On the Electrical Resistivity Measurement Methods and Properties of Conductive 3D-Printing PLA Filaments

In recent years, there has been a growing interest in and research efforts enabling the use of composite conductive 3D-printing filaments in material extrusion additive manufacturing processes, which can bestow novel and distinctive functions onto 3D-printed components. These composite filaments, in general blending a thermoplastic with carbon-based materials, open up new research and development avenues in electronics and sensors. Additionally, by exploring the underlying piezoresistivity of conductive filaments, they also enable the creation of novel structural components possessing integrated (intrinsic) self-sensing capabilities that can be effectively employed in structural health monitoring of critical components. However, piezoresistivity features require measuring the electrical resistance of structures made with these conductive filaments, which might be hard, especially when measuring small changes in resistance caused by mechanical loads on the component. The goal of this study is to compare the two- and four-probe methods for measuring the electrical resistance of 3D-printed parts and to look at how different types of electrical contacts and bonding may affect electrical resistivity measurement and self-sensing capabilities. The research is conducted on 3D-printed specimens using a conductive composite PLA (polylactic acid) filament from Protopasta. The efficiency of each method and the influence of the bonding and electrodes on the measurements are experimentally analyzed and discussed. Our experiments reveal that the four-probe method consistently yields resistivity values between 15.35 and 16.38 Ω·cm, while the two-probe method produces significantly higher values (up to 52.92–62.37 Ω·cm), underscoring the impact of wire and contact resistances on measurement accuracy.