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The replacement of carbon fiber reinforced epoxy resin matrix composite (CFRP) in the B-pillar of the body structure was discussed. Under the condition of ensuring crashworthiness, the lightweight application of B-pillar on the structural parts of the automobile was realized. Taking the steel B-pillar of a certain model as the prototype, CFRP is used for the same stiffness design, and the stiffness, crashworthine ss and lightweight performance of the composite B-pillar relative to the high-strength steel B-pillar are comprehensively analyzed. The results show that under the requirements of crashworthiness, the lightweight effect of CFRP on B-pillar is obvious, which is 26.27% lower than that of high-strength steel B-pillar. Therefore, under the equal stiffness design conditions, the composite material can better realize the lightweight requirements of the automobile B-pillar.

With the rapid development of the automotive industry, the number of cars has increased significantly. Driven by automobile safety collision and energy conservation and emission reduction regulations, reducing energy consumption and reducing pollution has become an urgent task for automobile development. Reducing the weight of automobiles is one of the effective ways to solve the above problems. The application of high-strength lightweight materials and lightweight structures has become an inevitable trend in the development of automobiles. Carbon fiber composites have become more and more widely used in the body due to their high specific strength and specific stiffness [

At present, the application of composite materials on the body at home and abroad still uses metal components for the entire body, and only composite materials are used on some of the components. Although the CFRP material has higher cost, its specific strength, specific modulus and other properties are the most superior among the existing structural materials, and its high strength and rigidity have become the hotspots of recent research at home and abroad. Wu Fanghe et al. [

There are relatively many researches on the application of carbon fiber composite materials to automobile body parts and covers, but the research and development of composite body frame and important structural parts are being developed and explored at home and abroad. Zhang Zipeng [

In this paper, a high-strength steel B-pillar of a certain model is replaced with a lightweight composite CFRP. The thickness is designed based on the principle of equal stiffness. Statics and collision performance analysis is performed on the original model, and the accuracy of the model is verified by energy analysis during the collision process. Compared with the model after material replacement, it is guaranteed that the B-pillar has the same bending stiffness in low-speed collision. This paper compares the light weight and crashworthiness of two light- weight materials, which provides a basis for the lightweight design of automotive B-pillars.

The B-pillar is located between the front door and the rear door and is an important bearing member during the side collision of the car. The overall shape of the B-pillar must be curved and consistent with the shape of the body. The B-column geometry model is imported into the HyperMesh pre-processing software, and the operations such as extracting the middle surface, geometric cleaning and meshing are performed, wherein the meshing is as much as possible using quadrilateral elements, and the number of triangular elements does not exceed 5% of the total number of cells, and the mesh size is 10 mm and the total number of grids is 11,363. The B-pillar is mainly connected by welding, high- strength steel DC590, material properties: elastic modulus is 210 Mpa, Poisson’s ratio is 0.3, density is 7850 kg/m^{3}. The established B-column finite element model is shown in

The static analysis of automobile B-pillars mainly includes the stress and strain under bending conditions, and all the translational degrees of freedom and rotational degrees of freedom at the four ends of the B-pillar are constrained. A concentrated load of 1000 N is applied along the Y+ direction at the middle position of the B-pillar. The analytical model is shown in

Based on the principle of equal stiffness replacement, the existing high-strength steel B-pillar is replaced by a carbon fiber composite material, and the B-column

lightweight design is designed to remove the reinforcing plate in the B-pillar. For the B-pillar design, three schemes are designed. The solution is to replace the inner and outer plates of the B-pillar with the composite material. The second scheme replaces the B-pillar front outer panel with the composite material. The third scheme replaces the B-pillar inner panel with the composite material, and determines the thickness of the inner and outer plates of the B-pillar through the equivalent stiffness approximation theory. among them:

E a I a = E b I b (a)

E a b a h a 3 12 = E b b b h b 3 12 (b)

For thin-walled structures, the width of the cross-sectional area:

b a = b b , h a = E b h b 3 E a 3 (c)

In the formula: E_{a} is the equivalent modulus of the laminate; I_{a} is the moment of inertia of the cross section of the composite structure; E_{b} is the modulus of elasticity of the original structural material; I_{b} is the moment of inertia of the cross section of the original structure; h_{a}, h_{b} is the cross section Height, also known as thickness.

