PSI - Issue 20

M.P. Lebedev et al. / Procedia Structural Integrity 20 (2019) 81–86 M.P. Lebedev et al. / Structural Integri y Procedia 00 (2019) 0 0 – 000

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Fig. 3. The change in flexural strength of fiberglass ST-69N-15P during exposure in a moderately cold climate

If the index kR changes non-monotonously (Fig. 3) by Kirillov V.N. (2010), then the indicator jumps with a high degree of probability as the result of methodological errors.

The analysis shows that the most common causes of methodological errors are: - violation of the requirements of the standards of mechanical measurements; - sample preparation errors; - uncontrolled reversible effect of the plasticizing action of moisture; - temperature effects of a generalized indicator of climatic aging; - differences in mechanical properties of PCM in a series of parallel samples; - scale factor (plate thickness and aging heterogeneity in thickness). 3. Conclusions

To improve the reliability of the determination of the mechanical properties of PCM during climatic aging in the initial state and after the completion of the next stages of exposure, it is necessary to provide the following methodological requirements: - in accordance with current standards, prepare samples for measurements and carry out preliminary assessments (influence of the shape and size of the samples, methods of securing the samples in the clamps, cutting angle of the samples to the main direction of reinforcement); - check the variation of indicators for sample cut from different plates, calculate the coefficients of variation, which determine the number of samples to ensure the required accuracy; - measure the monitored R value for several temperatures, including below and above the glass transition temperature of the polymer matrix; - perform measurements for samples in the state of delivery or the moment of removal, after complete drying and wetting at 60 о С. Without strict fulfillment of these requirements, high reliability of measurements of mechanical parameters will not be achieved and the cost of conducting long-term, costly climatic PCM tests will not be justified. Acknowledgment The work was carried out within the framework of the RFBR Project No. 18-29-05012 "Development of scientific bases for creation of new composite materials under the influence of abiogenic and biogenic factors in the Arctic and subarctic zones of the Republic of Sakha (Yakutia)".