# Investigation of Functionality of Vehicle Crumple Zones Recovered after a Traffic Accident
## 5 Conclusions  
Based on these results, the following observations have been made. A dynamic model that assesses the effect of individual regions of crumple zones on the overall deformation process was run. The course of deformation of the regions and the amount of energy absorbed were found to be affected by the adjacent regions. Therefore, damages in one zone may influence the overall deformation process. To assess the effectiveness of the crumple zone, it is necessary to analyse the collision velocities of different ranges: up to 50 km/h and above 50 km/h. The quasi-static and dynamic in situ experiments of part of crumple zone have demonstrated that damages alter the element's characteristics. During the quasi-static buckling of the specimen of restored geometry, the critical buckling force was reduced by 20% and the amount of absorbed energy was reduced by 5% with the specimen deformed to the same length. The experiments conducted on specimen buckling have demonstrated that, with the specimen subjected to buckling under dynamic load, the amount of energy absorbed by them is 90% higher than under quasi-static buckling. The effect of geometric deviations on the course of element deformation was found to be inconclusive. The effect of a single 0.5 mm geometric deviation was insignificant. Meanwhile, a 1.0 mm single deviation altered the location of formation of the first plastic deformation wave, but did not have any significant effect on the absorbed energy amount per length unit. Figure 25: Time-dependent distribution of the energy amount absorbed by the zones: with the 2 nd zone of original characteristics (**a**); with the damaged 2 nd zone (**b**); (1—1 st zone; 2—2 nd zone; 3—3 rd zone). The results obtained by numerical models corresponded to the results of the in situ experiments. To describe the damage of crumple zone elements, it is sufficient to adjust the descriptions of the materials and fabricated joints. During the modelling, the altered characteristics of the spot-welded joints, irrespective of their positions, were found to have the capacity to considerably influence the nature of the specimen deformation and amount of energy absorbed. The amount of energy absorbed decreased by 8% after the spot-welded joints were weakened by 50% in the middle zone of the specimen used during the experiment and deformation of the specimen to 1/2 length. With the element absorbing 1.77 kJ of energy, the axial shortening of the specimen subjected to buckling increased by 9% compared to the specimen with all original spot-welded joints. The axial weakening of the spot-welded joints located in the zone of formation of the first plastic deformation waves by 50% was equivalent to the absence thereof. Non-standard parts of the crumple zone used during the repair had a considerable effect on the vehicle safety. The HIC parameter almost doubled where non-standard parts were used and the crumple zone was repaired. The effect of changes in the characteristics of individual crumple zone regions on their functionality was determined:  
* An increase in stiffness of the 1 st and 2 nd crumple zone elements had a negative effect on car safety throughout the interval of investigated velocities. When the collision velocity increased, the negative effect decreased, but still remained considerable. * The reduction in stiffness of the 1 st and 2 nd crumple zone elements had a positive effect on the car safety at collision velocities up to 67 km/h. At higher velocities, weakening of the crumple zone elements had a negative effect on the car safety, and the effect continued increasing with the increasing collision velocity. Conceptualization, D.J. and V.L. ; methodology, D.J. and V.L. ; software, V.L. ; validation, D.J., V.L. and A.K. ; formal analysis, D.J., V.L. and A.K. ; investigation, D.J., V.L, A.K. and R.M. ; resources, R.M. ; data curation, D.J., V.L, A.K. and R.M. ; writing--original draft preparation, D.J., V.L. and A.K. ; writing--review and editing, D.J., V.L. and A.K. ; visualization, V.L. ; supervision, D.J., V.L., A.K.