In recent years, the automotive industry has increasingly focused on electric vehicles, with electric SUVs gaining prominence due to their versatility and environmental benefits. However, these vehicles face unique challenges in crash safety, particularly in low-speed collisions, where the bumper system plays a critical role in minimizing damage and repair costs. This study investigates the crashworthiness of a pure electric SUV’s front bumper under low-speed frontal impact conditions, based on the RCAR (Research Council for Automobile Repairs) bumper test protocols. We aim to analyze the energy absorption, deformation behavior, and structural integrity of the bumper system, and propose optimization strategies to enhance its performance while adhering to lightweight design principles. The growing adoption of electric SUVs necessitates a deeper understanding of their low-speed impact responses to improve vehicle insurance ratings and reduce maintenance expenses. Through finite element analysis and simulation, we evaluate the bumper’s behavior and identify key areas for improvement, ensuring compliance with RCAR standards and promoting safer, more economical electric SUV designs.
The RCAR low-speed bumper test is a standardized procedure designed to assess vehicle repair costs and crash performance in common urban collision scenarios. For frontal full-width impacts, the test requires the electric SUV to collide with a rigid barrier at a velocity of (10.0 ± 0.5) km/h, with the barrier height set at 455 mm ± 3 mm above ground level. The vehicle’s centerline must align with the barrier’s centerline, allowing a maximum lateral deviation of ±50 mm. During impact, the vehicle’s body height should not deviate by more than 10 mm from its static measurement. This setup ensures realistic simulation of low-speed accidents, focusing on the bumper system’s ability to absorb energy and protect critical components. The evaluation criteria include assessing structural deformations in chassis and body parts, preventing unintended activation of safety systems, and avoiding “ride-up” phenomena where the vehicle overrides the barrier. For electric SUVs, particular attention is paid to components like the fan and battery mounts, as their damage can lead to significant repair costs and safety hazards. The RCAR test provides a robust framework for comparing the low-speed crash performance of different electric SUV models, driving innovations in bumper design.
To simulate the low-speed frontal impact, we developed a detailed finite element model of the electric SUV using ANSA pre-processing software and LS-DYNA for dynamic analysis. The model incorporates the full vehicle structure, including the bumper system, chassis, and body panels, with simplifications applied to non-essential components to reduce computational complexity. Mesh generation adhered to strict quality standards, with element sizes ranging from 5 mm to 20 mm, ensuring accuracy in deformation and energy absorption predictions. The primary materials used for the bumper components, such as the crash beam and energy absorption boxes, were aluminum alloy 6005A, characterized by a yield strength of 215 MPa, tensile strength of 255 MPa, and elongation at break of 8%. Connections between parts included bolted, riveted, and welded joints, with contact definitions set to automatic single-surface and surface-to-surface interactions to mimic real-world behavior. The bumper barrier was modeled as a rigid body with dimensions conforming to RCAR specifications, and the entire system was subjected to gravitational acceleration of 9.81 m/s². The simulation parameters, including termination time and time step, were calibrated to ensure energy conservation and minimal hourglass energy, as validated by post-processing results. This finite element model serves as a reliable tool for analyzing the electric SUV’s low-speed crash response and guiding design improvements.
The energy analysis during the low-speed impact simulation confirmed the model’s reliability, with total energy remaining constant throughout the collision event. The kinetic energy of the electric SUV decreased initially as it contacted the barrier, then slightly recovered before stabilizing, while the internal energy increased correspondingly, indicating efficient energy absorption. The hourglass energy ratio peaked at only 0.428%, well below the acceptable threshold of 5%, demonstrating minimal numerical artifacts and high simulation fidelity. These energy trends are summarized in the following equations, where \( E_{\text{total}} \) represents the total energy, \( E_{\text{kinetic}} \) the kinetic energy, \( E_{\text{internal}} \) the internal energy, and \( E_{\text{hourglass}} \) the hourglass energy:
$$ E_{\text{total}} = E_{\text{kinetic}} + E_{\text{internal}} + E_{\text{other}} $$
$$ \Delta E_{\text{kinetic}} = -\Delta E_{\text{internal}} \quad \text{during impact} $$
Additionally, the deformation of the bumper system was critically analyzed. The crash beam exhibited significant bending, with a maximum intrusion of 96.85 mm in the x-direction, exceeding the 80 mm gap to the front-end module and risking fan damage. The energy absorption boxes showed minimal deformation, indicating that the crash beam’s insufficient stiffness prevented effective energy transfer. To quantify these observations, we measured the plastic deformation of key body and chassis components, as shown in Table 1. The front longitudinal beam recorded a plastic deformation of 7.02%, surpassing the 5% target and indicating visible structural damage, while other parts remained within acceptable limits.
