An optimization method for lightweight hybrid material automobile B-pillar structure

Abstract

A method for optimizing the lightweight hybrid material automotive B-pillar structure effectively solves the problem of single-material B-pillars being difficult to achieve in terms of achieving a balance between structural performance, lightweighting, and cost control. A layup scheme for the carbon fiber composite inner panel is determined based on the classic B-pillar operating conditions and the static and dynamic performance of the body-in-white (BIW). The optimal connection method for the hybrid material B-pillar is determined by analyzing the stress conditions of bolts, rivets, and adhesive layers in the BIW operating conditions, combined with the mechanical properties and cost of the selected materials. A finite element model of the vehicle side collision and pillar impact is established based on the C-NCAP test method. The hybrid material B-pillar is compared with the original metal B-pillar using the B-pillar intrusion volume and intrusion velocity as performance indicators. A Kriging approximation model is established using the structural parameters of the hybrid material B-pillar as design variables and the mass, intrusion volume, and intrusion velocity of the hybrid material B-pillar as indicators. The NSGA-II algorithm is used to perform lightweight multi-objective optimization of the hybrid material B-pillar.

Description

Technical Field

[0001] The present invention relates to the field of lightweight design of automobile parts, and in particular to a method for optimizing a lightweight hybrid material automobile B-pillar structure. Background Art

[0002] It's known that among the four types of collisions—frontal, side, rear, and rollover—side collisions occur in 42.4% of cases, with a mortality rate as high as 34%. In a side collision, the vehicle's side structure lacks the sufficient deformation and energy absorption space of its front and rear structures, resulting in more severe injuries to the driver and passengers. As a key structural component, the B-pillar minimizes deformation during a side collision, ensuring sufficient survivability and safety for the driver. Furthermore, extensive data and testing demonstrate that for every 10% reduction in electric vehicle mass, a 5%-10% increase in driving range can be achieved, saving 15%-20% in battery costs and 20% in daily wear and tear costs. Therefore, the design of the B-pillar must comprehensively consider both collision safety and lightweighting.

[0003] Currently, high-strength steel offers significant yield and tensile strengths and is relatively inexpensive. High-strength steel B-pillars can improve vehicle side impact safety while reducing manufacturing costs. However, high-strength steel suffers from disadvantages such as high density, heavy weight, difficulty in deformation, and susceptibility to cracking, limiting its widespread application. Compared to high-strength steel, aluminum alloy offers a more significant lightweighting effect and significant advantages in energy absorption. Replacing steel components with aluminum alloy can reduce weight by 69% and increase energy absorption by 50% under the same load. For the same energy absorption, thin-walled aluminum alloy components can reduce weight by approximately 50%. However, aluminum alloy's high plasticity makes single aluminum alloy B-pillars ineffective in protecting vehicle occupants in a collision, making it difficult to meet side impact safety requirements.

[0004] Carbon fiber, the most commonly used lightweight material for vehicle bodies, can effectively reduce weight by 25% to 30% and 40% to 60% compared to aluminum alloy and steel, respectively. Its strength and stiffness are 5 to 7 times that of steel, and it offers excellent corrosion, fatigue, and impact resistance. While carbon fiber B-pillars offer excellent overall performance, their processing efficiency is low. Composite material specialists are required to create complex molds, along with equipment such as autoclaves and vacuum lines, as well as auxiliary materials such as release agents and vacuum bags. Furthermore, carbon fiber is prohibitively expensive compared to steel and aluminum alloys. Single-material B-pillars struggle to simultaneously meet the requirements for structural performance, lightweighting, and cost control. Therefore, a method for optimizing lightweight hybrid automotive B-pillar structures is urgently needed. Summary of the Invention

[0005] To overcome the shortcomings of the background technology, the present invention provides a method for optimizing the lightweight hybrid material automobile B-pillar structure. The present invention uses carbon fiber composite materials for the inner panel, high-strength steel for the upper part of the reinforcing plate, and aluminum alloy for the lower part, thereby meeting the structural requirements of high rigidity and deformation resistance in the upper part of the B-pillar and low rigidity and strong energy absorption in the lower part, thereby achieving the purpose of maximizing occupant safety, improving lightweight effect and saving costs.

[0006] In order to achieve the above-mentioned purpose of the invention, the present invention adopts the following technical solution:

[0007] A method for optimizing a lightweight hybrid material automobile B-pillar structure, the method specifically comprising the following steps:

[0008] The first step is to import the geometric model of the car B-pillar assembly into Hypermesh software, use Automesh to divide it into meshes and assign materials and properties;

[0009] The second step is to import the finite element model of the automobile B-pillar assembly into the OptiStruct software and establish three-point bending, axial tension and lateral bending conditions. The welding method is simulated using ACM units.

[0010] The third step is to improve the structure, replace materials and change the connection method of the automobile B-pillar assembly before designing the carbon fiber layup. Because the lightweight hybrid material automobile B-pillar assembly needs to meet the structural characteristics of high stiffness and deformation resistance in the upper part and low stiffness and strong energy absorption in the lower part, the metal B-pillar reinforcement plate A and the metal B-pillar reinforcement plate B that enhance the stiffness of the upper area of ​​the automobile B-pillar are deleted, and the stiffness lost by deleting the metal B-pillar reinforcement plate A and the metal B-pillar reinforcement plate B is compensated by designing the carbon fiber layup. In the side impact test, the highest height between the energy absorption block at the front end of the impacted vehicle and the lowest point of the wheel is 800-900mm. Therefore, the metal B-pillar reinforcement plate C is divided into a high-strength steel B-pillar reinforcement plate and an aluminum alloy B-pillar reinforcement plate with the lowest point of the wheel at 800mm as the dividing line. The length of the high-strength steel B-pillar reinforcement plate and the aluminum alloy B-pillar reinforcement plate are each increased by 100mm, and the overlapping area with a length of 200mm is used as the connection area.

[0011] The high-strength steel B-pillar reinforcement plate is made of Q460 steel, the aluminum alloy B-pillar reinforcement plate is made of 6016 aluminum alloy, and the metal B-pillar inner panel is replaced with a carbon fiber composite B-pillar inner panel. The B-pillar assembly is connected by gluing the carbon fiber composite B-pillar inner panel to the high-strength steel B-pillar reinforcement plate and the aluminum alloy B-pillar reinforcement plate using "Adhesives+RBE3" elements. The aluminum alloy B-pillar reinforcement plate is tentatively connected to the high-strength steel B-pillar reinforcement plate and the metal B-pillar outer panel using "RBE2" elements.

[0012] Step 4. Import the hybrid material B-pillar model into the Optistruct software. In the connectors interface, select the area panel, select the adhesive area in the location field, select the carbon fiber composite B-pillar inner panel, high-strength steel B-pillar reinforcement plate, and aluminum alloy B-pillar reinforcement plate in the connect what field, set the type to adhesives, and then click create to generate the "Adhesives+RBE3" unit that simulates the adhesive connection.

[0013] During the layup design phase, the connection between the high-strength steel B-pillar reinforcement, the aluminum alloy B-pillar reinforcement, and the metal B-pillar outer panel is simulated using RBE2 elements. During the simulation, select rigid in the 1D interface, select the master node in independent, select the slave node in dependent, and click create to generate the RBE2 element that connects the master and slave nodes.

[0014] Step 5: In OptiStruct software, a multi-level optimization method, including free-size optimization, size optimization, and layup sequence optimization, was used to determine the ply block shape, number of plies, and layup sequence, ultimately determining the layup scheme for the carbon fiber composite B-pillar inner panel. To simplify the initial variables in the conceptual design phase, the thickness of each lay angle was primarily present as a set. That is, plies with the same lay angle were considered a set, called a super layer. For the carbon fiber composite inner panel modeled using shell elements, the super layer thickness was used as the design variable in the free-size phase, and each super layer was optimized for continuous variables. That is, by varying the thickness of each layer and the fiber direction of each element, the total thickness of the laminate varied continuously throughout the structure.

[0015] Since the super layer is made up of single-layer panels with the same laying angle, in order to determine the laying block shape of each single-layer panel, each super layer needs to be analyzed into ply blocks with different shapes. Since the ply block shape and laying position of each single-layer panel are not necessarily the same, the overall thickness of the super layer is also uneven. Therefore, the carbon fiber composite B-pillar inner panel is designed with constant stiffness and variable thickness to improve material utilization.

[0016] Step 6. After free size optimization, the thickness of each super layer and its ply cutting shape are obtained. Each super layer has four groups of different ply blocks. These four ply blocks stacked together can represent the optimization result of a super layer. However, since the optimized ply blocks are too ideal, the shapes of the ply blocks are often very irregular, which is not conducive to industrial cutting. Therefore, it is necessary to regularize the ply blocks after free optimization, that is, trim the irresponsible holes of the ply blocks into rectangular holes that are convenient for cutting to facilitate industrial ply cutting. When performing regular processing, in order to prevent the performance of the processed laminate from degrading, the boundaries of the rectangular holes cannot exceed the boundaries of the irregular holes; in order to prevent the lightweight effect from being reduced, the area of ​​the rectangular holes should be as large as possible;

[0017] In addition, the thickness of each ply obtained by free size optimization is different, which requires a high cost in actual production. In order to make the result more economical, a manufacturing constraint of a single layer thickness of 0.3mm is introduced to obtain a single ply with the same thickness. After introducing this manufacturing constraint and performing size optimization, the actual number of plies of each shape can be obtained. The actual number of plies is the thickness dimension T obtained after size optimization. i Divide by the thickness of the single layer 0.3;

[0018] Step 7: The optimized solution for the carbon fiber composite B-pillar inner panel obtained through continuous variable thickness optimization design meets the stiffness performance requirements. However, in engineering manufacturing, the carbon fiber composite B-pillar inner panel must also meet certain process constraints, constraints limiting the adverse internal forces caused by the layup sequence, and continuity constraints limiting fiber disconnection. In addition, a reasonable layup sequence can further improve the impact resistance of the hybrid material vehicle B-pillar.

[0019] Step 8: Import the BIW finite element models of the original metal and hybrid B-pillars into OptiStruct software. Build a BIW static bending and torsional finite element model based on the test conditions. When performing BIW free modal analysis, import the BIW finite element model into Nastran software for setup and solution.

