Car bumper is not only an important part of the appearance of a car, but also a core component of collision safety. At first glance, it appears to be a smooth plastic shell, but underneath is an intricate energy-absorbing structure and metal frames. The design of this ``flexo"meets the aesthetic requirements of daily driving, and has a multi-layered energy absorption mechanism, which can protect the crew and the vehicle in the event of collision. This article will delve into the differences between the bumper the "outer shell" and internal structure to reveal which parts are truly energy-absorbing.
The Bumper's "Outer Shell" of the buffer: the dual role of aesthetics and basic security
1.Material Selection: Plastic, lightweight balance and weatherproof
Bumper The "outer shell" are usually made of engineering plastics, most commonly a mixture of polypropylene (PP) and ethylene-propylene-diene monomer rubber (PP EPDM). This material has the following characteristics:
- Shock resistance: Polypropylene retains its toughness even at low temperatures, allowing it to withstand minor scratches and low-speed collisions.
- Weatherproof: the addition of ethylene propylene rubber can improve the material's ability to resist ultraviolet rays and chemical corrosion, extending its service life.
- Lightweight: Plastic is only one-fifth as dense as steel, greatly reducing vehicle weight and improving fuel efficiency.
- Plasticity: Through injection molding process, complex curves can be precisely molded and seamlessly integrated with the vehicle's body lines.
Some high-end models come in polycarbonate (PC) or carbon fiber reinforced plastics (CFRP), further enhancing strength and aesthetics. For example, some BMW models have PC + ABS alloys on the front bumper casing, which adds scratch resistance while maintaining lightweight performance.
2.Functional positioning: the first line of defense in architectural decoration
The main task of the bumper housing is to absorb energy from a low-speed collision. According to tests by the Insurance Institute for Highway Safety, the plastic casing absorbs about 60% of the impact through elastic deformation, preventing damage to the vehicle's body panels in collisions at speeds of 4 to 8 kilometers per hour. In addition, it has the following functions:
- Aerodynamic optimization: Streamlined designs can reduce drag coefficient and minimize energy consumption during high-speed driving.
- Equipment mounting carrier: It provides fixed position sensors such as fog lights, radar, and cameras.
Pedestrian Protection: the pavement material is relatively hard, can reduce the impact of pedestrian head injuries.
ii. The Bumper's Internal Structure: Synergy of Energy-Absorbing Cores and Support Frames
1.Energy-Absorbing Buffer Layers: From 'hard collisions' to 'Soft Landings'
There is usually a layer of absorbent material hidden under the plastic casing, which converts collision energy into controllable plastic deformation. Common materials include:
- Polyurethane foam: Low density, good elasticity, absorbs energy through compression during low speed collisions. Buick Buick, for example, have polyurethane PU foam layers that reduces impact on the vehicle's longitudinal beams.
- Honeycomb Honeycomb Aluminum Structures: Some high-performance models use aluminum honeycomb core materials. Their hexagonal cell structures can collapse on impact, layer by layer, absorbing energy three times as efficiently as solid aluminum.
- Air Cavity Structures: Energy is absorbed through compressed and sealed air cavities, which are common in electric concept cars, balancing lightweight and energy absorption requirements.
2. Impact beam: 'Last line of defence' for energy transfer
Impact beams are the core metal structures inside bumpers and are usually made of high-strength steel or aluminum alloy. Its design must be guided by two key principles:
- Rigidity and toughness balance: In high-speed collisions, structural integrity should be maintained by transferring energy to the longitudinal beams of the vehicle, while in low-speed collisions, local deformation should be achieved to avoid excessive maintenance costs.
- Geometric Optimization: The bending stiffness is enhanced by the use of closed cross-section shapes such as "日" (Chinese character for "sun") or "eye"" (Chinese for "eye"). Toyota Corolla, for example, has a 1.5-millimetre-thick U-shaped steel beam combined with an energy-absorbing box design that reduces engine compartment damage by 40% in a 50km/h crash.
3. Energy-Absorbing Boxes: a ``precision regulator"for energy management
The suction box is a short pipe structure connecting the impact beam with the vehicle's longitudinal beams of the vehicle. They are usually characterized by internal folds or holes to induce controlled collapse. When a collision occurs, the suction cartridge deforms along a predetermined path, reducing peak impact forces by 30%-50%. For example:
- BMW's Hydraulic Energy-Absorbing Boxes: During a collision, they absorb energy through the flow of hydraulic fluid, similar to "squeezing toothpaste" to further flatten impact force curve.
- Tesla's Aluminium Energy Absorption Box: A multi-stage variable cross section design with different wall thicknesses in different regions to achieve gradient controlled energy absorption.
III. Energy Absorption Mechanism: A Multi-Level Energy Attenuation Chain from Outside to Inside
The energy absorption process of the bumper is a multi-layered, phased process of energy decay, the core logic of which is "soft first, hard later, phased absorption":
- First Stage (0-15 km/h): The plastic outer shell absorbs about 60% of its energy through elastic deformation, while the buffer layer is further compressed and the absorber is still unformed.
- Second Stage (15-30 km/h): The shell reaches its deformation limit and the suction box begins to collapse, slightly deforming the impact beam and transferring energy to the vehicle's longitudinal beams.
- Third Stage (>30km/h): The impact beam and the longitudinal beam of the vehicle share the energy, dispersing the impact throughout the body through structural deformation.
The design ensures that in low-speed collisions, only the casing and suction box need to be replaced, reducing repair costs by more than 50%. In high-speed collisions, it protects the occupant compartment through multiple levels of energy absorption.
IV. INTRODUCTION Front and rear bumpers: structural differences and Functional Emphases
While both front and rear bumpers follow the basic structure of "housing + absorbent layer + impact beam," the design emphases varies depending on the location:
- Front bumpers: They need to protect core components such as engines and radiators, so impact beams are usually thicker (e.g. 2mm of high strength steel) and have foam to pedestrian protection.
- Rear bumper: The rear bumper focuses on protecting the safety of the trunk and rear seat crew, so impact beams can be made of aluminum alloys to reduce weight, and the suction box is designed to be more responsive to the energy absorption requirements of rear bumps.
V. Future Trends: Material Innovation and Intelligent Energy Absorption
As car safety standards improve, bumper designs are moving in the following directions:
Composite applications: The wide use of carbon fiber reinforced plastics (CFRP) and glass reinforced plastics (GFRP) improves energy absorption efficiency while reducing weight.
Active Energy Absorption Technologies: Through piezoelectric materials or shape memory alloys, the structure can be pre-deformation prior to impact, absorbing some energy in advance.
Integrated design: the bumper and battery pack housing, vehicle longitudinal beams combination, to form an ``energy absorption chamber '', to improve collision safety of electric vehicles.
Epilogue: From "Decorator" to "Security Guard"
The bumper The "outer shell" and internal structure combine to form a complex energy management system. From the elastic deformation of the plastic casing to the collapse of the absorber box and the rigid support of the impact beam, the design of each layer reflects engineers' relentless pursuit of safety and efficiency. In the future, as materials science merges with smart technology, bumpers will become more than just the "face" for cars, they will evolve into "smart shields" to safeguard lives.
