Experimental study on the actuation and fatigue behavior of the biopolymeric material Cottonid

Abstract

Saving and reducing the consumption of electrical energy is one of the major future challenges for industry and society. It would be desirable, if an actuator autonomously responds to an environmental stimulus like humidity, temperature or light. In this study, the actuation and fatigue behavior of the macromolecular cellulose-based material Cottonid is characterized. It is hygroscopic and possesses process-related anisotropic mechanical properties, which makes it an efficient adaptive material for humidity-driven actuators. A quantitative and qualitative evaluation of the passive movements of Cottonid-based bilayer structures in reaction to humidity absorption and desorption was performed concerning parameters like angle of deflection and saturation. To assess direction-dependent fatigue performance, specimens were prepared in 0° and 90° according to cellulose micro fibril orientation and cyclically loaded in load increase tests. 0° specimens reached highest stresses at failure whereas 90° specimens showed a pronounced loss of stiffness during the tests. Differences in damage development due to alternating micro fibril orientations could be visualized via computed tomography, which leads to a profound understanding of biomechanics