[0020] Step 9: Because the initially determined carbon fiber composite B-pillar inner panel only considers the performance requirements of the vehicle B-pillar assembly, but not the performance requirements of the entire vehicle, the thickness of the carbon fiber composite super layer fails to achieve the best match with other body-in-white components, and may even lead to a decrease in the static and dynamic performance of the body-in-white. Therefore, it is necessary to substitute the initially determined carbon fiber composite B-pillar inner panel into the body-in-white and perform static bending and torsional stiffness analysis and free modal analysis;

[0021] Based on the static and dynamic performance of the body-in-white (BIW), the size and layup sequence of the carbon fiber composite B-pillar inner panel were further optimized. This layup design does not degrade the static and dynamic performance of the BIW and ensures the practical use value of the hybrid material B-pillar. Since the BIW lightweight coefficient comprehensively considers the vehicle weight, projected area, and torsional stiffness performance indicators, it can better integrate its performance and lightweight design. Therefore, with the BIW lightweight coefficient as the optimization target, the size and layup sequence of the carbon fiber composite inner panel were optimized.

[0022] Step 10: Considering the composite layup process and manufacturing process, the composite layup design software FiberSIM was used to build a layup model for the carbon fiber composite B-pillar inner panel. The modeling method was to stack the individual plies to form a laminate structure. The layup information of each ply was then imported into the finite element software to complete the modeling of the lightweight hybrid material vehicle B-pillar.

[0023] A lightweight hybrid vehicle B-pillar joined using countersunk rivets, hexagonal bolts, adhesive bonding, and adhesive riveting was incorporated into the body-in-white (BIW) model. Finite element analysis of the BIW's static bending-torsion conditions and free modes was performed. The OptiStruct solver was used to determine the stresses on the countersunk rivets, hexagonal bolts, and adhesive layer under the BIW's static bending-torsion conditions and overall first-order bending-torsion modal vibration shapes. The optimal connection method for the lightweight hybrid vehicle B-pillar was determined by comprehensively considering the mechanical properties and cost of the selected materials.

[0024] Step 11: When conducting a side impact test of a deformable mobile barrier according to the C-NCAP side standard, a deformable honeycomb aluminum structure is placed at the front end of the mobile trolley. During the test, the mobile barrier impacts the left side of the test vehicle, i.e. the driver's side. The impact direction of the mobile trolley is perpendicular to the test vehicle. The center line of the mobile barrier is located 250mm behind the R point of the test vehicle. The collision speed is The distance between the longitudinal median vertical plane of the mobile dolly and the transverse vertical plane of the vehicle 250 mm rearward through the R point of the driver's seat must be within ±25 mm. A WorldSID50th and SID-IIs dummies are placed on the driver's seat and the left side of the rear seat, respectively, to simulate the injury conditions of the driver and rear seat occupants.

[0025] According to the C-NCAP side pole impact test method, the diameter of the rigid fixed cylinder is 254mm and it is located on the left side of the test vehicle. The collision speed of the test vehicle hitting the barrier is The collision velocity direction is 75±3° with the vehicle coordinate system's X-axis. A WorldSID50th dummy is placed in the front driver's seat of the test vehicle to simulate the driver's injury. The lower end of the fixed rigid cylinder cannot be higher than 102mm above the lowest point of the wheel on the impact side of the test vehicle, and the upper end must exceed the highest point of the test vehicle. The line connecting the center of the cylinder and the center of the dummy's head is consistent with the velocity direction.

[0026] According to the C-NCAP side impact test and side pole impact test methods, a full vehicle side impact model and a side pole impact model are established, and stiffness of 1×10 - 10 The finite element model is exported as a k-file and solved using the LS-DYNA solver. The intrusion amount and intrusion speed of the dummy's head, chest, abdomen, and pelvis are obtained based on the deformation of the spring unit.

[0027] Step 12: Substitute the hybrid material vehicle B-pillar into the vehicle side impact model and import it into HyperStudy for DOE design. Create variables based on the structural parameters of the carbon fiber composite B-pillar inner panel, high-strength steel B-pillar reinforcement plate, and aluminum alloy B-pillar reinforcement plate. Use the mass, intrusion amount, and intrusion speed of the hybrid material vehicle B-pillar as performance responses. The thickness of the carbon fiber composite B-pillar inner panel adopts a discrete value method, while the thickness and length of the high-strength steel B-pillar reinforcement plate and the aluminum alloy B-pillar reinforcement plate adopt a continuous value method. The value ranges of each design variable are as follows:

[0028]

[0029] Where: x1, x2 and x3 are the thicknesses of the carbon fiber composite B-pillar inner panel, high-strength steel B-pillar reinforcement plate and aluminum alloy B-pillar reinforcement plate respectively; x4 and x5 are the lengths of the high-strength steel B-pillar reinforcement plate and aluminum alloy B-pillar reinforcement plate respectively;

[0030] The optimal Latin hypercube design was used to sample in the design variable space. A total of 30 sample points were extracted to fit the Kriging approximation model of each performance response. In order to test the accuracy of the Kriging approximation model, 10 sample points were randomly selected for accuracy verification. The coefficient of determination (R 2 ) to evaluate the accuracy of the approximate model, R 2 The closer the value is to 1, the higher the overall prediction accuracy of the approximate model. The B-pillar assembly mass, side impact chest intrusion volume, and side impact chest intrusion velocity of the hybrid vehicle are 0.9181, 0.9287, and 0.9141, respectively. The determination coefficients of other performance indicators are also greater than 0.9, meeting the accuracy requirements.

[0031] The optimization mathematical model for lightweight multi-objective optimization of hybrid material automobile B-pillar is:

[0032]

[0033] Where: m(x) is the mass of the mixed material vehicle B-pillar assembly, kg; D sh (x), D sc (x), D sa (x) and D sp (x) is the intrusion amount of the dummy's head, chest, abdomen and pelvis corresponding to the position of the composite material B-pillar in the side collision of the vehicle, mm; D sh0 、D sa0 and D sp0 D is the maximum intrusion of the dummy's head, abdomen, and pelvis at the original metal B-pillar position in a side collision of the vehicle, mm; ch (x), D cc (x), D ca (x) and D cp (x) is the intrusion amount of the dummy's head, chest, abdomen and pelvis corresponding to the position of the composite material B-pillar in the side collision of the vehicle, mm; D ch0 、D cc0 、D ca0 and D cp0 is the maximum intrusion of the dummy's head, chest, abdomen, and pelvis at the position of the original metal B-pillar in a side column collision of the vehicle, mm; v sh (x), v sc (x), v sa (x) and v sp (x) is the penetration velocity of the dummy’s head, chest, abdomen, and pelvis at the position of the composite material B-pillar in the side collision of the vehicle, m / s; v c0 、v a0 and v p0 is the maximum intrusion velocity of the dummy's chest, abdomen, and pelvis at the position of the original metal B-pillar in a side collision of the vehicle, m / s; v ch (x), v cc (x), v ca (x) and v cp (x) is the penetration velocity of the dummy’s head, chest, abdomen, and pelvis at the position of the composite material B-pillar in the side collision of the vehicle, m / s; v ch0 、v cc0 、v ca0 and v cp0 The maximum penetration velocity of the dummy's head, chest, abdomen, and pelvis at the position of the original metal B-pillar in a side column collision with the vehicle, m / s;

[0034] The NSGA-II optimization algorithm was used to obtain a multi-objective optimization Pareto solution set by setting the population size to 40, the evolutionary generations to 30, and the crossover probability to 0.9. After 80 iterative calculations, a compromise solution was selected from the Pareto frontier and its design variable values ​​were rounded up. Based on the rounded design variables, a lightweight hybrid material vehicle B-pillar model was re-established and a vehicle side impact analysis was performed to verify the accuracy of the compromise solution.

[0035] The method for optimizing the lightweight hybrid material automobile B-pillar structure, in the first step, the automobile B-pillar assembly includes a metal B-pillar outer panel, a carbon fiber composite material B-pillar inner panel, a high-strength steel B-pillar reinforcement plate and an aluminum alloy B-pillar reinforcement plate, a high-strength steel B-pillar reinforcement plate is provided at the upper portion between the metal B-pillar outer panel and the carbon fiber composite material B-pillar inner panel, and an aluminum alloy B-pillar reinforcement plate is provided at the lower portion between the metal B-pillar outer panel and the carbon fiber composite material B-pillar inner panel.

[0036] In the optimization method for the lightweight hybrid material automobile B-pillar structure, when assigning materials and properties in the first step, the materials and properties are as follows:

[0037] The metal B-pillar inner panel is made of B280 / 440DP with a thickness of 1.2mm;

[0038] The material of the metal B-pillar reinforcement plate A is B340 / 590DP, with a thickness of 2mm;

[0039] The material of the metal B-pillar reinforcement plate B is B340 / 590DP, with a thickness of 1.6mm;

[0040] The metal B-pillar reinforcement plate C is made of Docol1400 with a thickness of 1.4mm.

[0041] The material of the metal B-pillar outer panel is DOC6 and the thickness is 0.7mm.

[0042] The optimization method for the lightweight hybrid material automobile B-pillar structure, the three-point bending working condition in the second step:

[0043] Constrain the degrees of freedom of the lower end of the B-pillar assembly to 12356, and the degrees of freedom of the upper end of the B-pillar assembly to 1256; apply an equivalent force in the Y-axis direction to the middle of the B-pillar outer panel;

[0044] Axial tension conditions:

[0045] Constrain the degrees of freedom of the lower end of the B-pillar assembly to 123456, and the degrees of freedom of the upper end of the B-pillar assembly to 12456, and apply a positive Z-axis force at the centroid of the upper part of the B-pillar;

[0046] Lateral bending conditions:

[0047] Constrain the degrees of freedom of the lower end of the B-pillar assembly to 123456, and the degrees of freedom of the upper end of the B-pillar assembly to 156, and apply a positive force along the X-axis at the centroid of the upper part of the B-pillar.

[0048] In the aforementioned method for optimizing the lightweight hybrid material automobile B-pillar structure, the materials and properties of the lightweight hybrid material automobile B-pillar without the layer design in the third step are as follows:

[0049] The carbon fiber composite material in the B-pillar inner panel is epoxy resin carbon fiber composite material T300 / 5208. The initial thickness is determined by layup design, and the optimal thickness will be determined through lightweight multi-objective optimization.

[0050] The high-strength steel B-pillar reinforcement is made of Q460 steel, with an initial thickness and length of 1.4mm and 1054mm, respectively. The optimal thickness and length will be determined through lightweight multi-objective optimization.

