layer, the solid content of the bio-based epoxy resin adhesive is not less than 90%. After the surface panel and the bottom panel are respectively bonded to the biomimetic lattice core, they are cured at 80°C to 100°C for 30 to 60 minutes. After curing, the shear strength of the adhesive layer is greater than 3.5 MPa and the interfacial bonding strength is greater than 15 MPa, which meets the bonding stability requirements of the three-layer structure of the surface panel, the bottom panel and the biomimetic lattice core.

[0017] Furthermore, the edge of the surface panel is provided with several positioning buckles, which are made of elastic bio-based plastic and are integrally embedded with the surface panel; four bolt mounting holes are provided through the corresponding positions of the surface panel, the biomimetic lattice core, and the bottom panel; a stainless steel insert is embedded in the bolt mounting hole of the bottom panel, the stainless steel insert having a thickness of 2.0mm to 2.5mm, and the inner hole size of the stainless steel insert being adapted to the nominal diameter of the connecting bolt.

[0018] This invention also provides a biomimetic polylactic acid (PLA)-based composite material for connecting automotive door covers. This automotive door cover connection process is adaptable to the various biomimetic PLA-based composite materials described above and includes the following steps:

[0019] Step 1, Pre-fabrication: Prepare the surface panel, biomimetic lattice core, bottom panel and positioning buckle respectively; the positioning buckle is integrally embedded with the surface panel;

[0020] The biomimetic lattice core is fabricated by continuously printing regions with the same process and segmentally docking regions with different processes. The specific process is as follows:

[0021] 1.1 A dual-nozzle FDM device is used to achieve continuous molding of the transition buffer zone and the central lightweight zone. Nozzle A is loaded with pure polylactic acid filament, corresponding to the central lightweight zone; nozzle B is loaded with glass fiber reinforced polylactic acid filament, corresponding to the transition buffer zone; the printing parameters are set as follows: nozzle temperature 220℃ to 230℃, platform temperature 60℃ to 80℃, layer thickness 0.1mm to 0.15mm, printing layer height 0.1mm to 0.2mm, the diameter of the transition buffer zone ribs gradually changes from 1.0mm to 0.8mm towards the central lightweight zone, and the length of the transition section is 15mm to 20mm. The material transition is achieved smoothly through synchronous extrusion of the dual nozzles, avoiding abrupt changes in performance.

[0022] 1.2 The edge impact-resistant zone is printed using SLA technology, with a layer thickness of 0.1mm to 0.15mm, a layer height of 0.1mm to 0.2mm, and a print fill rate of 80% to 90%. After printing, it is precisely connected to the transition buffer zone through a shared rib docking structure. The docking structure is designed with a pre-reserved insertion groove in the transition buffer zone, with a groove diameter of 0.7mm to 0.75mm, a length of 1mm to 2mm, and an inner wall roughness Ra of 0.2μm to 0.3μm. The edge impact-resistant zone is equipped with a matching insertion boss, with a boss diameter of 0.65mm to 0.7mm, a length of 1mm to 2mm, and a 0.1mm deep annular anti-slip texture on the surface. Through 3D printing precision control (SLA process dimensional accuracy ±0.02mm, FDM process dimensional accuracy ±0.05mm), the mating gap between the boss and the groove is ensured to be between 0.05mm and 0.1mm, which not only meets the assembly feasibility but also ensures uniform adhesive filling and strengthens the structural interlocking effect.

[0023] 1.3 Surface pretreatment before docking: Sand the docking surfaces with 400 to 600 grit sandpaper to ensure flatness does not exceed 0.1 mm. Then, treat with 80W to 120W plasma for 2 to 3 minutes to improve the adhesion of the adhesive. After the pretreatment, apply bio-based epoxy resin adhesive to the surfaces of the groove and boss, with an adhesive application amount of 0.08 g / cm² to 0.12 g / cm². Docking is carried out precisely according to the positioning benchmark, and the docking error is controlled within 0.2 mm to complete the prefabrication and assembly of the biomimetic lattice core.

