## 2 Additively Manufactured Electrically Conductive Structures
### Characterization of Electrically Conductive Composite Materials Additively Manufactured by MEX  
Several studies analyze different influencing factors on electrical resistivity of parts additively manufactured by MEX. Both influencing factors regarding material composition (e.g., type and loading of fillers) and effects of the variation of process-specific factors such as extrusion temperature, raster angle or build orientation are investigated. Mostly carbon allotropes, for instance, carbon nanotubes, carbon black and graphene, are used for the functionalization of the material composites. Besides effects on electrical conductivity, certain studies underline the positive effect of fillers on mechanical properties, especially [PERSON]'s modulus and tensile strength [PERSON] et al. (2018); [PERSON] et al. (2018); [PERSON] et al. (2018); [PERSON] et al. (2018); [PERSON] et al. (2018). Due to the direction of the deposited material, some fillers (e.g., graphene flakes) are oriented in the extrusion direction and, thus, the anisotropy of conductivity and tensile strength or Young's modulus increases [PERSON] et al. (2018). However, elongation at break decreases with increasing loading of filler, thus the fracture behavior possibly limits the maximum filler content specific to the application [PERSON] et al. (2018); [PERSON] et al. (2018). Further, a high loading of filler may restrict the printability [PERSON] et al. (2018). Besides these material-specific variations, process-specific anisotropies in resistivity are also analyzed in several studies (see Table 1). Both factors of influence regarding geometry, e.g., build orientation [PERSON] et al. (2018); [PERSON] et al. (2018); [PERSON] et al. (2018), and with regard to process are investigated, for instance, raster angle [PERSON] et al. (2017); [PERSON] et al. (2018), raster width [PERSON] et al. (2018), air gap or flow rate [PERSON] et al. (2017); [PERSON] et al. (2018) as well as active cooling [PERSON] et al. (2018), extrusion speed [PERSON] et al. (2018), and temperature [PERSON] et al. (2017); [PERSON] et al. (2018). In addition to electrical conductivity, [PERSON] et al. (2017) [PERSON] et al. (2017) [PERSON] et al. (2017) and [PERSON] et al. (2018) [PERSON] et al. (2018) [PERSON] et al. (2018) [PERSON] et al. (2018) investigated resistive heating due to process- and material-specific variations. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Variation Parameter**} & \multicolumn{10}{c}{**Study**} \\ \hline  & [1] & [2] & [3] & [4] & [5] & [18] & [19] & [20] & [21] & [22] & [23] & [24] \\  & Filter & CB & CNT & CNT, G\({}^{1}\) & CB & CB & Nickel, thin alloy & G, Super P, MWCNT\({}^{3}\) & G & CB & MWCNT\({}^{3}\) & CB & MWCNT\({}^{3}\) \\ Material & Filter Content & X & & X & X & X & X & X & X & \\  & Matrix Material & PLA & AHS & PFF\({}^{2}\) & PLA & PCL & PA, HDPE & PLA & PLA & PP & TPU & AHS & TPU \\  & Electric Bonding & & & X & & & X & & & & & & (X) \\ \hline  & Build Orientation & X & & & & X & & & & & & & & \\  & Layer Height & & & X & & & & & & & & & & \\  & Master Angle & X & (O) & & & & & & & & & & & \\  & Master Width & & & & & & & & & & & & \\  & Air Gap/Flow Rate & X & & & & & & & & & & & & \\  & Extension Temp. & X & & & X & & & & & & & & \\  & Extension Speed & & (O) & & X & & & & & & & & & \\  & Cooling & & & & X & & & & & & & & \\ \hline  & Young’s Modulus & & X & & & X & & & & & & & & \\  & Strength & X & & & & X & & & & & & & & \\  & Elongation & & & X & & & & X & & & & & & \\ Characterization & Storage Modulus & X & & X & & & & & & & & & \\  & Elect. Resistivity & X & X & X & X & X & X & X & X & X & X & X & X \\  & Resistive Heating & X & & X & & X & X & X & X & & & & \\  & Multi-Material MEX & X & & & & X & & X & & & & & \\ \hline \hline \end{tabular} \({}^{1}\) Graphene;\({}^{2}\) polybutylene terophthalate;\({}^{3}\) multiwalled carbon nanotube.  
\end{table} 
Table 1: Studies on electrical conductivity manufactured by material extrusion.