PSI - Issue 65

D.G. Solomonov et al. / Procedia Structural Integrity 65 (2024) 275–281 D.G. Solomonov and M.Sh. Nikhamkin / Structural Integrity Procedia 00 (2024) 000–000

280

6

Considering the dispersion of the high-cycle fatigue resistance characteristics of polymer composite materials, this accuracy can be considered acceptable.

Fig. 6. The mode of fatigue failure of the sample

Figure 6 shows the mode of fatigue failure of the samples under study. The failure is delamination between the shell and the flange. It starts in the most loaded zone A and spreads towards the flange corner. This representation is consistent with the thermograms shown in Fig. 3. Apparently, the intensification of sample self-heating at ε a > ε � is associated with a change in the mechanism of fatigue failure with the appearance of delamination. To assess the safety factor according to the high-cycle fatigue criterion, it is necessary to compare the obtained value of deformation amplitude ε � , corresponding to the fatigue limit, with the calculated or measured value of dynamic strain amplitude at the place of stiffener attachment to the full-scale structure under operating conditions. 4. Conclusion Within the framework of the IRT method, a technique has been developed for express experimental assessment of the strain amplitude corresponding to the fatigue limit of a typical structural element, namely the junction between a laminated carbon fiber shell and a flange. The technique is based on using the self-heating effect during the development of material fatigue damage and on infrared thermography used to record the temperature field on the surface of the object under study. The technique involves block cyclic loading of samples with a stepwise increase in the load amplitude in each subsequent cycle. In each loading block, the temperature field on the surface of the sample is recorded and the stabilization temperature is determined. The fatigue limit is determined by a sharp increase in temperature. A design and scheme for loading the samples, recording the parameters of loading and self-heating and processing the results have been developed. In particular, a procedure has been proposed to eliminate the human factor when approximating experimental data on the self-heating temperature of samples by using the coefficient of determination R 2 . It has been established that fatigue failure of the sample occurs in the area of the flange–shell connection. The most intense self-heating during cyclic loading is observed at this same zone. A comparison has been made of four versions of experimental data processing technique – namely, by the maximum stabilization temperature and by the stabilization temperature averaged over the most loaded zone of the sample, as well as by the maximum and average rates of temperature increase at the beginning of a block. All four options give consistent results.