# Bond Fatigue of TRC with Epoxy Impregnated Carbon Textiles
## 4 Summary, Conclusions, and Outlook  
Regarding the results from Section 3, it can be stated that the cyclic loading has no negative impact on the required anchorage length for the investigated material combination. This assertion is justified by the following. First, there was no further increase in deformation when the anchorage length was increased from 3\(a\) to 4\(a\) (Section 3.3.3). Additionally, there was no decrease in absolute stiffness regarding these specimens (Section 3.4.3). Finally, in testing the residual strength, there was no load increase from an anchorage length of 3\(a\), and some of these specimens failed by textile rupture at the level of the tensile strength, which is an indicator that the tested anchorage length is sufficient to transfer the complete tensile load, even after cyclic loading. In conclusion, it can be said that the bond fatigue behavior of the investigated material combination is quite good, provided that the anchorage length is sufficient. The development of the deformation and stiffness of a specimen during cyclic loading depends on the applied maximum load as well as on the related minimum load (Sections 3.3.2 and 3.4.2). However, even at high maximum loads (e.g., \(\sigma_{\text{max}}\) = 95%), runouts occurred (Section 3.5). The tested residual strengths of runouts were generally higher or at least at the same level than the reference strengths (Section 3.6). Regarding the stress-deformation curves, the curve of the residual strength meets the curves of the reference tests again (Section 3.2); thus--regarding runouts--no negative impact of the cyclic loading can be detected. However, as there was nearly no third section of the observed cyclic creep curves of the failed specimen (Section 3.3.1), one may assume that cyclic failure occurs quite abruptly without advance notice. For this reason, it is strongly recommended to not extrapolate the S-N curves over the experimentally proven load levels. Figure 16: Comparison of textile stresses and failure mechanisms in reference and residual strength tests with different anchorage lengths. Whilst doing the above described investigations, the following concerning the use of DPO tests was found by [PERSON] and [PERSON] in [28]: a material combination (carbon textile with polyacrylate-based impregnation and fine grain concrete) usually used for the strengthening of existing reinforced concrete structures was tested in static DPO tests. Independently of the anchorage length, all the specimens failed due to splitting at quite low loads, and no increase of load with increasing anchorage length could be detected. Firstly, it is assumed that due to eccentricity between the stuck steel plates and the textile layer, there is a moment leading to splitting, and secondly, that the stuck steel plates block the formation of cracks, except for the one in the middle of the specimen. At this point, the whole deformation is concentrated, and the critical deformation, leading to splitting, is reached quite early. The investigations with this material combination have shown that the DPO test only represents the bond behavior of some specific situations, and cannot be used to determine the necessary anchorage length for thin layers of this material combination. For this material combination, much more realistic results were reached with an overlap test (e.g., according to [29]). Even though the findings in [28] were made with a different material combination than in the research presented in Section 3, comparative studies using overlap tests with the material combination described in Section 2 of the present paper should be done to prove the obtained results. Conceptualization, M.C. ; Formal analysis, J.W. ; Funding acquisition, M.C. ; Investigation, J.W. ; Project administration, M.C. ; Supervision, M.C. ; Validation, [PERSON] and M.C. ; Visualization, J.W. ; Writing--original draft, [PERSON]; Writing--review & editing, M.C. This research was funded by the German Federal Ministry of Education and Research.