# Investigation of Functionality of Vehicle Crumple Zones Recovered after a Traffic Accident
## 4 Results
### The Effect of Damaged Crumple Zone Part on the Vehicle Dynamic Processes  
In this section, an investigation of the effect of damaged crumple zone on vehicle safety was conducted. For this investigation, an application developed on the basis of a four-mass dynamic model was used. In the application, a smaller distribution of force-deformation dependences was used for the description of the crumple zone rigidity characteristics. The stiffness characteristics of the part of crumple zone were described by its buckling force-displacement diagram approximated by an eight-point linear dependence. This method for describing the rigidity characteristics of the crumple zone enabled a more appropriate use of the buckling force dependences obtained during the in situ experiments or by using the numerical models.  
The modelling was performed using the chosen characteristics of the buckling forces. The model simulated the collision of the investigated vehicle with a fixed barrier at full frontal width, which corresponded to the National Highway Traffic Safety Administration (NHTSA) methodology. This kind of collision was chosen as, in this case, the longitudinal side-members were subject to the largest share of the absorbed energy, and the longitudinal member loading conditions caused their axially symmetric deformation. The buckling force-displacement diagrams used in the model were obtained under exactly the same load nature. Accelerations of the 3 rd zone with the 2 nd part having original characteristics and characteristics with post-repair damage are presented in Figure 24.  
Following the calculation of the HIC\({}_{36}\) parameter [50,51] based on the acceleration diagrams in Figure 24, at 40 km/h collision velocity and 2 nd zone of original characteristics: HIC = 117; at the damaged 2 nd zone: HIC = 94, at 50 km/h--295 and 313, at 64 km/h--790 and 840, at 75 km/h--1447 and 2340.  
Figure 25 shows time-dependent distribution of the amount of energy absorbed by individual crumple zone parts with different characteristics of the 2 nd zone.  
Figure 24: Accelerations of the 3 rd zone at different collision velocities: 40 km/h (**a**), 50 km/h (**b**), 64 km/h (**c**), 75 km/h (**d**); (1—2 nd zone of original characteristics; 2—damaged 2 nd zone).  
Changes in the characteristics of the crumple zone elements were clearly recorded with the change of the initial impact velocity. The results obtained by using the distributed mass elements were partially repeated. At lower velocities, the weaker 1 st and 2 nd crumple zone parts absorbed the energy more uniformly. As velocity increased, the effect was reduced. As soon as the 64 km/h velocity was exceeded, the energy was absorbed by the more rigid 3 rd zone, and the overloads acting on the crew increased.  
The investigations found the following:  
* The obtained acceleration-time dependences were closer to the in situ experiment results where adjusted crumple zone element characteristics were used; (Figure 25);
* The adjusted model enabled more accurate forecasting of the effect of individual elements on the course of deformation of the crumple zone;
* The weakening of the parts of the 1 st and 2 nd crumple zones had a negative effect on the car safety of the vehicle at collision speeds of 50 km/h and higher. With increasing collision velocity, the negative effect became more evident.