Viscoelastic behavior of composite rotors at elevated temperatures

The composite rotor of a pulsed-power machine is built with radial precompression to enhance mechanical performance; however, the preload might decrease due to the viscoelastic behavior of materials at elevated temperatures. In this investigation, an analytical solution is developed to study the viscoelastic problem of thick-walled cylinders. The analysis accounts for ply-by-ply variations of rotor structural properties, ply orientations, and temperature gradients through the thickness of rotors. Fiber-reinforced composite materials generally illustrate extreme anisotropy in viscoelastic behavior. The viscoelasticity exists mainly in matrix dominant properties, such as transverse and shear, while the fiber dominant properties behave more like elastic mediums. Accordingly, the viscoelastic characteristics of composite cylinders is quite different from those of isotropic cylinders. Currently, finite element packages such as ABAQUS, ANSYS, and DYNA3D are not very suitable for the viscoelastic analysis of composite cylinder because of the lack of anisotropic viscoelastic elements. The prestress in the hoop-wound fiber, which generates radial compression in the rotor, might decrease due to Poisson's effect alone from the creep behavior in the transverse properties of composite. The result also shows the effects of layup construction and fiber orientations on the anisotropic behavior of composite rotors.