Crashworthiness study of carbon fiber composite passenger compartment B-pillar reinforcement plate under multi-scale lightweight design strategy

B-pillar is a part of the automobile body structure, usually located between the cockpit and the rear door, carrying the weight of the vehicle top and side structure, but also an important structural component to protect the occupants in the event of a side collision [1–3]. Therefore, the B-pillar has an important influence on the structural strength and safety performance of the automobile.

As a key structural member of the side of the automobile, the structure and cross-section of the B-pillar of traditional automobiles are often complicated. Segmental strengthening technology reduces the tensile strength of the lower part of the B-pillar, thus improving the side impact safety more effectively. This is through the application of unequal thickness hot stamping B-pillar, crashworthiness can be more carefully controlled; based on the laser welding plate integral hot stamping, can more effectively improve the body stiffness and safety [4–6]. In addition, the hot stamping of pre-welded patch panels can help to strengthen the local structure and reduce the development cost [7–9]. However, hot stamping has the disadvantages of difficult mold design and processing, long manufacturing and debugging cycle, high price of the mold and its supporting tooling, and high maintenance cost [10–12]. Therefore, cost-effective materials need to be selected for body structure design. The composite materials have obvious damage impedance characteristics, which are manifested as follows: their low interlaminar properties are particularly sensitive to low-speed impacts, and low-speed impacts will generate stress waves in the thickness direction within the plywood, causing delamination and cracking [13–15]. Among them, fiber-reinforced composites have excellent mechanical properties and anti-fatigue properties as well as much lower density than metal, which become important lightweight materials for automotive structures, especially for body structure parts with high mechanical property requirements, and can realize weight reduction of the body while guaranteeing the stiffness, strength, and safety performance of the body [16–18]. Fiber-reinforced composites are used in the B-pillar of automobiles, which can obtain a larger lightweight and collision avoidance effect at the same time, the fixed investment in the production of carbon fiber composite bodywork is also significantly lower than that of metal bodywork [19–20].

In summary, B-pillar as a typical body structure in one of the important bearing parts, in the design of automobile lightweight to ensure that the body structure stiffness, strength and safety performance of the car is of great significance. Carbon fiber composites as an ideal lightweight material, but also in the damage impedance has its unique advantages.

Compared with the research on the application of carbon fiber composites in automotive cladding parts, its application in body structure parts is less. In this paper, based on the mechanical characteristics of the anisotropy of composite laminates, firstly, the mechanics of carbon fiber composites are analyzed to derive the factors affecting its stiffness. Secondly, the structural design and initial pavement design are carried out on the basis of topology optimization of B-pillar reinforcement plate, and the design of carbon fiber composite B-pillar reinforcement plate to meet the lightweight is proposed. Finally, the carbon fiber composite B-pillar reinforcement plate is subjected to stiffness simulation analysis and three-point bending test to evaluate its strength. And through the side impact simulation of the whole vehicle, the crashworthiness of the B-pillar reinforcement plate with carbon fiber composite material is verified.

2

Overview

Passenger safety has always been a hot issue, scholars have done a lot of research on optimizing automotive components, including the optimization of the B-pillar. The stiffness, tensile strength, and crashworthiness of the B-pillar are all important for the safety of the vehicle and the life and property of the passengers [21]. Secondly, automobile lightweighting is also a hot spot of concern. In this regard, scholars have done a lot of research on lightweighting while taking safety into account, such as the literature [22–24]. Carbon fiber composites have many applications in automotive lightweighting and safety, so the use of continuous fiber reinforced composites to improve the strength and stiffness of automobiles has become a key point, but its molding process also exists in delamination, wrinkles and other problems. In this regard, literature [25] uses segmented overlay design to form segmented cover layer, which is good to improve the lamination performance of continuous carbon fiber. In addition, the current B-pillar is composed of various shapes of steel reinforcement, and the use of carbon fiber reinforced plastic (CFRP) to replace the existing steel can reduce the weight of the B-pillar under the premise of ensuring the structural stability of the body [26]. Meanwhile, CFRP reinforcement can have the same or higher specific stiffness with lower production cost and saving processing time compared to existing steel reinforcement [27]. However, bonding problems between carbon fiber fabric and steel limit the combination of CFRP with most steel-containing components, which led to the emergence of prepreg compression molding (PCM) [28]. It is characterized by high quality, high productivity, and flexible manufacturing process [29]. In addition, literature [30] showed that continuous carbon fiber reinforced thermoplastic composites (CFRTP) for automotive B-pillar to improve the structural performance at the same time with better crashworthiness, but can not take into account the quality issues, and then optimized layer design of CFRTP can improve the B-pillar crashworthiness.

