How do crumple zones reduce the risk of injury?

Question

And what ideas is there to do with them about speed, forces and energy?

Answer 1

These are areas in a vehicle that are designed to absorb pressure during a collision and prevent damage to the passenger cabin.

Answer 2

When a car is in motion it possesses kinetic energy. The faster it is travelling the more kinetic energy the vehicle has.

When the vehicle is in a collision there is a momentum change over a very short period of time. To change the momentum the thing that you've hit applies an equal and opposite force on your vehicle. The energy of your initial momentum has to be absorbed. Crumple zones are structure designed so that the impact force does work on them rather than your body.  Work is required to bend a material or structure (i.e. you'd have to use energy to bend an iron bar).

Crumple zones absorb a high proportion of the energy transfer in a collision so that less energy is imparted on the occupants, reducing the risk of injury.

Answer 3

Old school thinking was that car bodies should be made stronger to withstand a collision or impact.  The problem with this thought is that when an impact occurs, a vehicle stops suddenly but the occupant(s) in the vehicle continue to travel at the same speed.

With crumple zones, the areas outside of the safety cell ( the vehicle's interior or cabin ) are designed to absorb the impact which slows the car down at a slower rate.  This energy absorption helps offset or minimize the injuries to the occupants.

Answer 4

Crumple zones work by managing the crash energy so that it is absorbed within the frontal section of the vehicle (energy is transformed by the deformation instead of being directly transmitted through the body of the occupants), while also preventing intrusion into or deformation of the passenger cabin. This acts to ensure that car occupants are better protected against injury. In simplistic terms, this is done by controlled weakening of outer parts of the car while strengthening the inner (passenger cabin) part of the body by using more reinforcing beams and increasingly, higher strength steels.

A common misconception about crumple zones is that they reduce safety by allowing the vehicle's body to collapse, crushing the occupants. In fact, crumple zones are located in front and behind of the main body of the car, compacting within the space of the engine compartment or boot. The marked improvement over the past two decades in high speed crash test results and real-life accidents also belies any such fears. Modern vehicles using what are commonly termed 'crumple zones' provide, on average, far superior protection for their occupants in severe tests than older models.

The only other general downside to crumple zones is that repair costs are higher in "fender bender" accidents.