[0024] Step 2, Overall Surface Pretreatment: The lower surface of the top panel, the upper surface of the bottom panel, and the upper and lower surfaces of the biomimetic lattice core are sanded with 400 to 600 grit sandpaper to remove surface burrs and impurities; the non-adhesive surfaces of the top panel are treated with 80W to 120W plasma for 3 to 5 minutes, and then a 5μm to 10μm thick polytetrafluoroethylene coating is sprayed on and allowed to air dry naturally until there are no drips on the surface;

[0025] Step 3, Adhesive Assembly: Apply bio-based epoxy resin adhesive evenly to the lower surface of the surface panel, the upper surface of the bottom panel, and the upper and lower surfaces of the biomimetic lattice core. The amount of adhesive applied is 0.05 g / cm² to 0.1 g / cm², forming a first adhesive layer between the surface panel and the biomimetic lattice core, and a second adhesive layer between the bottom panel and the biomimetic lattice core. Precisely place the pre-assembled biomimetic lattice core on top of the bottom panel, and then cover the biomimetic lattice core with the surface panel. Use positioning fixtures to ensure that the bolt mounting holes of the three are coaxially aligned, with an alignment error not exceeding 0.1 mm.

[0026] Step 4, Curing and Molding: Place the assembled structure in a constant temperature curing oven and cure for 40 to 50 minutes at 80℃ to 90℃ and 0.1MPa to 0.15MPa pressure. This process achieves a dual curing effect: it cures the adhesive at the joint of the biomimetic lattice core and the adhesive layer between the surface panel and the bottom panel and the biomimetic lattice core. No secondary heating is required, avoiding interlayer cracking caused by thermal stress. After curing, the structure is cooled to room temperature in the oven at a rate controlled within 5℃ / minute.

[0027] Step 5, Connecting to Automotive Components: Use the cured composite material as the inner lining of the car door cover. Initially snap it into position with the inner panel of the car door cover using the positioning clips on the edge of the surface panel, ensuring that the bolt mounting holes are fully aligned. Then, pass the connecting bolts through the bolt mounting holes and engage them with the threaded holes of the car door cover base. Tighten them to the set torque using a torque wrench to achieve dual fixation of snap-fit ​​and bolt connection, ensuring assembly stability.

[0028] Beneficial effects

[0029] Compared with existing polylactic acid-based automotive materials and bonding technologies, this invention has the following outstanding advantages:

[0030] 1. This invention has significant biomimetic advantages, replicating the dense edge and gradually changing center of the nacreous layer of a seashell to resist impact, while integrating the lightweight characteristics of honeycomb porous high-efficiency load-bearing. It breaks through the bottleneck of traditional blocky polylactic acid components that are light but not strong, and achieves significant weight reduction while improving impact resistance, making it suitable for the lightweight and impact-resistant requirements of scenarios such as automotive door panels.

[0031] 2. Outstanding Environmental Attributes: The core materials utilize bio-based materials such as biodegradable polylactic acid and polyhydroxyalkanoates, combined with bio-based adhesives, resulting in an overall bio-based content of no less than 85%. The natural degradation rate after disposal exceeds 90%, effectively solving the environmental pollution problems associated with traditional plastic parts. The application of natural plant fibers such as flax and sisal further reduces carbon emissions during material production. The polylactic acid-based material used in this invention belongs to polyester biodegradable plastics, possessing not only excellent biodegradability and mechanical adjustability but also achieving high-performance applications of polyester materials in automotive parts through biomimetic structural design. This provides a new technological path for the industrialization of polyester biodegradable plastics in the new energy vehicle field.

[0032] 3. Strong connection stability: It adopts a dual connection method of positioning buckle and connecting bolt fastening. By matching the tightening torque of the torque wrench with the reinforcement effect of the stainless steel insert, the connection stability is greatly improved compared with the single buckle connection.

[0033] 4. Excellent functionality and practicality: The wear-resistant coating on the surface panel and the anti-slip texture on the bottom panel improve surface durability and assembly stability, respectively, and extend the service life of the components.

[0034] 5. Good process adaptability: The curing temperature of the bonding process, from 80℃ to 100℃, matches the thermal stability range of polylactic acid, avoiding thermal deformation of the material and adapting to the needs of mass production. Attached Figure Description

[0035] Figure 1 A schematic diagram of a structure using polylactic acid-based materials from existing technologies as automotive door liner materials;

[0036] Figure 2 A schematic diagram of the microstructure of the nacreous layer of a seashell;

[0037] Figure 3 This is a schematic diagram of a honeycomb structure;

[0038] Figure 4 This is a schematic diagram of the biomimetic lattice core according to an embodiment of the present invention;

[0039] Figure 5 This is a schematic diagram of the biomimetic polylactic acid-based composite material structure according to an embodiment of the present invention;

[0040] Figure 6 This is a schematic diagram of the stress-displacement relationship of the biomimetic polylactic acid-based composite material according to an embodiment of the present invention;

[0041] Figure 7 This is a schematic diagram of the side plane where the bottom panel of the present invention is attached to the automotive component, according to an embodiment of the present invention.

