Guidelines for pedestrian friendly windscreen designs considering probabilistic fracture behavior

If adult pedestrians are being struck by passenger cars with short bonnets, head contact usually occurs in the wind-screen area. In test procedures for regulation and consumer protection, this impact type is being assessed using so-called pedestrian head impactors. The head injury risk is being evaluated based on the acceleration signal using the so-called Head Injury Criterion (HIC). Corresponding experimental impactor tests in the windscreen center show large scatter. Main reason for the observed scatter is the fracture initiation of glass as already published in several studies. Thus, for a head impact in the windscreen center an early fracture initiation results in a small head injury risk, while a late fracture initiation increases the injury risk significantly. In the design of measures for the enhancement of vehicle sided pedestrian safety, this scatter is currently neglected. Based on a theoretical description of the probabilistic fracture mechanics of glass, a methodology for designing pedestrian friendly windscreens considering the probabilistic fracture mechanics of glass will be described in the present paper. This methodology consists of two steps. First, the probability for certain fracture initiation times are assessed, considering probabilistic fracture mechanics and the tensile stress distribution on the glass surfaces during head impact. In a second step, the head injury risks for the different fracture initiation times are evaluated. In order to show the potential impact of the described methodology, a windscreen of a vehicle model is being assessed and optimized. The findings of this optimization process are being used to derive guidelines for pedestrian friendly windscreens.