Ultra-Fast and Tunable Liquid Nanofoam Load Limiter

The seat belt system has long been recognized as the most important safety device in a vehicle. The seat belt retractor, a key component in seat belt system, locks up and provides webbing payout during a crash with the intent to limit chest loading on the occupant. Traditional belt retractor design employs the twisting of a metallic torsion bar as its load limiting mechanism. In this study, we present a novel design of a seat belt retractor system with ultra-fast response and high tunability. A highly compressible liquid, i.e. liquid nanofoam (LN), has been utilized as the load limiting component to allow for additional webbing payout. Dynamic sled tests have been performed to evaluate the performance of LN-functionalized seat belt retractor. Results show that the response time as well as the excess webbing payout of the LN-functionalized seat belt retractor are significantly reduced compared with the traditional seat belt retractor. This is due to the ultra-fast deformation mechanism of the LN load limiter. In addition, we have also demonstrated that the force response of the LN-functionalized seat belt retractor can be tuned by controlling the working pressure of the LN load limiter. These results suggest that LN has the potential to be used as novel functioning material in the seat belt retractor system to achieve targeted dummy responses in crash tests.