[0042] Figure 8 This is a schematic diagram of a biomimetic polylactic acid-based composite material used as an automotive door liner in an embodiment of the present invention.

[0043] In the diagram: 1. Surface panel, 2. Bionic lattice core, 21. Impact-resistant edge zone, 22. Transition buffer zone, 23. Central lightweight zone, 3. Bottom panel, 4. First adhesive layer, 5. Second adhesive layer, 6. Bolt mounting holes, 7. Stainless steel insert, 8. Connecting bolt, 9. Positioning clip, 10. Anti-slip texture, 11. Car door cover, 12. Car door cover liner. Detailed Implementation

[0044] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0045] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0047] Example 1, please refer to Figures 2 to 8 A biomimetic polylactic acid-based composite material, using polylactic acid as the core substrate and with an overall bio-based content of not less than 85%, is based on a dual biomimetic prototype of a pearl layer gradient structure and a honeycomb porous lattice structure. It includes a surface panel 1, a biomimetic lattice core 2, a bottom panel 3, and a first adhesive layer 4 and a second adhesive layer 5. The surface panel 1 is bonded to the upper surface of the biomimetic lattice core 2 via the first adhesive layer 4, and the bottom panel 3 is bonded to the lower surface of the biomimetic lattice core 2 via the second adhesive layer 5. All three are integrally bonded. Both the first adhesive layer 4 and the second adhesive layer 5 use bio-based epoxy resin adhesive. The first adhesive layer 4 and the second adhesive layer 5 do not form an independent plate structure, but rather are a single adhesive layer. Figure 6The transparent panel is used to indicate the location of the structure; the surface panel 1 is made of polylactic acid and flax fiber composite; the bottom panel 3 is made of bio-based polyhydroxyalkanoate and sisal fiber composite.

[0048] The biomimetic lattice core 2 is located between the surface panel 1 and the bottom panel 3. It is a gradient porosity frame-type porous structure, which includes an edge impact-resistant zone 21, a transition buffer zone 22, and a central lightweight zone 23 from the edge to the center. The three zones adopt a composite design of gradient materials and gradient structures: the edge impact-resistant zone 21 is made of bio-based epoxy resin and carbon fiber composite, with a porosity of 15% to 20%, and uses rhombic dodecahedral lattice units with a unit size of 5×5×5mm; the transition buffer zone 22 is made of polylactic acid and glass fiber composite, with a porosity of 25% to 30%, and uses tetrahedral lattice units with a unit size of 10×10×10mm; the central lightweight zone 23 is made of pure polylactic acid material, with a porosity of 40% to 45%, and uses octahedral lattice units with a unit size of 12×12×12mm.

[0049] Please refer to Figures 2 to 3 The gradient layered structure of nacre exhibits excellent impact resistance. Example 1 simulates the layered reinforcement mechanism of nacre through a material gradient from the edge to the center (carbon fiber reinforcement → glass fiber reinforcement → pure polylactic acid). The porous nature of the honeycomb structure is the core of lightweight design. A gradient porosity of 15% to 45% simulates the porous weight reduction design of the honeycomb structure, and the combination of the two achieves a synergistic effect of "impact resistance and lightweight". The edge impact-resistant zone uses rhombic dodecahedral lattice units with a size of 5×5×5mm, which have strong spatial stability. Combined with a low porosity of 15% to 20%, it can maximize the edge load-bearing capacity. The central lightweight zone uses octahedral lattice units with a size of 12×12×12mm, combined with a high porosity of 40% to 45%, to minimize material usage while ensuring basic support.

[0050] In Example 1, the volume fraction of carbon fiber in the edge impact-resistant zone 21 is 25% to 30%, the unit node diameter is 2.2 to 2.5 mm, the rib diameter is 1.0 to 1.2 mm, the impact strength is not less than 18 kJ / m², and it is prepared by stereolithography (SLA) process. It can simulate the dense structure of the nacreous layer of a shell to improve the load-bearing capacity and meet the requirements of impact resistance performance.