[0051] The aluminum alloy B-pillar reinforcement plate is made of 6016 aluminum alloy, with an initial thickness and length of 1.4mm and 395mm respectively. The optimal thickness and length will be determined through lightweight multi-objective optimization.

[0052] The material of the metal B-pillar outer panel is DOC6 and has a thickness of 0.7mm.

[0053] In the optimization method of the lightweight hybrid material automobile B-pillar structure, in the fourth step, when the high-strength steel B-pillar reinforcement plate, the aluminum alloy B-pillar reinforcement plate and the carbon fiber composite material B-pillar inner plate are adhesively connected, the adhesive joint is often subjected to tension, shear force, tearing force and peeling force. Under the action of tensile or compressive loads, the basic failure forms of the adhesive joint are mainly shear failure, tensile or bending failure and peeling failure. The connection between the carbon fiber composite material B-pillar inner plate and the high-strength steel B-pillar reinforcement plate and the aluminum alloy B-pillar reinforcement plate is a surface-to-surface connection. When subjected to load, the adhesive layer mainly bears shear stress. In order to verify the feasibility of the adhesive joint, it is necessary to perform strength verification on the adhesive joint unit. By comparing the shear resistance allowable value of the adhesive joint unit with the weld joint unit, the feasibility of the adhesive joint in the structure is verified, as follows:

[0054] A. Calculate the allowable shear resistance of the welds between the original metal B-pillar inner panel and the metal B-pillar reinforcement plate A, metal B-pillar reinforcement plate B, and metal B-pillar reinforcement plate C using the following formula:

[0055] F ss =π×(D / 2) 2 ×0.577×σ s

[0056] Where: D is the diameter of the welding spot, mm; σ s is the shear strength of the parent material, MPa;

[0057] B. Calculate the allowable shear strength of the adhesively bonded carbon fiber composite B-pillar inner panel to the high-strength steel B-pillar reinforcement panel and the aluminum alloy B-pillar reinforcement panel using the following formula:

[0058] F=A×σ / λ

[0059] asas

[0060] Where: A is the adhesive area, mm 2 ; σ as is the shear strength of the adhesive, MPa; λ is a constant, usually defined as 10.

[0061] In the optimization method for the lightweight hybrid material automobile B-pillar structure, the expression for the body-in-white lightweight coefficient in the ninth step is as follows:

[0062]

[0063] Where: L is the lightweight coefficient; M is the mass of the body in white, in kg; K t is the torsional stiffness of the body in white, in N·mm / °; A is the body footprint area (average wheelbase × wheelbase), in mm 2 .

[0064] By adopting the above technical solution, the present invention has the following advantages:

[0065] The present invention effectively solves the problem of single-material B-pillars being difficult to achieve in terms of achieving a balance between structural performance, lightweighting, and cost control. The lightweight hybrid material automobile B-pillar comprises a carbon fiber composite inner panel, a high-strength steel reinforcement panel, an aluminum alloy reinforcement panel, and a steel outer panel. The optimal connection method for the hybrid material B-pillar is determined by analyzing the stress conditions of hexagonal bolts, rivets, and adhesive layers under static bending-torsion conditions and first-order bending-torsion modal vibration modes of the body-in-white (BIW), in combination with the mechanical properties and cost of the materials. A preliminary layup scheme for the carbon fiber composite inner panel is determined based on the classic B-pillar working conditions and the principle of equal stiffness. A layup scheme for the carbon fiber composite inner panel is determined based on the static and dynamic performance of the body-in-white (BIW). A finite element model of the vehicle side collision and pillar impact is established based on the C-NCAP test method. The hybrid material B-pillar is compared with the original metal B-pillar using the B-pillar intrusion volume and intrusion velocity as performance indicators. A Kriging approximation model is established using the structural parameters of the hybrid material B-pillar as design variables, and the mass, intrusion volume, and intrusion velocity of the hybrid material B-pillar as indicators. The lightweight multi-objective optimization of the hybrid material B-pillar is performed using the NSGA-II algorithm. The present invention has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a flowchart of the present invention;

[0067] Figure 2This is an assembly model of a metal B-pillar in an embodiment of the present invention;

[0068] Figure 3 is a finite element model of the three-point bending condition of the metal B-pillar in an embodiment of the present invention;

[0069] Figure 4 is a finite element model of the lateral bending condition of the metal B-pillar in an embodiment of the present invention;

[0070] Figure 5 This is the finite element model of the metal B-pillar under axial tension conditions in an embodiment of the present invention;

[0071] Figure 6 This is a hybrid material B-pillar assembly model in an embodiment of the present invention;

[0072] Figure 7 is a schematic diagram of super layer definition in an embodiment of the present invention;

[0073] Figure 8 Schematic diagram of optimized thickness distribution of super layers in an embodiment of the present invention;

[0074] Figure 9 Schematic diagram of a super layer parsing ply block in an embodiment of the present invention;

[0075] Figure 10 is the free size optimization result of the preliminary solution in the embodiment of the present invention;

[0076] Figure 11 This is the free size optimization result of the 0° ply in the initial solution in the embodiment of the present invention;

[0077] Figure 12 This is the result of the 90° ply free size optimization of the initial solution in the embodiment of the present invention;

[0078] Figure 13 This is the free size optimization result of the 45° ply in the initial solution in the embodiment of the present invention;

[0079] Figure 14 This is the free size optimization result of the -45° ply in the preliminary scheme in the embodiment of the present invention;

[0080] Figure 15 2. Schematic diagram of regularized processing of ply blocks in an embodiment of the present invention;

[0081] Figure 16 is the size optimization result of the initial solution in the embodiment of the present invention;

[0082] Figure 17 is the optimization result of the ply sequence of the initial scheme in the embodiment of the present invention;

[0083] Figure 182 is a schematic diagram of a static bending working condition of a body-in-white according to an embodiment of the present invention;

[0084] Figure 19 2 is a schematic diagram of a static torsion working condition of a body-in-white according to an embodiment of the present invention;

[0085] Figure 20 is the size optimization result of the final solution in the embodiment of the present invention;

[0086] Figure 21 is the ply layup sequence optimization result of the final solution in the embodiment of the present invention;

[0087] Figure 22 Schematic diagram of the drilling positions on the aluminum alloy reinforcement plate in an embodiment of the present invention;

[0088] Figure 23 This is a schematic diagram of a rivet connection in an embodiment of the present invention;

[0089] Figure 24 Schematic diagram of hexagonal bolt connection in an embodiment of the present invention;

[0090] Figure 25 Schematic diagram of adhesive connection in an embodiment of the present invention;

[0091] Figure 26 This is a schematic diagram of a riveting connection in an embodiment of the present invention;

[0092] Figure 27 2. This is a schematic diagram of a C-NCAP vehicle side collision in an embodiment of the present invention;

[0093] Figure 28 2. This is a schematic diagram of a C-NCAP vehicle side column impact test in an embodiment of the present invention;

[0094] Figure 29 The positions of the dummy's head, chest, abdomen, and pelvis corresponding to the B-pillar in the embodiment of the present invention;

[0095] Figure 30 is the Pareto solution set in the embodiment of the present invention;

[0096] In the figure: 1. Metal B-pillar inner panel; 2. Metal B-pillar reinforcement plate A; 3. Metal B-pillar reinforcement plate B; 4. Metal B-pillar reinforcement plate C; 5. Metal B-pillar outer panel; 6. Carbon fiber composite material B-pillar inner panel; 7. High-strength steel B-pillar reinforcement plate; 8. Aluminum alloy B-pillar reinforcement plate; 9. Hole; 10. Countersunk rivet; 11. Hexagonal head bolt; 12. Nut; 13. Glue layer; 14. Test vehicle; 15. Mobile trolley; 16. Rigid fixed cylinder; 17. Compromise solution. DETAILED DESCRIPTION

[0097] The present invention can be explained in more detail by the following examples, but the present invention is not limited to the following examples;

[0098] In the description of the present invention, it should be understood that the terms "center", "lateral", "length", "width", "height", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "side", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0099] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0100] Combined with attachment Figures 1 to 30 The method for optimizing the lightweight hybrid material automobile B-pillar structure specifically comprises the following steps:

[0101] The first step is to import the geometric model of the car B-pillar assembly into Hypermesh software, use Automesh to divide it into meshes and assign materials and properties. The finite element model is as follows: Figure 2 As shown, when assigning materials and properties, the materials and properties are as follows:

[0102] The material of the metal B-pillar inner panel 1 is B280 / 440DP, with a thickness of 1.2mm;

[0103] The metal B-pillar reinforcement plate A2 is made of B340 / 590DP and has a thickness of 2mm.

[0104] The metal B-pillar reinforcement plate B3 is made of B340 / 590DP and has a thickness of 1.6mm.

[0105] The material of the metal B-pillar reinforcement plate C4 is Docol1400, with a thickness of 1.4mm;

[0106] The material of the metal B-pillar outer panel 5 is DOC6 and has a thickness of 0.7 mm.

[0107] In the second step, the finite element model of the automobile B-pillar assembly was imported into the OptiStruct software to establish three-point bending, axial tension and lateral bending working conditions. The welding method was simulated using ACM units. In the working conditions, degrees of freedom 1-3 are translations in the x, y, and z directions, respectively, and degrees of freedom 4-6 are rotations in the x, y, and z directions, respectively. In the specific implementation, the three-point bending working condition:

[0108] Constrain the degrees of freedom of the lower end of the B-pillar assembly to 12356, and the degrees of freedom of the upper end of the B-pillar assembly to 1256; apply an equivalent force in the Y-axis direction to the middle of the B-pillar outer panel, such as Figure 3 As shown;

[0109] Axial tension conditions:

[0110] Constrain the degrees of freedom of the lower end of the B-pillar assembly to 123456, and the degrees of freedom of the upper end of the B-pillar assembly to 12456, and apply a positive Z-axis force at the centroid of the upper part of the B-pillar, such as Figure 4 As shown;

[0111] Lateral bending conditions:

[0112] Constrain the degrees of freedom of the lower end of the B-pillar assembly to 123456, and the degrees of freedom of the upper end of the B-pillar assembly to 156. Apply a positive force along the X axis at the centroid of the upper part of the B-pillar, such as Figure 5 shown.

