Loading-Unloading Compressive Response and Energy Dissipation of Liquid Crystal Elastomers and Their 3D Printed Lattice Structures at Various Strain Rates

Nematic liquid crystal elastomers (LCEs) are a unique class of network polymers with potential for excellent mechanical energy absorption and dissipation capacity due to their ability to change the nematic director under mechanical loading (sometimes called soft-elasticity) in addition to the viscoelastic behavior of the remaining polymer network. This additional inelastic mechanism makes them appealing as candidate damping materials in a variety of applications from vibration to impact. The lattice structures made from the LCEs provide further mechanical energy absorption and dissipation capacity associated with packing out the porosity. Understanding the extent of mechanical energy absorption versus dissipation depends on the mechanical stress-strain response under both loading and unloading. In the past, the loading-unloading stress-strain response was only obtained within quasi-static (slow) strain rates on standard material test frames. In this study, we used a newly developed bench-top linear actuator to characterize the loading-unloading compressive response of polydomain and monodomain LCE polymers and polydomain LCE lattice structures with two different porosities (nominally, 62% and 85%) at both low and intermediate strain rates at room temperature. As a reference material, a bisphenol A (BPA) polymer with a similar glass transition temperature (9 °C) as the nematic LCE (4 °C) was also characterized at the same conditions for comparing to the LCE polymers. Based on the loading-unloading stress-strain curves, the energy absorption and dissipation for each material at different strain rates (0.001, 0.1, 1, 10 and 90 s−1) were able to be calculated. The strain-rate effect on the mechanical response and energy absorption and dissipation behaviors was determined.