Расчетный метод оценки морозостойкости лакокрасочных покрытий воздушных судов

Abstract

The paper considers the issues of temperature cycling and ice accretion on external paint coatings of aircraft as well as the negative effects of these processes expressed in periodic tension-compression strain and absorption of atmospheric moisture by surface microasperities with its subsequent freezing resulting in gradual cavity wedging. We note that laboratory testing methods recreating the temperature cycling that simulates actual operating conditions of aircraft paint coatings are increasingly labour-intensive. We substantiate the feasibility of developing a computational method for frost resistance estimation in specific operating conditions. The method takes into account the combination of contraction stresses, excessive cooling and wedging caused by ice build-up. We assume the main physical and mechanical properties of ice and paint to be homogeneous and equal to cumulative average values, and the linear thermal expansion coefficients of the substrate and coating to be constant and not dependent on temperature. We disregard ice friction over the microasperity cavities and in-flight loads on the paint coating caused by incident air flows and structural deformations of the aircraft. We present a method of computing frost resistance of aircraft paint coating subjected to cyclical ice accretion, which is based on the method of equivalent stresses. We tested frost resistance of a polyesterurethane coating over a duralumin plate in the range of --50 to 25 °C for F = 2000 freezing and thawing cycles. We performed a temperature cycling computation of the factor of safety for frost resistance in the case of periodic ice accretion. The results obtained are in good agreement with experimental data