Efficient three-dimensional geometrically nonlinear analysis of variable stiffness composite beams using strong Unified Formulation

The use of composite laminates for advanced structural applications has increased recently, due in part to their ability for tailoring material properties to meet specific requirements. In this regard, variable stiffness (VS) designs have potential for improved performance over constant stiffness designs, made possible by fibre placement technologies which permit steering of the fibre path to achieve variable in-plane orientation. However, due to the expanded, large design space, computationally expensive routines are required to fully explore the potential of VS designs. This computational requirement is further complicated when VS composites are deployed for applications involving nonlinear large deflections which often necessitate complex 3D stress predictions to accurately account for localised stresses. In this work, we develop a geometrically nonlinear strong Unified Formulation (SUF) for the 3D stress analysis of VS composite structures undergoing large deflections. A single domain differential quadrature method-based 1D element coupled with a serendipity Lagrange-based 2D finite element are used to capture the kinematics of the 3D structure in the axial and cross-sectional dimensions, respectively. Predictions from SUF compare favourably against those in the literature as well as with those from ABAQUS 3D finite element models, yet also show significant enhanced computational efficiency. Results from the nonlinear large deflection analysis demonstrate the potential of variable stiffness properties to achieve enhanced structural response of composite laminates due to the variation of coupling effects in different loading regimes.