[0113] The third step is to improve the structure, replace materials and change the connection mode of the automobile B-pillar assembly before designing the carbon fiber layer. The lightweight hybrid material automobile B-pillar model is as follows: Figure 6 As shown, because the lightweight hybrid material automobile B-pillar assembly needs to meet the structural characteristics of high stiffness and deformation resistance at the upper part and low stiffness and strong energy absorption at the lower part, the metal B-pillar reinforcement plate A2 and the metal B-pillar reinforcement plate B3 that enhance the stiffness of the upper area of ​​the automobile B-pillar are deleted, and the stiffness lost by deleting the metal B-pillar reinforcement plate A2 and the metal B-pillar reinforcement plate B3 is compensated by designing a carbon fiber ply; in the side impact test, the highest height between the energy absorbing block at the front end of the impacted vehicle and the lowest point of the wheel is 800-900 mm, so the metal B-pillar reinforcement plate C4 is divided into a high-strength steel B-pillar reinforcement plate 7 and an aluminum alloy B-pillar reinforcement plate 8 with the lowest point of the wheel at 800 mm as the dividing line, the length of the high-strength steel B-pillar reinforcement plate 7 and the aluminum alloy B-pillar reinforcement plate 8 are each increased by 100 mm, and the overlapping area with a length of 200 mm is used as the connection area;

[0114] The high-strength steel B-pillar reinforcement plate 7 is made of Q460 steel, and the aluminum alloy B-pillar reinforcement plate 8 is made of 6016 aluminum alloy. The metal B-pillar inner panel 1 is replaced with a carbon fiber composite B-pillar inner panel 6. The connection method of the automobile B-pillar assembly is to use the "Adhesives+RBE3" unit to connect the carbon fiber composite B-pillar inner panel 6 with the high-strength steel B-pillar reinforcement plate 7 and the aluminum alloy B-pillar reinforcement plate 8. The connection method of the aluminum alloy B-pillar reinforcement plate 8 with the high-strength steel B-pillar reinforcement plate 7 and the metal B-pillar outer panel 5 is tentatively connected using the "RBE2" unit.

[0115] When implementing it specifically, Figure 6 As shown, the hybrid material automobile B-pillar assembly includes a metal B-pillar outer panel 5, a carbon fiber composite material B-pillar inner panel 6, a high-strength steel B-pillar reinforcement plate 7, and an aluminum alloy B-pillar reinforcement plate 8. The high-strength steel B-pillar reinforcement plate 7 is provided at the upper portion between the metal B-pillar outer panel 5 and the carbon fiber composite material B-pillar inner panel 6, and the aluminum alloy B-pillar reinforcement plate 8 is provided at the lower portion between the metal B-pillar outer panel 5 and the carbon fiber composite material B-pillar inner panel 6. The materials and properties of the lightweight hybrid material automobile B-pillar without a layup design are as follows:

[0116] The carbon fiber composite material in the B-pillar inner panel 6 is epoxy resin carbon fiber composite material T300 / 5208. The initial thickness is determined by layup design, and the optimal thickness will be determined through lightweight multi-objective optimization.

[0117] The high-strength steel B-pillar reinforcement plate 7 is made of Q460 steel, with an initial thickness and length of 1.4mm and 1054mm, respectively. The optimal thickness and length will be determined through lightweight multi-objective optimization.

[0118] The aluminum alloy B-pillar reinforcement plate 8 is made of 6016 aluminum alloy, with an initial thickness and length of 1.4mm and 395mm respectively. The optimal thickness and length will be determined through lightweight multi-objective optimization.

[0119] The material of the metal B-pillar outer panel 5 is DOC6, and the thickness is 0.7 mm.

[0120] Step 4. Import the hybrid material B-pillar model into the Optistruct software. In the connectors interface, select the area panel, select the adhesive area in the location field, select the carbon fiber composite B-pillar inner panel 6, the high-strength steel B-pillar reinforcement plate 7, and the aluminum alloy B-pillar reinforcement plate 8 in the connect what field, set the type to adhesives, and then click create to generate the "Adhesives+RBE3" element that simulates the adhesive connection.

[0121] During the layup design phase, the connection between the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8, and the metal B-pillar outer panel 5 is simulated using the RBE2 element. During the simulation, select rigid in the 1D interface, select the master node in the independent field, select the slave node in the dependent field, and click create to generate the RBE2 element that connects the master and slave nodes.

[0122] During specific implementation, when the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8 and the carbon fiber composite material B-pillar inner plate 6 are adhesively connected, the adhesive joints are often subjected to tension, shear force, tearing force and peeling force. Under the action of tensile or compressive loads, the basic failure forms of the adhesive joints are mainly shear failure, tensile or bending failure and peeling failure. The connection between the carbon fiber composite material B-pillar inner plate 6 and the high-strength steel B-pillar reinforcement plate 7 and the aluminum alloy B-pillar reinforcement plate 8 is a surface-to-surface connection. When subjected to load, the adhesive layer mainly bears shear stress. In order to verify the feasibility of the adhesive joint, it is necessary to perform strength verification on the adhesive joint unit. By comparing the shear resistance allowable values ​​of the adhesive joint unit and the weld joint unit, the feasibility of the adhesive joint in the structure is verified, as follows:

[0123] A. Calculate the allowable shear resistance of the welds between the original metal B-pillar inner panel 1 and the metal B-pillar reinforcement panels A2, B3, and C4 using the following formula:

[0124] F ss =π×(D / 2) 2 ×0.577×σ s

[0125] Where: D is the diameter of the welding spot, mm; σ s is the shear strength of the parent material, MPa;

[0126] B. Calculate the allowable shear resistance of the adhesively bonded carbon fiber composite B-pillar inner panel 6, high-strength steel B-pillar reinforcement panel 7, and aluminum alloy B-pillar reinforcement panel 8 using the following formula:

[0127] F=A×σ / λ

[0128] asas

[0129] Where: A is the adhesive area, mm 2 ; σ as is the shear strength of the adhesive, MPa; λ is a constant, usually defined as 10.

[0130] Step 5: In the OptiStruct software, a multi-level optimization method, including free size optimization, size optimization, and ply sequence optimization, was used to determine the ply block shape, number of plies, and ply sequence, and to determine the ply layup scheme for the carbon fiber composite B-pillar inner panel 6. To simplify the initial variables in the conceptual design phase, the thickness of each ply angle was primarily presented as a set. That is, plies with the same ply angle were considered a set, called a super layer, e.g. Figure 7 As shown in the figure. For the carbon fiber composite inner panel modeled with shell elements, the thickness of the super layer is used as the design variable in the free size stage, and the continuous variable optimization design of each super layer is performed. That is, by changing the thickness of each layer and the fiber direction of each unit, the total thickness of the laminate changes continuously throughout the structure. The process is shown in the figure. Figure 8 .

[0131] Because the superlayer is composed of single-layer panels laid up with the same lay angle, each superlayer needs to be parsed into differently shaped ply blocks to determine the appropriate block shape for each individual panel. Since the block shape and placement of each individual panel may not be identical, the overall thickness of the superlayer is also uneven. This allows for a constant stiffness and variable thickness design of the carbon fiber composite B-pillar inner panel, thereby improving material utilization. Figure 9 The optimal thickness of each super layer obtained by free size optimization and the different shapes of ply blocks resolved by each super layer are shown.

[0132] Furthermore, the carbon fiber composite inner panel of the present invention is stacked with four plies at 0°, 45°, -45°, and 90°. These four ply angles are easy to implement, simplifying the production process and meeting design requirements. Since free size optimization mainly involves thinning the material, the super layer created must have sufficient design margin. The mathematical model for free size optimization of the carbon fiber composite B-pillar inner panel is:

[0133]

[0134] Where: x f1 、x f2 、x f3 and x f4 are the thicknesses of the four super layers at 0, 45°, -45°, and 90° in the inner panel of the hybrid material B-pillar, mm; m(x f ) is the mass of the mixed material B-pillar, kg; D a (x f ), D l (x f ) and D t (x f ) are the maximum displacements of the hybrid material B-pillar assembly under axial tension, lateral bending and three-point bending conditions, mm; Da0 、D l0 and D t0 is the maximum displacement of the original metal B-pillar assembly under axial tension, lateral bending and three-point bending conditions, mm; CT f To serve as a manufacturing constraint in the free size optimization stage, the proportion of plies at each angle is no less than 10% and no more than 60%, and the thickness and shape of the ±45° super layers remain consistent.

[0135] The free size optimization results are as follows Figure 10 As shown, the shape and thickness distribution of each layer are as follows Figures 11-14 Because ±45° ply is laid in a symmetrical manner, Figures 13-14 The optimization results are consistent with .

[0136] Step 6. After free size optimization, the thickness of each super layer and its ply cutting shape are obtained. Each super layer has four groups of different ply blocks. These four ply blocks stacked together can represent the optimization result of a super layer. However, since the optimized ply blocks are too ideal, the shapes of the ply blocks are often very irregular, which is not conducive to industrial cutting. Therefore, it is necessary to regularize the ply blocks after free optimization, that is, trim the irresponsible holes of the ply blocks into rectangular holes that are convenient for cutting to facilitate industrial ply cutting. When performing regular processing, in order to prevent the performance of the processed laminate from degrading, the boundaries of the rectangular holes cannot exceed the boundaries of the irregular holes; in order to prevent the lightweight effect from being reduced, the area of ​​the rectangular holes should be as large as possible; Figure 15 The difference before and after the regularization of the four ply blocks in the super layer is shown.

[0137] In addition, the thickness of each ply obtained by free size optimization is different, which requires a high cost in actual production. In order to make the result more economical, a manufacturing constraint of 0.3mm single layer thickness is introduced to obtain single plies of the same thickness. After introducing this manufacturing constraint and performing size optimization, the actual number of plies of each shape can be obtained. The actual number of plies is the thickness dimension T obtained after size optimization. i Divide by the monolayer thickness 0.3.

[0138] Furthermore, the mathematical model for optimizing the size of the carbon fiber composite B-pillar inner panel is:

[0139]

[0140] Where: x s1 ,x s2 ,,x fn are the thicknesses of the four super layers at 0, 45°, -45°, and 90° in the inner panel of the hybrid material B-pillar, mm; m(x s) is the mass of the mixed material B-pillar, kg; D a (x s ), D l (x s ) and D t (x s ) are the maximum displacements of the hybrid material B-pillar assembly under axial tension, lateral bending and three-point bending conditions, mm; D a0 、D l0 and D t0 is the maximum displacement of the original metal B-pillar assembly under axial tension, lateral bending and three-point bending conditions, mm; CT s As a manufacturing constraint in the size optimization stage, the thickness of a single layer is 0.3 mm.

