In recent years, the rapid growth in the adoption of electric SUV vehicles has heightened concerns about their safety performance in various collision scenarios. Among these, the frontal 25% offset collision, often referred to as small overlap collision, represents a significant portion of frontal accidents. This type of collision poses unique challenges due to the limited engagement of traditional energy-absorbing structures, making it crucial to evaluate and enhance the crashworthiness of electric SUV models. The Insurance Institute for Highway Safety (IIHS) has established specific test protocols for such collisions, which are not yet fully incorporated into regional standards like China’s C-NCAP. This study focuses on simulating and optimizing a pure electric SUV under these conditions to improve occupant safety. The integration of advanced materials and structural modifications is explored to address deficiencies in crash energy management and cabin integrity. Through finite element analysis and orthogonal experiments, we aim to develop effective strategies for mitigating collision impacts on electric SUV designs.
The finite element model of the electric SUV was developed using ANSA software, encompassing key components such as the body-in-white, passenger compartment, powertrain, battery pack, steering system, and suspension. The model, with a mass of 1,778 kg, consisted of 2,669,002 elements and 2,271,259 nodes. Shell elements were used for sheet metal parts, while rigid bodies represented high-stiffness components like the motor and transmission. The battery pack, positioned under the chassis, was modeled to assess its integrity during impact. Boundary conditions followed IIHS guidelines: a 25% overlap with a rigid barrier, a speed of 64 km/h, and a simulation time of 0.12 s. Friction coefficients were set at 0.15 for the barrier and 0.1 for the ground. LS-DYNA explicit solver was employed for the analysis, ensuring energy conservation and validity with a hourglass energy ratio below 5%. The initial simulation revealed critical issues, including excessive acceleration peaks and significant cabin intrusion, highlighting the need for structural enhancements in this electric SUV.
Analysis of the baseline electric SUV model showed a peak acceleration of 56.54g in the X-direction at the left B-pillar, exceeding the IIHS target of 50g, which could lead to severe occupant injuries. The Y-direction acceleration peaked at 26.83g, further compounding the risk. The front dash panel experienced a maximum intrusion of 246.59 mm, far beyond acceptable limits for occupant safety. Energy absorption data indicated that key components like the crash boxes and front longitudinal beams were ineffective in dissipating impact energy, with only 1.0 kJ and 4.22 kJ absorbed, respectively. Instead, the upper longitudinal beam, A-pillar, and mid-floor side beam became primary load paths, absorbing 9.39 kJ, 8.82 kJ, and 19.4 kJ, respectively. This misallocation of energy led to severe deformation in the passenger compartment. Structural ratings based on IIHS criteria were “poor” for the upper cabin areas, such as the instrument panel and upper hinge, due to excessive intrusion, while the lower cabin rated “good.” The battery pack maintained a safe distance from deformation, preserving high-voltage system integrity but not improving the overall rating. These findings underscore the urgency for optimizing the electric SUV’s frontal structure to enhance crashworthiness.
| Component | Energy Absorbed (kJ) | Percentage (%) |
|---|---|---|
| Front Bumper Beam | 2.88 | 1.34 |
| Left Crash Box | 1.00 | 0.47 |
| Right Crash Box | 0.23 | 0.11 |
| Left Front Longitudinal Beam | 4.22 | 1.97 |
| Right Front Longitudinal Beam | 1.54 | 0.72 |
| Left Upper Longitudinal Beam | 9.39 | 4.39 |
| Right Upper Longitudinal Beam | 0.55 | 0.26 |
| Left A-Pillar | 8.82 | 4.11 |
| Right A-Pillar | 0.11 | 0.05 |
| Left Mid-Floor Side Beam | 19.40 | 9.06 |
| Right Mid-Floor Side Beam | 0.19 | 0.09 |
To address these issues, two optimization phases were implemented for the electric SUV. The first phase focused on improving the collision force transmission path by modifying the front-end structure. Inspired by designs like the Honda Civic, the front bumper beam was extended with an internal sleeve, the crash box front cross-section was enlarged, the upper longitudinal beam was lengthened with a larger cross-sectional area, and a connecting rod was added between the front and upper longitudinal beams. These changes aimed to engage traditional energy-absorbing components more effectively. The second phase enhanced the passenger compartment stiffness using lightweight aluminum alloys. Ribs were added to the mid-floor side beams, and the A-pillar reinforcement was extended. Material properties were upgraded: A-pillar outer and inner panels were changed to 215 MPa strength with thicknesses of 1.2 mm and 2.0 mm, respectively; sill beams and mid-floor side beams used 280 MPa strength with thicknesses of 1.8 mm and 2.8 mm, respectively. The mass increased slightly from 1,778 kg to 1,784 kg, with the body-in-white mass rising from 365.047 kg to 370.078 kg. These optimizations aimed to reduce intrusion and improve the structural rating of the electric SUV.
