Micromotions matter: an investigation of mechanical metamaterials in the plane

Abstract

Mechanical metamaterials (MMs) are artificial structures that derive unique mechanical properties from their geometry rather than composition. Traditional continuum models often fail to capture the full complexity of these architected materials, especially when micro-rotational effects are significant. This thesis presents an experimental validation of the decoupled micropolar elastic constants of a planar chiral mechanical metamaterial unit cell. A novel, assumption-free experimental framework is developed to isolate and measure all components of the decoupled micropolar elasticity (DME) tensor, without relying on symmetry constraints or reduced formulations. The method is applied to a specific unit cell geometry, yielding a complete elastic tensor that is compared against analytical models and symmetry-based predictions. Results show agreement along diagonal components but reveal discrepancies in off-diagonal coupling terms, suggesting physical couplings exist that are presently often assumed negligible. The findings highlight the importance of higher-order continuum theories in capturing the true mechanical response of MMs, especially for applications in compact motion systems. The approach offers a foundation for future extensions to three-dimensional geometries and supports the development of inverse design strategies using micropolar elasticity as a predictive tool.