[0141] The results of size optimization are as follows Figure 16 As shown in FIG, the number of plies of the carbon fiber composite material B-pillar inner panel is 20, with 5 plies each at 0°, 90°, and ±45°.

[0142] Step 7: The optimized solution for the carbon fiber composite B-pillar inner panel 6 obtained through continuous variable thickness optimization design meets the stiffness performance requirements. However, in engineering manufacturing, the carbon fiber composite B-pillar inner panel 6 must also meet certain process constraints, constraints limiting the adverse internal forces caused by the layup sequence, and continuity constraints limiting fiber disconnection. In addition, a reasonable layup sequence can further improve the impact resistance of the hybrid material vehicle B-pillar.

[0143] Furthermore, the mathematical model for optimizing the ply layup sequence of the carbon fiber composite material B-pillar inner panel 6 is:

[0144]

[0145] Where: x r1 ,x r2 ,,x rn The different arrangement orders are design variables, m is the actual number of layers obtained after free size optimization; S(x r ) is the stiffness of the hybrid material B-pillar, N / mm; CT r As a manufacturing constraint in the ply sequence optimization stage, the outermost layer is laid as a 45° ply, no more than two layers can appear consecutively in the same direction, and ±45° plies appear in pairs.

[0146] The optimized ply sequence is shown in Figure 17, where the first digit "1" represents a 0° layup, "2" represents a 90° layup, "3" represents a 45° layup, and "4" represents a -45° layup. After optimizing the layup sequence, the ply angles for layers 1 to 20 are: 45°, -45°, 90°, 90°, 45°, -45°, 90°, 90°, 0°, 90°, 0°, 45°, -45°, 45°, -45°, 0°, 45°, -45°, 0°, 0°. The optimal layup sequence is [45 / -45 / 90 / 90 / 45 / -45 / 90 / 90 / 0 / 90 / 0 / 45 / -45 / 45 / -45 / 0 / 45 / -45 / 0 / 0].

[0147] Step 8: Import the BIW finite element models of the original metal and hybrid B-pillars into OptiStruct software. Build a BIW static bending and torsional finite element model based on the test conditions. When performing BIW free modal analysis, import the BIW finite element model into Nastran software for setup and solution.

[0148] Static bending conditions of body in white:

[0149] Constrain the front shock absorber support mounting hole freedom 123 and the rear subframe rear connection hole freedom 123, and apply a negative Z-axis force at point R of the seat, as shown in the schematic diagram. Figure 18 shown.

[0150] Static torsion condition of body in white:

[0151] Constrain the degrees of freedom 123456 at the rear subframe connection hole, and apply a pair of equal and opposite Z-axis forces at the front shock absorber support mounting hole, as shown in the schematic diagram. Figure 19 shown.

[0152] Free mode settings:

[0153] The Lanczos method is used to extract the natural frequency of the body in white. The first-order mode is set to start from 1 Hz, and the first ten elastic modes are extracted.

[0154] Step 9: Because the initially determined carbon fiber composite B-pillar inner panel 6 only considers the performance requirements of the automobile B-pillar assembly, but does not consider the performance requirements of the entire vehicle, the thickness of the carbon fiber composite super layer does not achieve the best match with other body-in-white components, and may even cause the static and dynamic performance of the body-in-white to deteriorate. Therefore, it is necessary to substitute the initially determined carbon fiber composite B-pillar inner panel 6 into the body-in-white and perform static bending and torsional stiffness analysis and free modal analysis;

[0155] Based on the static and dynamic performance of the body-in-white (BIW), the size and layup sequence of the carbon fiber composite B-pillar inner panel 6 were further optimized. This layup design does not degrade the static and dynamic performance of the BIW and ensures the practical use value of the hybrid material B-pillar. Since the BIW lightweight coefficient comprehensively considers vehicle weight, projected area, and torsional stiffness performance indicators, it can better integrate its performance and lightweight design. Therefore, with the BIW lightweight coefficient as the optimization target, the size optimization method and layup sequence of the carbon fiber composite inner panel were carried out.

[0156] Furthermore, the expression of the white body lightweight coefficient is as follows:

[0157]

[0158] Where: L is the lightweight coefficient; M is the mass of the body in white, in kg; K t is the torsional stiffness of the body in white, in N·mm / °; A is the body footprint area (average wheelbase × wheelbase), in mm 2 ;

[0159] The mathematical model for optimizing the size of the carbon fiber composite material B-pillar inner panel 6 based on the static and dynamic performance of the body-in-white is:

[0160]

[0161] Where: x b1 ,x b2 ,,x bn are the thickness of each ply block; n is the number of ply blocks; L(x b ) is the lightweight coefficient of the body-in-white with a mixed material B-pillar; BS(x b ) is the static bending stiffness of the body-in-white with the hybrid material B-pillar, N / mm; BS0 is the static bending stiffness of the body-in-white with the original metal B-pillar, N / mm; BF(x b ) and TF(x b ) are the first-order bending mode and first-order torsional mode of the body-in-white of the hybrid material B-pillar, Hz; BF0 and TF0 are the first-order bending mode and first-order torsional mode of the body-in-white of the original metal B-pillar, Hz; CT b As a manufacturing constraint in the size optimization stage, the thickness of a single layer is 0.3 mm;

[0162] The results of size optimization are as follows Figure 20 As shown in the figure, the carbon fiber composite material B-pillar inner panel has 17 layers, of which 5 are 0° layers, and 4 are 90° and ±45° layers.

[0163] The mathematical model for optimizing the layup sequence of the carbon fiber composite B-pillar inner panel based on the static and dynamic performance of the body-in-white is as follows:

[0164]

[0165] Where: x o1 ,x o2 ,,x om The different arrangement orders are design variables, m is the actual number of layers obtained after free size optimization; L(x o ) is the lightweight coefficient of the body-in-white with a mixed material B-pillar; CT o As a manufacturing constraint in the ply sequence optimization stage, the outermost layer is laid as a 45° ply, no more than two layers can appear consecutively in the same direction, and ±45° plies appear in pairs.

[0166] Further, the optimized ply sequence is shown in Figure 21 The laying order is [45 / -45 / 45 / -45 / 0 / 90 / 0 / 45 / -45 / 90 / 0 / 90 / 45 / -45 / 0 / 90 / 0].

[0167] Step 10: Considering the composite layup process and manufacturing process, the composite layup design software FiberSIM was used to create a layup model for the carbon fiber composite B-pillar inner panel 6. The modeling method was to stack the individual plies to form a laminate structure. The layup information of each ply was then imported into the finite element software to complete the modeling of the lightweight hybrid vehicle B-pillar.

[0168] The lightweight hybrid material automobile B-pillar connected by countersunk rivets 10, hexagonal head bolts 11, adhesive bonding and adhesive riveting was respectively substituted into the body-in-white model, and finite element analysis of the body-in-white static bending-torsion condition and free mode was carried out. The OptiStruct solver was used to solve the static bending-torsion condition and the overall first-order bending-torsion mode vibration mode of the body-in-white, and the stress conditions of the countersunk rivet 10, hexagonal head bolt 11 and adhesive layer 13 were obtained. The optimal connection method of the lightweight hybrid material automobile B-pillar was determined by comprehensively considering the mechanical properties and cost of the selected materials.

[0169] Furthermore, when connecting with rivets and bolts, it is necessary to drill holes first. The drilling position diagram of the aluminum alloy B-pillar reinforcement plate 8 is shown in FIG. Figure 22 , schematic diagram of rivet, bolt, adhesive and riveting connection is shown in Figures 23-26In order to determine the optimal connection method for the lightweight hybrid material automobile B-pillar, it is necessary to establish 3D models of the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8, the carbon fiber composite material B-pillar inner panel 6, the hexagonal head bolt 11 and the countersunk rivet 10. The 3D models of the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8 and the carbon fiber composite material B-pillar inner panel 6 can be generated according to their shape and thickness. The 3D models of the countersunk rivet 10 and the hexagonal head bolt 11 need to match the hole 9. When meshing, the countersunk rivet 10 and the hexagonal head bolt 11 are the main targets of analysis in this stage and are divided into hexahedral meshes. In order to facilitate the use of mesh deformation technology to scale the drilled holes of the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8 and the metal B-pillar outer panel 5, the drilled holes are meshed with hexahedral elements, and the rest of the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8 and the metal B-pillar outer panel 5 are divided into tetrahedral meshes.

[0170] In OptiStruct, open the Connector panel and find the created Adhesive connection. Set its HexaThickness to const thickness and fill in the Const thickness box below with values ​​for different adhesive layer thicknesses to simulate the connection effect with different adhesive layer thicknesses.

[0171] When analyzing the countersunk rivet 10 and the hexagonal head bolt 11, it is necessary to set the contact between the countersunk rivet 10 and the hexagonal head bolt 11 and the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8, and the metal B-pillar outer plate 5, as well as the static and dynamic friction coefficients of these contacts. When setting the contact, it is necessary to first set the contact surfaces between the countersunk rivet 10, the hexagonal head bolt 11, the hole 9, the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8 and the metal B-pillar outer plate 5 as contact surfaces, and then set the master and slave contact surfaces. In the contact between the countersunk rivet 10, the hexagonal head bolt 11 and the hole 9, the side surfaces of the countersunk rivet 10 and the hexagonal head bolt 11 are the master contact surfaces, and the surface of the hole 9 is the slave contact surface; in the contact between the countersunk rivet 10 and the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement In the contact between the high-strength steel B-pillar reinforcement plate 8 and the metal B-pillar outer panel 5, the surfaces of the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8 and the metal B-pillar outer panel 5 are the main contact surfaces, and the contact surfaces of the heads of the countersunk rivets 10 and the two are the secondary contact surfaces; in the contact between the hexagonal head bolts 11 and the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8 and the metal B-pillar outer panel 5, the surfaces of the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8 and the metal B-pillar outer panel 5 are the main contact surfaces, and the contact surfaces of the heads of the hexagonal head bolts 11 and the two are the secondary contact surfaces; in the contact between the high-strength steel B-pillar reinforcement plate 7, the aluminum alloy B-pillar reinforcement plate 8 and the metal B-pillar outer panel 5, the surface of the metal B-pillar outer panel 5 is the main contact surface, and the surfaces of the high-strength steel B-pillar reinforcement plate 7 and the aluminum alloy B-pillar reinforcement plate 8 are the secondary contact surfaces;

[0172] Furthermore, the materials selected for the countersunk rivet 10 are AZ91D, 5056, 2A10, and 6061, numbered R1, R2, R3, and R4, respectively; the materials selected for the hexagonal bolt 11 are 45#, SUS304, SUS316, and 6061, numbered B1, B2, B3, and B4, respectively; and the materials selected for the adhesive layer 13 are epoxy resin glue A, acrylic resin glue B, acrylic resin glue C, and epoxy resin glue D, numbered A1, A2, A3, and A4, respectively. Therefore, the design variables for the countersunk rivet 10, hexagonal bolt 11, and adhesive layer 13 are as follows:

[0173]

[0174] Where: M r 、M b and M a Respectively represent the materials of the countersunk rivet 10, the hexagonal bolt 11, and the adhesive layer 13; D b and D r Diameters of countersunk rivets 10 and hexagonal bolts 11, mm; T a Represents the thickness of the adhesive layer 13.

