## 3 Results
### Dynamical Testing  
In addition to the quasi-static testing, dynamical testing is carried out for all specimen types. The mechanical results are shown in Figure 9 and a comparative analysis is given in Table 3. The dynamical stiffness is plotted against the number of cycles for both temperatures. Moreover, mean values for initial stiffness and cycles to failure are shown in Figure 9d. Looking at Figure 9a, one could assume that there is a significant difference in lifetime of the PPA-GF30 specimens, but the rest of the specimens do not support this hypothesis. Regarding the PPA-GF30 specimens, it can be noted directly that the number of cycles both specimens withstand is comparably low. There is no evident difference in lifetime between the two temperatures, but there is a small difference in the dynamical stiffness that can be explained due to the viscoelastic behaviour of polymers. The wide error bars of the PPA-GF30 experiments result from the logarithmic representation and the very few  
Figure 8: Two-dimensional projections of te hybrid specimens: (**a**) reference, (**b**) tested @ 23 \({}^{\circ}\)C, and (**c**) tested @ 60 \({}^{\circ}\)C (70 kV acceleration voltage, 49 \(\upmu\)m pixel size), respectively. Figure 9: Results from dynamical testing for (**a**) PPA-GF30, (**b**) CFRP, and (**c**) hybrid specimens; (**d**) mean values of initial stiffness and cycles to failure. cycles. Furthermore, there is a small linear decrease in mechanical stiffness with increasing cycles for the PPA-GF30 specimens. This effect can be observed for the CFRP specimens at both temperatures as well. In addition, there is no failure over the examined one million cycles in CFRP and also a small difference in the initial stiffness. The error bars of the CFRP experiments are minimal in both directions. The scattering in the x-direction is non-existent because all three tests were stopped at one million cycles. This points out the good fatigue performance of the CFRP compared to the other specimen types. The good reproducibility and the well-defined test parameters lead to a small error bar in y-direction. The temperature shift seems to have the most effect on the hybrids. The initial stiffness at 60 \({}^{\circ}\)C is considerably smaller than at 23 \({}^{\circ}\)C. The hybrid tested at the higher temperature also seem to withstand a lower number of cycles. Furthermore, the stiffness decreases faster at 60 \({}^{\circ}\)C. For both temperatures, three phases of damage can be observed, forming an \"S\" shaped curve. It first comes to a fast reduction of the dynamical stiffness followed by a smaller linear reduction over the most cycles. In the final stage, the reduction of the dynamical stiffness accelerates again until failure. Looking at the error bars in Figure 9d, different things must be pointed out. To understand these observations, it is necessary to consult the non-destructive testing results in Figure 10.  
First, it can be noted that the PPA-GF30 specimens at both temperatures become noticeably warmer during the short testing period. Differences up to 6 \({}^{\circ}\)C in surface temperature can be measured between start of experiment and failure. This strong heating mirrors the high damping in the polymer. It must be considered here that the force-controlled experimental set-up leads to a higher deformation speed with decreasing stiffness compared to CFRP or hybrid specimens. The PPA-GF30 specimens are the least stiff specimens examined here, which means they are tested with the highest deformation speed. Furthermore, the included glass fibre can increase the inner friction and thus the damping. The high damping along with the high deformation speed could also be the reason for the