The Formation of Microcracks during Climatic Aging of Polymer-Composite Materials

This review article substantiates the need to take into account internal stresses when predicting mechanical parameters in polymer-composite materials (PCMs) subject to climatic aging. The patterns of formation and development of microcracks under cyclic mechanical loads are considered. It is shown that similar microcracks are formed in PCMs due to the action of internal stresses during thermal and thermal-moisture cycling, during the transformation of sorbed water into ice. The nature of microcracking depends on the properties and morphology of polymer matrices and fibers, the number of cycles, the type of stacking, temperature difference, bond strength, the ratio of strength and deformation at the micro- and macrolevels, and other factors. The processes of thermal oxidation and photo-oxidation activate microcracking of polymer matrices in PCMs, proving the need for a profound inquiry into the density of microcracks in open climatic conditions.