[0175] The mathematical model for optimizing the B-pillar connection of lightweight hybrid vehicles is:

[0176]

[0177] Where: P(x L ) is the sum of the prices of the countersunk rivet 10 or hexagonal bolt 11 and the adhesive layer 13 in the selected connection scheme, σ r1 , σ r2 , σ r3 and σ r4 Respectively represent the maximum stress of the countersunk rivet 10 in the static bending, static torsion, first-order bending mode and first-order torsion mode of the body in white, MPa; σ b1 , σ b2 , σ b3 and σ b4 Respectively represent the maximum stress of the hexagonal bolt 11 in the static bending, static torsion, first-order bending mode and first-order torsion mode of the body in white, MPa; σ a1 , σ a2 , σ a3 and σ a4 Respectively represent the maximum stress of the adhesive layer 13 in the static bending, static torsion, first-order bending mode and first-order torsion mode of the body in white, MPa; σ r0 , σ b0 and σ a0They respectively represent the yield strength of the materials used for the countersunk rivet 10, the hexagonal bolt 11, and the adhesive layer 13. The optimization results show that the optimal connection method for the lightweight hybrid material automobile B-pillar of the present invention is riveting.

[0178] Step 11: C-NCAP side impact test method Figure 27 As shown, when conducting a side impact test of a deformable mobile barrier according to the C-NCAP side standard, a deformable honeycomb aluminum structure is placed at the front end of the mobile trolley 15. During the test, the mobile barrier impacts the left side of the test vehicle 14, i.e., the driver's side. The impact direction of the mobile trolley 15 is perpendicular to the test vehicle 14. The centerline of the mobile barrier is located 250 mm behind the R point of the test vehicle 14. The collision speed is (The speed must not be less than 50 km / h). The distance between the longitudinal median vertical plane of the mobile trolley 15 and the transverse vertical plane of the vehicle 250 mm rearward through the driver's seat R point must be within plus or minus 25 mm. A WorldSID50th and SID-IIs dummies are placed on the driver's seat and the left side of the rear seat, respectively, to simulate the injury conditions of the driver and rear seat passengers.

[0179] C-NCAP side column impact test method is as follows Figure 28 As shown, according to the C-NCAP side pole impact test method, the diameter of the rigid fixed cylinder 16 is 254 mm and is located on the left side of the test vehicle. The collision speed of the test vehicle 14 hitting the barrier is The collision velocity direction is 75±3° with the X-axis of the vehicle coordinate system. A WorldSID50th dummy is placed in the front driver's seat of test vehicle 14 to simulate the driver's injury. The lower end of the fixed rigid cylinder 16 cannot be higher than 102mm above the lowest point of the wheel on the impact side of the test vehicle, and the upper end must exceed the highest point of the test vehicle. The line connecting the center of the cylinder and the center of the dummy's head is consistent with the velocity direction.

[0180] According to the C-NCAP side impact test and side pole impact test methods, a full vehicle side impact model and a side pole impact model are established, and stiffness of 1×10 - 10 N / mm spring unit, the position of the dummy's head, chest, abdomen and pelvis corresponding to the B-pillar is shown in Figure 29 , the above finite element model is exported in k file format and solved using LS-DYNA solver. The intrusion amount and intrusion speed of the dummy's head, chest, abdomen and pelvis are obtained according to the deformation of the spring unit;

[0181] Step 12: Substitute the hybrid material car B-pillar into the whole vehicle side impact model and import it into HyperStudy for DOE design. Create variables based on the structural parameters of the carbon fiber composite B-pillar inner panel 6, the high-strength steel B-pillar reinforcement panel 7, and the aluminum alloy B-pillar reinforcement panel 8. Use the mass, intrusion amount, and intrusion speed of the hybrid material car B-pillar as performance responses. The thickness of the carbon fiber composite B-pillar inner panel 6 is discretely valued, while the thickness and length of the high-strength steel B-pillar reinforcement panel 7 and the aluminum alloy B-pillar reinforcement panel 8 are continuously valued. The value ranges of each design variable are as follows:

[0182]

[0183] Where: x1, x2 and x3 are the thicknesses of the carbon fiber composite B-pillar inner panel 6, the high-strength steel B-pillar reinforcement panel 7 and the aluminum alloy B-pillar reinforcement panel 8, respectively; x4 and x5 are the lengths of the high-strength steel B-pillar reinforcement panel 7 and the aluminum alloy B-pillar reinforcement panel 8, respectively;

[0184] The optimal Latin hypercube design was used to sample in the design variable space. A total of 30 sample points were extracted to fit the Kriging approximation model of each performance response. In order to test the accuracy of the Kriging approximation model, 10 sample points were randomly selected for accuracy verification. The coefficient of determination (R 2 ) to evaluate the accuracy of the approximate model, R 2 The closer the value is to 1, the higher the overall prediction accuracy of the approximate model. The B-pillar assembly mass, side impact chest intrusion volume, and side impact chest intrusion velocity of the hybrid vehicle are 0.9181, 0.9287, and 0.9141, respectively. The determination coefficients of other performance indicators are also greater than 0.9, meeting the accuracy requirements.

[0185] The optimization mathematical model for lightweight multi-objective optimization of hybrid material automobile B-pillar is:

[0186]

[0187] Where: m(x) is the mass of the mixed material vehicle B-pillar assembly, kg; D sh (x), D sc (x), D sa (x) and D sp (x) is the intrusion amount of the dummy's head, chest, abdomen and pelvis corresponding to the position of the composite material B-pillar in the side collision of the vehicle, mm; D sh0 、D sa0 and D sp0 D is the maximum intrusion of the dummy's head, abdomen, and pelvis at the original metal B-pillar position in a side collision of the vehicle, mm; ch (x), D cc (x), D ca (x) and Dcp (x) is the intrusion amount of the dummy's head, chest, abdomen and pelvis corresponding to the position of the composite material B-pillar in the side collision of the vehicle, mm; D ch0 、D cc0 、D ca0 and D cp0 is the maximum intrusion of the dummy's head, chest, abdomen, and pelvis at the position of the original metal B-pillar in a side column collision of the vehicle, mm; v sh (x), v sc (x), v sa (x) and v sp (x) is the penetration velocity of the dummy’s head, chest, abdomen, and pelvis at the position of the composite material B-pillar in the side collision of the vehicle, m / s; v c0 、v a0 and v p0 is the maximum intrusion velocity of the dummy's chest, abdomen, and pelvis at the position of the original metal B-pillar in a side collision of the vehicle, m / s; v ch (x), v cc (x), v ca (x) and v cp (x) is the penetration velocity of the dummy’s head, chest, abdomen, and pelvis at the position of the composite material B-pillar in the side collision of the vehicle, m / s; v ch0 、v cc0 、v ca0 and v cp0 The maximum penetration velocity of the dummy's head, chest, abdomen, and pelvis at the position of the original metal B-pillar in a side column collision with the vehicle, m / s;

[0188] The NSGA-II optimization algorithm is set to have a population size of 40, an evolutionary generation of 30, and a crossover probability of 0.9. After 80 iterations, the multi-objective optimization Pareto solution set is obtained (e.g. Figure 30 A compromise solution 17 was selected from the Pareto frontier and its design variable values ​​were rounded up. Based on the rounded design variables, a lightweight hybrid material vehicle B-pillar model was re-established and a full-vehicle side impact analysis was performed to verify the accuracy of compromise solution 17.

[0189] Furthermore, the original metal B-pillar had a mass of 9.831 kg, a side impact chest intrusion of 92.57 mm, and a side impact chest intrusion velocity of 5.21 m / s. After lightweight multi-objective optimization, the hybrid B-pillar had a mass of 7.087 kg, a 27.91% reduction; the maximum side impact chest intrusion was 89.41 mm, a 3.41% reduction; and the maximum side impact chest intrusion velocity was 4.97 m / s, a 4.61% reduction. Furthermore, other performance indicators also improved. The lightweight hybrid automotive B-pillar of this invention not only improves the overall vehicle's crashworthiness and safety, but also significantly reduces weight.

[0190] The present invention effectively solves the problem of achieving a balance between structural performance, lightweighting, and cost control when using a single-material B-pillar. The lightweight hybrid material automobile B-pillar is composed of a carbon fiber composite inner panel, a high-strength steel reinforcement panel, an aluminum alloy reinforcement panel, and a steel outer panel. The optimal connection method for the hybrid material B-pillar is determined by analyzing the stress conditions of bolts, rivets, and adhesive layers under the static bending and torsional working conditions and the first-order bending and torsional modal vibration mode of the body-in-white, combined with the mechanical properties and cost of the materials. The layup scheme of the carbon fiber composite inner panel is initially determined based on the classic working conditions of the B-pillar and the principle of equal stiffness; the layup scheme of the carbon fiber composite inner panel is determined based on the static and dynamic performance of the body-in-white; a finite element model of the vehicle side collision and pillar collision is established according to the C-NCAP test method, and the hybrid material B-pillar is compared with the original metal B-pillar using the B-pillar intrusion volume and intrusion speed as performance indicators; a Kriging approximation model is established using the structural parameters of the hybrid material B-pillar as design variables, and the mass, intrusion volume, and intrusion speed of the hybrid material B-pillar as indicators, and the NSGA-II algorithm is used to perform lightweight multi-objective optimization of the hybrid material B-pillar. The mass of the hybrid material B-pillar after lightweight multi-objective optimization is 7.087 kg, a reduction of 27.91%. The maximum side impact chest intrusion amount is reduced by 3.41%, and the maximum side impact chest intrusion speed is reduced by 4.61%.

