Literature Review
Impact Mitigation
Intelligent locomotive bumper designs have been touted as possible life-savers for pedestrians. Paden, Kelly, Hines, Botham and Simms explored the feasibility of a life-saving locomotive bumper (103). There were several motivations behind their paper. Perhaps the most important one was the high number of pedestrians that were killed every year in train impacts. Between the years 2007 and 2012, about 10,950 non-suicide deaths were attributed to train impact on humans. Including suicide deaths on railroads, 28,800 pedestrians were killed during that 6-year period. Also, Paden et al., noted that passenger trains served densely populated areas (103). They noted that unlike automobile bumpers, locomotive bumpers would not impact the overall design, weight, cost, and size considerably. They explored four different high-level bumper concepts that could be used to reduce train-human impact, and the resulting likelihood of head injuries upon landing. Paden et al suggested four idealized bumper systems to control the trajectory of the pedestrian and degree of collision upon impact (104). The ideal bumper 1 works by catching the pedestrian and minimizing the impact duration to a time T. it carries the pedestrian until the point where it can stop. A crushable foam is suggested for this concept, where the pedestrian is tightly ensconced and held, followed by deceleration of the train. The Ideal bumper 2 system reduces the impact on the pedestrian to a duration of t< T and accelerates them laterally off the rail/ track. Although the lateral velocity resulting from the impact is significant, but ground impact has minimal fatality risks. The Ideal bumper 3 system first causes acceleration of the pedestrian before decelerating them laterally and placing them trackside at zero velocity. The ideal bumper 4 involves a mechanism that detaches itself away from the locomotive during impact. It could be a rocket-propelled airbag system.
The second approach evident from the review of literature is bumper structure and the location of holes in the bumper. Lv, Huang, Gu, Liu and Li proposed a system that protects the pedestrian’s lower extremities using optimization of bumper holes (2). They noted that the optimization of bumper structure using Flex-PLI tests had not been covered adequately in research despite its high potential in pedestrian safety. They conducted tests to determine the extent of tibia and knee injuries. Lv et al., noted that the rigidity of the spoiler support plate and energy-absorbing plate has a considerable effect in the legform injury to the pedestrian (7). They consider the vehicle bumper structure hole geometry.
The third approach for pedestrian safety involves pedestrian detection and deployment of external airbags. Choi, Jang, Oh and Park developed a methodology focused on evaluating how effective an integrated pedestrian protection system (IPPS) could be based on simulations (473). The system comprises of an active hood lift system (AHLS) and a pedestrian warning information system (PWIS) (Choi, Jang, Oh and Park 473). The systems have two important durations- before collision and after. Before collision, the vehicle detects the presence of a pedestrian in close proximity to the vehicle. It also provides advance warning to the pedestrian and reduces vehicle speed drastically. After collision, the vehicle lifts up the bonnet to absorb the impact energy. Also, it deploys external airbags to shield the pedestrian. Similarly, Yang, Yun and Park examined the feasibility of using airbag systems (1). They experimented with different airbag heights and inflator types and came up with a satisfactory design. Lim et al., also explored the design of airbag systems that could save pedestrians in vehicle-to-pedestrian crashes. Lim et al., reference the pop-up hood and pedestrian airbag but cite its inadequacies of design and effects. Lim et al., explored computational impact analysis to reduce head injuries using the airbag system. They made recommendations to the designs of the airbag housing as well as the airbag itself. They also selected appropriate materials for the airbag housing. In addition, Lim at al., used an orthogonal array and response surface method to reduce the degree of head injuries. These three studies are based on the finding that when pedestrians collide with an automobile’s frontal structure, most of the fatalities are as a result of head injuries. Head injuries usually occur when heads collide with had objects such as the engine under the hood, lower part of windshield, or the A-pillar. The degree of the head injury is a function of the stiffness of the vehicle surface with which the head collides and the deformation allowance of that surface. The various tests conducted by Liu et al., Choi, Jang, Oh and Park, and Yang, Yun and Park take into account adult and child head forms in their calculations. Upon impact, the adult’s head hits a different section of the car surface from that of the child. In most designs, the pedestrian airbag is located under the hood near the bottom of the windshield for obvious reasons.