| Component | Plastic Deformation (%) | Target Value (%) |
|---|---|---|
| Front Longitudinal Beam | 7.02 | 5 |
| Upper Longitudinal Beam | 2.43 | 5 |
| Front Bottom Guard | 2.90 | 5 |
| Front Wall Panel | 3.21 | 5 |
| A-Pillar Outer Panel | 0.13 | 5 |
| A-Pillar Inner Panel | 0.93 | 5 |
| A-Pillar Reinforcement | 0.02 | 5 |
| Floor Side Beam | 0.18 | 5 |
| Storage Box Bottom Bracket | 0.13 | 5 |
Further, the displacement of chassis components was evaluated at 10 measurement points, with results indicating that the front longitudinal beam points exceeded the 3 mm maximum allowable change, as detailed in Table 2. This underscores the need for bumper system enhancements to protect the electric SUV’s integral structures.
| Point Number | Displacement Before (mm) | Displacement After (mm) | Maximum Displacement (mm) |
|---|---|---|---|
| 1 | 3141.60 | 3137.57 | 4.03 |
| 2 | 2989.25 | 2985.48 | 3.87 |
| 3 | 2850.83 | 2847.31 | 3.52 |
| 4 | 2827.41 | 2824.64 | 2.87 |
| 5 | 2764.57 | 2763.01 | 1.56 |
| 6 | 2730.60 | 2731.61 | 1.01 |
| 7 | 2776.63 | 2776.10 | 0.53 |
| 8 | 2340.83 | 2340.79 | 0.04 |
| 9 | 2253.20 | 2253.18 | 0.02 |
| 10 | 2195.63 | 2195.63 | 0.00 |
The energy absorption characteristics of the crash beam and energy absorption boxes were analyzed to identify performance gaps. The crash beam absorbed over one-third of the total energy, while the energy absorption boxes contributed minimally, highlighting an imbalance in the energy management system. The energy distribution can be expressed mathematically, where \( E_{\text{beam}} \) is the energy absorbed by the crash beam, \( E_{\text{box}} \) is the energy absorbed by the energy absorption boxes, and \( E_{\text{total}} \) is the total energy absorbed:
$$ E_{\text{total}} = E_{\text{beam}} + E_{\text{box}} + E_{\text{other components}} $$
In our simulation, \( E_{\text{beam}} \) was significantly higher than \( E_{\text{box}} \), indicating that the crash beam’s excessive deformation diverted energy away from the energy absorption boxes. This inefficiency prompted the development of optimization strategies to improve the electric SUV’s low-speed crashworthiness.
Three optimization schemes were proposed to enhance the crash beam’s strength and stiffness, addressing the issues of excessive deformation and inadequate energy absorption. Scheme 1 involved changing the material from aluminum alloy 6005A to 6082, which has a higher yield strength, thereby increasing the beam’s resistance to deformation without adding weight. Scheme 2 increased the beam thickness from 2.8 mm to 3.0 mm, boosting stiffness but slightly increasing mass. Scheme 3 modified the beam’s cross-section from a “日”-shaped structure to a “目”-shaped design, adding reinforcement ribs to improve rigidity. Each scheme was simulated under the same RCAR test conditions, and the results were compared based on deformation, energy absorption, and component damage. The optimization aimed to ensure that the electric SUV meets RCAR requirements while maintaining lightweight attributes, crucial for electric vehicle efficiency.
