Deterioration and recovery of electrical conductivity during fatigue testing of stretchable wires printed onto fabrics u
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Deterioration and recovery of electrical conductivity during fatigue testing of stretchable wires printed onto fabrics using Ag-loaded electrically conductive pastes Masahiro Inoue1, Yasunori Tada1, Yosuke Itabashi2 and Tomohiro Tokumaru3 1 ASRLD Unit, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan 2 Faculty of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan 3 Biosignal Co., Ltd., 2-1-37 304 Honjyo-nishi, Kita-ku, Osaka 531-0073, Japan ABSTRACT Stretchable wires were printed on fabrics using an acrylic-based paste loaded with Ag flakes, and their fatigue properties examined. The electrical conductivity of the wires significantly decreased during a cyclic tensile test, because of a decrease in their elastic moduli (Mullins softening) as well as fatigue cracking. Because the electrical resistance and elastic moduli of the damaged samples were partially recovered by annealing at 100 °C, fatigue damage introduced to the wires was divided into reversible and irreversible components, where cracking is the irreversible damage. Although crack bridging by fibrils could occur during the fatigue test, no crack healing was observed during annealing. In contrast, fatigue damage from Mullins softening of the wires could be recovered during annealing. The recovery of electrical conductivity occurs mostly in the initial stage of rearrangement of polymer structure during annealing. INTRODUCTION Recently, stretchable microsystems [1] have attracted great interest for developing novel human-machine interfaces such as tactile sensor systems for humanoid robots and healthcare devices. Because novel wiring processes for stretchable electric circuits must be developed to establish these microsystems, several types of stretchable wires, including metallic wires with wave shapes [2], wires printed from elastomer-based electrically-conductive pastes [3] and wires consisting rubber tubes filled with liquid metal [4], have been proposed. The present authors have been developing stretchable wires by printing with electricallyconductive pastes. For example, prototype wearable E-textiles for monitoring several biological signals have been successfully developed using the additive printing method [5]. The terminal of the wires was connected to a portable acquisition device. We could monitor human biological signals, such as electrocardiogram (ECG) and electromyogram (EMG), using a personal computer, via wireless communication from the acquisition device. Because these E-textiles contained stretchable wires and electrodes, the effect of deformation of the wires on the measurement of biological signals was investigated. Although electrical resistance of the stretchable wires increases during deformation, the ECG was clearly detected with no significant noise [5]. However, fatigue behavior of the stretchable wires needs to be examined further, because increases in their electrical resistance caused by fatigue damage can lead to serious problems when measuring biological signals. In the present work, we
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