PSI - Issue 54

Artur Kuchukov et al. / Procedia Structural Integrity 54 (2024) 369–375 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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b) Fig. 2. K B ( n ) dependency (a), K E ( n ) dependency (b)

The influence of the type of stress state during preliminary cyclic exposure on the nature of the change in residual mechanical characteristics is noted. However, the method used has some disadvantages. Firstly, in some cases, a preliminary cyclic load exceeding unity can be applied to the samples without destruction occurring. This is due to a significant spread in the durability determined from the results of fatigue tests. Secondly, the obtained dependences look non-monotonic: for example, from the form of the K E ( n ) dependence it seems that after a certain value of the preliminary influence an increase in the Young's modulus is observed. In this regard, we can conclude that it is necessary to improve the used methodology by calculating the durability of the sample based on the initial section of the fatigue sensitivity curve and adjusting the value of the preliminary cyclic impact. 3. Microstructural analysis of sample fracture patterns A study was carried out of the fracture surfaces of fiberglass tubular samples tested under conditions of quasi-static tension, torsion and proportional tension with torsion at different ratios of the normal and tangential components of the stress tensor. A visual inspection of undamaged samples after preliminary cyclic impacts with different modes revealed that under pre-tension conditions, transverse cracks relative to the loading direction (normal separation) were recorded on the surface of the samples across the entire surface. As the duration of pre-exposure increased, the formation of delaminations was observed (Fig. 3).

Fig. 3. Photographs of the surfaces of fiberglass samples after preliminary cyclic stretching (from left to right: n’=0.403; 0.716; 0.996; 0.491)