The last decades have witnessed the development of advanced transportation and the growth in the number of vehicles. Enormous efforts have been made to improving the occupant protection performance of vehicles in the past decades. In a vehicle, seat belt system is recognized as one of the most important safety devices. During a crash, the seat belt retractor locks up and provides appropriate webbing, securing the occupant in position with a limiting force. Traditional seat belt retractor system uses a metallic torsion bar as load limiter. The twisting of the torsion bar provides a constant force to the webbing. In this study, a novel seat belt retractor design with liquid nanofoam-based load limiter is presented. Liquid nanofoam (LN), a highly compressible material composed of nanoporous particles and liquid, is employed as the energy absorber in the load limiting device. When a critical load is applied, the surface energy barrier of the hydrophobic nanopores is overcome and the liquid is driven into the nanopores, maintaining the system at a constant pressure. Therefore, as the webbing is tightened up, the constant pressure in the LN is converted into the limiting load in the webbing, providing proper seat belt payout.

Various LN materials have been applied to the seat belt retractor and the performance of these LN-based seat belt retractor is first evaluated by quasi-static pulling test at a constant loading speed of 500 mm/min using an Instron universal tester. Results show that the limiting load on the webbing provided by the LN load limiter is proportional to the working pressure of the LN material. By tuning the working pressure of LN material from 7.5 MPa to 80 MPa, the limiting load of the seat belt retractor can be adjusted from 0.3 kN to 2.7 kN. Moreover, the dynamic response of the LN-based seat belt retractor is characterized by standard sled test at an incident speed of 4.5 m/s. Comparing with traditional retractors, the excess webbing payout of LN-based seat belt retractor during the activation process has been significantly reduced from 27.5 mm/kN to 4 mm/kN. This unprecedented response of LN-based retractor is due to the fast deformation mechanism of LN material, which is the ultra-fast activation and liquid flow in hydrophobic nanopores. These findings suggest that the LN is a promising load limiter candidate in seat belt retractor system and shed light on the design of energy absorption devices for vehicle crashworthiness.


A a Liquid Nanofoam-Based Seat Belt Retractor Design With Ultra-Fast Response and High Tunability

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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