Thin-walled tubes are one of the most widely used energy absorption structures in automotive, aerospace, and other applications, because of their lightweight, high energy absorption efficiency and low cost. However, their mechanical properties and service life are vulnerable to structural imperfections. It has been demonstrated that the load carrying capacity, the post-buckling strength and the energy absorption capacity of thin-walled tubes are significantly reduced when structural imperfections exist. There is lack of an economical solution to reduce the cost on quality control and handling of thin-walled structures.

In this study, we have employed liquid nanofoam (LN), a novel nanofluidics-based energy absorption material, as a filler. The LN filler is a mixture of hydrophobic nanoporous material and a non-wettable liquid. The energy absorption mechanism is based on the liquid intrusion into the hydrophobic nanopores. At ambient condition, the liquid molecules cannot flow into the nanopores spontaneously due to the capillary effect. When an external pressure is applied and reaches a critical value, namely the infiltration pressure (*P*~in~) of LN, the liquid molecules infiltrate into the nanopores and large amount of energy is absorbed during the nanopore filling process. With the high energy absorption capacity and fluid-like nature of LN, we hypothesize that the mechanical performance of LN-filled tubes (LNFTs) can be inert to the existence of structural imperfections on the tube. To test this hypothesis, we have investigated the mechanical properties of the LNFTs with and without dent under quasi-static compression tests. The effect of dent depth and location has been revealed.

Our results show that the LN filler not only effectively suppress the negative impacts of structural imperfections, but also increases the energy absorption capacity of thin-walled tubes. Specifically, empty tube is susceptible to structural imperfection, as a v-shaped dent with 1.5 mm depth reduces its energy absorption capacity by about 20%. In contrast, the mechanical properties of LNFT, such as yield strength, post-buckling strength, and energy absorption capacity, are insensitive to the existence and depth of the dent. The enhanced imperfection insensitivity of LNFT is due to the intimate liquid-solid interaction at the LN filler and the tube wall interface, which effectively suppresses the curvature growth of the dent and the localized folding. In addition, the mechanical response of LNFTs with different dent locations is stable, indicating the dent location effect is negligible. This is further validated by the specific energy absorption capacity that the dent-suppression effect of the LN-filler is independent from the dent location. In a summary, these findings provide an efficient approach for designing and engineering thin-walled energy absorption devices that are resilient and of high energy absorption capacity.


Enhanced Structural Imperfection Resistance of Thin-Walled Tubes by Liquid Nanofoam Filler

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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