[0191] Compared with the prior art, the advantages of the present invention are as follows:

[0192] 1. The lightweight hybrid material automobile B-pillar of the present invention can simultaneously meet the requirements of structural performance, lightweighting and cost control. At this stage, the design of the B-pillar is mainly carried out by designing a variable thickness B-pillar and designing carbon fiber plies for the reinforcement plate. Although this achieves a balance between lightweight effect and structural performance, it does not take into account cost issues and fully tap the potential for lightweighting. Compared with the variable thickness B-pillar, the lightweight hybrid material automobile B-pillar of the present invention uses carbon fiber composite materials and aluminum alloys, so the lightweighting effect is more significant; compared with the B-pillar of the steel / CFRP composite structure, the hybrid material B-pillar of the present invention uses aluminum alloy and high-strength steel to improve stiffness and energy absorption capacity, thereby reducing the use of carbon fiber composite materials and reducing costs.

[0193] 2. This invention uses finite element analysis to determine the optimal B-pillar connection method for lightweight hybrid vehicles through static bending-torsional stiffness and free modal analysis of the body-in-white. The proposed design concept can be applied to the connection of other lightweight hybrid vehicle B-pillars, ensuring that each unique lightweight hybrid vehicle B-pillar connection method is optimized based on vehicle performance and cost considerations.

[0194] The parts not described in detail in this invention are prior art.

[0195] The embodiments selected herein for the purpose of disclosing the invention are presently considered suitable, but it should be understood that the invention is intended to include all variations and modifications of the embodiments that fall within the scope of the concept and invention.

Claims

1. A method for optimizing a lightweight hybrid material automobile B-pillar structure, characterized by: The method specifically comprises the following steps: The first step is to import the geometric model of the car B-pillar assembly into Hypermesh software, use Automesh to divide it into meshes and assign materials and properties; The second step is to import the finite element model of the automobile B-pillar assembly into the OptiStruct software and establish three-point bending, axial tension and lateral bending conditions. The welding method is simulated using ACM units. The third step is to improve the structure, replace the materials and change the connection mode of the automobile B-pillar assembly before designing the carbon fiber ply. Because the lightweight hybrid material automobile B-pillar assembly needs to meet the structural characteristics of high upper stiffness and deformation resistance, low lower stiffness and strong energy absorption, the metal B-pillar reinforcement plate A (2) and the metal B-pillar reinforcement plate B (3) that enhance the stiffness of the upper area of ​​the automobile B-pillar are deleted, and the stiffness lost by deleting the metal B-pillar reinforcement plate A (2) and the metal B-pillar reinforcement plate B (3) is compensated by designing the carbon fiber ply. In the side impact test, the highest height between the energy absorption block at the front end of the impacted vehicle and the lowest point of the wheel is 800-900 mm, so the metal B-pillar reinforcement plate C (4) is divided into a high-strength steel B-pillar reinforcement plate (7) and an aluminum alloy B-pillar reinforcement plate (8) with the lowest point of the wheel at 800 mm as the dividing line, and the length of the high-strength steel B-pillar reinforcement plate (7) and the aluminum alloy B-pillar reinforcement plate (8) is increased by 100 mm respectively, and the overlapping area with a length of 200 mm is used as the connection area. The material of the high-strength steel B-pillar reinforcement plate (7) is Q460 steel, the material of the aluminum alloy B-pillar reinforcement plate (8) is 6016 aluminum alloy, the metal B-pillar inner plate (1) is replaced with a carbon fiber composite material B-pillar inner plate (6), and the connection method of the automobile B-pillar assembly is that the carbon fiber composite material B-pillar inner plate (6) is glued to the high-strength steel B-pillar reinforcement plate (7) and the aluminum alloy B-pillar reinforcement plate (8), and the "Adhesives+RBE3" unit is used to achieve it; the connection method of the aluminum alloy B-pillar reinforcement plate (8) to the high-strength steel B-pillar reinforcement plate (7) and the metal B-pillar outer plate (5) is tentatively determined to be connected using the "RBE2" unit; Step 4. Import the hybrid material B-pillar model into the Optistruct software. In the connectors interface, select the area panel, select the adhesive area in the location field, select the carbon fiber composite material B-pillar inner panel (6), high-strength steel B-pillar reinforcement plate (7), and aluminum alloy B-pillar reinforcement plate (8) in the connect what field, set the type to adhesives, and then click create to generate the "Adhesives+RBE3" unit that simulates the adhesive connection. During the layup design phase, the connection between the high-strength steel B-pillar reinforcement plate (7), the aluminum alloy B-pillar reinforcement plate (8) and the metal B-pillar outer plate (5) is simulated using the RBE2 unit. During the simulation, select rigid in the 1D interface, select the master node in independent, select the slave node in dependent, and click create to generate the RBE2 unit that connects the master and slave nodes. Step 5: In OptiStruct software, a multi-level optimization method, including free-size optimization, size optimization, and layup sequence optimization, was used to determine the ply block shape, number of plies, and layup sequence, ultimately determining the layup scheme for the carbon fiber composite B-pillar inner panel. To simplify the initial variables in the conceptual design phase, the thickness of each lay angle was primarily present as a set. That is, plies with the same lay angle were considered a set, called a super layer. For the carbon fiber composite inner panel modeled using shell elements, the super layer thickness was used as the design variable in the free-size phase, and each super layer was optimized for continuous variables. That is, by varying the thickness of each layer and the fiber direction of each element, the total thickness of the laminate varied continuously throughout the structure. Since the super layer is made up of single-layer panels with the same laying angle, in order to determine the laying block shape of each single-layer panel, each super layer needs to be analyzed into ply blocks with different shapes. Since the ply block shape and laying position of each single-layer panel are not necessarily the same, the overall thickness of the super layer is also uneven. Therefore, the carbon fiber composite B-pillar inner panel is designed with constant stiffness and variable thickness to improve material utilization. Step 6. After free size optimization, the thickness of each super layer and its ply cutting shape are obtained. Each super layer has four groups of different ply blocks. These four ply blocks stacked together can represent the optimization result of a super layer. However, since the optimized ply blocks are too ideal, the shapes of the ply blocks are often very irregular, which is not conducive to industrial cutting. Therefore, it is necessary to regularize the ply blocks after free optimization, that is, trim the irresponsible holes of the ply blocks into rectangular holes that are convenient for cutting to facilitate industrial ply cutting. When performing regular processing, in order to prevent the performance of the processed laminate from degrading, the boundaries of the rectangular holes cannot exceed the boundaries of the irregular holes; in order to prevent the lightweight effect from being reduced, the area of ​​the rectangular holes should be as large as possible; In addition, the thickness of each ply obtained by free size optimization is different, which requires a high cost in actual production. In order to make the result more economical, a manufacturing constraint of a single layer thickness of 0.3mm is introduced to obtain a single ply with the same thickness. After introducing this manufacturing constraint and performing size optimization, the actual number of plies of each shape can be obtained. The actual number of plies is the thickness dimension T obtained after size optimization. i Divide by the thickness of the single layer 0.3; Step 7: The optimized solution for the carbon fiber composite B-pillar inner panel obtained through continuous variable thickness optimization design meets the stiffness performance requirements. However, in engineering manufacturing, the carbon fiber composite B-pillar inner panel must also meet certain process constraints, constraints limiting the adverse internal forces caused by the layup sequence, and continuity constraints limiting fiber disconnection. In addition, a reasonable layup sequence can further improve the impact resistance of the hybrid material vehicle B-pillar. Step 8: Import the BIW finite element models of the original metal and hybrid B-pillars into OptiStruct software. Build a BIW static bending and torsional finite element model based on the test conditions. When performing BIW free modal analysis, import the BIW finite element model into Nastran software for setup and solution. Step 9: Because the initially determined carbon fiber composite B-pillar inner panel only considers the performance requirements of the vehicle B-pillar assembly, but not the performance requirements of the entire vehicle, the thickness of the carbon fiber composite super layer fails to achieve the best match with other body-in-white components, and may even lead to a decrease in the static and dynamic performance of the body-in-white. Therefore, it is necessary to substitute the initially determined carbon fiber composite B-pillar inner panel into the body-in-white and perform static bending and torsional stiffness analysis and free modal analysis; Based on the static and dynamic performance of the body-in-white (BIW), the size and layup sequence of the carbon fiber composite B-pillar inner panel were further optimized. This layup design does not degrade the static and dynamic performance of the BIW and ensures the practical use value of the hybrid material B-pillar. Since the BIW lightweight coefficient comprehensively considers the vehicle weight, projected area, and torsional stiffness performance indicators, it can better integrate its performance and lightweight design. Therefore, with the BIW lightweight coefficient as the optimization target, the size and layup sequence of the carbon fiber composite inner panel were optimized. Step 10: Considering the composite material layup process and manufacturing process, the composite material layup design software FiberSIM is used to establish a layup model of the carbon fiber composite material B-pillar inner panel (6). The modeling method is to stack the single layers to form a laminate structure, and then import the layup information of each layer into the finite element software to complete the modeling of the lightweight hybrid material automobile B-pillar; The lightweight hybrid material automobile B-pillar connected by countersunk rivets (10), hexagonal bolts (11), adhesive bonding and adhesive riveting is respectively substituted into the body-in-white model, and the finite element analysis of the body-in-white static bending and torsion working conditions and free modes is performed. The OptiStruct solver is used to solve the static bending and torsion working conditions and the overall first-order bending and torsion modal vibration mode of the body-in-white to obtain the stress conditions of the countersunk rivets (10), hexagonal bolts (11) and the adhesive layer (13). The mechanical properties and cost of the selected materials are comprehensively considered to determine the optimal connection method of the lightweight hybrid material automobile B-pillar; Step 11: When conducting a side impact test of a deformable mobile barrier according to the C-NCAP side standard, a deformable honeycomb aluminum structure is placed at the front end of the mobile trolley (15). During the test, the mobile barrier impacts the left side of the test vehicle (14), i.e., the driver's side. The impact direction of the mobile trolley (15) is perpendicular to the test vehicle (14). The center line of the mobile barrier is located 250 mm behind the R point of the test vehicle (14). The collision speed is At the same time, the distance between the longitudinal median vertical plane of the mobile trolley (15) and the transverse vertical plane of the vehicle passing through the R point of the driver's seat and 250 mm backward is required to be within plus or minus 25 mm, and a WorldSID50th and SID-IIs type dummy are placed on the left side of the driver's seat and the rear seat respectively to simulate the injury conditions of the driver and the rear seat passengers; According to the C-NCAP side column impact test method, the diameter of the rigid fixed cylinder (16) is 254mm and it is located on the left side of the test vehicle. The collision speed of the test vehicle (14) hitting the barrier is The collision velocity direction is 75±3° with the X-axis of the vehicle coordinate system. A WorldSID50th dummy is placed in the front driver's seat of the test vehicle (14) to simulate the driver's injury. The lower end of the fixed rigid cylinder (16) cannot be higher than 102mm above the lowest point of the wheel on the impact side of the tested vehicle, and the upper end must exceed the highest point of the test vehicle. The line connecting the center of the cylinder and the center of the dummy's head is consistent with the velocity direction. According to the C-NCAP side impact test and side pole impact test methods, a full vehicle side impact model and a side pole impact model are established, and stiffness of 1×10 -10 The finite element model is exported as a k-file and solved using the LS-DYNA solver. The intrusion amount and intrusion speed of the dummy's head, chest, abdomen, and pelvis are obtained based on the deformation of the spring unit. Step 12: Substitute the hybrid material car B-pillar into the whole vehicle side impact model and import it into HyperStudy for DOE design. Create variables with the structural parameters of the carbon fiber composite material B-pillar inner panel (6), the high-strength steel B-pillar reinforcement panel (7) and the aluminum alloy B-pillar reinforcement panel (8). Take the mass, intrusion amount and intrusion speed of the hybrid material car B-pillar as performance responses. The thickness of the carbon fiber composite material B-pillar inner panel (6) adopts a discrete value method, and the thickness and length of the high-strength steel B-pillar reinforcement panel (7) and the aluminum alloy B-pillar reinforcement panel (8) adopt a continuous value method. The value ranges of each design variable are as follows: Wherein: x1, x2 and x3 are the thicknesses of the carbon fiber composite material B-pillar inner plate (6), the high-strength steel B-pillar reinforcement plate (7) and the aluminum alloy B-pillar reinforcement plate (8), respectively; x4 and x5 are the lengths of the high-strength steel B-pillar reinforcement plate (7) and the aluminum alloy B-pillar reinforcement plate (8), respectively; The optimal Latin hypercube design was used to sample in the design variable space. A total of 30 sample points were extracted to fit the Kriging approximation model of each performance response. In order to test the accuracy of the Kriging approximation model, 10 sample points were randomly selected for accuracy verification. The coefficient of determination R was used to determine the accuracy of the Kriging approximation model. 2 To evaluate the accuracy of the approximate model, R 2 The closer the value is to 1, the higher the overall prediction accuracy of the approximate model. The B-pillar assembly mass, side impact chest intrusion volume, and side impact chest intrusion velocity of the hybrid vehicle are 0.9181, 0.9287, and 0.9141, respectively. The determination coefficients of other performance indicators are also greater than 0.9, meeting the accuracy requirements. The optimization mathematical model for lightweight multi-objective optimization of hybrid material automobile B-pillar is: Where: m(x) is the mass of the mixed material automobile B-pillar assembly, in kg; D sh (x), D sc (x), D sa (x) and D sp (x) is the intrusion amount of the dummy's head, chest, abdomen, and pelvis corresponding to the position of the composite material B-pillar in the side collision of the vehicle, in mm; D sh0 、D sa0 and D sp0 D is the maximum intrusion of the dummy's head, abdomen, and pelvis at the original metal B-pillar position in a side collision of the vehicle, in mm; ch (x), D cc (x), D ca (x) and D cp (x) is the intrusion amount of the dummy's head, chest, abdomen, and pelvis corresponding to the position of the composite material B-pillar in the side collision of the vehicle, in mm; D ch0 、D cc0 、D ca0 and D cp0 v is the maximum intrusion of the dummy's head, chest, abdomen and pelvis at the position of the original metal B-pillar in the case of a side column collision of the vehicle, in mm; sh (x), v sc (x), v sa (x) and v sp (x) is the penetration velocity of the dummy’s head, chest, abdomen, and pelvis at the position of the composite material B-pillar in the side impact of the vehicle, in m / s; v sh0 (x), v sa0 (x) and v sp0 (x) is the maximum penetration velocity of the dummy’s head, abdomen, and pelvis at the position of the original metal B-pillar in a side collision of the vehicle, in m / s; v ch (x), v cc (x), v a (x) and v p (x) is the penetration velocity of the dummy’s head, chest, abdomen, and pelvis at the position of the composite material B-pillar in the side impact of the vehicle, in m / s; v ch0 、v cc0 、v ca0 and v cp0 The maximum penetration velocity of the dummy's head, chest, abdomen, and pelvis at the position of the original metal B-pillar in a side column collision of the vehicle, in m / s; The NSGA-II optimization algorithm is set to a population size of 40, an evolutionary generation of 30, and a crossover probability of 0.