[0051] The transition buffer 22 has a glass fiber length of 0.2 to 0.5 mm and a volume fraction of 20% to 25%, and is prepared by dual-nozzle fused deposition modeling (FDM) process; the unit size of 10×10×10 mm is the enclosing size of the unit's outer cube, with a node diameter of 1.8 to 2.0 mm and a rib diameter of 0.8 to 1.0 mm, serving as an intermediate transition structure to achieve a smooth connection of mechanical properties.

[0052] The central lightweight zone 23 is continuously printed with the transition buffer zone 22 using a dual-nozzle fused deposition modeling (FDM) process. The unit size of 12×12×12mm is the enclosed size of the unit's outer cube, with a node diameter of 1.4 to 1.6mm and a rib diameter of 0.6 to 0.8mm. This can simulate a honeycomb porous structure to achieve a weight reduction effect. The central lightweight zone 23 and the transition buffer zone 22 are connected by a gradual change in rib diameter, and the transition of rib diameter at the connection point is smooth without stress concentration.

[0053] Please refer to Figure 5 , Figure 7 In Example 1, the surface panel 1 has a thickness of 0.6 to 0.8 mm and a flax fiber volume fraction of 30% to 40%. After plasma treatment, the surface of the surface panel 1 is coated with a polytetrafluoroethylene (PTFE) wear-resistant coating with a thickness of 5 to 10 μm. The bottom panel 3 has a thickness of 0.4 to 0.6 mm and a sisal fiber volume fraction of 25% to 35%. The bottom panel 3 has an anti-slip texture 10 on the side that contacts the automotive component, with a texture depth of 0.3 to 0.5 mm. These measures improve surface durability and assembly stability, which is beneficial for extending the service life of new energy vehicle components.

[0054] The thickness of the first adhesive layer 4 and the second adhesive layer 5 is 0.1 mm to 0.2 mm. In the first adhesive layer 4 and the second adhesive layer 5, the solid content of the bio-based epoxy resin adhesive is not less than 90%. After the surface panel and the bottom panel are bonded to the biomimetic lattice core, they are cured at 80°C to 100°C for 30 to 60 minutes. After curing, the shear strength of the adhesive layer is greater than 3.5 MPa and the interfacial bonding strength is greater than 15 MPa, which meets the bonding stability requirements of the three-layer structure of the surface panel, the bottom panel and the biomimetic lattice core, thereby improving the strength of the automotive door panel component.

[0055] Please refer to Figure 5 The edge of the surface panel 1 is provided with several positioning buckles 9, which are made of elastic bio-based plastic and are integrally embedded with the surface panel 1. Four bolt mounting holes 6 are provided through the corresponding positions of the surface panel 1, the biomimetic lattice core 2, and the bottom panel 3. A stainless steel insert 7 is embedded in the bolt mounting holes 6 of the bottom panel 3. The thickness of the stainless steel insert 7 is 2.0mm to 2.5mm, and the inner hole size of the stainless steel insert 7 is adapted to the nominal diameter of the connecting bolt 8.

[0056] Please refer to Figure 6 This is a schematic diagram of the stress-displacement relationship of the biomimetic polylactic acid (PLA)-based composite material according to an embodiment of the present invention. The diagram reflects the "gradient load-bearing and energy absorption synergistic response" of the biomimetic PLA-based composite material in Example 1 under impact or compressive loads. The stress first rises rapidly with displacement, then fluctuates and dissipates, and finally stabilizes slowly. This is matched by a biomimetic structural design that features "edge impact resistance, transition buffering, and center lightweighting," achieving a performance balance of "strong load-bearing capacity, high energy absorption, and lightweighting." Specifically:

[0057] 1. The stress in the edge impact resistance zone (displacement 0-20mm) rises rapidly from 0 to approximately 15000MPa; "strong load-bearing characteristics" (simulating the nacreous layer of a shell) This area has a high fiber content and high filling rate structure, which can quickly bear external loads, effectively resist the initial impact, and avoid direct material failure; it serves as the "first line of defense against impact" to ensure that the material does not undergo brittle fracture in the early stage of impact.

[0058] 2. The stress in the transition buffer zone (displacement 20-50mm) fluctuates (without significant decrease), and remains in the range of 10000-15000MPa. In terms of "energy dissipation capacity", this area dissipates impact energy through gradual changes in structure and materials, using rib deformation, nodal friction, etc., to avoid stress abruptly transmitting to the central area. As a "performance transition zone", it connects the edge and the central area to prevent local failure due to performance discontinuity.

