PSI - Issue 20

M.P. Lebedev et al. / Procedia Structural Integrity 20 (2019) 81–86 M.P.Lebedev et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Polymeric materials (PM) and polymer composite materials (PCM) due to the diversity of their properties are most widely used in all spheres of human life, including, usage under extreme climatic conditions as reviewed by Kablov E.N. (2013). When choosing a material for a particular use in industry, in construction, in transport, in everyday life, from a large number of possible options, its composition is selected that will provide a combination of the required indicators at an acceptable cost. The most important advantage of a material is its ability to preserve its working capacity as long as possible, that is, to resist aging - a combination of physicochemical reversible and irreversible transformations under the influence of aggressive external factors (temperature, humidity, solar radiation, mechanical stresses, etc), as shown by Kablov(2011). The set of required indicators PM at its acceptable cost and ability to resist aging are the basis for making decisions about the use of the material. PM and PKM are dominant, capable of functioning without replacement for 20-30 years, and in necessary cases for more than 50 years. The need to justify the long-term performance of PM and PCM increases the relevance of environmental testing as pointed by Martin (2008), Pochiraju (2012) and White (2017). The problem is that there are no universal programs for such tests. In practice, usually programs are used that take into account the composition of the material and the conditions of its operation. The approach of finding the best option from a set of similar materials is common. In this case, one conducts comparative tests of materials candidates with accelerated methods in climatic chambers according to the modes with increased aggressiveness and chooses the most resistant material. The advantage of this approach is its efficiency, and the disadvantage is the need to correct the findings when moving from overly aggressive test regimes in climate chambers to actual operating conditions, where the mechanisms and kinetics of aging can vary significantly as found by Startsev (2009). For example, by Wang Z.K. (2016) the effect of an aggressive solution imitating a concrete medium on the tensile strength of basalt plastic reinforcing rods was experimentally studied. Samples of this material were kept in a salt-alkaline solution for 21, 42, 63 days at temperatures of 32, 40, 55 ° C. Using the universal law of Arrhenius on the accelerating effects of temperature, they gave a forecast about the duration of work of basalt plastic in 5 regions of Australia, provided that the residual strength remains 50% (the estimate showed from 2.6 to 21 years). If we extend these calculations to the climate of Yakutsk, then at an average annual air temperature of - 8.8 ° C, the service life would exceed 550 years . However, it is easy to take into account that only 3 summer months in Yakutsk with an average temperature of 17 ° C by Startsev V.O (2018) will cause the indicated decrease in strength after 18 years. Therefore, for each specific material, the reliability of prediction of properties under real operating conditions according to the results of accelerated tests should be justified. This is of particular importance in determining the correspondence between the results of accelerated tests and the initial stage of field tests in order to reduce the likelihood of erroneous conclusions due to the influence of uncontrollable factors.

Nomenclature a,b

rate constants for destruction and structuring of epoxy matrices

elastic modulus

E

critical energy release rate relative coefficient of persistence

G IC

k R

crack length

l 0

PM

polymeric materials

PCM R 0 ,R R 1 ,R 2

polymer composite materials

baseline value and limit value of R at t →

preexponential factors

μ Poisson coefficient σ b ,E b , τ, G bend and interlayer shear strength limits and moduli σ k is the critical value of stress σ t ,E t , σ c ,E c tensile and compression strength limits and moduli