Citation

DuBois D, Zellmer H, Markiewicz E. Int. J. Impact Eng. 2009; 36(6): 763-774.

Copyright

(Copyright © 2009, Elsevier Publishing)

DOI

10.1016/j.ijimpeng.2008.11.006

PMID

unavailable

Abstract

Automotive manufacturers and suppliers commonly conduct crash tests in order to assess the performance of safety systems on new vehicles. Crash scenarios are reproduced using dynamic tests. For instance, the EuroNCAP protocol; a 64 km/h frontal impact in a 40% offset deformable barrier, is used to simulate a car to car impact. An assessment protocol is then applied to achieve a rating for each body region. The head acceleration, the chest deflection, the femurs loading, compression/extension/flexion of the neck are measured on crash test dummies and a star rating is given. The safest cars obtain a 5-star performance. During the vehicle deceleration, the dummies are subjected to the collision forces and in the case of a frontal impact, they move forward. To prevent severe contacts between the passenger and the car interior (dashboard, steering wheel), a three-point seat belt restrains the passenger's motion. In parallel, the driver and the passenger airbags reduce the acceleration peak applied to the occupant and distribute the restraint loads on the upper part of the body. To take benefit of their coupled actions, these restraint systems are developed in interaction. Nevertheless, although an airbag has a spectacular action during a collision, the belt, part of the passive restraint system, is the only protection against the ejection of the passenger away from his vehicle.

In current cars, loops are commonly used to redirect the webbing which reels out from the retractor to the passenger's shoulder. Some types of pillar loops, also called D-rings, lead to a non-systematic instability. The webbing, which should scroll without hindrance through the D-ring, laterally shifts, bunches and produces the overturning of the ring.
In this paper, this so-called seat belt bunching phenomenon is parsed during a first step with sled test campaigns data. The results of designs of experiments are analysed and discussed.
To expertize this instability issue, an innovative fixture is exploited during a second step to reproduce the phenomenon in a fully controlled manner for dynamic and quasi-static loadings. To assess these sub-system tests, a Digital Images Correlation system is employed to evaluate the strain distribution of seat belt webbing during the bunching phase. Based on these local measurements, a correlation of a Finite Element model of seat belt bunching is achieved using a new shell element for webbing fabric, before proposing an explanation of the phenomenon.