UC San Diego

Composite materials play an important role in the aerospace industry. They are increasingly used in primary structures, and recent manufacturing technology advancements are making Variable Angle Tow (VAT) composites a valuable option for the design of innovative airplanes. One of the challenges of the future of aviation is to have aerodynamically efficient configurations, which often result in very flexible structures. Thus, the large deformation analysis of VAT composites is a necessary phase of the design. A difficulty is often represented by the higher degree of anisotropy of these structures, which needs to be taken into account with the necessary computational flexibility and without a compromise on the accuracy of the evaluations, especially on the determination of stress levels.

This dissertation introduces a finite-element based computational framework for the variable kinematic analysis of geometrically nonlinear variable-stiffness composite laminates. A unified approach allows the analyst to master a virtually infinite number of types of elements. They are based on a compact writing of the equations of motion so that each layer can be independently modeled with an axiomatic approach, or effective equivalent single layer models, able to correctly take into account the zig-zag form of the displacements, can be used. In particular, formulations originally developed for linear classical composites, are now introduced for the large displacement analysis of VAT laminates. The accurate prediction of transverse stresses is achieved by a quasi-3D recovery procedure originally proposed and based on integration of the Second-Piola Kirchhoff Stress Tensor. It is demonstrated that the level of accuracy is comparable to the more computationally demanding three-dimensional finite element approaches