The Effect of Natural Climatic Aging on Damage Accumulation Kinetics in the Structure of Epoxy Polymers Under Tensile Loads

Abstract

The approach is proposed for assessing the “critical” state of polymer materials under the effect of aggressive media. Changes in kinetics of failure accumulation of three compositions of epoxy polymers based on ED-20, Etal-247 and Etal-370 epoxy resins cured by Etal-1440 in 45, 90, 180, 270 and 360 days of natural climatic exposure were analyzed. We have identified changes in the rate of damage accumulation when the total level of failures exceeds 70÷80% of their maximum corresponding to the achievement of maximum tensile stresses. Damage accumulation kinetics was calculated based on the author’s method using methods of fractal analysis of deformation curves for polymer materials samples under tension. This approach involves determining the coordinates of “critical” points of deformation curves for which the fractality index values calculated over the previous short time intervals using the least coverage method, were less than 0.5. High stability of epoxy polymer parameters based on modified Etal-247 resin under the natural climatic factors has been found. After a year of full-scale exposure, for this type of epoxy polymer the “critical” levels of tensile stresses and their corresponding relative elongation are reduced by 11% and 16%. At the same time, for polymers based on ED-20 and Etal-370 epoxy resins, these figures are 1.9 and 2.7 ($\sigma_{crit.}^{70}$) and 2.7 and 5.1 ($\varepsilon_{crit.}^{70}$) times reduced, respectively, which indicates a significant damage accumulation.