Due to extremly different vehicle structural performanse it is required to individualy analyze vehicle stiffness in any situation where acurate results of calculating crash speed are needed. From the begginings of vehicle stiffness modeling, by Emori, Campbell or any of there successors, methods of establishing equations are constantly improved. Nowdays, it is well known that normalized crush energy (known as EAF-Energy of Approach Factor) vs deformation can be succesfuly approximated with linear relationship using results from NHTSA 30 m/h frontal crash test speed. For higher speeds, bi-linear appeared to be accurate enough in most cases. But, there are certain cases where different relationship could give better results. Some researchers showed that nonlinear relationships could be also succesfuly used.

In this work, all known attempt from previous researchers where exercized on a YUGO GV vehicle. For this vehicle there are three NHTSA full frontal tests available. Using those results, it was concluded that, altough bi-linar relationship could be succesfuly used, best performanse was achived by combined approximation. Linear up to speed of 30 m/h and quadratic above that speed. This approximation gives best results in upper register of speeds, thus it is usefull for very deep crash deformations. Using computer for analysis eliminate complicated calculations, so establishing such relationships is no more hard job. It is important to notice that this kind of approximation can’t be aplied in situation where only one crash test point is known. So, field of application is very limited.