Comparative analysis of the three schemes revealed that Scheme 1 performed best overall. The crash beam intrusion in the x-direction was reduced to 77.21 mm, below the 80 mm threshold, preventing contact with the front-end module and fan. The energy absorption boxes in Scheme 1 exhibited noticeable crushing, indicating effective energy dissipation. In contrast, Schemes 2 and 3 showed higher intrusions (94.59 mm and 95.62 mm, respectively) and minimal energy absorption box deformation. The energy absorption data, summarized in Table 3, demonstrates that Scheme 1 achieved the highest total energy absorption and optimal distribution between the crash beam and energy absorption boxes, aligning with the goal of enhancing the electric SUV’s low-speed impact performance.
| Scheme | Total Energy Absorbed (J) | Crash Beam Energy (J) | Energy Absorption Box Energy (J) |
|---|---|---|---|
| Scheme 1 | Approx. 15,000 | Approx. 6,000 | Approx. 4,500 |
| Scheme 2 | Approx. 14,500 | Approx. 6,500 | Approx. 3,000 |
| Scheme 3 | Approx. 14,000 | Approx. 5,500 | Approx. 2,800 |
Additionally, the plastic deformation of body and chassis components was re-evaluated for all schemes, as shown in Table 4. Scheme 1 reduced the front longitudinal beam deformation to 2.29%, within the 5% target, and maintained other components below deformation limits. Schemes 2 and 3 also improved performance but were less effective in minimizing mass increase. The displacement measurements for chassis points across all schemes remained under 3 mm, satisfying RCAR criteria. These results validate Scheme 1 as the superior option for the electric SUV, balancing crashworthiness with lightweight design.
| Component | Scheme 1 Deformation (%) | Scheme 2 Deformation (%) | Scheme 3 Deformation (%) |
|---|---|---|---|
| Front Longitudinal Beam | 2.29 | 1.79 | 2.31 |
| Upper Longitudinal Beam | 0.79 | 2.41 | 2.33 |
| Front Bottom Guard | 1.02 | 0.00 | 0.00 |
| Front Wall Panel | 4.52 | 3.49 | 3.61 |
| A-Pillar Outer Panel | 0.63 | 0.12 | 0.11 |
| A-Pillar Inner Panel | 0.00 | 0.00 | 0.00 |
| A-Pillar Reinforcement | 0.92 | 0.80 | 0.69 |
| Floor Side Beam | 0.45 | 0.19 | 0.22 |
| Storage Box Bottom Bracket | 0.24 | 0.15 | 0.16 |
The optimization process underscores the importance of material selection and structural design in enhancing the low-speed crash performance of electric SUVs. By adopting Scheme 1, the electric SUV achieves a balance between strength and weight, reducing repair costs and improving safety. The mathematical representation of the crash beam’s bending behavior can be described using beam theory, where the bending stress \( \sigma \) is given by:
$$ \sigma = \frac{M y}{I} $$
Here, \( M \) is the bending moment, \( y \) is the distance from the neutral axis, and \( I \) is the moment of inertia. For a rectangular cross-section, \( I = \frac{b h^3}{12} \), where \( b \) is the width and \( h \) is the height. In Scheme 3, the “目”-shaped cross-section increases \( I \), reducing stress and deformation, but Scheme 1’s material change provides a more mass-efficient solution. This approach not only meets RCAR standards but also supports the broader adoption of electric SUVs by addressing key safety concerns.
In conclusion, this study demonstrates the critical role of bumper system design in the low-speed crashworthiness of electric SUVs. Through finite element simulation and RCAR-based analysis, we identified weaknesses in the original crash beam, such as excessive deformation and inadequate energy absorption, which could lead to costly repairs and safety issues. The proposed optimization schemes, particularly Scheme 1 with its material upgrade to aluminum alloy 6082, significantly improved performance by reducing intrusions and enhancing energy distribution. This optimization ensures that the electric SUV complies with RCAR requirements, minimizes damage to critical components like the fan, and supports lightweight objectives. Future work could explore additional materials or hybrid designs to further advance electric SUV safety, contributing to sustainable and economical vehicle development. The insights gained here provide a foundation for manufacturers to enhance low-speed impact resilience, ultimately benefiting consumers and the automotive industry.