When a car collides, it will produce a huge impact force. If the impact force directly acts on the body, the body will be deformed or even damaged in a large range. If the impact energy generated acts on the passengers, the passengers will be seriously injured; Most modern body designs will consider energy absorption design, which can be divided into collapse energy absorption and disassembly energy absorption. To prevent the secondary damage of debris after impact and secondary damage to the surrounding environment, most civil vehicles use collapse energy absorption, and most special vehicles such as racing cars use disassembly energy absorption. Military lightning protection and other special scenes use energy-absorbing materials to directly absorb impact energy. This paper mainly discusses civil vehicles.
1 the function of the energy-absorbing structure of the vehicle body the earliest design purpose of the vehicle collapse is to absorb the impact force generated by the collision with the deformation of the non-key parts of the vehicle body. When the vehicle decelerates suddenly after the collision, the passengers still move forward at high speed under the inertia, which is far beyond the bearing capacity of the human body. Collapse design is used to provide a certain buffer for sudden deceleration, to reduce the maximum damage that passengers may suffer. In the automotive industry all over the world, collapse design has become an important basis to measure the safety of a vehicle.
2 in traditional engineering materials, pores (macroscopic or microscopic) are considered to be a structural defect because they are often the core of crack formation and propagation, and have adverse effects on the physical and mechanical properties of materials. However, when the number of pores in the material increases to a certain extent, the material will produce some special functions due to the existence of holes, thus forming a new material category, that is, the so-called porous (porous) material, also known as a foam material. Foam metal has a series of excellent properties: high porosity, high specific strength, high specific stiffness, energy absorption, good damping, and shock absorption, corrosion resistance, high-temperature resistance, electromagnetic shielding, non-toxic, easy to process, and can be applied to surface treatment of coating. Because of its excellent physical and mechanical properties, foam metals can be used as structural materials as well as functional materials. In general, it has the dual functions of function and structure. It is a multifunctional engineering material with excellent performance integrating function and structure. Because of its physical, thermal, acoustic, and electromagnetism properties, the foam metal itself has many physical properties. The foam metal structure material is used to absorb energy by the super light structure and the energy absorption characteristics of the foam. At present, aluminum foam is the most widely used porous metal in China. So the major manufacturers now use foam aluminum as the preferred material for energy-absorbing filling materials.
Properties of 3 aluminum foam aluminum
Aluminum foam aluminum has ultra-low density. At present, the international advanced foam aluminum technology has been able to achieve precise control of molding density between 0.25-0.8g/cm3, which is a lightweight high-quality metal material. At the same time, it has high strength, and its bending specific stiffness can reach 1.3-1.5 times that of steel; An energy absorbing platform capable of reaching 2-10mpa in energy absorption; In terms of sound absorption performance, through the test data, the sound absorption coefficient can be more than 0.9 and the noise reduction coefficient is 0.5; The damping performance can reduce the mechanical vibration by two orders of magnitude, and the damping performance can reach 5-10 times that of metal aluminum alloy through calculation; In terms of protection performance, it can make the explosion shock wave decay exponentially, and its energy absorption capacity is 3-6kj / cm2.
4 typical application scenarios of foam aluminum in automobile structure
4.1 front and rear anti-collision unit the front anti-collision energy absorption of the car is between the front of the car and the cab. Starting from the front of the car, metal materials with different strengths are designed into stepped areas with different strengths. In case of collision, the most vulnerable front of the car will collapse and deform first, followed by the second section, and then the third section. In the sequential collapse and deformation, gradually maximize the impact energy generated by the collision, To ensure the safety of the passenger compartment, an energy-absorbing box is designed based on a passenger car. The energy-absorbing box adopts aluminum foam aluminum as core energy absorbing and damping material, and core aluminum foam is filled with a thickness of 20mm and density of 0.6g/cm3-0.8g/cm3. The outer skeleton adopts a 6061 aluminum alloy structure, and the collapse point is set on the outer skeleton. The two are brazed and combined. In this way, the lightweight automobile energy absorption box can be realized and has a good function of absorbing impact kinetic energy; Cooperate with the structural design of installation point and installation form to meet the requirements of automobile installation.
4.2 the use of aluminum foam aluminum for the passenger compartment floor has good energy absorption and sound absorption characteristics. It can use a sandwich foam aluminum material to make an automobile floor. It can effectively achieve the effect of isolation and sound insulation while ensuring strength and rigidity. It can reduce noise by 2-4 times compared with a physical plate, thereby enhancing vehicle comfort and greatly reducing noise during vehicle running.
4.3 the electric vehicle battery box has excellent vibration damping by using aluminum foam aluminum. The pure electric vehicle battery box filled with aluminum foam on the floor and side panels can effectively absorb energy and prevent earthquakes and protect the battery. If the car body collides, the side panel of the battery box will collapse and absorb energy. At the same time, the force will be transferred to a certain extent through the structure, which can effectively prevent damage to the battery cell and reduce the possibility of explosion and fire after the collision to a certain extent. Similarly, the aluminum foam has good fire resistance characteristics. The treated aluminum foam can maintain 25 minutes without melting at 700 degrees centigrade. Even when the battery is burning, it can effectively form protection and win the critical time for passengers to escape. Taking an innovative design plan as an example, a battery box of a new energy electric vehicle filled with aluminum foam aluminum material is designed. The first mode of 40Hz can be achieved by simulation calculation. Under the condition that the mass of battery modules and other components is evenly distributed in the layout area of the battery system, the model applies various strength conditions such as z-4g acceleration, x-1g ± 1g acceleration, positive x-1g, and negative z-1g acceleration, negative x-1g and negative z-1g acceleration, positive y-1g and negative z-1g acceleration, negative y-1g and negative z-1g acceleration respectively. The final result can realize that the bottom deformation is less than 1.5mm without yielding and stress concentration; In the process of half-cylinder extrusion of parts, straight half-cylinders with a radius of 50mm, 75mm, and height of 500mm are respectively used to apply unit load for the test. The test results show that the deformation of the battery box is less than the space gap between the box and the module, and the deformation will not affect the battery pack. In conclusion, the design scheme of the battery box with a "sandwich" structure can meet the design and use requirements, Through significant lightweight effect, it can effectively improve the capacity density of the battery and increase the endurance of the vehicle.
4.4 local energy absorption structure of the body with the development of new energy electric vehicles, the body structure has gradually changed from a steel structure to a steel-aluminum hybrid body, and now the all-aluminum body is becoming more and more mature. If the aluminum alloy body is filled with aluminum foam, the stiffness is expected to increase by more than 1.5-2 times, and the damping capacity and the shockproof capability can be increased by more than 2 times.
Because of its ultra-low density, high specific strength, high specific stiffness, and energy absorption, Al-based aluminum foam can be used as an important energy-absorbing structural member on a lightweight body. It can effectively enhance vehicle body energy-absorbing platform and improve vehicle body stiffness on the premise of ensuring lightweight index. With the maturity of the process and the improvement of the composite means, the composite foam aluminum material will bring greater changes to various structural parts of the automobile.