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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Visual inspection of undamaged samples after preliminary cyclic torsion made it possible to detect cracks near the gripping parts. At the number of cycles closest to the value corresponding to fatigue failure, defects in the form of delaminations were noted (Fig. 4).

Fig. 4. Photographs of the surfaces of fiberglass samples after preliminary cyclic torsion (from left to right: n’=0.284; 0.557; 0.628; 0.468)

Under conditions of proportional biaxial cyclic action (proportional 1), the formation of mixed type cracks (diagonally to the sample axis) was recorded. As cycling progressed, an increase in the number of cracks was observed on the surface of the samples with the propagation of delaminations with cracks near the gripping parts (Fig. 5). This pattern is explained by the large value of the tangential components of the cyclic stress in mode proportional 1. The type of surface damage was similar to the samples after preliminary cyclic torsion.

Fig. 5. Photographs of the surfaces of fiberglass samples after preliminary proportional cyclic stretching with torsion (proportional 1) (from left to right: n’=0.162; 0.449; 0.735; 0.989; 0.953)

When visually inspecting samples after cyclic proportional tension with torsion at increased values of the normal components (proportional 2), it was recorded that a gradual increase in the duration of exposure contributed to the growth of type I cracks (normal separation) with delaminations over the entire surface of the samples (Fig. 6).