## 4 Results and Discussion
### Heat Resistivity
#### 4.2.2 Dependencies of Currencies, Electrical Power, and Resistance on Voltage  
To analyze the dependencies of current, electrical power and resistance on voltage similar to heat distribution, only one specimen per process parameter set was tested. The test specimens were manufactured by using the same process parameter sets and the same batch of material. Due to process-related inaccuracies in the manufacturing of the specimens, the initial individual resistances of the utilized specimens in Sections 4.2.1 and 4.2.2 vary and, thus, are not quantitatively comparable. Each specimen was tested three times to determine mean and standard deviation. Before testing, the specimens were energized two times by the previously determined individual maximum voltage for 15 min each. This is because exceeding the glass transition temperature of the matrix polymer due to resistive heating leads to an annealing of the specimens that changes the resistance of the specimens. During cooling, the specimens were taken from the measurement set-up so that no clamping restricts their shrinkage and, thus, damages them. Based on the results in Section 4.2.1, the following maximum voltages were used for the experimental investigations of the different materials and raster angle orientations: PPC (0\({}^{\circ}\), \(\pm\)45\({}^{\circ}\) and 90\({}^{\circ}\)) 30 V, 3 dk (0\({}^{\circ}\), \(\pm\)45\({}^{\circ}\) and 90\({}^{\circ}\)) 40 V, FFE (0\({}^{\circ}\)) 12 V, FFE (\(\pm\)45\({}^{\circ}\)) 12 V, FFE (90\({}^{\circ}\)) 20 V, and M3D (0\({}^{\circ}\), \(\pm\)45\({}^{\circ}\) and 90\({}^{\circ}\)) 6 V.  
Figure 17 shows PPC's current-voltage characteristics and the dependencies of the electrical power and the resistance on the voltage. Besides the mean value, the standard deviation of the  
Figure 16: Distortion of the specimen caused by exceeding the glass transition temperature of the matrix polymer and the temperature gradient (**left**); and heat distribution at 12 V (**right**). three measurement cycles is represented for each raster angle orientation. Electrical current reaches a maximum between 15 V and 20 V depending on the raster angle due to the different resistance of the specimens. From about 5 V to 18 V, electrical power is almost linear. The decrease of current is caused by an exponential increase of the resistance depending on specimen's temperature due to resistive heating that is shown in the right diagram. Resistance increases by a factor of about 3 between 0 V and 30 V, however, electrical power rises with increasing voltage. As in the previous investigation regarding resistivity, the dependency of specific values on the raster angle is visible, even though the difference between the raster angles of 0\({}^{\circ}\) and \(\pm\)45\({}^{\circ}\) is lower than to 90\({}^{\circ}\). The scattering is high compared to the other materials. This is caused by a decrease of the specimen's resistance between the individual measurement cycles probably due to a further annealing of the specimen by exceeding the glass transition temperature. The power-voltage characteristics of 3 dk are almost linear in a range from about 12 V to 40 V (see Figure 18). Due to the higher resistance of 3 dk compared to PPC, the resulting current and, thus, electrical power is lower. Consequently, the heating temperature of the specimens is also lower than the glass transition temperature of the matrix material (PLA) so that no annealing occurs that could change the resistance of the specimens. Therefore, the scattering of the values is significantly lower compared to PPC. Furthermore, the current does not fall within the measuring range, however, an approximation to a maximum value similar to PPC is noticeable at about 40 V. The temperature dependency of the resistance due to the filler (CB) is also visible. It is worth noting that the resistance of the 0\({}^{\circ}\) raster angle is higher than that of \(\pm\)45\({}^{\circ}\) and 90\({}^{\circ}\), which does not correspond to the results in Section 4.1.2 (Figure 11).