The most direct and simple way to strengthen the crashworthiness of the B-pillar is to set up the reinforcement plate, and the literature [31] study shows that the 2 patches added in the B-pillar have improved the safety of the occupants in the side impact of the car according to the results of simulation tests. And literature [32] study optimized the carbon fiber composite b-pillar reinforcement plate from the three aspects of size, free size, and lamination direction, which can maintain the stiffness, strength, and side impact resistance on the basis of more than 75% lightweighting. Similarly, literature [33] also optimized the three aspects of dimensions, free dimensions, and laminate order, and the results showed that the mass of the B-pillar decreased and the lightweight and crashworthiness increased after replacing the material, and further reducing the mass of the B-pillar can continue to improve the lightweight and crashworthiness. Carbon fiber composite B-pillar reinforcement plate is guaranteed to improve crashworthiness and safety, but it needs to be optimized for both lightweight.

3

Basic theory of composite materials

3.1

Fundamentals of anisotropic elastodynamics

Composite material is a typical anisotropic material, in the external force is in equilibrium or in motion, the continuous elastomer deformation, the stress-strain state of any point in the x, y, z coordinate system, can be expressed in terms of the stress component and the corresponding strain component as: 1 $σ = [\begin{matrix} σ_{x} & τ_{x y} & τ_{x z} \\ τ_{y x} & σ_{y} & τ_{y z} \\ τ_{z x} & τ_{z y} & σ_{z} \end{matrix}], ε = [\begin{matrix} ε_{x} & ε_{x y} & ε_{x z} \\ ε_{y x} & ε_{y} & ε_{y z} \\ ε_{z x} & ε_{y y} & ε_{z} \end{matrix}]$

Among them, there are six stress components, including three shear stresses τ_xy = τ_yz, τ_xz = τ_zx, τ_yz = τ_zy, and three principal stresses σ_x, σ_y, σ_z; and there are also six strain components, of which ε_x, ε_y, and ε_z are line strains, $ε_{x y} = \frac{1}{2} γ_{x y}$ , $ε_{x z} = \frac{1}{2} γ_{x z}$ , and $ε_{y z} = \frac{1}{2} γ_{y z}$ are tensor shear strains, and γ_xy, γ_xz, and γ_xz are engineering shear strains.

Based on the three equations of equilibrium of motion, small deformation geometric relations and deformation coordination equations of the elastomer the σ – ε intrinsic relations are derived as: 2 $[\begin{matrix} σ_{1} \\ σ_{2} \\ σ_{3} \\ τ_{23} \\ τ_{31} \\ τ_{12} \end{matrix}] = [\begin{array}{l} C_{11} & C_{12} & C_{13} & C_{14} & C_{15} & C_{16} \\ C_{21} & C_{22} & C_{23} & C_{24} & C_{25} & C_{26} \\ C_{31} & C_{32} & C_{33} & C_{34} & C_{35} & C_{36} \\ C_{41} & C_{42} & C_{43} & C_{44} & C_{45} & C_{46} \\ C_{51} & C_{52} & C_{53} & C_{54} & C_{55} & C_{56} \\ C_{61} & C_{62} & C_{63} & C_{64} & C_{65} & C_{66} \end{array}] [\begin{matrix} ε_{1} \\ ε_{2} \\ ε_{3} \\ γ_{23} \\ γ_{31} \\ γ_{12} \end{matrix}]$

C₁₁, C₁₂, … C₆₆ in the matrix is the stiffness coefficient, the strain potential energy of the elastomer is analyzed to obtain C_ij = C_p, i, j = 1, 2, 3…6, then only 21 stiffness coefficients in Eq. (2) are independent, and the flexibility matrix S is the inverse matrix of the stiffness matrix C, and if the material at this time is orthotropic and anisotropic, C₁₄ = C₁₅ = C₁₆ = C₂₄ = C₂₆ = C₃₄ = C₃₆ = C₃₅ = C₄₅ = C₄₆ = C₅₆ = 0, then only 9 independent stiffness coefficients are left in the material, and at this time the σ – ε relationship is expressed as Eq. (3). 3 $[\begin{array}{l} σ_{1} \\ σ_{2} \\ σ_{3} \\ τ_{23} \\ τ_{31} \\ τ_{12} \end{array}] = [\begin{array}{l} C_{11} & C_{12} & C_{13} \\ C_{21} & C_{22} & C_{23} \\ C_{31} & C_{32} & C_{33} \\ C_{44} \\ C_{55} \\ C_{66} \end{array}] [\begin{matrix} ε_{1} \\ ε_{2} \\ ε_{3} \\ γ_{23} \\ γ_{31} \\ γ_{12} \end{matrix}]$

