Liquid crystal elastomers (LCEs) are one of the most fascinating materials in industrially important areas with high demand in mechanical energy dissipation including automotive, aerospace and personal protection, due to their extreme damping behavior emerging from an internal degree of freedom of liquid crystal (LC) molecules, which is coupled to elastic deformations of the polymer network. It has been reported that LCEs exhibit enhanced mechanical loss factor compared to other materials and highly rate-dependent mechanical behaviors with significantly enhanced hysteresis over a wide range of strain rates. 

 

In this study, we report the extreme impact energy absorption behaviors of architected LCE. An architected material (or metamaterial) is a class of materials that provide new properties that are not observed in natural materials or from a bulk material that the “material” is made of. We utilize energy dissipation mechanisms across different length scales by utilizing architected liquid crystalline elastomers (LCEs). We have synthesized LCEs through a two-stage thiol–acrylate reaction to consider the effects of the alignment of LC molecules within LCE beam elements. The energy-absorbing capability of bistable beams with differently arranged LC molecules is characterized at various strain rates from 10^-4^/s to 10^3^/s, using a universal testing system and drop tower. 

 

We observed that structures based on LCE showed 1 to 3 orders of magnitudes higher energy absorption compared with those based on polydimethylsiloxane (PDMS), with an increase of the energy absorption as a function of strain rate. Due to the interplay of nonlinear behaviors of materials and structures, the architected LCEs show approximately an order of magnitude higher specific energy dissipation at quasi-static conditions compared with the previous studies and even higher energy dissipation at faster strain rates with power-law relation. Moreover, the strain-rate dependency could be tuned through controlling different degrees of alignment by simply varying the tensile strain applied during the specimen preparation step. Then, we further investigated the rate-dependent energy absorbing mechanisms for a better understanding of the extreme energy dissipation mechanism.

 

We envision that our study can contribute to harnessing the interplay between snapping-based structures and enhanced dissipation of LCEs to enable the soft materials with extreme energy absorbing capabilities, which will be beneficial for various applications, including aerospace, automotive, and personal protection  
  
Acknowledgements: This research is supported by the U.S. Army Research Office (Award No: W911NF-17-1-0165, Program Manager: Drs. David Stepp and Daniel Cole) and the Start-Up Fund of Whiting School of Engineering at Johns Hopkins University.


Strain Rate-Adaptive Extreme Energy Absorption via Architected Liquid-Crystalline Elastomers

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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