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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3. Results of Fatigue Tests at Increased Temperatures The results of the preliminary quasistatic tension tests of glass fiber plastic specimens at 22, 120 и 200ºС temperatures are given in Table 1.

Таble 1. Results of preliminary static tensile tests at normal and increased temperatures Temperature , °С strength limit σ B , MPa Young's modulus E, GPa 22 329±28 26,5±1,5 120 295±24 22,8±1,4 200 165±8 13,5±1,5

As a result of the cyclic tests, the values of fatigue life of the fiberglass specimens were obtained. The effect of the increased temperatures is reflected in the fatigue life degradation diagram (Fig. 1). To describe the behavior of the specimens during cyclic tests at increased temperatures, we introduce n’ value reflecting the change in the value of fatigue life as a result of damage accumulation, which is expressed as: ′ = ⁄ (1) where n is a number of cycles up to failure at different testing temperatures; N is the nominal number of cycles up to failure at room temperature.

Fig. 1. Diagram of dependence fatigue life - high temperatures for fiberglass samples at the parameters of cyclic loading: σ max = 0,5∙σ B , R = 0,1, ν = 20 Hz The diagram of the fatigue life degradation is non-linear in nature. To predict the residual life of the PCM specimens at increased temperatures, a trend line was plotted on the diagram. The change in the stiffness properties of fiberglass specimens, as a result of the fatigue damage accumulation was evaluated using the indirect technique based on measuring the amplitude of displacements of the loading pattern specimen/traverse during the test. The change in the amplitude of the movements was recorded using WaveMatrix software. For example, Fig.2 shows characteristic diagrams of changes stiffness values of specimen during fatigue tests at various temp eratures. The ordinate axis is R, and the abscissa axis n’ is the relative number of cycles to failure at various temperatures.