[0059] 3. In the central lightweight zone (after a 50mm displacement), stress rises slowly and tends to stabilize (the overall process is gradual); "Balancing deformation and load-bearing capacity" (simulating a honeycomb porous structure), the high porosity design allows for some deformation while maintaining the foundation's load-bearing capacity, avoiding a sudden drop in stress; achieving the "lightweight" goal while ensuring the material still possesses effective load-bearing capacity under large displacements, avoiding complete instability. The stress-displacement relationship curve verifies the effectiveness of the biomimetic structure: the edge zone solves the problem of "insufficient impact resistance"; the transition zone solves the problem of "stress concentration fracture"; the central zone solves the problem of the "contradiction between lightweight and load-bearing capacity"; overall, it meets the core usage requirements of "lightweight and energy absorption" for automotive door panels.

[0060] This invention also provides a biomimetic polylactic acid (PLA)-based composite material for connecting automotive door covers. This automotive door cover connection process is adaptable to any of the aforementioned biomimetic PLA-based composite materials and includes the following steps:

[0061] Step 1, Pre-fabrication: Prepare the surface panel 1, the biomimetic lattice core 2, the bottom panel 3, and the positioning buckle 9 respectively; the positioning buckle 9 is integrally embedded with the surface panel 1.

[0062] The biomimetic lattice core is fabricated by continuously printing regions with the same process and segmentally docking regions with different processes. The specific process is as follows:

[0063] 1.1 A dual-nozzle FDM device is used to achieve continuous molding of the transition buffer zone and the central lightweight zone. Nozzle A is loaded with pure polylactic acid filament, corresponding to the central lightweight zone; nozzle B is loaded with glass fiber reinforced polylactic acid filament, corresponding to the transition buffer zone; the printing parameters are set as follows: nozzle temperature 220℃ to 230℃, platform temperature 60℃ to 80℃, layer thickness 0.1mm to 0.15mm, printing layer height 0.1mm to 0.2mm, the diameter of the transition buffer zone ribs gradually changes from 1.0mm to 0.8mm towards the central lightweight zone, and the length of the transition section is 15mm to 20mm. The material transition is achieved smoothly through synchronous extrusion of the dual nozzles, avoiding abrupt changes in performance.

[0064] 1.2 The edge impact-resistant zone is printed using SLA technology, with a layer thickness of 0.1mm to 0.15mm, a layer height of 0.1mm to 0.2mm, and a print fill rate of 80% to 90%. After printing, it is precisely connected to the transition buffer zone through a shared rib docking structure. The docking structure is designed with a pre-reserved insertion groove in the transition buffer zone, with a groove diameter of 0.7mm to 0.75mm, a length of 1mm to 2mm, and an inner wall roughness Ra of 0.2μm to 0.3μm. The edge impact-resistant zone is equipped with a matching insertion boss, with a boss diameter of 0.65mm to 0.7mm, a length of 1mm to 2mm, and a 0.1mm deep annular anti-slip texture on the surface. Through 3D printing precision control (SLA process dimensional accuracy ±0.02mm, FDM process dimensional accuracy ±0.05mm), the mating gap between the boss and the groove is ensured to be between 0.05mm and 0.1mm, which not only meets the assembly feasibility but also ensures uniform adhesive filling and strengthens the structural interlocking effect.

[0065] 1.3 Surface pretreatment before docking: Sand the docking surfaces with 400 to 600 grit sandpaper to ensure flatness does not exceed 0.1 mm. Then, treat with 80W to 120W plasma for 2 to 3 minutes to improve the adhesion of the adhesive. After the pretreatment, apply bio-based epoxy resin adhesive to the surfaces of the groove and boss, with an adhesive application amount of 0.08 g / cm² to 0.12 g / cm². Docking is carried out precisely according to the positioning benchmark, and the docking error is controlled within 0.2 mm to complete the prefabrication and assembly of the biomimetic lattice core.

