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Worldwide, the pace of development in pedestrian countermeasures is increasing rapidly. To better understand the state of the art in bumper design for pedestrian impact, a survey of literature and patents has been performed. Two general approaches to reducing the severity of pedestrian lower limb impacts were identified: (a) Provide cushioning and support of the lower limb with a bumper and a new lower stiffener, or (b) Use the bumper as a platform for impact sensors and exterior airbags. This study focused on the first approach. Excluding bumper sensors, airbags, and non-design-related articles, a total of 130 relevant technical articles and 147 patents were identified. The most common method proposed for cushioning the lower limb in an impact uses an energy absorber (plastic foam or ‘egg-crate’) in front of a semi-rigid (steel or aluminum) beam. There are also proposals for ‘spring-steel’, steel-foam composites, crush-cans, and plastic beams.

In 1996, the European Enhanced Vehicle Safety Committee, Working Group 17 (EEVC WG17) proposed a set of impact procedures to evaluate the pedestrian injury risk of vehicle fronts. These procedures address three aspects of pedestrian protection – head impacts, lower limb impacts, and thigh impacts – through vehicle subsystem tests. The criteria assessed during these impact tests are affected by the design of most parts of the vehicle body front-end. One of the challenges to vehicle design introduced by these tests is the impact of an adult pedestrian headform to the top of the fender. The proposed acceptance level for Head Injury Criterion (HIC) is less than 1000 during impacts at 40 km/h. This paper uses the finite element (FE) method to predict the influence of proposed fender and shotgun design modifications aimed at meeting this target. In addition, the known issues with the implementation of these proposed changes are discussed.

Lower limb injury is becoming an increasingly important concern in vehicle safety for both occupants and pedestrians. To enable vehicle manufacturers to better understand the biomechanical effects of design changes, it is deemed beneficial to employ a biomechanically fidelic finite element model of the human lower limb. The model developed in this study includes long bones (tibia, fibula, femur) and flat bone (patella) as deformable bodies. The pelvis and foot bones are modeled as rigid bodies connected to the femur and tibia/fibula via rotational spring-dashpots. The knee is defined by scanned bone surface geometry and is surrounded by the menisci, major ligaments, and patellar tendon. Finite elements used to model include 6- and 8-node solids for cartilage, menisci, surrounding muscles, and cancellous bone; 3- and 4-node shells for skin and cortical bone; and nonlinear spring-dashpots for ligaments.

The European Commission is proposing legislation aimed at reducing the severity of injuries sustained by pedestrians in the event of an impact with the front-end of a motor vehicle. One aspect of this proposed legislation is reducing the pedestrian's leg injuries due to contact with the bumper and frontal surfaces of a vehicle, assessed using a ‘pedestrian leg impact device,’ or ‘leg-form.’ This proposed legislation presents the challenge of designing a bumper system which achieves the required performance in the leg-form impact-without sacrificing the bumper's primary function of vehicle protection during low-speed impacts. The first step in meeting this challenge is to understand what effects the front-end geometry and stiffness have on the leg-form impact test results. These results will then need to be compared to low-speed impact performance to assess if the two requirements are compatible.

To design a cost, weight, and energy efficient bumper foam energy absorber, it is important to consider optimizing the shape of coring employed in the design of the system. In this paper, a number of foam coring patterns are studied by both empirical and analytical methods. The size and shape of proposed core designs are studied in detail with consideration given to several different densities of expanded polypropylene (EPP) foam. Using the finite element method of structural analysis, it is possible to have an inside look at the stress distribution during deformation of foam structures. An optimization study using the finite element method is conducted using the energy absorption ratio as an efficiency parameter. Several coring patterns are studied and recommended for bumper foam core design based on high energy absorption efficiency and low tear stress.