Hysteresis and Time-Dependent Effects on the Coupled Mechanical-Electrical Response of Unconstrained Carbon Nanotube Yarns Subjected to Uniaxial Tensile Loading

Abstract

Carbon nanotube (CNTs) yarns or fibers have extraordinary mechanical, electrical and thermal properties that make them attractive as reinforcements in high-performance and multifunctional composites. They also exhibit a unique piezoresistance response when subjected to mechanical strain. This characteristic is of interest for sensing applications in strain measurement and damage monitoring when integrated into polymeric and composite materials. Thus there is a need to understand the coupled mechanical and electrical behavior of the CNT yarns to fully comprehend the entire scope of their sensing applications. Of particular interest is to determine those characteristics when the CNT yarns are used as piezoresistive strain sensors in structures that are subjected to dynamic loading (fatigue or impact) or quasi-static loading and unloading. This paper presents a study about the presence of hysteresis and other time-dependent effects observed in carbon nanotube yarns during repeated loading and unloading cycles under uniaxial tension. By simultaneously taking four probe electrical resistance history measurements and load and displacement history measurements, any direct correlations between the mechanical and electrical characteristics are investigated including the effect of hysteresis and other time-dependent nonlinearities.