Chapter 13
Enhanced Structural Imperfection Resistance in Thin-Walled Tubes
Filled with Liquid Nanofoam
Mingzhe Li, Fuming Yang, and Weiyi Lu
Abstract Thin-walled structures have been widely used in automotive and aerospace industries to improve the system
crashworthiness and impact protection. However, during manufacturing, transporting and handling processes, initial geometric imperfections are inevitably introduced to the thin-walled structures, which imposes negative impacts to the mechanical
performance and service life of the thin-walled structures. In this study, we have introduced structural imperfection with
controlled geometry and dimension to thin-walled steel tubes and characterized the mechanical response of these empty tubes
and LN-filled tubes by quasi-static compression tests. Results show, the structural imperfection reduces the energy absorption
capacity of empty tubes by about 20%. As the tube is filled with LN, the structural imperfection does not affect the energy
absorption capacity of LN filled tube. The enhanced imperfection resistance is attributed to the suppression of imperfection
growth caused by the strong liquid-solid interaction between the LN and tube wall. These findings suggest that the LN filling
material can effectively reduce the adverse impact of structural imperfection and shed light on future design of thin-walled
energy absorption devices.
13.1 Introduction
Thin-walled structures have been widely used in automotive and aerospace industries to improve the system crashworthiness
and impact protection due to its light weight and good energy absorption performance [1]. For instance, thin-walled alloy
structures have been fabricated to function as rocket engine thrusters at higher temperature [2]. However, during the processes
of manufacturing, transporting and handling of thin-walled structures, initial structural imperfections are inevitably introduced, which imposes adverse impacts to the mechanical performance and service life of the thin-walled structures. For
example, dent imperfections have led to 33% reduction of the load carrying capacity of thin-walled tubes [3]. While the
buckling behavior of dented thin-walled structures have been thoroughly studied [4–6], approaches to mitigate the negative
effect of these structural imperfections on thin-walled structures are still lacking.
Recently, a novel hybrid thin-walled structure, namely liquid nanofoam-filled tube (LNFT), is designed with considerably
enhanced energy absorption density compared to solid foam-filled tubes [7, 8]. The significantly improved energy absorption
capacity of the LNFT is due to much-enhanced liquid-solid interaction at the LN-tube wall interface as well as the mechanical
response of the liquid nanofoam (LN) filler. The intrinsic fluidity of the LN filler creates a nearly perfect liquid-solid
“bonding” at the interface and results in a much higher strengthening effect of the LNFT. Thus, the LN, endowed with the
unique liquid-solid interaction, is a promising filler to reduce or even eliminate the adverse effect of structural imperfections
on the mechanical performance of thin-walled structures.
The LN is composed of hydrophobic nanoporous material and a non-wettable liquid [9–11]. Due to the surface
hydrophobicity of nanoporous particles, the liquid molecules cannot go into the nanopores spontaneously at ambient
condition. As an external pressure is exerted and reaches a critical value, the energy barrier is overcome and the liquid
molecules are continually driven into the nanopores. The mechanical energy is then converted to the liquid-solid interfacial
energy at the liquid-nanopore wall interface. Since the nanoporous materials possess ultra-high nanopore surface area
(~100–1000 m
2 /g [12]), massive amount of energy is mitigated.
In this study, we examine the suppression effect of LN on thin-walled tubes with structural imperfection. Dents with
controlled depths have been introduced to the thin-walled tubes and quasi-static compression tests have been performed on the
M. Li (*) · F. Yang · W. Lu
Department of Civil and Environmental Engineering, Michigan State University, East Lansing, MI, USA
e-mail: limingzh@egr.msu.edu; yangfumi@msu.edu; wylu@egr.msu.edu
© The Society for Experimental Mechanics, Inc. 2021
R. P. Singh, V. Chalivendra (eds.), Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 6,
Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59868-6_13
89
Enhanced Structural Imperfection Resistance in Thin-Walled Tubes
Filled with Liquid Nanofoam
Mingzhe Li, Fuming Yang, and Weiyi Lu
Abstract Thin-walled structures have been widely used in automotive and aerospace industries to improve the system
crashworthiness and impact protection. However, during manufacturing, transporting and handling processes, initial geometric imperfections are inevitably introduced to the thin-walled structures, which imposes negative impacts to the mechanical
performance and service life of the thin-walled structures. In this study, we have introduced structural imperfection with
controlled geometry and dimension to thin-walled steel tubes and characterized the mechanical response of these empty tubes
and LN-filled tubes by quasi-static compression tests. Results show, the structural imperfection reduces the energy absorption
capacity of empty tubes by about 20%. As the tube is filled with LN, the structural imperfection does not affect the energy
absorption capacity of LN filled tube. The enhanced imperfection resistance is attributed to the suppression of imperfection
growth caused by the strong liquid-solid interaction between the LN and tube wall. These findings suggest that the LN filling
material can effectively reduce the adverse impact of structural imperfection and shed light on future design of thin-walled
energy absorption devices.
13.1 Introduction
Thin-walled structures have been widely used in automotive and aerospace industries to improve the system crashworthiness
and impact protection due to its light weight and good energy absorption performance [1]. For instance, thin-walled alloy
structures have been fabricated to function as rocket engine thrusters at higher temperature [2]. However, during the processes
of manufacturing, transporting and handling of thin-walled structures, initial structural imperfections are inevitably introduced, which imposes adverse impacts to the mechanical performance and service life of the thin-walled structures. For
example, dent imperfections have led to 33% reduction of the load carrying capacity of thin-walled tubes [3]. While the
buckling behavior of dented thin-walled structures have been thoroughly studied [4–6], approaches to mitigate the negative
effect of these structural imperfections on thin-walled structures are still lacking.
Recently, a novel hybrid thin-walled structure, namely liquid nanofoam-filled tube (LNFT), is designed with considerably
enhanced energy absorption density compared to solid foam-filled tubes [7, 8]. The significantly improved energy absorption
capacity of the LNFT is due to much-enhanced liquid-solid interaction at the LN-tube wall interface as well as the mechanical
response of the liquid nanofoam (LN) filler. The intrinsic fluidity of the LN filler creates a nearly perfect liquid-solid
“bonding” at the interface and results in a much higher strengthening effect of the LNFT. Thus, the LN, endowed with the
unique liquid-solid interaction, is a promising filler to reduce or even eliminate the adverse effect of structural imperfections
on the mechanical performance of thin-walled structures.
The LN is composed of hydrophobic nanoporous material and a non-wettable liquid [9–11]. Due to the surface
hydrophobicity of nanoporous particles, the liquid molecules cannot go into the nanopores spontaneously at ambient
condition. As an external pressure is exerted and reaches a critical value, the energy barrier is overcome and the liquid
molecules are continually driven into the nanopores. The mechanical energy is then converted to the liquid-solid interfacial
energy at the liquid-nanopore wall interface. Since the nanoporous materials possess ultra-high nanopore surface area
(~100–1000 m
2 /g [12]), massive amount of energy is mitigated.
In this study, we examine the suppression effect of LN on thin-walled tubes with structural imperfection. Dents with
controlled depths have been introduced to the thin-walled tubes and quasi-static compression tests have been performed on the
M. Li (*) · F. Yang · W. Lu
Department of Civil and Environmental Engineering, Michigan State University, East Lansing, MI, USA
e-mail: limingzh@egr.msu.edu; yangfumi@msu.edu; wylu@egr.msu.edu
© The Society for Experimental Mechanics, Inc. 2021
R. P. Singh, V. Chalivendra (eds.), Mechanics of Composite, Hybrid and Multifunctional Materials, Volume 6,
Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59868-6_13
89