PSI - Issue 18

Staroverov Oleg A. et al. / Procedia Structural Integrity 18 (2019) 757–764 Staroverov O.A., Wildemann V.E., Tretyakov M.P., Yankin A.S./ Structural Integrity Procedia 00 (2019) 000–000

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range (0.3–0.55)∙n’. When stress to σ max =0.4∙σ B , the decrease in residual strength in the area of initial fatigue sensitivity was 15%; however, with such parameters of preliminary cyclic loads, the stabilization section was the longest (0.2–0.8)∙n’

Fig. 4. Diagram of the fatigue sensitivity of fiberglass samples with different parameters of loads

In the course of the study, an assessment was made of the effect of various preliminary cyclic effects on stiffen residual characteristics of fiberglass specimens. By analogy with the method of constructing a diagram of fatigue sensitivity, Figure 5 shows a diagram of the change in stiffness of glass-plastic specimens in relative coordinates of K Еn ’; n’. The values of the residual static Young's modulus were determined on the linear part of the deformation diagram.

Fig. 5. Diagram of changes in the rigidity of fiberglass samples with different parameters of loads

When analyzing the diagram of changes in stiffness of glass-plastic specimens (Fig. 5), it is noted that variations in the parameters of the preliminary cyclic impact did not affect the appearance of the curves describing the change in residual stiffness in the process of fatigue accumulation of damage. For the studied material in the range of cyclic exposure (0.4–0.6)∙σ max , the threshold of fatigue sensitivity is n' 0.02 , the beginning is n' s1 and the end is n' s2 of the stabilization section, and the section of exacerbation of fatigue sensitivity has similar values. Figure 6 shows the surfaces of the working area of the samples before and after the preliminary cyclic loading. On the surface of the samples, local stratification zones formed in the process of fatigue damage accumulation are visible for all tested samples.