In recent years, the rapid depletion of global fossil resources and the environmental pollution caused by traditional fuel vehicles have accelerated the development of new energy vehicles. As a key component, the EV power battery is typically mounted at the bottom of the vehicle to optimize the center of mass and passenger space. However, this placement makes the battery pack vulnerable to impacts from road debris and protruding objects during high-speed driving, leading to mechanical damage and potential safety hazards such as fires or explosions. In China, the EV battery industry has grown significantly, emphasizing the need for robust protection systems. This study focuses on the design and evaluation of a trapezoidal corrugated sandwich structure for the bottom protection of China EV battery packs. We investigate the static indentation performance of this structure under two connection methods—bonding and riveting—using an electronic universal testing machine. Our aim is to analyze the protective capabilities and provide insights for enhancing the safety of EV power battery systems in real-world conditions.
The trapezoidal corrugated sandwich structure consists of an upper panel, a core layer, and a lower panel. In our design, the upper and lower panels were fabricated from 1.5 mm thick 6061 aluminum alloy using laser cutting, while the core layer was formed from 1.5 mm thick Q235 carbon steel through bending processes to create a corrugated shape. The overall dimensions of the structure were 400 mm × 800 mm × 14.3 mm, chosen to balance density and the typical size of EV power battery packs. To examine the influence of connection methods on protective performance, we prepared two sets of specimens: one with epoxy resin bonding and the other with mechanical riveting. The bonding method ensured full contact between the core and panels, whereas riveting involved fastening with rivets, leaving potential gaps at the interfaces. This comparative approach allows us to assess how connection integrity affects the structural response under static indentation loads, which is critical for China EV battery applications where impact resistance is paramount.
| Component | Material | Thickness (mm) | Connection Method |
|---|---|---|---|
| Upper Panel | 6061 Aluminum Alloy | 1.5 | Bonding / Riveting |
| Core Layer | Q235 Carbon Steel | 1.5 | Bonding / Riveting |
| Lower Panel | 6061 Aluminum Alloy | 1.5 | Bonding / Riveting |
Static indentation tests were conducted to simulate scenarios where the bottom of an EV power battery pack encounters obstacles, such as stones or uneven road surfaces. According to industry standards, a spherical indenter with a diameter of 150 mm was used to apply a compressive force at the weakest point of the protection structure. The test was performed at a constant speed of 0.25 mm/s, and the loading was stopped when the force reached 25 kN, representing 110% of the full vehicle load capacity. This setup ensures that the evaluation aligns with real-world demands for China EV battery safety. We employed an electronic universal testing machine to precisely control the indentation process and measure force-displacement responses. The specimens were securely fixed using a box-type fixture, which was mounted on the testing platform to prevent slippage. Linear displacement sensors were attached to the fixture to record real-time deformations of the lower panel, providing accurate data for analysis.
The force-displacement curves obtained from the static indentation tests reveal significant differences between the bonded and riveted specimens. For the bonded structure, the curve initially showed a steep rise, indicating high stiffness due to the uniform stress distribution facilitated by the epoxy resin. As displacement increased, a sudden drop and fluctuations occurred, corresponding to the debonding of the core and panels. In contrast, the riveted specimen exhibited a more gradual force increase, with no sharp declines, suggesting that the load was primarily borne by localized contact points at the rivets. At the target force of 25 kN, the maximum deformation for the bonded structure was 10.97 mm, whereas the riveted one deformed by 19.4 mm. This translates to a 43.45% improvement in protective performance for bonding over riveting, highlighting the importance of connection methods in enhancing the safety of EV power battery packs. The deformation patterns observed post-test included plastic indentation on the upper panel and bulging on the lower panel, with no fractures, indicating that both designs met basic integrity requirements but bonding offered superior resistance.
