Effect of anisotropic stiffness degradation on the forced vibration of cylindrical shells

Structural defects are commonly encountered in engineering applications. They can significantly affect not only the structural integrity but also the natural frequencies and vibration responses of cylindrical shells subject to external loading. This study proposes a novel concept of stiffness degradation to analyze the effect of defects on the vibration of shell structures. Specifically, stiffness degradation factors (SDFs) are introduced into the model of a cylindrical shell based on Sanders shell theory, and their influences on the dynamic response of an infinitelength cylindrical shell are evaluated by analyzing vibrations at multiple locations. The results show that vertical vibrations at receiver points located away from the driving point are more susceptible to the stiffness degradation, particularly at higher frequencies. The degradation of flexural stiffness has a greater effect on the vibration of cylindrical shells than the degradation of membrane stiffness, particularly in terms of the resonant frequency decrease. Furthermore, stiffness degradation in the circumferential direction has a greater effect on shell vibration than in the longitudinal direction. By examining the effects of eight SDFs separately, it is revealed that the vibration response of a cylindrical shell is affected by the directions and types of stiffness degradation, the frequency range, and the observation point. Overall, this study provides a general analytical framework for analyzing the vibration response of cylindrical shells including the effect of anisotropic stiffness degradation, which could be applied to composite shell structures with directional fiber orientations and shell structures with various defect modes.