9. After 80 iterative calculations, a multi-objective optimization Pareto solution set is obtained. A compromise solution (17) is selected from the Pareto frontier and its design variable values ​​are rounded up. Based on the rounded design variables, the lightweight hybrid material automobile B-pillar model is re-established and a vehicle side impact analysis is performed to verify the accuracy of the compromise solution (17).

2. The method for optimizing the lightweight hybrid material automobile B-pillar structure according to claim 1, characterized in that: In the first step, the automobile B-pillar assembly comprises a metal B-pillar outer panel (5), a carbon fiber composite material B-pillar inner panel (6), a high-strength steel B-pillar reinforcement panel (7), and an aluminum alloy B-pillar reinforcement panel (8); the high-strength steel B-pillar reinforcement panel (7) is provided at the upper portion between the metal B-pillar outer panel (5) and the carbon fiber composite material B-pillar inner panel (6); and the aluminum alloy B-pillar reinforcement panel (8) is provided at the lower portion between the metal B-pillar outer panel (5) and the carbon fiber composite material B-pillar inner panel (6).

3. The method for optimizing the lightweight hybrid material automobile B-pillar structure according to claim 1, characterized in that: When assigning materials and properties in the first step, the materials and properties are as follows: The material of the metal B-pillar inner panel (1) is B280 / 440DP, with a thickness of 1.2 mm; The material of the metal B-pillar reinforcement plate A (2) is B340 / 590DP, with a thickness of 2 mm; The material of the metal B-pillar reinforcement plate B (3) is B340 / 590DP, with a thickness of 1.6 mm; The material of the metal B-pillar reinforcement plate C (4) is Docol1400, with a thickness of 1.4 mm; The material of the metal B-pillar outer plate (5) is DOC6 and has a thickness of 0.7 mm.

4. The method for optimizing the lightweight hybrid material automobile B-pillar structure according to claim 1, characterized in that: The three-point bending condition in the second step: Constrain the degrees of freedom of the lower end of the B-pillar assembly to 12356, and the degrees of freedom of the upper end of the B-pillar assembly to 1256; apply an equivalent force in the Y-axis direction to the middle of the B-pillar outer panel; Axial tension conditions: Constrain the degrees of freedom of the lower end of the B-pillar assembly to 123456, and the degrees of freedom of the upper end of the B-pillar assembly to 12456, and apply a positive Z-axis force at the centroid of the upper part of the B-pillar; Lateral bending conditions: Constrain the degrees of freedom of the lower end of the B-pillar assembly to 123456, and the degrees of freedom of the upper end of the B-pillar assembly to 156, and apply a positive force along the X-axis at the centroid of the upper part of the B-pillar.

5. The method for optimizing the lightweight hybrid material automobile B-pillar structure according to claim 1, characterized in that: The materials and properties of the lightweight hybrid vehicle B-pillar in the third step without laminate design are as follows: The carbon fiber composite material in the carbon fiber composite material B-pillar inner panel (6) is epoxy resin carbon fiber composite material T300 / 5208, the initial thickness is determined by layer design, and the optimal thickness will be determined by lightweight multi-objective optimization; The material of the high-strength steel B-pillar reinforcement plate (7) is Q460, and the initial thickness and length are 1.4 mm and 1054 mm respectively. The optimal thickness and length will be determined through lightweight multi-objective optimization. The material of the aluminum alloy B-pillar reinforcement plate (8) is 6016 aluminum alloy, and the initial thickness and length are 1.4 mm and 395 mm respectively. The optimal thickness and length will be determined through lightweight multi-objective optimization. The material of the metal B-pillar outer panel (5) is DOC6, and the thickness is 0.7 mm.

6. The method for optimizing the lightweight hybrid material automobile B-pillar structure according to claim 1, characterized in that: In the fourth step, when the high-strength steel B-pillar reinforcement plate (7), the aluminum alloy B-pillar reinforcement plate (8) and the carbon fiber composite material B-pillar inner plate (6) are glued together, the glued parts are often subjected to tension, shearing force, tearing force and peeling force. Under the action of tensile or compressive load, the basic failure forms of the glued parts are mainly shear failure, tensile or bending failure and peeling failure. The connection between the carbon fiber composite material B-pillar inner plate (6) and the high-strength steel B-pillar reinforcement plate (7) and the aluminum alloy B-pillar reinforcement plate (8) is a surface-to-surface connection. When subjected to load, the adhesive layer mainly bears shear stress. In order to verify the feasibility of the glued parts, it is necessary to perform strength verification on the glued parts. By comparing the shearing force allowable values ​​of the glued parts and the welded parts, the feasibility of the glued parts in the structure is verified. The details are as follows: A. Calculate the allowable shear resistance of the welds between the original metal B-pillar inner panel (1) and the metal B-pillar reinforcement plate A (2), metal B-pillar reinforcement plate B (3), and metal B-pillar reinforcement plate C (4) using the following formula: F ss =π×(D / 2) 2 ×0.577×σ s Where: D is the diameter of the solder joint, in mm; σ s is the shear strength of the base material, in MPa; B. Calculate the allowable shear resistance of the carbon fiber composite material B-pillar inner plate (6) and the high-strength steel B-pillar reinforcement plate (7) and the aluminum alloy B-pillar reinforcement plate (8) by adhesive bonding, according to the following formula: F as =A×σ as / l Where: A is the adhesive area, unit is mm 2 ; σ as is the shear strength of the glue, in MPa; λ is a constant, usually defined as 10.

7. The method for optimizing the lightweight hybrid material automobile B-pillar structure according to claim 1, characterized in that: The expression of the lightweight coefficient of the body in white in the ninth step is as follows: Where: L is the lightweight coefficient; M is the mass of the body in white, in kg; K t is the torsional stiffness of the body in white, in N·mm / °; A is the body footprint area (average wheelbase × wheelbase), in mm 2 .

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