| Connection Method | Maximum Deformation at 25 kN (mm) | Force at Initial Drop (kN) | Performance Improvement (%) |
|---|---|---|---|
| Bonding | 10.97 | Approx. 18 | 43.45 |
| Riveting | 19.4 | N/A | Baseline |
To further quantify the energy absorption characteristics, we analyzed the area under the force-displacement curves, which represents the energy dissipated during indentation. The energy absorption for a structure can be expressed as: $$ E = \int_{0}^{d} F \, dx $$ where \( E \) is the absorbed energy, \( F \) is the force, and \( x \) is the displacement. For the bonded specimen, the energy up to 25 kN was higher due to the larger force sustained before debonding, whereas the riveted one had lower energy absorption because of earlier yielding at the rivet points. This emphasizes that for EV power battery applications, maximizing energy dissipation is crucial to mitigate impact effects. Additionally, the stress distribution in the core layer can be modeled using the following relation for sandwich structures: $$ \sigma = \frac{F}{A} + \frac{M y}{I} $$ where \( \sigma \) is the stress, \( F \) is the applied force, \( A \) is the cross-sectional area, \( M \) is the bending moment, \( y \) is the distance from the neutral axis, and \( I \) is the moment of inertia. In bonded configurations, the stress is more evenly distributed, reducing peak stresses and delaying failure, which is vital for the longevity of China EV battery systems.
The deformation morphology of the specimens provided visual insights into the failure mechanisms. In bonded samples, debonding occurred between the core and panels under high displacement, leading to a loss of stiffness but without complete structural collapse. For riveted specimens, gaps at the interfaces allowed for relative movement, resulting in larger deformations but maintained connectivity through the rivets. This suggests that while riveting offers ease of assembly, bonding provides better overall protection for EV power battery packs by minimizing deformation under identical load conditions. We also considered the effects of material properties on performance; the use of aluminum alloys for panels and carbon steel for the core contributed to a lightweight yet strong design, aligning with the demands for efficiency in China EV battery technologies. The equivalent stiffness \( k \) of the sandwich structure can be approximated as: $$ k = \frac{E_p A_p}{L} + \frac{E_c A_c}{H} $$ where \( E_p \) and \( E_c \) are the Young’s moduli of the panel and core materials, \( A_p \) and \( A_c \) are their cross-sectional areas, \( L \) is the length, and \( H \) is the height. This formula highlights how material selection and geometry influence the structural response, underscoring the optimization potential for EV power battery protection.
| Parameter | Bonded Structure | Riveted Structure |
|---|---|---|
| Energy Absorbed at 25 kN (J) | Approx. 275 | Approx. 195 |
| Equivalent Stiffness (N/mm) | High | Moderate |
| Failure Mode | Debonding | Localized Yielding |
In discussion, the superior performance of bonded connections can be attributed to the continuous interface, which eliminates stress concentrations and enhances load transfer. This is particularly important for China EV battery packs, where repeated impacts from road conditions could accumulate damage. The 43.45% improvement in deformation resistance with bonding demonstrates that connection method is a critical factor in design optimization. However, bonding may be susceptible to environmental factors like temperature and humidity, which could degrade the epoxy over time. Riveting, while less effective in this test, offers mechanical reliability and ease of repair. For future developments, welding could be explored as an alternative to combine the benefits of both methods, providing even stronger connections for EV power battery protection. Moreover, the integration of smart materials or composite layers could further enhance energy absorption, contributing to the advancement of China EV battery safety standards. The dynamic response under impact loads could be modeled using differential equations: $$ m \frac{d^2 x}{dt^2} + c \frac{dx}{dt} + k x = F(t) $$ where \( m \) is mass, \( c \) is damping coefficient, \( k \) is stiffness, and \( F(t) \) is the time-dependent force. Such models would allow for predictive simulations in designing next-generation protection systems.
In conclusion, our static indentation tests on trapezoidal corrugated sandwich structures reveal that bonding significantly outperforms riveting in protecting EV power battery packs, with a 43.45% reduction in deformation at the standard load of 25 kN. The bonded configuration ensures better stress distribution and higher energy absorption, making it a preferable choice for China EV battery applications where impact resistance is crucial. The findings underscore the importance of connection integrity in sandwich structures and suggest that further research into welding or advanced composites could yield even better results. As the demand for new energy vehicles grows, optimizing bottom protection systems will play a key role in ensuring the safety and reliability of EV power batteries, contributing to sustainable transportation solutions globally.