Quasi-trivial solutions for uncoupled, homogeneous and quasi-homogeneous laminates with high number of plies

Quasi-trivial (QT) sequences are a class of lamination stacks for which, in the framework of Classical Laminate Theory (CLT), the properties of uncoupling and/or homogeneity are verified in a closed-form solution [1]. These sequences have received great attention from the scientific community as they have proved to be an extremely powerful tool for the design and optimization of composite laminates. Nevertheless, two main reasons limit their adoption: first, to find QT sequences, a complex algorithm is required; second, calculations become computationally intensive for long QT sequences, thus limiting the maximum number of plies attainable. This constrains the use of QT stacks to applications involving only thin laminates. In order to exploit QT stacks for thick laminates new tools are proposed. Firstly, a new and more efficient algorithm for finding QT stacking sequences is developed and an original procedure is devised to effectively code it. The proposed algorithm finds a greater number of QT solutions, with respect to those given in [1]. Additionally, analytical relationships to obtain new QT sequences by superposition of known QT sequences are presented in [2]. Thanks to this new class of closed-form solutions, laminates can be designed using QT stacking sequences without limitations on the maximum number of plies. The results presented in this work open new possibilities for the design and optimisation of thick laminates. In addition, laminates with special requirements may be designed by superposition of QT stacks, thus reaching specific design goals that cannot otherwise be met.