Abstract
Conductive carbon nanotubes (CNT)/acrylonitrile butadiene styrene (ABS) nanocomposites parts were easily and successfully manufactured by fused filament fabrication (FFF) starting from composite filaments properly extruded at a laboratory scale. Specific specimens for strain monitoring application were properly evaluated in both short term and long term mechanical testing. In particular, samples of ABS filled with 6 wt% of CNT were additively manufactured in two different infill patterns: HC (0°/0°) and H45 (−45°/+45°). The piezoresistivity behaviour was investigated under various loading conditions such as ramp tensile tests at different rate and extension, and also creep and cyclic loading at room temperature. Experimental work revealed that the resistance changes in the conductive samples were properly detectable during stress or strain modification, as consequence of damage and/or reassembling of the percolation network. The measurement of the gauge factor in various testing conditions evidenced an initial higher sensitivity of the 3D-built parts within H45 pattern in comparison to the correspondent HC counterparts. The CNT conductive network path in the investigated samples seems to be reformed during creep and cycling experiments, showing a progressive reduction of gauge factor that seems to stabilize at about 2.5 for both HC and H45 samples after long term testing. These findings suggest that conductive CNT/ABS nanocomposites at 6 wt% of loading can be successfully processed by FFF to produce stable strain sensors in the range -25° and +60°C, as confirmed by the constancy of resistivity at these temperatures.
Highlights
Polymer composites with carbonaceous micro and nano-scale reinforcement have been extensively investigated due to their outstanding mechanical, electrical, and thermal properties
It should be noted that the percolation threshold of carbon nanotubes (CNT) in acrylonitrile butadiene styrene (ABS) has been determined at 0.42 vol.% and no electrical conductivity has been observed for CNT content lower than 2 %wt. (Dul et al, 2018b)
In order to confirm the conductivity of 3D-printed samples, their electrical resistivity was assessed at values of 17.2 ± 1.5 and 31.2 ± 4.9 .cm for horizontal concentric (HC) and horizontal 45◦angle (H45) items, respectively
Summary
Polymer composites with carbonaceous micro and nano-scale reinforcement have been extensively investigated due to their outstanding mechanical, electrical, and thermal properties. Highly conductive ABS/CNT nanocomposites with 6 wt.% of nanofillers were successfully 3Dprinted through FFF process and their extensive characterization including tensile, thermal and electrical properties was reported (Dul et al, 2018a). Electrical and magnetic properties for high CNT content (Dul et al, 2020) Another recent work reported about piezoresistivity of ABS filled with 5% CNT nanocomposites through 3D printing with resistivity of about 100 .cm. Two different raster angles and different testing conditions cyclic test were evaluated and compared to test the piezoresistive behavior of 3D-printed parts, in short term testing (i.e., temperature effect, fracture test, and applied strain rate), and in long term testing such as creep experiments and cycling test, for the evaluation and evolution of gauge factor. R/R0 in figures; tables with data of each specimen are reported in Supplementary Materials
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