We have been discussing about important safety devices in today's cars which, if not able to prevent the accident, at least save the occupants' lives. In our series, we have discussed about the ever important airbags, the electronic stability program and the anti lock braking systems. In continuation to our previous devices, we will be discussing the Crumple Zone.
Our discussion will include, what is a crumple zone, where is a crumple zone located and the science behind crumple zone.
What is a Crumple Zone?
The crumple zone (also called crush space) is a structural feature used in automobiles to absorb the energy of impact. This way, when someone crashes with your car, the force of impact is much higher than the realized force. The reason is due to the design of crumple zone, which generally uses methods of controlled deformation in the area between outer shell and inner body.
Where is a Crumple Zone located?
A more usual crumple zone is located in the front part of the vehicle, to absorb much severe head-on collision, which results in maximum number of accidents in a car. But much safer cars now-a-days are employing crumple zones in the frontal three quarters of the car, to reduce side impacts too, where the occupants are more prone for a fatal damage. According to a British Motor Insurance Repair Research Centre study, 65% of the accidents faces front impacts, 25% rear impacts, 5% left side, and 5% right side.
Why we need a Crumple Zone?
Why do we need a Crumple Zone is a basic question of physics that we have been discussing in all of our previous series discussions. It's all due to the Interia or momentum! Inertia or momentum is that force which acts when a vehicle and all its contents, including passengers and luggage are travelling at speed, but are stopped immediately (which in this case is the accident). Now in the event of a sudden deceleration, the occupants will continue moving forward at their previous speed due to inertia, and will hit the dashboard or vehicle interiors at a force equivalent to many times their normal weight due to gravity. This is where Crumple Zone comes and slows down the collision and to absorb energy to reduce the difference in speeds between the vehicle and its occupants.
Now one may argue that seatbelt and airbags do the same thing, slow down the impact of the occupants. This may be right to an extent, but the final impact after a passenger's body hits the car interior, airbag or seat belts will deploy only to hurt the internal organs like ribcage or skull due to high inertia. 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.
What Crumple Zone does is, reduce the overall inertia of the body as a whole. This combined technology of crumple zone — seatbelt — airbags — padded interior—are designed to work together as a system to reduce the force of the impact on the outside of the passenger(s)'s body and the final impact of organs inside the body.
How does Crumple Zone function?
As we have told earlier, crumple zone is nothing but a space between the outer shell and the inner shell of the car, which absorbs the majority of impact force when a vehicle faces accident, saving the occupants' lives. To achieve so, the body designers sacrifice the outer body shell by weakening it and hence making it lightweight. On the contrary, the inner shell is toughened and made strong by deploying various strengthening materials like composites and steel.
But why make the outer shell weak and inner strong? Various studies have proven that the impact energy that reaches into a safety cell is spread over more widely and hence reduces deformation. But what is a safety cell? Safety cell is nothing but the cabin of the car, which is converted into a safety cell by increasing the rigidity of the cabin. So now designers know that it is safe to build a strong safety cell, but a string safety cell means more materials, resulting in increased weight. Now in a vehicle, as much as safety is essential, so is the performance and an increased weight lowers the performance many folds. So to reduce the weight of the car, exterior body is sacrificed by building low weight and relatively weak exterior shell.
Materials used for building Crumple Zone
A typical Crumple Zone is built up of many materials, combinedly known as the impact attenuator. The majorly used materials to form an impact attenuator is a high tensile steel, composites, carbon fibre and aluminium. Some of the most advanced racing cars also use a high grade energy absorbing foam that forms an impact attenuator to dissipate the crash energy using a much smaller volume and lower weight than road car crumple zones. Volvo is credited for being the pioneer in setting up proper Crumple Zones in cars and it also introduced the first, side crumple zone with the SIPS (Side Impact Protection System) in the early 1990s.
Is Crumple Zone really safe?
There is a huge misconception among many that the Crumple zone is designed in such a way that the weak outside shell could lead to reduced safety of the occupants, resulting in crushing of the occupants. In reality, though, the safety cell helps saving the occupants life more effectively than any other system. Many crash tests have proven that the modern vehicles provide far more superior protection as compared to the older cars with no crumple zones.
Also, it has been proven that a vehicle with a crumple zone when collides with a vehicle without crumple zone, benefits both the involved cars, as the impact force is taken from the crumple zone of the former car. This case is usually an improvement over the cases when both the cars colliding doesn't have any crumple zones.