Then similarly the flexibility coefficient has 9 mutually independent coefficients, with the relationship expression 4 $[\begin{matrix} ε_{1} \\ ε_{2} \\ ε_{3} \\ γ_{23} \\ γ_{31} \\ γ_{12} \end{matrix}] = [\begin{array}{l} S_{11} & S_{12} & S_{13} \\ S_{21} & S_{22} & S_{23} \\ S_{31} & S_{32} & S_{33} \\ S_{44} \\ S_{55} \\ S_{66} \end{array}] [\begin{matrix} σ_{1} \\ σ_{2} \\ σ_{3} \\ τ_{23} \\ τ_{31} \\ τ_{12} \end{matrix}]$

It can be concluded that for orthotropic anisotropic materials, positive stresses cause only line strains and shear stresses do not cause line strains and are not coupled to each other.

Since orthotropic anisotropic materials can also be characterized by engineering elastic constants, which are the modulus of elasticity E_i, Poisson's ratio v_ij, and shear modulus G_ij, and the acquisition of these constants can be obtained by mechanical property tests, the σ – ε ontological relationship expressed by the engineering constants is: 5 $[\begin{array}{l} ε_{1} \\ ε_{2} \\ ε_{3} \\ γ_{12} \\ γ_{23} \\ γ_{31} \end{array}] = [\begin{matrix} \frac{1}{E_{1}} & - \frac{v_{21}}{E_{2}} & - \frac{v_{31}}{E_{3}} & 0 & 0 & 0 \\ - \frac{v_{12}}{E_{1}} & \frac{1}{E_{2}} & - \frac{v_{32}}{E_{3}} & 0 & 0 & 0 \\ - \frac{v_{13}}{E_{1}} & - \frac{v_{23}}{E_{2}} & \frac{1}{E_{3}} & 0 & 0 & 0 \\ 0 & 0 & 0 & \frac{1}{G_{12}} & 0 & 0 \\ 0 & 0 & 0 & 0 & \frac{1}{G_{23}} & 0 \\ 0 & 0 & 0 & 0 & 0 & \frac{1}{G_{31}} \end{matrix}] [\begin{array}{l} σ_{1} \\ σ_{2} \\ σ_{3} \\ τ_{12} \\ τ_{23} \\ τ_{31} \end{array}]$ written in the form of ε = Sσ, then the flexibility matrix is expressed as: 6 $\begin{array}{l} S & = [\begin{matrix} \frac{1}{E_{1}} & - \frac{v_{12}}{E_{2}} & - \frac{v_{13}}{E_{3}} & 0 & 0 & 0 \\ - \frac{v_{21}}{E_{1}} & \frac{1}{E_{2}} & - \frac{v_{23}}{E_{3}} & 0 & 0 & 0 \\ - \frac{v_{31}}{E_{1}} & - \frac{v_{32}}{E_{2}} & \frac{1}{E_{3}} & 0 & 0 & 0 \\ 0 & 0 & 0 & \frac{1}{G_{23}} & 0 & 0 \\ 0 & 0 & 0 & 0 & \frac{1}{G_{31}} & 0 \\ 0 & 0 & 0 & 0 & 0 & \frac{1}{G_{12}} \end{matrix}] \\ = [\begin{array}{l} S_{11} & S_{12} & S_{13} \\ S_{21} & S_{22} & S_{23} \\ S_{31} & S_{32} & S_{33} \\ S_{44} \\ S_{55} \\ S_{66} \end{array}] \end{array}$

