Extensions of the U* theory for applications on orthotropic composites and nonlinear elastic materials

To improve the performance and the efficiency of a structure, it is essential to understand how the applied loads are transferred through the structure. The U* index was introduced as one of the methods for identifying the load transfer paths within structures. It has increasingly been used by industry due to its unique capability in structural analysis and design. However, the feasibility of the U* theory for composite materials has not been demonstrated yet. Meanwhile, the U* index was only arisen for linear elastic materials, as a result it is invalid for materials with nonlinear elasticity. In this paper, two modified load transfer indexes for orthotropic composites ( $$U_O^*$$ ) and nonlinear elastic materials ( $$U_NL^*$$ ) are proposed based on the basic U* theory, respectively. The computational process of both the $$U_O^*$$ and the $$U_NL^*$$ indexes is presented. The effectiveness of the proposed indexes on load transfer analysis is demonstrated through four case studies.