FULL AND VON KARMAN GEOMETRICALLY NONLINEAR ANALYSES OF LAMINATED CYLINDRICAL PANELS

A total Lagrangian-type nonlinear analysis for prediction of large def ormation behavior of thick laminated composite cylindrical shells and panels is presented, The analysis, based on the hypothesis of layerwis e linear displacement distribution through thickness, accounts for ful ly nonlinear kinematic relations, in contrast to the commonly used von Karman nonlinear strain approximation, so that stable equilibrium pat hs in the advanced nonlinear regime can be accurately predicted. The r esulting degenerated surface-parallel quadratic (16-node) layer elemen t, with 8 nodes on each of the top and bottom surfaces of each layer, has been implemented in conjunction with full and reduced numerical in tegration schemes to efficiently model both thin and thick shell behav ior, The modified Newton-Raphson iterative scheme with Aitken accelera tion factors is used to obtain hitherto unavailable numerical results corresponding to fully nonlinear behavior of the analyzed panels, A tw o-layer [0/90] thin/shallow clamped cylindrical panel is investigated to assess the convergence rate for full and reduced integration scheme s and to check the accuracy of the present degenerate cylindrical shel l layer element. Accuracy of the von Karman nonlinear approximation, c urrently employed in many investigations on buckling/postbuckling beha vior of thin shells, is assessed, in the case of laminated thin cylind rical panels, by comparing the numerical results obtained using this a pproximation with those due to fully nonlinear kinematic relations, es pecially in the advanced stable postbuckling regime.