E₁, E₂, E₃ are the three elastic principal directions of tensile (or compressive) elastic modulus, G₁₂, G₃₁, G₃₁ is the shear modulus, v₁₂, v₁₃, v₂₃ represents Poissonss ratio, engineering generally through mechanical testing to determine the individual engineering constants, and then in accordance with Eq. (6) to calculate the flexibility matrix S, in accordance with Eq. (7) to calculate the stiffness matrix C: 7 $\begin{array}{l} C_{11} = \frac{1 - v_{2} v_{32}}{E_{2} E_{3} Δ}, C_{12} = \frac{v_{12} + v_{32} v_{13}}{E_{1} E_{3} Δ}, C_{13} = \frac{v_{13} + v_{12} v_{23}}{E_{1} E_{2} Δ} \\ C_{22} = \frac{1 - v_{31} v_{13}}{E_{1} E_{3} Δ}, C_{23} = \frac{v_{23} + v_{21} v_{13}}{E_{1} E_{2} Δ}, C_{33} = \frac{1 - v_{12} v_{21}}{E_{1} E_{2} Δ} \\ C_{44} = G_{23}, C_{55} = G_{31}, C_{66} = G_{12} \\ Δ = \frac{1 - v_{12} v_{21} - v_{23} v_{32} - v_{3} v_{13} - 2 v_{12} V_{23} v_{31}}{E_{1} E_{2} E_{3}} \end{array}}$

Since composite materials mostly exhibit orthotropic anisotropy, the study of such elastic mechanical properties plays a fundamental role in analyzing the mechanical properties of composite materials.

3.2

Macromechanical analysis of composite materials

3.2.1

Classical plywood theory

Composite plywood is a single-ply board laid into a laminated form according to a specific fiber direction and sequence, bonded and cured by heating to form a whole structural board. Therefore, for composite laminates, the basic properties of monolayers, the angle of fiber lay-up, and the laminated order of sheets are all factors that affect the mechanical properties of laminates. For stress-strain analysis of composite plywood, it is necessary to assume that the ply meets three conditions: 1)

Consistency of deformation between plies: the displacement at the connection between plies and plies in the laminate is continuous without relative slip;

2)

Straight normal invariant: a straight line perpendicular to the center face of the plywood before deformation, after deformation by external force, is still perpendicular to the center face, and the length is unchanged;

3)

Equal thickness of the thin plates in the plywood.

From the classical plywood assumptions it can be seen that the strain change in the thickness direction is continuous, the strain equation for the change along the thickness direction is: 8 $[\begin{array}{l} ε_{x} \\ ε_{y} \\ γ_{x y} \end{array}] = [\begin{array}{l} ε_{x}^{0} \\ ε_{y}^{0} \\ γ_{x y}^{0} \end{array}] + z [\begin{array}{l} k_{x} \\ k_{y} \\ k_{x y} \end{array}]$

In the equation, $ε_{x}^{0}$ , $ε_{y}^{0}$ and $ε_{z}^{0}$ are the strains of the middle face of the plywood in three directions, k_x and k_y are the bending deflection rate of the middle face of the plywood, k_xy is the twisting rate of the middle face of the plywood, and z is the coordinate value of a single-layer plywood in the direction of thickness relative to the middle face.

Through the above equation, the strain of other layers of the laminate can be obtained from the strain of the center face of the laminate, the bending deflection rate and the twisting rate. After calculating the strain of k layers, the stress-strain relationship of k layers can be obtained according to the stress-strain relationship of single-layer plate, as follows: 9 ${[\begin{array}{l} σ_{x} \\ σ_{y} \\ τ_{x y} \end{array}]}_{k} = {[\begin{matrix} {\bar{Q}}_{11} & {\bar{Q}}_{12} & {\bar{Q}}_{16} \\ {\bar{Q}}_{12} & {\bar{Q}}_{22} & {\bar{Q}}_{26} \\ {\bar{Q}}_{16} & {\bar{Q}}_{26} & {\bar{Q}}_{66} \end{matrix}]}_{k} {[\begin{array}{l} ε_{x}^{0} \\ ε_{y}^{0} \\ γ_{x y}^{0} \end{array}] + z [\begin{array}{l} k_{x} \\ k_{y} \\ k_{x y} \end{array}]}$

3.2.2

Stiffness analysis of classical laminates

Figure 1 shows a force diagram of a laminate under the assumptions of the classical plywood theory. By integrating the stresses and moments in the stress-median plane applied to a single ply in the direction of the thickness z, the combined forces and moments applied to the laminate can be obtained, which are expressed as N_x, N_y, N_xy, M_x, M_y, M_xy:

