PSI - Issue 30

A.K. Kychkin et al. / Procedia Structural Integrity 30 (2020) 173–178 Kychkin A.K., Struchkov N.F., Vinokurov G.G. et al. / Structural Integrity Procedia 00 (2020) 000–000

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Thus, the formation of local porosity of the composite material occurs at the “matrix-fiber” interface. During climatic tests, due to the degradation of the composite material, the physical and mechanical properties of the matrix and reinforcing material change over time. As a result, their difference leads to the appearance of microdamages and porosity at the matrix-reinforcing material interface, which contribute to the formation of porosity in basalt fiber reinforced polymers (see Fig. 2).

P о ,%

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Fig. 3. Average open porosity of basalt-plastic composite materials: 1- initial porosity, experiment; 2 - linear dependence (1) for the initial porosity, the thickness of the degraded layer d 0 = 0.1 mm; 3 - porosity after degradation, experiment; 4 - linear dependence (1) for a degraded material, the thickness of the degraded layer d 0 = 1 mm. Therefore, in this work, the open porosity of basalt fiber reinforced polymers during their aging was investigated by the method of hydrostatic weighing. Figure 3 shows the experimental data of the average open porosity of basalt fiber reinforced polymers in the initial state and after exposure with markers. As can be seen from the graphs, there is an increase in the average open porosity of basalt fiber reinforced polymers with an increase in their cross sectional diameter. As expected, degradation of the composite material leads to a significant increase in its average open porosity. Thus, the largest increase in the average porosity is observed for basalt-plastic reinforcement with a smaller diameter of 6 mm by a factor of about 4. For basalt-plastic reinforcement with a diameter of 8 mm, a significant increase in open porosity by ≈ 2.5 times was also established. The obtained analytical results suggest that the average porosity of the rods is proportional to the amount of reinforcing fibers in the degraded outer annular layer of the cylindrical basalt fiber reinforced polymer rebar. The number of reinforcing fibers decreases linearly with decreasing radius of the basalt fiber reinforced polymer. This follows from the uniform distribution of the reinforcing fibers (the circumference of the annular layer is proportional to the radius). Let d0 be the depth of the outer layer subject to degradation with a fixed duration of climatic tests. It should be assumed that the depth of the outer layer d0 is also the same for all types of basalt fiber reinforced polymer. When the composite material degrades from the outer surface under the influence of the same external conditions, this depth will be the same, at least for the initial stage of climatic tests. Then, to estimate the average porosity P о of a cylindrical composite material, the following linear expression can be applied: P о ~ ) ( ) ] ( [ 0 0 2 0 2 nd D d R d nS n R         , (1) where n is the concentration of reinforcing roving fibers, S is the cross-sectional area, D = 2 R is the diameter of the cross-section of the basalt fiber reinforced polymer, d 0 is the depth of the outer layer subject to degradation. In fig. 3, lines 2 and 4 show the dependences for assessing the average porosity, obtained according to this expression (1). Calculations have established that the linear dependence of the average porosity more satisfactorily