Vibration, Buckling and Parametric Instability of Delaminated Composite Panels in Hygrothermal Environment

Abstract

The present investigation deals with free vibration, static and dynamic stability performance of bidirectional delaminated composite flat and curved panels with inplane periodic loading in hygrothermal environment.The dynamic instability under in-plane periodic forces for delaminated woven fiber composite panels are studied in varying environmental conditions of temperature and moisture using finite element method (FEM). Numerical analysis by FEM and experimental studies are conducted on free vibration and buckling response of bidirectional delaminated composite panels in hygrothermal environment. The influences of various parameters such as hygrothermal conditions, area and strip delaminations, boundary conditions, ply orientations, stacking sequence, curvatures, static and dynamic load factors on the free vibration, static and parametric instability characteristics of bidirectional composite panels are considered in the present study. A finite element model is developed having 8-noded isoparametric element with 5 degrees of freedom (DOF) per node for the vibration, static and dynamic instability characteristics of delaminated bidirectional composite flat and curved panels under hygrothermal environment utilizing first order shear deformation theory (FSDT). Principal instability zones are located by solutions of Mathieu-Hill equations using Bolotins approach. Based on principle of minimum potential energy, the elastic stiffness matrix, geometric stiffness matrix due to hygrothermal and applied loads, mass matrix and load vectors are formulated. Provision for area and strip delamination modeling is also made in the numerical analysis using multi-point constraint algorithm. A general formulation for vibration, buckling and dynamic stability characteristics of bidirectional delaminated composite flat and curved panels under in-plane periodic forces is presented.The materials utilised for casting of specimens are bidirectional Glass fiber, epoxy as resin, hardener, polyvinyl alcohol as a releasing agent and Teflon film for introducing artificial delaminations. The material constants are calculated from the tensile tests of coupons under varying temperature and moisture conditions as per appropriate ASTM standards. For free vibration testing, FFT analyzer with PULSE Labshop software is used. A test set up is fabricated for vibration test of composite plates under different boundary conditions.The Universal testing machine INSTRON 8862 is used for determination buckling loads experimentally. A good matching is observed between predicted and test results for free vibration and buckling of delaminated composite panels in hygrothermal field. The natural frequencies and buckling loads are observed to decrease with increase in delamination at elevated temperature and moisture conditions under different boundary conditions. However, an increment in the fundamental frequencies is found at sub-zero temperatures up to cryogenic range as against ambient conditions because of development of