Influence of Substrate Material and Sensor Geometry Variations on the Performance of Fused Deposition Modeling-Printed Strain Sensors

3D printing technology has made fabrication of electronics and sensors a cost-effective and customisable approach. Fabrication of 3D-printed strain gauges through fused deposition modeling technology offers compatibility and flexibility in adopting different substrate and conductive materials. The performance of a 3D-printed strain sensor depends on the selection of the conductive and substrate materials. This work focuses on the effects of substrate material variations and sensor geometrical variations on sensitivity, accuracy, stability, and working range of conductive polylactic acid (CPLA)-based 3D-printed strain sensor. Four variants of thermoplastic polyurethane (TPU) materials with different shore hardness values such as thermoplastic elastomer (TPE) 70A, eLastic TPE 83A, eFlex TPU 87A, and eTPU 95A have been chosen as the substrate materials. Strain sensors are 3D printed with all TPU substrate variants with CPLA in five different configurations, namely linear, serpentine, square, triangular, and trapezoidal. The resistance change ratios of the printed sensors, gauge factor, strain limits, and hysteresis error are computed by loading the sensor over various strain values under multiple cycles. Results revealed that the CPLA-eTPU 95A in triangular configuration outperforms other TPU variants in terms of gauge factor and hysteresis error. The gauge factor and hysteresis error exhibited by the CPLA-eTPU 95A in triangular configuration are 18.63% higher and 18.37% lower than that of CPLA-eFlex TPU 87A sensor, respectively. This happens due to high elastic modulus and shape recovery characteristics of eTPU 95A substrate; whereas the stretching limit of eTPU 95A is 25% lower than the eFlex TPU 87A substrate. Finally, by changing the vertical distance between the surface layers of the sensing element and the substrate material as 0.1 mm, a significant increase of 54% in the working range of CPLA-eTPU 95A strain sensor was observed.