[0066] Step 2, overall surface pretreatment: The lower surface of the surface panel 1, the upper surface of the bottom panel 3, and the upper and lower surfaces of the biomimetic lattice core 2 are sanded with 400 to 600 grit sandpaper to remove surface burrs and impurities; the non-adhesive surfaces of the surface panel are treated with 80W to 120W plasma for 3 to 5 minutes, and then a 5μm to 10μm thick polytetrafluoroethylene coating is sprayed on and allowed to air dry naturally until there are no drips on the surface;

[0067] Step 3, Adhesive Assembly: Apply bio-based epoxy resin adhesive evenly to the lower surface of the surface panel 1, the upper surface of the bottom panel 3, and the upper and lower surfaces of the biomimetic lattice core 2. The amount of adhesive applied is 0.05 g / cm² to 0.1 g / cm², so that a first adhesive layer 4 is formed between the surface panel 1 and the biomimetic lattice core 2, and a second adhesive layer 5 is formed between the bottom panel 3 and the biomimetic lattice core 2. Precisely place the pre-assembled biomimetic lattice core 2 on top of the bottom panel 3, and then cover the biomimetic lattice core 2 with the surface panel 1. Use positioning fixtures to ensure that the bolt mounting holes 6 of the three are coaxially aligned, with an alignment error of no more than 0.1 mm.

[0068] Step 4, Curing and Molding: Place the assembled structure in a constant temperature curing oven and cure for 40 to 50 minutes at 80℃ to 90℃ and 0.1MPa to 0.15MPa pressure. This process achieves a dual curing effect: it cures the adhesive at the joint of the bionic lattice core 2 and the adhesive layer between the surface panel 1 and the bottom panel 3 and the bionic lattice core 2. No secondary heating is required, which avoids interlayer cracking caused by thermal stress. After curing, the structure is cooled to room temperature in the oven at a rate controlled within 5℃ / minute.

[0069] Step 5, Connecting to Automotive Components: The cured composite material is used as the inner lining 12 of the automotive door cover. It is initially snapped and positioned with the inner panel of the automotive door cover 11 by the positioning buckle 9 on the edge of the surface panel 1, ensuring that the bolt mounting holes are fully aligned. Then, the connecting bolts 8 with a nominal diameter of 6mm to 8mm are passed through the bolt mounting holes 6 and engaged with the threaded holes of the automotive door cover 11 base. The bolts are tightened with a torque wrench to a torque of 8 to 10 N·m, completing the double fixation of snap-fit ​​and bolt connection, ensuring assembly stability.

[0070] Please refer to Figure 8 Example 1 demonstrates significant biomimetic advantages: It accurately replicates the impact-resistant structure of the pearl layer of seashells, which is "dense at the edges and gradually changes in the center," and the lightweight characteristics of honeycomb, which is "porous and efficient in bearing load." Compared with traditional blocky polylactic acid components, the impact resistance is increased by more than 30%, while the weight is reduced by 40% to 50%, thus solving the bottleneck of polylactic acid materials being "light but not strong."

[0071] The above performance improvement data (impact resistance increased by more than 30%, weight reduced by 40% to 50%) and Figure 6 The stress-displacement curve shown is based on the sample prepared using the material structure and process parameters described in this embodiment. The test was conducted in accordance with the national standards GB / T 1043-2008 "Determination of Impact Properties of Simply Supported Beams of Plastics" and GB / T 6343-2009 "Determination of Apparent Density of Foamed Plastics and Rubber", and was compared with solid polylactic acid sheets of the same projected area.

[0072] The above embodiments and accompanying drawings are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. The present invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the present invention do not depart from the spirit of the present invention and should also fall within the protection scope of the claims of the present invention. Other related technical structures not disclosed in detail in the present invention are existing technologies in the art.

