Parametric Instability of Square Laminated Plates in Hygrothermal Environment

The present paper investigates the parametric instability of square laminated plates subjected to periodic dynamic loadings in hygrothermal environment. The effects of various parameters like the increase in static load factor and the degree of orthotropy of simply supported composite plates at elevated temperatures and moisture concentrations on the principal instability regions are investigated using finite element method. The effects of transverse shear deformation and rotary inertia are used to study the antisymmetric angle-ply square plates. A simple laminated plate model is developed for the parametric instability of square laminated plates subjected to hygrothermal loading. A computer program based on FEM in MATLAB environment is developed to perform all necessary computations. The results show that instability of square laminated plates occurs for different parameters with an increase in temperature and moisture environment. The onset of instability occurs earlier, and the width of dynamic instability regions increases with a rise in temperature and moisture for different parameters. The effect of damping shows that there is a finite critical value of dynamic load factor for each instability region below which the square laminated plates cannot become unstable. 1. Introduction There is a tremendous increase in the utilization of composite materials in thin-walled structural components of high speed aircrafts, submarines, automobiles and other high-performance application areas. When exposed to high temperature and moisture, the changes in vibration and static and dynamic stability characteristics have necessitated a strong need to understand their dynamic behavior under different loading conditions. L. W. Chen and Y. M. Chen [1] studied the free vibration of the laminated rectangular composite plate exposed to steady state hygrothermal environment using finite element method. Sai Ram and Sinha [2] investigated the effects of moisture and temperature on the free vibration of laminated composite plates using finite element method. Huang et al. [3] discussed the effects of hygrothermal conditions on the dynamic response of shear deformable laminated plates resting on elastic foundations using a micro-to-micromechanical analytical model. Thangaratnam et al. [4] studied the buckling analysis of composite laminates for critical temperature. The mathematical formulation is based on linear theory and the finite element method using semiloof elements. Ram and Sinha [5] investigated the effects of moisture and temperature on the static stability of