ON THE USE OF GENERALIZED BEAM THEORY TO ASSESS THE BUCKLING AND POSTBUCKLING BEHAVIOR OF LAMINATED CFRP CYLINDRICAL STIFFENED PANELS

This paper presents the numerical implementation and illustrates the application and potential of a nonlinear elastic generalised beam theory (GBT) beam finite formulation to analyze the postbuckling behavior of laminated CFRP composite thin-walled prismatic cylindrical panels. This formulation (i) is based on a novel GBT cross-section analysis approach, (ii) accounts for the presence of initial geometrical imperfections and (iii) adopts an incremental iterative solution procedure employing the Newton-Raphson method and an arclength control strategy. No stiffness degradation or ply failure is taken into consideration and the material is deemed linear elastic and orthotropic. Numerical results concerning the local buckling and postbuckling behavior of stiffened CFRP cylindrical panels are presented and discussed-one of these panels was experimentally tested and numerically investigated in the context of the COCOMAT project. Taking full advantage of the GBT unique modal features, one is able to (i) examine the nature of the panel structural response, which is expressed in terms of deformation mode participations, and (ii) perform analyses involving very few d.o.f. (by preselecting a small set of deformation modes). The panel buckling loads and deformed configurations obtained from the GBT analyses are validated through comparison with either experimental data or values yielded by shell finite element analyses carried out in the code ABAQUS. In order to assess how the curvature affects the panel buckling and initial postbuckling behavior, a stiffened plate having a width identical to the cylindrical panel is also analyzed and the results obtained are compared with those determined for the corresponding curved panels.