Diagram and Parameters of Fatigue Sensitivity for Evaluating the Residual Strength of Layered GFRP Composites After Preliminary Cyclic Loadings

In this paper, the questions concerning the investigation of fatigue characteristics of composite materials are discussed and the changes in their static deformation and strength properties caused by preliminary cyclic actions are estimated. The aim of the work was to obtain new experimental data on damage accumulation processes in GFRP composite materials under combined cyclic and quasistatic loadings. An analysis of processes of fatigue damage accumulation in the composite materials is performed, and stages of change in the residual mechanical properties of the materials during cyclic loadings are noted. Temperature fields in the working section of samples are analyzed, and the characteristics features of temperature distribution in their destruction zone are revealed. Functions describing damage accumulation and changes in the strength and stiffness properties of the composites are introduced, which can be used to describe the behavior of the materials under fatigue loadings. A new form of representation of experimental data in the form of a fatigue sensitivity diagram is proposed, which can be employed to analyze the residual strength of structures made from composite materials. The characteristic stages of change in their residual static strength are presented in relation to the degree of preliminary cycling. It is proposed to use new material characteristics — the fatigue sensitivity threshold and the coefficient of static strength preservation.