Elastodynamic mechanical analyzer for high strain-rate mechanical characterization.

Latch-mediated spring actuation (LaMSA) mechanisms are common in nature and hold great promise for ultra-fast synthetic systems across a range of behaviors including jumping, striking, and throwing. However, the quantitative study of LaMSA systems demands similarly high speed experimental tools accompanied with high temporal resolution data collection. Addressing this need, we introduce the elastodynamic mechanical analyzer (EMA) to characterize the mechanical properties of components in LaMSA systems at speeds relevant to LaMSA dynamics down to millimeter size-scales. Here we present the design and validation of EMA to characterize elastic spring materials. EMA performs tests that match the conditions of typical LaMSA systems in which springs are slowly loaded while a latch is engaged and rapidly unloaded as a latch disengages. The instrument directly measures displacement and force during high-rate unloading of elastic materials. These measurements reveal internal energy loss to the material and external energy losses during unlatching. We validate EMA by testing a coiled metal spring, and find that its response is rate-independent, as expected, with external energy losses dominant compared to the energy loss in the spring itself. We then test elastic latex fabric and polyurethane rubber. Despite their inherent elasticity, we find that both materials exhibit strain and strain rate dependent recoil behavior, demonstrating significant hysteresis during EMA's asymmetric loading and unloading tests. We calculate the instantaneous modulus under various conditions and assess the resulting complex relationships among stress, strain, and strain rate during recoil. EMA offers new opportunities for studying material behavior at high strain rates and large deformations through the instrument's ability to measure material performance as strain energy is released dynamically. Through our tests of common materials and structures through this new instrument, we offer insights into the behavior of materials under the extreme conditions characteristic of LaMSA systems.

Duke Scholars

Author Sheila N Patek Biology