page_title: Crumple zone
section_title: Function
hierarchical_section_title: Crumple zone / Function
caption_attribution_description: English: Volkswagen Polo after a full frontal crash test into a deformable wall at the Transportation Research Laboratory.
context_page_description: Crumple zones, crush zones, or crash zones, are a structural safety feature used in vehicles, mainly in automobiles, to increase the time over which a change in velocity occurs from the impact during a collision by controlled deformation; in recent years also incorporated into trains and railcars.
  Crumple zones are designed to increase the time over which the total force from the change in momentum is applied to an occupant, as the average force applied to the occupants is inversely related to the time over which it is applied.
  where is the force, is the time, is the mass, and is the velocity of the body. In SI units, force is measured in newtons, time in seconds, mass in kilograms, velocity in metres per second, and the resulting impulse is measured in newton seconds.
  Typically, crumple zones are located in the front part of the vehicle, in order to absorb the impact of a head-on collision, though they may be found on other parts of the vehicle as well. According to a British Motor Insurance Repair Research Centre study of where on the vehicle impact damage occurs: 65% were front impacts, 25% rear impacts, 5% left side, and 5% right side.
context_section_description: Crumple zones work by managing crash energy and increasing the time over which the deceleration of the occupants of the vehicle occurs, while also preventing intrusion into or deformation of the passenger cabin. This better protects car occupants against injury. This is achieved by controlled weakening of sacrificial outer parts of the car, while strengthening and increasing the rigidity of the inner part of the body of the car, making the passenger cabin into a "safety cell", by using more reinforcing beams and higher strength steels. Impact energy that does reach the "safety cell" is spread over as wide an area as possible to reduce its deformation. Volvo introduced the side crumple zone with the introduction of the SIPS (Side Impact Protection System) in the early 1990s.
  When a vehicle and all its contents, including passengers and luggage are travelling at speed, they have inertia / momentum, which means that they will continue forward with that direction and speed (Newton's first law of motion). In the event of a sudden deceleration of a rigid framed vehicle due to impact, unrestrained vehicle contents will continue forwards at their previous speed due to inertia, and impact the vehicle interior, with a force equivalent to many times their normal weight due to gravity. The purpose of crumple zones is to slow down the collision to increase the time over which the occupants decelerate so as to decrease the peak force imparted on the occupants over a given time.
  Seatbelts restrain the passengers so they don't fly through the windshield, and are in the correct position for the airbag and also increase the time over which the occupants decelerate. Seat belts also absorb passenger inertial energy by being designed to stretch during an impact, again to increase the time over which an occupant decelerates. In short: a passenger whose body is decelerated more slowly due to the crumple zone (and other devices) over a longer time survives much more often than a passenger whose body indirectly impacts a hard, undamaged metal car body which has come to a halt nearly instantaneously. It is like the difference between slamming someone into a wall headfirst (fracturing their skull) and shoulder-first (bruising their flesh slightly) is that the arm, being softer, has tens of times longer to slow its speed, yielding a little at a time, than the hard skull, which isn't in contact with the wall until it has to deal with extremely high pressures. The stretching of seatbelts while restraining occupants during an impact, means that it is necessary to replace them if a vehicle is repaired and put back on the road after a collision. They should also be replaced if their condition has deteriorated e.g. through fraying or mechanical or belt mounting faults. In New Zealand it is officially mandatory to replace worn inertia reel type seatbelts only with "webbing grabber" type belts that have less play and are more effective on older cars. Newer cars have electronically fired pre-tension seatbelts that are timed to work with the airbag firing. Buying used seatbelts is not a good idea even in countries where it is legal to do so, because they may have already been stretched in an impact event and may not protect their new users as they should.
  The final impact after a passenger's body hits the car interior, airbag or seat belts is that of the internal organs hitting the ribcage or skull due to their inertia. The force of this impact is the way by which many car crashes cause disabling or life-threatening injury. Other ways are skeletal damage and blood loss, because of torn blood vessels, or damage caused by sharp fractured bone to organs and/or blood vessels. The sequence of speed-reducing technologies—crumple zone — seat belt — airbags — padded/deformable interior—are designed to work together as a system to reduce the peak force of the impact on the outside of the passenger(s)'s body by lengthening the time over which this force is imparted. In a collision, slowing down the deceleration of the human body by even a few tenths of a second drasti
caption: Volkswagen Polo after a full frontal crash test into a deformable wall at the Transport Research Laboratory
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