Sensitivity increase of 3D printed, self-sensing, carbon fibers structures with conductive filament matrix due to flexural loading

TL;DR

The paper investigates 3D-printed continuous carbon fiber reinforced beams as self-sensing structures and demonstrates an irreversible increase in gauge factor by subjecting the sensors to high compressive bending (breaking-in). It develops a mechanical-electrical framework incorporating transformed-section beam theory, residual thermal stress, and a linear ΔR–ε relationship, and compares PETG and conductive Protopasta matrices with Coextruded carbon fibers. Key findings show gauge factors up to 126 after breaking-in, with higher sensitivity achieved on compression, and that coextruded conductive filament reduces noise and improves electrical contact. The work points to a promising avenue for high-sensitivity, 3D-printed structural sensors while noting limitations such as drift, fiber damage, and measurement configuration that warrant further study.

Abstract

The excellent structural and piezoresistive properties of continuous carbon fiber make it suitable for both structural and sensing applications. This work studies the use of 3D printed, continuous carbon fiber reinforced beams as self-sensing structures. It is demonstrated how the sensitivity of these carbon fiber strain gauges can be increased irreversibly by means of a pretreatment by ``breaking-in'' the sensors with a large compressive bending load. The increase in the gauge factor is attributed to local progressive fiber failure, due to the combination of the thermal residual stress from the printing process and external loading. The coextrusion of conductive filament around the carbon fibers is demonstrated as a means of improving the reliability, noise and electrical connection of the sensors. A micrograph of the sensor cross section shows that the conductive filament contacts the various carbon fiber bundles. All-in-all, the use of ``breaking-in'' carbon fiber strain gauges in combination with coextrusion of conductive filament hold promises for 3D printed structural sensors with a high sensitivity.

Figures (9)

• Figure 1: A. Sample design with dimensions, where the thick black lines represent the carbon fiber and the green and red lines indicate sawn off ends. B. 3D-printed sample with PETG, with sawed off ends and electrical connections.
• Figure 2: Experimental setup to characterize the electromechanical sensor response. For the Medium and Tall samples, 4 of additional weight is attached to the linear actuator. For the Short samples, 3 of additional weight is used.
• Figure 3: Visualization of the force waveform applied on the samples during the three-point bending test. The green regions measure the sensitivity of the sample, while the red regions "break in" the samples.
• Figure 4: Cross-section of beam, showing the carbon fiber monofilaments in white, encased by the Anisoprint resin and the co-extruded Protopasta/PETG depending on the sample (black). The rest of the structure is made up of PETG extruded from the plastic nozzle (in yellow) and a hollow core (in white).
• Figure 5: Experimental results of a Protopasta sample. A) Part of a "break-in" experiment, in which the force applied to the sample and the resistance of the strain gauges are plotted over time. The high amplitude loading causes a higher sensitivity even during low subsequent loading. B) Resistance against strain of a strain gauge in compression during low amplitude loading of the sample, after the sample has been fully "broken in".