10

[\begin{array}{l} N_{x} \\ N_{y} \\ N_{x y} \end{array}] = {\sum_{k = 1}^{n} \int_{z_{i - 1}}^{z_{i}} [\begin{array}{l} σ_{x} \\ σ_{y} \\ τ_{x y} \end{array}]}_{k} d z, [\begin{array}{l} M_{x} \\ M_{y} \\ M_{x y} \end{array}] = {\sum_{k = 1}^{n} \int_{z_{z - 1}}^{z_{i}} [\begin{array}{l} σ_{x} \\ σ_{y} \\ τ_{x y} \end{array}]}_{k} z d z

Substituting Eq. (9) into Eq. (10) gives: 11 $[\begin{array}{l} N_{x} \\ N_{y} \\ N_{x y} \end{array}] = [\begin{matrix} A_{11} & A_{12} & A_{16} \\ A_{12} & A_{22} & A_{26} \\ A_{16} & A_{26} & A_{66} \end{matrix}] [\begin{array}{l} ε_{x}^{0} \\ ε_{y}^{0} \\ γ_{x y}^{0} \end{array}] + [\begin{matrix} B_{11} & B_{12} & B_{16} \\ B_{12} & B_{22} & B_{26} \\ B_{16} & B_{26} & B_{66} \end{matrix}] [\begin{array}{l} k_{x} \\ k_{y} \\ k_{x y} \end{array}]$ 12 $[\begin{array}{l} M_{x} \\ M_{y} \\ M_{x y} \end{array}] = [\begin{matrix} B_{11} & B_{12} & B_{16} \\ B_{12} & B_{22} & B_{26} \\ B_{16} & B_{26} & B_{66} \end{matrix}] + [\begin{matrix} D_{11} & D_{12} & D_{16} \\ D_{12} & D_{22} & D_{26} \\ D_{16} & D_{26} & D_{66} \end{matrix}] [\begin{array}{l} k_{x} \\ k_{y} \\ k_{x y} \end{array}]$

Among them: 13 $\begin{array}{l} [A] & = \sum_{i = 1}^{N} [\bar{Q}] (Z_{i} - Z_{i - 1}) \\ [B] & = \frac{1}{2} \sum_{i = 1}^{N} [\bar{Q}] (Z_{i}^{2} - Z_{i - 1}^{2}) \\ [D] & = \frac{1}{3} \sum_{i = 1}^{N} [\bar{Q}] (Z_{i}^{3} - Z_{i - 1}^{3}) \end{array}$

In Eq. (13), A is the in-plane stiffness matrix, the B matrix is the coupled stiffness matrix for tension and bending, and matrix D is the bending stiffness matrix.

4

Carbon fiber composite B-pillar reinforcement plate design for lightweighting

The B-pillar assembly consists of an inner plate, a reinforcement plate and an outer plate. Since the B-pillar is a key component in side impacts, the reinforcement plate is added to give the vehicle sufficient strength in side impacts. The carbon fiber composite B-pillar reinforcement plate is designed on the basis of the original metal B-pillar, retaining the design hard points.

4.1

Topology optimization

Before the structural design of the carbon fiber composite B-pillar reinforcement plate, topology optimization of the steel material structure is required to obtain the best material distribution. Topology optimization, an optimization method based on cell density, can be interpreted as the partial derivatives of the structural performance parameters with respect to the structural design parameter Xi, i.e: 14 $S e n (\frac{T_{i}}{x_{i}}) = \frac{\partial T_{i}}{\partial x_{i}}$

Where j is denoted as T_j for the first function and i is denoted as the i th independent variable of x_i, where the sensitivity analysis can show the advantages and disadvantages of structural performance. In this paper, using Nastran, the thickness of the body parts is used as a design variable to identify the key components using the magnitude of the sensitivity of the thickness of the parts to the structural performance, and then the thickness of the body parts is used for the optimal design of the body.

The material distribution is calculated using topology optimization. 15 $ρ (x) = {\begin{matrix} 1 & (χ \in Ω^{m a t}) \\ 0 & (χ \in Ω | Ω^{m a t}) \end{matrix}$

Then the topology optimization model of the structure can be described as 16 $\begin{matrix} \min_{ρ} ϕ (ρ) \\ s . t . \int_{Ω} ρ d Ω \leq \nabla \\ ρ (x) = 0 o r 1 (\forall_{χ} \in Ω) \end{matrix}$

According to the finite element numerical method, it is dispersed and the density function is approximated as a n -dimensional vector X = (x_l, x₂, ⋯ x_n), where x_i density values. 17 $\begin{matrix} \min_{X} ϕ (X) \\ s . t . V (X) = \sum_{i = 0}^{n} ρ_{i} v_{i} \leq \nabla \\ ρ_{i} = 0 o r 1 (i = 1, 2, \dots, n) \end{matrix}$ 18 $\begin{matrix} \min_{X} ϕ (X) \\ s . t . V (X) = \sum_{i = 0}^{n} ρ_{i} v_{i} \leq \nabla \\ 0 < δ \leq ρ_{i} \leq 1 (i = 1, 2, \dots, n) \end{matrix}$ where is a very small positive number e.g. (10⁻⁴) to avoid stiffness matrix singularities.

