Analysis of strain sensitivity under flexural load of 3D printed carbon nanotube-doped epoxy circuits

Abstract

A 3D printing system able to print circuits of conductive epoxy resin doped with carbon nanotubes (CNTs) has been proposed. Different simple circuits, more specifically, lines and strain gauge patterns, made of resins reinforced with 0.3, 0.5, 0.8 and 1 wt.% of CNTs have been printed on the surface of glass fiber laminates. It has been observed that increasing the CNT reduces the wettability of the printed circuits to the glass fiber substrate. Anyway, in every case, the contact angle is far below 90º. Furthermore, strain sensing capabilities have been analyzed under flexural load showing that the sensitivity increased with CNT content (with gauge factor values from 1.5 to 2.5), due to the prevalent effect of well dispersed areas due to a reduction on the tunneling distance. On the other hand, the strain gauges showed a lower sensitivity (around 20-40% below, depending on the condition) when compared to line circuits due to localized compressive effects. Furthermore, a good repeatability of the strain sensors was proved during cycling tests which similar baseline and peak values of the electrical resistance in each single cycle. Therefore, the proposed materials show a high potential and applicability for Structural Health Monitoring purposes.