# A Study on Shock Absorption Characteristics of Honeycomb-Inserted Bollards
## 5 Summary and Conclusions  
This research, conducted with LS-DYNA simulations and vehicle-bolland collision tests, was motivated to design in-plane honeycomb bollards in order to improve shock absorption capability of steel bollards by adding in-plane bolland units and consequently reduce damage to vehicle and its occupants. Findings from this research can be summarized as follows:  
1. Honeycomb unit specimen with varying honeycomb cell wall length (\(l\)) and thickness (\(t\)) were manufactured with PLA materials for compression tests, which confirmed that the honeycomb strength is inversely proportional to \(l^{2}\) and proportional to \(t^{2}\), as reported in the literature. 2. Maximum accelerations at the vehicle front bumper frame and the B-pillar were simulated with various yield strengths. Compared to steel bollard, simulations with 20 MPa in-plane honeycomb bolland, when impacted by the vehicle at 10 km/h, showed the maximum acceleration time being delayed by 0.017 \(s\), the peak acceleration value decreased to 37.4% of the steel bollard's peak, and maximum deformation time increased by 0.083 s. The maximum acceleration of the B-pillar decreased by 13% when compared to that of steel bollard. 3. From the analysis of the vehicle-bolland collision experiment videos, the maximum acceleration occurrence time at the bumper cover has increased by 0.783 s.
4. The maximum accelerations, measured during the experiment and calculated from the simulation, were 0.35 \(\times\) 10\({}^{3}\) m/s\({}^{2}\) and 0.388 \(\times\) 10\({}^{3}\) m/s\({}^{2}\), respectively. This proves the similarity in the acceleration and damage characteristics between the experiment and the simulation. 5. From the vehicle-bolland collision experiments, it was observed that the steel bollard not only caused damage to the test vehicle front bumper frame as in the simulation but also to its radiator. With only minor bumper frame deformation for the test against honeycomb bollard, this research proves the improved shock absorption characteristics of the proposed in-plane honeycomb bollards. 6. Vehicle-bolland collision tests against in-plane honeycomb bollards showed damages concentrated to three locations along the bollard--the front bumper contact point, base and support interfacing point, and the bollard bottom end. This coincides with the simulation results to further prove the consistency and reliability of the research results. Vehicle-bolland collision tests against in-plane honeycomb bollards showed damage concentrated to three locations along the bollard-front bumper contact point, base and support interfacing point, and the billiard bottom end. This coincides with the simulation results to further prove the consistency and reliability of the research results. It can be concluded from this research that the proposed in-plane honeycomb bollards can decrease damage to the vehicle and its occupants with its improved shock absorption capability compared to the conventional steel bollards. With the in-plane honeycomb units designed to be readily manufacturable with extruders, the honeycomb bollards can also be produced with minimal cost increase while bringing  
Figure 22: Comparison of bottom honeycomb unit and damaged honeycomb simulation: (**a**) Simulation results; (**b**) Collision test results. the benefit of reducing vehicle repair cost and medical bills for injured drivers and passengers. This research was also designed in a manner that other variants of the in-plane honeycomb units can be simulated, manufacture, and tested to further improve the shock absorption capability of proposed design in this paper. S.S. conducted a collision experiment to acquire data; K.K. supported the setting of the experimental equipment and conducted preliminary experiments; S.S. arranged and analyzed the acquired data; S.S. and K.K.