Session: 03-04-01: Emerging Materials Technology

Paper Number: 137793

137793 - On Measuring the Elastic Constants of Chiral Cellular Metamaterials 

Chirality is a property of asymmetry universal in nature. A cellular metamaterial is said to be chiral if it is distinguishable from its mirror image. Examples include missing-rib and tetrachiral lattices. Chiral cellular metamaterials are recently found to exhibit shear couplings rather than previously believed auxeticity.  Consequently, there is a lack of established methodologies to correctly measure their elastic constants experimentally. The objective of this presentation is to propose an approach to correctly measuring the elastic constants of chiral cellular metamaterials. For the sake of simplicity, it focuses on metamaterials with unit cells (UCs) exhibiting 90-degree rotational symmetry. The elastic constants of these metamaterials include one Young’s modulus, one Poisson’s ratio, one shear coupling coefficient, and one shear modulus. The selected testing methods for measuring these elastic constants includes uniaxial compression testing, equal biaxial compression testing, and picture frame shear testing (PFST). Proofs are presented to ascertain or refute the existence of an end constraint effect during each testing method. In addition, analytical solutions for nonuniform local stress and strain fields in the presence of the end constraint effect are derived. The proposed approach involves the following steps: (1) calibrate Young’s modulus, Poisson’s ratio, the shear coupling coefficient via uniaxial and biaxial compression testing, (2) calibrate the shear modulus via PFST, (3) eliminate the end constraint effect with the aforementioned analytical solutions, (4) reduce the size effect of the measured elastic constants by identifying the minimum acceptable number of UCs each specimen. The proposed approach is then applied to a series of missing-rib and tetrachiral lattices with various design parameters through numerical experiments. The calibrated elastic constants are found to agree well with those predicted by the mechanics of structure genome, indicating the effectiveness of the proposed approach in measuring elastic constants of chiral cellular metamaterials. It can be further extended to handle metamaterials with UCs exhibiting 180-degree rotational symmetry.

Presenting Author: Liang Zhang AnalySwift LLC

Presenting Author Biography: Senior Research Scientist at AnalySwift, Dr. Liang Zhang earned his PhD in Mechanical Engineering from Texas A&M University in 2011. His expertise lies in nonlinear homogenization of composites, plasticity, damage, fracture, and fatigue. Dr. Zhang has authored over 20 journal articles and conference proceedings. Additionally, he has successfully undertaken several projects, including NASA STTR, Air Force STTR, and Army Research Laboratory initiatives.