Dynamic stability of composite shells subjected to hygrothermal enviornment

Abstract

Structural components subjected to in plane periodic loads may undergo instability due to certain combinations of natural frequency and in plane load parameters which is called parametric resonance. Composite structural components are often subjected to various environmental loads during their service life. The presence of temperature and moisture concentration may significantly reduce the stiffness and strength of the structures and may affect some design parameter such as vibration and stability characteristics of the structures. To avoid the typical problems caused by vibrations and stability, it is important to determine natural frequency, critical buckling load and excitation frequency of the composite laminated structures, under hygrothermal conditions. Therefore the vibration, buckling and dynamic stability behavior of laminated composite shells subjected to hygrothermal loadings are studied in the present investigation. A simple laminated model is developed for the vibration and stability analysis of laminated composite shells subjected to hygrothermal conditions. A computer program based on FEM in MATLAB environment is developed to perform all necessary computations. An eight-node isoparametric element is employed in the present analysis with five degrees of freedom per node. Element elastic stiffness matrices, mass matrices, geometric stiffness matrix due to mechanical and hygrothermal loads and load vectors are derived using the principle of minimum potential energy. They are evaluated using the Gauss quadrature numerical integration technique. Quantitative results are presented to show the effects of curvature, ply-orientation, degree of orthotropy, geometry and number of layers of laminate on vibration, buckling and dynamic stability of composite shells for different temperatures and moisture concentrations.