Thermal-vibration aging of fiber-reinforced polymer cylindrical shells with polyurea coating: Theoretical and experimental studies

Abstract

Polyurea coating (PC) is a promising surface treatment technology for improving structural static and dynamic mechanical properties in a thermal environment. However, rare studies have been reported on thermal-vibration aging issues of composite shell structures treated with polyurea coating. In this paper, the thermal-vibration aging behaviors of fiber-reinforced polymer (FRP) cylindrical shells with PC are investigated both experimentally and theoretically. Initially, thermal-vibration aging experiments are performed on the four FRP cylindrical shell specimens with or without polyurea coating. The natural frequency and dynamic stiffness values of the specimens are achieved to estimate their aging behaviors, from which the dynamic aging resistance of PC is quantitatively determined. Then, an aging model for PC- FRP cylindrical shells subjected to impulse excitations in a uniform thermal environment is proposed on the basis of the first-order shear deformation theory, the multi-segment partition technique, and the virtual spring technology. The dynamic elastic moduli of FRP and PC materials are assumed to be functions of temperature change and aging time simultaneously, and the equations of motion involving thermal aging effect are derived for predicting the natural frequencies and dynamic stiffness functions. After the iterative identification principle of fitting coefficients of FRP and polyurea materials is clarified based on the artificial bee colony algorithm, the present model is verified against the experimental results when investigating the thermal-vibration aging behaviors of two new specimens. Finally, by employing the validated model, the influences of critical geometric and material parameters of the PC-FRP cylindrical shell structures on dynamic aging behavior are discussed to reveal their aging mechanism and to improve the thermal-vibration aging resistance.