Ok, here we go...
Firstly, what is the goal of designing vehicle structures for crashworthiness? Its simply to obtain an optimised vehicle structure that can absorb the crash energy, by means of controlled vehicle deformations, while maintaining an adequate design envelope, such that the residual energy pulse can be managed by the restraint systems, to minimize the load transfer to the occupants.
The laws of physics cannot be beaten … if the vehicle is traveling at v kph, we all know from basic physics that the vehicle with its mass, m then has kinetic energy… 1/2mv^2. Energy as we all know cannot be destroyed, but only transferred to another form. The impact load on the steel structures which form the vehicle BIW must then absorb this energy. Typically, the crush load, F is found by measuring deceleration of the vehicle, g using accelerometers at various positions, then multiplying by the deformation, which is measured, x. A plot of F vs x can then be obtained, and the integral or the area under the curve gives the work done by the structures. Simple?
The tricky bit now starts. The vehicle must be able to pass several legislations even before it undergoes independent testing such as EuroNCAP. These legislations vary from continent to continent, but it is generally fair to say that they are all almost similar in nature. Most of them consist of a full frontal, frontal offset, side and rear impact tests.
Speeds of the test vary from one legislation to another, but are generally based on statistical numbers, compiled over long years of research….ie, for frontal impact, it was determined that upon impact, a driver would’ve managed to brake from a “legal” driving speed of 120kph to about half…ie, 60kph, etc. There are also test to ensure minimum damage to the vehicle at low and ultra low speeds.
It is a known fact that the most challenging testing is for the EuroNCAP protocol. What is this? EuroNCAP is an independent body formed by the FIA and several other governing bodies in Europe. Their testing is made more difficult, as vehicles are actually BOUGHT off any showroom to provide randomness to the vehicle manufacture batch. This way, the test vehicle is then tested in-situ, with the manufacturer actually unaware that that specific car would be undergoing the test, thus eliminating the duit kopi scenario!!! :blush:
The 2 tests that are conducted which leads to the popular star ratings are the 64kph 60% frontal ODB collision and the 50kph lateral impact. For more information, u can read it up yourself at
www.euroncap.com
In designing the structures for these set of test, several factors are taken into consideration:
1) The bumper beam and foam padding (usually behind the plastic bumper fascia) must be able to deform and absorb ultra low speed impacts (5 kph) with minimal or zero damage to the steel structures behind it…ie, the longitudinals/rails, ( UK/US terminology)
2) The longitudinals (longits in short) must be easily repairable by cutting and rewelding back if necessary for low speeds. (
