PSI - Issue 17

Dmitrii S. Lobanov et al. / Procedia Structural Integrity 17 (2019) 651–657 Lobanov Dmitrii S., Staroverov Oleg A./ Structural Integrity Procedia 00 (2019) 000 – 000

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cyclic loadings; ′ = ⁄

(4) is the relative number of cycles of preliminary loading, with n — the number of cycles of preliminary cyclic loading and N — the limiting number of cycles to failure at given parameters.

Fig. 4. Diagrams of fatigue sensitivity at normal and elevated temperatures (120°C)

The test results analysis at increased temperatures showed that, compared to the specimens tested at normal temperature, the decrease in the value of the residual tensile strength occurred in two stages, without a zone of the initial fatigue sensitivity (Fig.4). In the interval of fatigue sensitivity (0.1 – 0.8) n’ , the change in the value of the coefficient of static strength retaining under cyclic loading (K Bn ’) did not exceed 5%, which corresponds to the stabilization stage. For the specimens under room temperature, the K Bn ’ value in the interval of stabilization was 15% lower, compared to the specimens tested at increased temperatures. At the aggravation interval (0,8 – 1) n’ , a sharp decrease in the residual strength followed by fatigue failure of the specimens occurred.

n ’ = 0 ,1

n ’ = 0 ,2

n ’ = 0 ,4

n ’ = 0 ,6

n ’ = 0 ,8

n ’ = 1

Fig. 5. Development of zones of local delamination on the surface of the working area of fiberglass specimens depending on the number of cycles passed

Fig.5 shows the surfaces of the working area of the specimens after preliminary cyclic loading with different cycle numbers. There are local delamination zones formed in the process of fatigue damage accumulation on the surface