Strain sensing characteristics of 3D-printed conductive plastics

This study electrically characterizes three types of commercially available conductive three-dimensional (3D) printing filament for use in 3D printed functional devices. The three plastics were carbon dispersed acrylonitrile butadiene styrene (ABS), carbon dispersed polylactic acid (PLA) and graphene dispersed PLA. The method of 3D printing used was material extrusion and prints were made in both single and dual extrusion modes. The plastics were found to be piezoresistive, enabling them to be characterized as strain sensors. The electrical characteristics of these materials enabled the measurement of strain using low cost, readily available prototyping equipment and minimising the requirement for dedicated instrumentation components (e.g. Wheatstone bridges). Increasing the thickness of the plastics improved conductivity. However, this also decreased the reliability and reproducibility of strain sensor data due to a complex internal 3D structure. The recommendation for reliable use in prototyping and manufacturing is to print tracking under 0.8mm thickness, thus producing resistance measurements that are predictable and follow a linear regression up to R2 = 0.9991. A dual extruded 3D print was fabricated as a final demonstration. A force sensing resistor (FSR) interface was created. The final demonstration uses a PIC18F45K20 microcontroller to process sensor inputs, outputting to an alphanumeric LCD.