The fourth pedestrian protection system involves optimizing the designs of the frontal structures on vehicles to reduce injury risks. Lee, Joo, Park, Kim and Yim explored a robust design that minimized a flex pedestrian leg-form impactor’s (Flex-PLI) injury risks (757). These researches noted that in Germany, the legs and head are injured the most frequently in fatal accidents involving pedestrians. They also noted that current vehicle designs decreased the space between the impact beam and the fascia, making it more difficult for designs to incorporate pedestrian protection. Lee et al., employed contribution analysis and a model to show that frontal ca design can be optimized for reduced severity of head and leg injuries.
Blast Wave Mitigation Techniques
The blast wave produced during the detonation of an explosive produces a high peak pressure for a very short duration. Such a blast wave is able to penetrate hardened structures with ease and with low attenuation. It may be damaging to structures as well as military personnel. Some of the approaches that have been explored in different researches include blast absorption materials as well as heterogeneous systems. Su, Peng, Zhang, Gogos, Skaggs and Cheeseman indicate that one of the new innovations that may be used to reduce the damage potential of a blast wave is a novel blast wave mitigation device (338). This device comprises of a piston-cylinder assembly. Air or other gases are usable in this device. Piston dampers in this system diminish mechanical vibration and a blow-off valve modulates the pressure in the damper (Su, Peng, Zhang, Gogos, Skaggs and Cheeseman 338). The viscosity in this damper helps to dampen the blast wave. The shock wave is propagated within the mitigation device and reflects repeatedly within it. It converts the wave to a low-pressure, long-duration impact. The device may be used to cover military structures, reducing personnel injuries and equipment damage significantly (Su, Peng, Zhang, Gogos, Skaggs and Cheeseman 338).
Works Cited
Choi, S. et al. "Safety Benefits Of Integrated Pedestrian Protection Systems". International Journal Of Automotive Technology, vol 17, no. 3, 2016, pp. 473-482. Springer Nature, doi:10.1007/s12239-016-0049-2.
Lee, Y. H. et al. "Robust Design Optimization Of Frontal Structures For Minimizing Injury Risks Of Flex Pedestrian Legform Impactor". International Journal Of Automotive Technology, vol 15, no. 5, 2014, pp. 757-764. Springer Nature, doi:10.1007/s12239-014-0079-6.
Lim, J.-H. et al. "Design Of An Airbag System Of A Mid-Sized Automobile For Pedestrian Protection". Proceedings Of The Institution Of Mechanical Engineers, Part D: Journal Of Automobile Engineering, vol 229, no. 5, 2014, pp. 656-669. SAGE Publications, doi:10.1177/0954407014551186.
Lv, Xiaojiang et al. "Reliability-Based Multiobjective Optimization Of Vehicle Bumper Structure Holes For The Pedestrian Flexible Legform Impact". International Journal Of Crashworthiness, vol 21, no. 3, 2016, pp. 198-210. Informa UK Limited, doi:10.1080/13588265.2016.1155527.
Paden, Brad E. et al. "On The Feasibility Of Life-Saving Locomotive Bumpers". Accident Analysis & Prevention, vol 89, 2016, pp. 103-110. Elsevier BV, doi:10.1016/j.aap.2015.12.025.
Su, Zhenbi et al. "Numerical Simulation of a Novel Blast Wave Mitigation Device". International Journal of Impact Engineering, Vol. 35, no. 5, 2008, pp. 336-346. Elsevier BV, doi:10.1016/j.ijimpeng.2007.04.001.
Yang, H.-I. et al. "Design Of A Pedestrian Protection Airbag System Using Experiments". Proceedings Of The Institution Of Mechanical Engineers, Part D: Journal Of Automobile Engineering, vol 230, no. 9, 2015, pp. 1182-1195. SAGE Publications, doi:10.1177/0954407015603854.