The commonly used density penalty models for intermediate materials are the SMIP method and the RAMP method.

The SIMP method is expressed by the equation 19 $E (x_{i}) = E_{\min} + {(x_{i})}^{p} (E_{0} - E_{\min})$ where

E(x_i) - modulus of elasticity after interpolation

E₀ - modulus of elasticity of the solid part of the material

E_min - modulus of elasticity of the material in the hole part

p - penalty factor

x_i - the relative density of the unit, the

Where, x = 1, then it is empty (without strengthening)

x = 0, then it should be kept (strengthened)

The SIMP method can be expressed by the formula 20 $E (x_{i}) = {(x_{i})}^{p} E_{0}$ where x_i is the relative density of the i nd unit.

Topology optimization analysis, the unit density is the unit, and the optimization objective is the maximum stiffness.

In this paper, in order to meet the design requirements, the main optimization is carried out by constraining the load of the B columns and determining the material distribution in them in order to obtain the optimal shape. In topology optimization, it is assumed that there is no relation between the physical constants of the material and the density, and the B -column reinforcing plate is set as a finite element model with the same unit density in the optimization, and the design variable is its unit density, and the design objective is the minimum weighted stiffness of the B -column assembly structure, and the design constraint is the volume of the reinforcing plate, which is usually the minimum volume, and the optimization of the B -column reinforcing plate is carried out according to the structure of the topology optimization, so that a reasonable reinforcement plate shape and suitable reinforcement plate structure, the optimization problem of topology optimization is expressed as: 1)

Design objective: the assembly stiffness of the composite B -column reinforcing plate is maximized, i.e.: 21 $W = f (x) = f (x_{1}, x_{2}, \dots \dots x_{n}) \to M I N$

Weighted flexibility was used for the flexibility of the B -column assembly structure in this study: 22 $W = \sum W C_{i}$

Eq. W_i is the weighted weights and C_i is the flexibility of each part.

2)

Design variables: $\bar{η} = {(η_{1}, η_{2}, \dots \dots η_{n})}^{T}$

3)

Design constraints: it mainly utilizes volume constraints, so its constraint equation is: 23 $W e i g h t \sum v, η_{i} \leq Ω$

4)

Analysis of working conditions: According to the above to determine its three working conditions are axial tensile conditions, lateral bending and inward bending conditions;

5)

Optimization analysis results: B column reinforcing plate unit density for the larger part needs to be retained, the unit density of the smaller part of the structural improvement can be carried out.

This paper combines the comparison of two kinds of B -column reinforcing plate, and at the same time consider the carbon fiber composite material molding and manufacturing process on the performance of its impact on the carbon fiber composite material B -column reinforcing plate for structural design.

4.2

Structural design of reinforcement plates

Carbon Fiber Composites B Column Reinforcement Plate Structural Design Principles: 1)

Typical stamping characteristics of the original metal solution;

2)

Localized welded surfaces of the original metal scheme;

3)

Original metal program closed angle structure;

4)

Drain holes affect the strength of carbon fiber, as far as possible to remove;

5)

The radius of the round corner of the original metal program, under the premise of not affecting the strength of the fit and connection, try to increase the radius of the round corner, R > 5mm is the best.

The overall structure of the automobile B -column reinforcing plate is obtained through the above steps, and then the structural model is provided for the finite element modeling pre-treatment, and the generation of the B -column structure also has a certain influence on the layup of carbon fiber, and the length, thickness and so on of the B -column are determined in the design process, and the comparison of the B -column reinforcing plate and the steel B -column reinforcing plate of carbon fiber composite material in the later stage provides a basis.

