Torsion of variable stiffness composite laminated beams

A shear-deformable beam theory is proposed to model the torsional behavior of laminated beams composed of variable stiffness layers. The displacement field is derived by expanding mid-surface displacements in Taylor series in width coordinate and by retaining first-order terms. Stiffness of the beam is made variable by using curvilinear fibers in layers. Variable stiffness layers are categorized into three types as symmetric, asymmetric and anti-symmetric based on their fiber paths. A displacement-based finite element method is used to solve the analytical model and to predict rotations of the beam under torsional load. Beams constructed with symmetric, antisymmetric and asymmetric variable stiffness layers are investigated for several lay-ups by both including and neglecting axial displacement terms. Acquired results are compared with the results of a finite element analysis software. It is observed that the developed model is working properly for beams with variable stiffness layers and including axial displacement terms in calculations improved the model`s performance.