The optimization results demonstrated significant improvements in the electric SUV’s crash performance. After the first phase, the maximum intrusion of the front dash panel decreased to 173.24 mm, and further to 151.29 mm after the second phase, representing a 38.65% reduction from the baseline 246.59 mm. The structural rating improved from “poor” to “good,” with most measurement points showing reduced intrusion. However, the peak acceleration in the X-direction increased from 49.77g to 55.25g after the second phase due to heightened stiffness, posing a risk to occupants. This trade-off necessitated further refinement through orthogonal experimentation to balance acceleration and intrusion in the electric SUV.
| Component | Original Strength (MPa) | Original Thickness (mm) | New Strength (MPa) | New Thickness (mm) |
|---|---|---|---|---|
| A-Pillar Outer Panel | 125 | 1.0 | 215 | 1.2 |
| A-Pillar Inner Panel | 125 | 1.8 | 215 | 2.0 |
| Sill Beam | 215 | 1.5 | 280 | 1.8 |
| Mid-Floor Side Beam | 215 | 2.5 | 280 | 2.8 |
An L9(3^4) orthogonal experiment was conducted to optimize the electric SUV further, focusing on reducing peak acceleration while maintaining low intrusion. The factors included crash box thickness (A: 2.8, 3.0, 3.2 mm), front longitudinal beam thickness (B: 2.8, 3.0, 3.2 mm), A-pillar reinforcement thickness (C: 1.5, 1.8, 2.0 mm), and A-pillar reinforcement material (D: HC340/590DP, HC550/980DP, HC600/980QP). The target responses were peak acceleration and front dash panel intrusion. The orthogonal array and results are summarized below, with the optimal combination derived from range analysis.
| Experiment | A | B | C | D | Peak Acceleration (g) | Intrusion (mm) |
|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 1 | 1 | 43.00 | 154.87 |
| 2 | 1 | 2 | 2 | 2 | 51.90 | 151.93 |
| 3 | 1 | 3 | 3 | 3 | 55.86 | 147.27 |
| 4 | 2 | 1 | 2 | 3 | 55.14 | 146.57 |
| 5 | 2 | 2 | 3 | 1 | 49.25 | 151.36 |
| 6 | 2 | 3 | 1 | 2 | 56.31 | 146.49 |
| 7 | 3 | 1 | 3 | 2 | 54.15 | 149.08 |
| 8 | 3 | 2 | 1 | 3 | 52.20 | 151.48 |
| 9 | 3 | 3 | 2 | 1 | 55.19 | 148.20 |
Range analysis was performed to determine the influence of each factor on the responses. For peak acceleration, the mean values \( k_i \) and ranges \( R_j \) were calculated using the formulas:
$$ k_i = \frac{\sum k_{ij}}{3} $$
$$ R_j = \max[k_i] – \min[k_i] $$
where \( k_{ij} \) is the sum of results for factor j at level i. The results indicated that factor B (front longitudinal beam thickness) had the greatest influence on peak acceleration (\( R_j = 5.024 \)), followed by D (material, \( R_j = 4.853 \)), A (crash box thickness, \( R_j = 3.594 \)), and C (A-pillar thickness, \( R_j = 3.574 \)). For intrusion, factor B was also most influential (\( R_j = 4.27 \)), with A (\( R_j = 3.217 \)), D (\( R_j = 3.037 \)), and C (\( R_j = 2.047 \)) following. The optimal combination for minimizing acceleration was A1B1C1D1, and for minimizing intrusion was A2B3C2D3. Balancing cost, lightweight requirements, and influence, the final combination selected was A2B2C1D2 (crash box thickness 3.0 mm, front longitudinal beam thickness 3.0 mm, A-pillar reinforcement thickness 1.5 mm, and material HC550/980DP).
Validation of this optimal combination for the electric SUV showed a peak acceleration of 44.77g, a reduction of 10.48g (18.97%) from the pre-orthogonal value of 55.25g, and within the IIHS target. The front dash panel intrusion was 146.49 mm, lower than the pre-orthogonal 151.29 mm. This demonstrates the effectiveness of the orthogonal experiment in refining the electric SUV design to achieve a balance between safety and performance.
In conclusion, this study successfully addressed the crash safety challenges of a pure electric SUV in frontal 25% offset collisions through finite element simulation and multi-stage optimization. The initial design exhibited inadequate energy absorption and excessive cabin deformation, leading to a “poor” IIHS rating. By improving collision force paths and enhancing passenger compartment stiffness with aluminum alloys, the electric SUV achieved a “good” rating with a 38.65% reduction in intrusion. The orthogonal experiment further optimized the design, reducing peak acceleration by 18.97% while maintaining low intrusion. These findings highlight the importance of integrated structural and material approaches in developing safer electric SUV vehicles. Future work should explore occupant injury metrics and system-level interactions to comprehensive enhance electric SUV crashworthiness.