37
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
L. Lamberson et al. (eds.), Dynamic Behavior of Materials, Volume 1, Conference Proceedings of the Society
for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59947-8_7
Chapter 7
Ultra-Fast and Tunable Liquid Nanofoam Load Limiter
Mingzhe Li, Robert McCoy, Dean Jaradi, and Weiyi Lu
Abstract 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.
Keywords Liquid nanofoam · Seat belt retractor · Load limiter · Impact · Vehicle crashworthiness · Energy absorption
7.1 Introduction
The seat belt is one of the key safety devices in a vehicle (Fig. 7.1a). During car crashes, the seat belt helps to control occupant movement to reduce the risk of injury or death (Fig. 7.1b) [1]. When a vehicle is involved in a crash of sufficient severity,
the seat belt retractor locks up (Fig. 7.1c). In a traditional retractor system, the progressive pulling of the webbing leads to
the nonlinear twisting of a metallic torsion bar (Fig. 7.1d). The twisting of the torsion bar provides limiting load to the retractor and allows for additional webbing payout.
In this study, we propose a novel material, liquid nanofoam (LN) [2–4], that has the potential to enhance the load limiting
performance of a retractor as compared to a metal torsion bar design. LN is a mixture of hydrophobic nanoporous particles
and a non-wettable liquid. Commonly used nanoporous materials include nanoporous silica, carbon, and alumina. Since the
nanopore surface is hydrophobic, the liquid molecules stay outside of the nanopores. As the external force applied on LN
exceeds a critical value, the liquid molecules are driven into the nanopores and the external force is maintained as a constant.
Mechanical energy can be converted to the solid-liquid interfacial energy and further dissipated as heat upon removal of the
external force. The LN possesses tunability by controlling the pore size [5, 6], surface coverage [7–9], viscosity of the liquid
phase [10, 11], temperature [12–17], ion concentration of the liquid phase [18–20], etc. Moreover, the unit of LN has micron
level size, making it adaptive to shape. With a proper modification of the nanopore surface, the LN has the potential to be
made fully reusable. Given these advantages, LN is a promising load limiter candidate in the seat belt retractor system. Here,
we present a novel design of an LN-based load limiting device in the seat belt retractor system. Results show that the LN load
limiter possesses ultra-fast response and high tunability.
M. Li (*) · W. Lu
Department of Civil and Environmental Engineering, Michigan State University, East Lansing, MI, USA
e-mail: limingzh@msu.edu; wylu@egr.msu.edu
R. McCoy · D. Jaradi
Ford Research and Innovation Center, Ford Motor Company, Dearborn, MI, USA
e-mail: rmccoy2@ford.com; djaradi@ford.com
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
L. Lamberson et al. (eds.), Dynamic Behavior of Materials, Volume 1, Conference Proceedings of the Society
for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59947-8_7
Chapter 7
Ultra-Fast and Tunable Liquid Nanofoam Load Limiter
Mingzhe Li, Robert McCoy, Dean Jaradi, and Weiyi Lu
Abstract 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.
Keywords Liquid nanofoam · Seat belt retractor · Load limiter · Impact · Vehicle crashworthiness · Energy absorption
7.1 Introduction
The seat belt is one of the key safety devices in a vehicle (Fig. 7.1a). During car crashes, the seat belt helps to control occupant movement to reduce the risk of injury or death (Fig. 7.1b) [1]. When a vehicle is involved in a crash of sufficient severity,
the seat belt retractor locks up (Fig. 7.1c). In a traditional retractor system, the progressive pulling of the webbing leads to
the nonlinear twisting of a metallic torsion bar (Fig. 7.1d). The twisting of the torsion bar provides limiting load to the retractor and allows for additional webbing payout.
In this study, we propose a novel material, liquid nanofoam (LN) [2–4], that has the potential to enhance the load limiting
performance of a retractor as compared to a metal torsion bar design. LN is a mixture of hydrophobic nanoporous particles
and a non-wettable liquid. Commonly used nanoporous materials include nanoporous silica, carbon, and alumina. Since the
nanopore surface is hydrophobic, the liquid molecules stay outside of the nanopores. As the external force applied on LN
exceeds a critical value, the liquid molecules are driven into the nanopores and the external force is maintained as a constant.
Mechanical energy can be converted to the solid-liquid interfacial energy and further dissipated as heat upon removal of the
external force. The LN possesses tunability by controlling the pore size [5, 6], surface coverage [7–9], viscosity of the liquid
phase [10, 11], temperature [12–17], ion concentration of the liquid phase [18–20], etc. Moreover, the unit of LN has micron
level size, making it adaptive to shape. With a proper modification of the nanopore surface, the LN has the potential to be
made fully reusable. Given these advantages, LN is a promising load limiter candidate in the seat belt retractor system. Here,
we present a novel design of an LN-based load limiting device in the seat belt retractor system. Results show that the LN load
limiter possesses ultra-fast response and high tunability.
M. Li (*) · W. Lu
Department of Civil and Environmental Engineering, Michigan State University, East Lansing, MI, USA
e-mail: limingzh@msu.edu; wylu@egr.msu.edu
R. McCoy · D. Jaradi
Ford Research and Innovation Center, Ford Motor Company, Dearborn, MI, USA
e-mail: rmccoy2@ford.com; djaradi@ford.com