High Strain-Rate Responses of Mechanical Metamaterials

Abstract

Mechanical metamaterials—materials with deterministic microstructures that attain unique combinations of properties—have revolutionized the parameter space of engineering materials over the last decade. While their quasi-static mechanical responses have been thoroughly characterized, their responses in the dynamic regime are not fully understood, especially at strain rates above 10^3 s^−1. Using microscale uniaxial compression and custom microscale Kolsky bar capabilities, we uncover the strain rate dependence of mechanical metamaterials over eight orders of magnitude, ranging from strain rates of 10^−3 to 10^5 s^−1. Herein, we describe the development and execution of direct impact experiments using a custom-built micro Kolsky bar set-up, delving into the details of its design, fabrication, and data analysis. We first characterize the rate dependence of the polymer used for sample fabrication, IP-S, and relate it to the responses of different metamaterial morphologies at the same strain rates. The results of these experiments uncover how geometry greatly affects rate dependence of mechanical properties in the dynamic regime. Understanding the high strain rate behavior of metamaterials is necessary to ensure reliable performance in real-world applications.