Claims

1. A biomimetic polylactic acid-based composite material, characterized in that: The device includes a surface panel, a biomimetic lattice core, a bottom panel, and a first adhesive layer and a second adhesive layer. The surface panel is bonded to the upper surface of the biomimetic lattice core via the first adhesive layer, and the bottom panel is bonded to the lower surface of the biomimetic lattice core via the second adhesive layer. Both the first and second adhesive layers are made of bio-based epoxy resin adhesive. The surface panel is made of polylactic acid and flax fiber composite. The bottom panel is made of bio-based polyhydroxyalkanoate and sisal fiber composite. The biomimetic lattice core is located between the surface panel and the bottom panel. It is a gradient porosity frame-type porous structure, which includes an edge impact-resistant zone, a transition buffer zone, and a central lightweight zone from the edge to the center. The three zones adopt a composite design of gradient materials and gradient structures: the edge impact-resistant zone is made of bio-based epoxy resin and carbon fiber composite, with a porosity of 15% to 20%, using rhombic dodecahedral lattice units with a unit size of 5×5×5mm; the transition buffer zone is made of polylactic acid and glass fiber composite, with a porosity of 25% to 30%, using tetrahedral lattice units with a unit size of 10×10×10mm; the central lightweight zone is made of pure polylactic acid material, with a porosity of 40% to 45%, using octahedral lattice units with a unit size of 12×12×12mm. The volume fraction of carbon fiber in the edge impact-resistant zone is 25% to 30%, the unit size of 5×5×5mm is the enclosed size of the unit's outer cube, the node diameter is 2.2mm to 2.5mm, the rib diameter is 1.0mm to 1.2mm, and it is prepared by stereolithography (SLA) process. The glass fiber of the transition buffer zone has a length of 0.2 mm to 0.5 mm and a volume fraction of 20% to 25%, and is prepared by a dual-nozzle fused deposition modeling (FDM) process; the unit size of 10×10×10 mm is the enclosed size of the unit's outer cube, with a node diameter of 1.8 mm to 2.0 mm and a rib diameter of 0.8 mm to 1.0 mm; The central lightweight area is continuously printed using a dual-nozzle fused deposition modeling (FDM) process and a transition buffer zone; the unit size of 12×12×12mm is the enclosed size of the unit's outer cube, with node diameters ranging from 1.4mm to 1.6mm and rib diameters ranging from 0.6mm to 0.8mm.

2. The biomimetic polylactic acid-based composite material according to claim 1, characterized in that: The surface panel has a thickness of 0.6 mm to 0.8 mm and a flax fiber volume fraction of 30% to 40%.

3. The biomimetic polylactic acid-based composite material according to claim 1, characterized in that: The surface of the panel is treated with plasma and then coated with a wear-resistant polytetrafluoroethylene coating with a thickness of 5μm to 10μm.

4. The biomimetic polylactic acid-based composite material according to claim 1, characterized in that: The bottom panel has a thickness of 0.4mm to 0.6mm and a sisal fiber volume fraction of 25% to 35%; the bottom panel has an anti-slip texture on the side that is in contact with the automotive parts, with a texture depth of 0.3mm to 0.5mm.

5. The biomimetic polylactic acid-based composite material according to claim 1, characterized in that: The thickness of both the first adhesive layer and the second adhesive layer is 0.1 mm to 0.2 mm.

6. The biomimetic polylactic acid-based composite material according to claim 1, characterized in that: The edge of the surface panel is provided with several positioning buckles, which are made of elastic bio-based plastic and are integrally embedded with the surface panel. Four bolt mounting holes are provided through the corresponding positions of the surface panel, the biomimetic lattice core, and the bottom panel. Stainless steel inserts are embedded in the bolt mounting holes of the bottom panel. The thickness of the stainless steel inserts is 2.0mm to 2.5mm, and the inner hole size of the stainless steel inserts is adapted to the nominal diameter of the connecting bolts.

7. A biomimetic polylactic acid-based composite material connection process for automotive door covers, characterized in that: The method of using the biomimetic polylactic acid-based composite material as described in claim 1 includes the following steps: Step 1, Pre-fabrication: The surface panel, biomimetic lattice core, and bottom panel are fabricated separately. The biomimetic lattice core is fabricated by continuous printing in the same process area and segmented docking in different process areas. The specific process is as follows: 1.1 A dual-nozzle FDM device is used to achieve continuous molding of the transition buffer zone and the central lightweight zone; 1.2 The edge impact-resistant area is printed using SLA technology. After printing, it is connected to the transition buffer zone through a shared rib docking structure. 1.3 Before docking, surface pretreatment is performed, followed by coating with bio-based epoxy resin adhesive and precise docking to complete the prefabrication and assembly of the biomimetic lattice core. Step 2, overall surface pretreatment: polish the lower surface of the surface panel, the upper surface of the bottom panel, and the upper and lower surfaces of the biomimetic lattice core; Step 3, gluing and assembly: Apply bio-based epoxy resin adhesive evenly to the lower surface of the top panel, the upper surface of the bottom panel, and the upper and lower surfaces of the biomimetic lattice core. Place the biomimetic lattice core on top of the bottom panel, and then cover the top panel with the top panel. Step 4, Curing and Molding: Place the assembled structure in a constant temperature curing chamber and cure for 40 to 50 minutes at 80℃ to 90℃ and 0.1MPa to 0.15MPa pressure. Step 5, Connecting to Automotive Parts: The cured composite material is used as the interior lining of the automotive door panel for installation and fixation.

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