According to the expression (c), the thickness of the replacement material can be initially determined. In order to ensure the rigidity of the structure after the replacement of the material, the thickness adjustment is often performed based on the position of the different plates. In addition, the stiffness of a single sheet metal member is a nonlinear function of thickness, and the approximate relationship is expressed as：

K = C E t θ (d)

where: C is the geometric coefficient; E is the elastic modulus; t is the material thickness; θ is the thickness index coefficient. According to the expression (d), the ratio of the thickness of the material before and after the stiffness replacement:

t 1 t 0 = ( E 0 E 1 ) 1 θ (e)

where: t_{0} and t_{1} are the thicknesses before and after material replacement; E_{0} and E_{1} are the elastic moduli before and after material replacement; by expressions (d) and (e), the thickness elastic modulus of the material is equal to stiffness. Inverse ratio. For the body structure θ is usually between 1 - 2.

Based on the above theory, the thickness values of the inner and outer plates of the B-pillar after material replacement are shown in

Option 1 replace the inner and outer plates of the B-pillar with equal stiffness. The CFRP inner plate thickness is 4 mm, the CFRP outer plate thickness is 4 mm, the CFRP thickness is 0.25 mm, and the inner and outer plates are 16 layers, according to 0˚/45˚/90˚/−45˚ way to laminate.

Option 2 replace the outer plate of the B-pillar with equal rigidity. The thickness of the CFRP outer plate is 4.12 mm, the thickness of each layer of CFRP is 0.25 mm, and the inner and outer plates are laid 16 layers, paved according to 0˚/45˚/90˚/−45˚. The inner plate is of the original metal structure and is rigidly connected.

Alternative scheme for B column design | Material | Equivalent elastic modulus /GPa | thickness/mm | ||
---|---|---|---|---|---|

Basic model | Inner plate | DC590 | 210 | 1.6 | |

Outer plate | DC590 | 210 | 1.8 | ||

Programme 1 | Inner plate | CFRP | 40 | 4 | |

Outer plate | CFRP | 40 | 4 | ||

Programme 2 | Inner plate | DC590 | 210 | 1.6 | |

Outer plate | CFRP | 40 | 4 | ||

Programme 3 | Inner plate | CFRP | 40 | 4 | |

Outer plate | DC590 | 210 | 1.8 | ||

Option 3 replaces the inner plate of the B-pillar with equal rigidity. The inner thickness of the CFRP plate is 4 mm, the thickness of each layer of the CFRP is 0.25 mm, and the inner and outer plates are laid 16 layers, and the layers are laid in the manner of 0˚/45˚/90˚/−45˚. The outer plate is of original metal structure and is rigidly connected.

The same static analysis conditions as the basic model were adopted, and the load and constraints were consistent. The comparison of the analysis results is shown in

quality /kg | deformation/mm | stress /Mpa | |
---|---|---|---|

Basic model | 15.72 | 0.704 | 102 |

Programme 1 | 11.59 | 0.591 | 34.5 |

Programme 2 | 12.88 | 0.525 | 31.4 |

Programme 3 | 14,44 | 0.286 | 88.4 |

model, the deformation of the B-pillar of the scheme 1 is reduced by 16%, the deformation of the B-pillar of the scheme 2 is decreased by 25%, the maximum stress position of the overall structure of the B-pillar is the same, and the maximum stress value of the scheme 1 and the scheme 2 is the same. Greatly reduced.

Through the design analysis and comparison of the three schemes, the replacement of the composite material inside and outside the B-pillar, the small stress value of the deformation of the B-pillar is small, and the weight reduction effect is better. Therefore, in the first option, the replacement study of the composite material of the B-pillar is carried out. The following is a study on the collision of the composite B-pillar with the original high-strength steel.

The analysis of the impact performance of the B-pillar of the car mainly considers the working conditions of the side impact [

By analyzing the change between the energy of the collision of the metal B column in

Taking the same collision analysis conditions as the basic model, the comparison of the intrusion amount and the intrusion velocity on the B-pillar is shown in

In this paper, the lightweight design of B-pillars was carried out, CFRP carbon fiber composites were selected instead, and the thickness of B-pillars was designed according to the principle of equal stiffness. Three lightweight schemes were designed. The finite element model is established, and the static and collision analysis of the B-pillar is carried out. It is known from the simulation results that: while ensuring the crashworthiness of the B-pillar, the B-pillar improves the crashworthiness, and the quality of the CFRP material is reduced by 26%. The advantages of lightweight and comprehensive performance are obvious. CFRP material is superior to the original high-strength steel material and is a lightweight composite material with great reference value.

The authors declare no conflicts of interest regarding the publication of this paper.

Sun, D.M. and Tao, C. (2018) Lightweight Study of Carbon Fiber Composite B-Pillar Based on Equal Stiffness Principle. Open Access Library Journal, 5: e4822. https://doi.org/10.4236/oalib.1104822