4.3

Initial pavement design

According to the mechanical properties of carbon fiber composite B column reinforcement plate, determine the total number of layers of the reinforcement plate, set the percentage of the angle of each layer, and the order of stacking in each direction. The main steps are as follows: 1)

The axial force of the layup should be consistent with the direction of the corresponding force;

2)

0° or ±45° layup is more suitable for the outside of the plywood;

3)

Due to the characteristics of the resin, avoiding the resin should be indirectly loaded;

4)

The same ply should not occur 4 times in a row;

5)

The ply angle should be specified within a certain range, generally less than 60°.

In this study, the initial ply was selected as: [0/45/90/-45/0/45/0/0/-45]s, the thickness of a single layer was 0.3mm, and the total number of layers was 16.

5

Carbon fiber composite B-pillar reinforcement plate crashworthiness study

5.1

Comparison of stiffness results

Comparison of the results of solved calculations for the stiffness analysis of the B-pillar assembly of the original metal B-pillar assembly and the B-pillar assembly of the initial layup of carbon fiber composites is shown in Table 1.

Table 1.

Comparison of stiffness results

	Project	Raw steel reinforcement plate scheme	4.8mm symmetrical paving scheme
Parameter	Outer plate thickness/mm	3	3
	Reinforcing plate thickness/mm	2.8	4.8
	Outer plate mass/kg	6.25	6.25
	Reinforcing plate mass/kg	2.4	0.42
Mass	Total mass/kg	8.04	6.15
Mode	Torsional mode	70.98	75.36
Mode	Bending mode	148.21	155.39
Axial direction	Deformation/mm	1.520	1.427
Backward direction	Deformation/mm	9.871	9.021
Side direction	Deformation/mm	8.179	7.382
Weight loss	Weight loss ratio of reinforced plate/%		23.5
Weight loss	Weight loss/kg		1.890

From the comparison results, it can be seen that the stiffness of the carbon fiber composite B-pillar reinforcement plate with carbon fiber composites [0/45/90/-45/0/45/0/-0/-45]s of 16-ply layups is 6.1% higher than that of the original steel B-pillar reinforcement plate in terms of axial stiffness, 8.6% higher than that of the backward stiffness, 9.7% higher than that of the lateral bending performance, and 23.5% lower than the original steel B-pillar reinforcement plate in terms of weight reduction. The above results show that the overall stiffness of the carbon fiber composite material is increased, and there is a significant reduction in mass compared with the original steel material, which obviously achieves the purpose of lightweight.

5.2

Comparison of three-point bending results

Usually the performance evaluation of components needs to be realized in the body or the whole vehicle system, but the carbon fiber composite B-pillar often needs external resources to accomplish in the development, and also needs to be evaluated for individual parts, which usually take the equivalent alternative to the subsystem test. For the B-pillar, the most usual is the hydrostatic test of three-point bending of the B-pillar.

In this paper, a three-point bending analysis is performed on an assembly of carbon fiber composite B-pillar reinforcement plates, and a comparison of the strength results is shown in Table 2.

Table 2.

Comparison of strength results

Type of test		Maximum displacement D/mm	Maximum contact force F_N/N	Failure location	Failure mode
Metal material simulation		98.235	34168	Middle and upper B-column	variant
CFRP simulation		83.19	34850	Middle and upper B-column	variant
CFRP sample test	Test1	83.01	32893	Rigid column down position	fibre breakage
	Test2	82.86	33917
	Test3	82.64	34289
	Mean value	82.84	33700

From the comparison of the maximum deformation of the B-pillar assembly in Table 2, it can be seen that in the sample test, the average deformation of the B-pillar assembly is 82.84mm, and the maximum deformation is in the position of the metal stiffener column under pressure, which is also in the middle of the B-pillar, which is in line with the simulation. Within the allowable range of process and error, the simulation results are consistent with the test results, indicating that the strength of the carbon fiber composite B-pillar reinforcement plate is higher than that of the original steel material, which verifies the three-point bending performance of the carbon fiber composite B-pillar reinforcement plate.

5.3

Verification of vehicle side impact performance

Although through the stiffness comparison and three-point bending comparison study, we get the conclusion that the stiffness and hardness of the carbon fiber composite B-pillar reinforcement plate are better than the original steel material B-pillar reinforcement plate under the lightweight design, the final crashworthiness of the carbon fiber composite B-pillar reinforcement plate needs to be verified by the collision analysis of the whole vehicle model. Replace the steel B-pillar reinforcement plate with carbon fiber composite material in the original vehicle, and conduct side impact analysis.

Carbon fiber composite B-pillar model and the original steel material B-pillar model B-pillar intrusion speed comparison is shown in Figure 2.

