## 6 Results
### Long-Term Durability Tests  
After the reference failure stress (3050 MPa) was determined, constant load levels were selected for the long-term durability tests. For the first load level the aim was to achieve failure within a few hundred hours based on the testing concept [19]. Subsequently, the load levels were to be reduced to reach test times of 1000 and 5000 h.  
Table 3 provides an overview of the performed long-term durability tests (CLTT--Carbon Long-Term Tests). Specimens that failed during loading were excluded.  
As displayed in Table 3, the specimens did not fail, with one exception, at loads exceeding 90% of the reference load, so that a few tests were stopped after 5000 to 6000 h to determine the residual capacity of the specimens. The failure of the specimen CLTT-6 is attributed to the non-applied preloading.  
No decrease in strength could be observed in the residual load capacity--the ultimate capacity was even higher than the short-term strength. It is assumed that the preloading and the constant loading lead to an uniformization of the individual yarns and of the filaments in each yarn regarding stress and strain levels. This would increase the load capacity of the reinforcement. The effect of a preloading is presented in the next section and discussed in Section 7.  
In Figure 5a the results of the long-term durability tests from Table 3 are plotted in a semi-logarithmic diagram. The red arrows in Figure 5a symbolize the ongoing tests. CLTT-1,  
Figure 4: Results of the first (**a**) and second (**b**) short-term test series.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Tests** & **Constant Load [MPa]** & **Test Time [h]** & **Temperature [\({}^{\dagger}\)C]** & **Ratio \(\sigma_{\text{U}}\)/\(\sigma_{\text{U}}\) [-1]** & **Residual Capacity [MPa]** \\ \hline CLTT-1\({}^{1}\) & 2168 & 11,000 & 40 & 0.71 & - \\ CLTT-2 & 2685 & 5117 & 40 & 0.88 & 3360 \\ CLTT-3\({}^{1}\) & 2795 & 7175 & 40 & 0.90 & - \\ CLTT-4 & 2813 & 5400 & 40 & 0.92 & 3504 \\ CLTT-5 & 2865 & 5300 & 40 & 0.94 & 3582  \\ CLTT-6\({}^{2}\) & 2933 & 811 & 60 & 0.96 & - \\ CLTT-7\({}^{1}\) & 2958 & 5930 & 40 & 0.97 & - \\ \hline \hline \end{tabular}
\end{table}
Table 3: Overview of the long-term durability tests.  
which was started as a pretest and whose load level is clearly below that of the other tests, is not plotted in the diagram. Figure 5b displays the tests which were stopped after 5000 to 6000 h, as well as their respective residual capacities.  
The dotted lines represent the maximum textile stress (3476 MPa), the reference stress (3050 MPa) and the lowest textile stress (2532 MPa) achieved in the short-term tests (Section 6.1). The upper and lower lines represent the scatter range of the ultimate stresses of the textile.  
As described before, the original aim was the derivation of a time to failure curve for the tested material combination. Based on the test results, however, it is not possible to identify such a curve to determine the strength losses at the end of the service life. For this purpose, a starting point of the time to failure curve must be determined first. Since no failure of the long-term durability tests could be achieved within a few hundred hours due to the constant load levels and environmental factors, preloading tests are carried out.  
Figure 5b clearly shows that the stopped tests still had a residual capacity of 24 to 26% above the constant load or 10 to 17% above the reference load, respectively. Therefore, no loss of strength could be detected. However, it is presumed that an alignment of the filaments occurs, which leads to an increase of the load capacity compared to the reference load. The results of the preloading tests are presented in the next section.