Prestressed Vibration of Stiffened Variable-Angle Tow Laminated Plates

Compared to straight fiber path laminates, variable-angle tow (VAT) laminates are known to redistribute the in-plane stress resultants for improving structural buckling response. The VAT laminates can also be used to improve the free vibration response by tailoring the structural elastic stiffness. This paper studies the prestressed vibration response of a stiffened, VAT laminated plate under a uniform end shortening. Because there are both spatially dependent stiffener and fiber path orientations for a stiffened, VAT laminated plate, a separate modeling of the plate and stiffeners is considered. This method avoids placing common nodes at stiffener-plate and stiffener-stiffener interfaces. This allows one to study mesh convergence for the plate and the stiffeners, separately. It also improves the efficiency and robustness of the finite element model. The finite element code based on the present method is verified extensively using examples that are either available in literature or are analyzed using commercial software. Parametric studies show that, depending on the in-plane load and boundary condition, the VAT laminates with linearly varying (LV) fiber paths can increase the prestressed vibration fundamental frequency when compared to the straight fiber path laminates. Optimization studies found that using nonlinearly varying fiber paths, when compared to the LV fiber paths, causes a significant increase in the buckling load but only a slight increase in the case of free or prestressed vibration fundamental frequencies. The VAT laminates appear to mainly tailor the panel's elastic stiffness for improving the prestressed vibration response for the stiffened plates with clamped edges. However, for the simply supported stiffened plate, the VAT laminates are mainly used to change both the elastic and geometric stiffness matrices for improving the prestressed vibration response.