Roles of prestrain and hysteresis on piezoresistance in conductive elastomers for strain sensor applications

Abstract

Simultaneous experimental measurements of stress, strain and electrical resistivity were carried out by exposing two carbon black filled cross-linked elastomers and two nanocomposites of thermoplastic polyurethane and multiwalled carbon nanotubes to a series of cyclic strain histories. It was found that the resistivity–strain relationships of the materials exhibited different hysteresis and dependence on prestrain. The resistivity of the nanotube filled elastomers changed dramatically with prestrain, making them suitable for memory sensor applications. During cyclic loading, the carbon black filled elastomers exhibit a lower resistivity during the loading part of the cycles than during the unloading part; the opposite effect was seen in the nanotube filled elastomers. The phenomena can be explained in terms of plastic flow processes in the thermoplastics, and of cohesive forces between carbon black particles in the cross-linked elastomers. Bending and buckling of the nanotubes give rise to a region of strain at constant resistance, making them unsuitable for real time sensing.