Protecting Occupants

Passenger vehicles come in many shapes and sizes, yet they have at least one thing in common: they need to protect the occupants in an accident. Vehicle manufacturers design and test for a number of crash scenarios including front, rear, and side impact and roll-over. The goal is not to prevent vehicle damage; instead, it is to design the body structure to absorb or deflect energy to protect the passenger compartment.

Success Stories 

Crash Management

The governing body in North America is the National Highway Traffic Safety Administration (NHTSA), along with the Insurance Institute for Highway Safety (IIHS), which does extensive testing because of coverage of accidents by auto insurance companies. IIHS evaluates a vehicle's crashworthiness with the help of six tests: moderate overlap front, driver-side small overlap front, passenger-side small overlap front, side, roof strength, and head restraints & seats.[1]

For crash management, the vehicle is designed to provide a load path that protects the occupants. Think of the force of a car hitting another vehicle in the side. The load path is one where the incoming vehicle hits the rocker panel and the door first. These systems are designed to absorb and deflect energy from the passenger compartment. See the Tesla Model Y in Success Stories for a great video by Tesla on how crash management works. The AEC has already profiled rockers and roof supports; hence the focus here is on front and rear crashes. 

Structural Benefit

The load path at the front and the rear: the point of impact is the fascia, which is an aesthetic plastic cover with little structural benefit. Doing the energy absorption work is the bumper beam, and behind it, the crash cans behind it. Follow the arrows on the image here to see how the crash energy is directed around the passenger compartment.

Today, we are studying the bumper beam, which will be referred as the bumper, and secondly, by the crash cans, also referred as crash boxes or crush cans.

Bumper & Crash Cans

The bumper and crash cans are the first line of defense to protect against impact in the front or rear. These components are positioned far from the center of gravity of the vehicle, which is advantageous in maintaining a low weight.

Extruded aluminum bumper systems are found on more than 50% of the vehicles, from the older and economical Chevy Cruz, to the newly designed 2021 Ford Mach-E electric car. The versatility and value are further recognized by the usage across powertrains, internal combustion engine (ICE), and electric (EV), and across body-in-white materials, steel, and aluminum-intensive body structures.

Aluminum Alloys

On a unit-weight basis, aluminum alloys show higher energy absorption than steels of equivalent yield strength. Energy absorption can be increased by increasing the gauge thickness; but since that will result in increasing weight, a better approach is to select a material with a higher yield strength[3].

Perhaps the EVs are the most impressive application of all because the gross vehicle weight is around 450 kg more than a comparable ICE and because the battery pack is large and crash-sensitive, leaving less room to absorb energy. Even with the higher weight and reduced space, aluminum extrusions are still the choice for the new Ford Mustang Mach-E electric car!

Vehicle Bodies

The Ford Mach-E body is more than 90% steel, the vehicle is 36% heavier than the baseline Mustang, and there is 10% less space in the crumple zone—yet Ford decided that the best solution for the front bumper system was extruded aluminum.[2]


The Mustang Mach-E program paid particular attention to the small offset reinforced barrier (SORB) test. Ford set their sights on a 5-star rating. To achieve it, the bumper beam was extended outward from the crash cans in both directions. This image highlights the bumper beam extended portion, as well as the reinforcement in the crash can.

Bumpers & Crash Cans

In an automotive crash that meets the bumper, the first goal is to both absorb the energy, and secondly to divert the impact load away from the passenger compartment. The bumper beam is engineered to absorb the load, which is why it is commonly produced in high-strength aluminum alloys, such as the high crush alloy 6082. The beams have multiple hollows, forcing the energy to crush multiple regions before transferring further into the vehicle. Multi-material solutions are growing in popularity by many OEMs.

Multi-Hollow Bumper Beams

Crash Cans

Behind the bumper beam are the crash cans. These cans look like simple shapes, and are often welded to the beams, yet they are well-engineered products. Proper alloy design typically involves yield strength along with a measure of cracking tendency, according to an excellent technical paper from the Eleventh International Aluminum Extrusion Technology Seminar-ET '16, "Extrusions for Automotive Crash Applications" by N. Parsons, J-F. Beland, and J. Fourmann of Rio Tinto Aluminum. The properly designed can crushes like an accordion, without cracking. Each fold happens in a specific location as initiated by a physical modification to the corners - the Jeep Compass has holes on the corners, whereas the can below has impressions on the flat surfaces.

It is imperative to use computer-aided engineering (CAE) tools to simulate reality in the materials and in the systems to produce a reliable car or truck in a timely and profitable fashion. Millions of hours are spent doing CAE across the car, and it is equally important that the CAE engineers have good material data for their models.

Simulations for Optimal Design

The extrusion community has been generating good data through simulation on real vehicles and with consistent manufacturing processes. The images here show how a well simulated crash can performs to the real crash can. Source: SAPA presentation, Dr. David Lukasak, 2017.

Why Are Extrusions Well-Suited for Crash Management Solutions?

Extrusions deliver an efficient geometry providing multiple functions and benefits:

  • Lightweighting
  • Energy absorption is greater than steel for equivalent weight
  • Superior fracture resistance
  • Ease to produce multi-hollows
  • Ease of assembly & integration
  • Ease to tailor alloy & geometry for energy absorption
  • Vehicle is more stable with lightweight components far from CG

Versatile & Innovative Integration

  • Welding
  • Fasteners
  • Rivets (Aluminum to Steel) 

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