It can be seen that the overall intrusion velocity of the whole vehicle with carbon fiber composite B-pillar reinforcement plate is not much different from that of the original steel B-pillar reinforcement plate, but for the peak intrusion velocity, the carbon fiber composite material is lower.

Carbon fiber composite B-pillar model and the original steel B-pillar model side impact B-pillar and door intrusion speed and intrusion amount are shown in Table 3.

Table 3.

Comparison of side impact results

Measured item		Raw steel B-column model	Carbon fiber composite B-column model
Measured item		Raw steel B-column model	Analysis result	Variation
B column mass/kg		4.97	3.41	↓1.56
B-column invasion rate(m/s)	Head	4.1	4.3	↑0.2
	Chest	6.6	5.8	↓0.8
	Abdomen	6.8	6.3	↓0.5
	Pelvis	6.7	6.2	↓0.5
Door penetration speed(m/s)	Chest	6.4	6.1	↓0.3
	Abdomen	7.3	6.8	↓0.5
	Pelvis	7.3	6.5	↓0.8
B-column intrusion/mm	Head	58	69	↑11
	Chest	109	101	↓8
	Abdomen	135	121	↓14
	Pelvis	133	117	↓16
Door penetration/mm	Chest	138	131	↓7
	Abdomen	142	135	↓13
	Pelvis	145	129	↓16

Compared with the original steel B-pillar model, the B-pillar of the carbon fiber composite B-pillar model corresponds to the reduction of the intrusion speed of the dummyss chest, abdomen and pelvis by 0.8m/s, 0.5m/s and 0.5m/s respectively, and the amount of intrusion is reduced by 8mm, 14mm, 16mm; and the door corresponds to the reduction of the intrusion speed of the dummyss chest, abdomen and pelvis by 0.3m/s, 0.5m/s and 0.8m/s respectively, and the amount of intrusion is reduced by 7mm, 13mm, 16mm. It can be seen that the use of carbon fiber composite B-pillar, which is designed for lightweighting, can improve the crashworthiness of the whole vehicle.

6

Conclusion

This paper proposes a carbon fiber composite passenger compartment B-pillar reinforcement plate design scheme based on the lightweight design strategy, and analyzes the crashworthiness of the carbon fiber composite B-pillar reinforcement plate.

The results of stiffness simulation analysis show that the stiffness of carbon fiber composite B-pillar reinforcement plate is 6.1% higher than that of the original steel B-pillar reinforcement plate in terms of axial stiffness, 8.6% higher in terms of rearward stiffness, 9.7% higher in terms of lateral bending performance, and 23.5% weight reduction. The three-point bending test shows that the displacement of the carbon fiber composite B-pillar is 15.045mm lower than that of the original steel material B-pillar with a contact force 682N higher than that of the original steel material B-pillar.

Through the collision analysis of the whole vehicle model, the peak intrusion velocity of carbon fiber composite B-pillar reinforcement plate is lower than that of the original steel material B-pillar reinforcement plate, and the intrusion velocities of the corresponding dummyss thorax, abdomen and pelvis are reduced by 0.8m/s, 0.5m/s and 0.5m/s, respectively, and the amount of intrusion is reduced by 8mm, 14mm and 16mm, which proves that the adoption of the lightweight-oriented design of the carbon fiber composite B-pillar has the best performance in the resistance to impact. This proves that the carbon fiber composite B-pillar with lightweight-oriented design is better than the original steel B-pillar in terms of crashworthiness.

Langue:: Anglais

Périodicité:: 1 fois par an
Sujets de la revue:: Sciences de la vie, Sciences de la vie, autres, Mathématiques, Mathématiques appliquées, Mathématiques générales, Physique, Physique, autres

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Crashworthiness study of carbon fiber composite passenger compartment B-pillar reinforcement plate under multi-scale lightweight design strategy

Haiyang Yang

Zhaopeng Cao

Jinhao Wu

Xin He

Keyan Liu

Yinjie Lou

Wei Wang

Publié en ligne: 19 mars 2025

Reçu: 15 nov. 2024

Accepté: 15 févr. 2025

DOI: https://doi.org/10.2478/amns-2025-0498

Mots clésCarbon fiber composite material, Lightweight, B-pillar reinforcement plate, Optimized design, Crashworthiness

© 2025 Haiyang Yang et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Mots clés
Carbon fiber composite material, Lightweight, B-pillar reinforcement plate, Optimized design, Crashworthiness