Strain sensing behavior of FDM 3D printed carbon black filled TPU with periodic configurations and flexible substrates

Carbon black particles (CBPs) as the conductive fillers and thermoplastic polyurethane (TPU) elastic polymer were uniformly mixed to form composite filaments for exclusive use in fused deposition modeling (FDM). The FDM was performed to print CBPs/TPU composite flexible strain sensors with 88 wt% TPU and 12 wt% CBPs. The unique periodic configurations of the as-printed sensors were carefully designed to improve structural flexibility. This work was devoted to the fabrication processes and strain sensing behaviors of the produced CBPs/TPU composite sensors. After an extensive work of material and process parameter optimization, FDM filaments of the CBPs/TPU composite were prepared with an expected good formability for FDM 3D printing on pure TPU film substrates. The sensing mechanisms of the as-printed CBPs/TPU composite benefit from the CBPs conductive network disconnection mechanism and the tunneling effect. The sensing performances were able to be adjusted via designing the sensor geometrical configurations. For sensitivity analyses of the flex-sensors with different configurations, the experimental test results were roughly in agreement with the deduction from the geometric structure calculation and numerical simulation. The satisfactory sensing performances of the as-printed sensor with S-shaped zigzag periodic configuration and TPU film substrate were displayed satisfactorily, also proving that the sensor was feasible in human health monitoring.