Large deflection analysis of thermally prestressed composite beams using strong Unified Formulation

Large deflection analysis is an essential requirement to characterize the behavior of flexible beam structures including wings and rotor blades that undergo large displacements during service. The introduction of composite materials and particularly variable angle tow (VAT) technology make it possible to meet the lightweight and high-strength requirements of such flexible structures due to increased design space to achieve fiber tailoring. The behavior of these structures is further complicated by the presence of thermal prestresses (in the form of residual stresses during thermal curing processes), which studies have shown to significantly contribute to the buckling behavior of VAT structures. To handle these complex material and structural features of flexible composite structures, an enhanced geometrically nonlinear Strong Unified Formulation (SUF) is developed in this study to model large deflection of prestressed constant and variable stiffness beams. The enhanced SUF is derived based on 2D Serendipity Lagrange-based cross-sectional kinematics coupled with 1D differential quadrature element while the solution of the nonlinear static response is obtained using the Riks method. The numerical examples of compressive-loaded prestressed cantilevered beams show that the proposed SUF offers predictions in satisfactory agreement with ABAQUS 3D FE solution while offsetting more than 99% of the DOF required for ABAQUS. The effect of prestress in the postbuckling behavior of the beams is found to be dominant up to the moderate loading regime while the effect is neutralized in the deep postbuckling phase due to large rotations and axial deformation.