Validation, extensions, and applications of the U* index theory for load transfer analysis of vehicle structures

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Wang, Qingguo
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A basic function of engineering structures is transferring the forces from the loading points to the supporting points. Understanding of the load transfer behavior is the foundation for engineering structural design. U* index, which was introduced in 2005, is an indicator of load paths within structures. Load transfer analysis based on the U* index has been developed as a new design paradigm for engineering structures. However, the U* index theory has not been experimentally validated yet. Moreover, the U* index theory is restricted to isotropic materials. Meanwhile, in the U* index theory, the rotational DOFs are not considered. Consequently, it is imperative for the engineering community to validate and extend the U* index theory. In this thesis, firstly, an experimental study was performed to validate the U* index theory. Secondly, a revised design of a vehicle component was accomplished based on the U* index theory to demonstrate the effectiveness of the U* related design criteria. Then, two new U* indices (U*O and U*M) were proposed to eliminate the restrictions of the original U* index. The proposed U*O index extended the application of the U* index theory to orthotropic composite materials. The new U*M index was formulated by considering both translational and rotational DOFs, which makes the U* index theory applicable for mechanical models under six DOFs. At the meantime, two applications were presented to show the capability of the newly proposed U*M index in automotive structural design. The applications demonstrate the load transfer analysis based on the newly proposed U*M index is an effective tool for designing desired automotive structures. The thesis as a whole improved the U* index theory to be more mature and capable for solving engineering problems with the higher complexities in both the material and the mechanical models. In addition to the structural analysis of ground vehicles, the extended U* index theory has great potential to be applied in other kinds of engineering structures such as aircraft and ships.
Vehicle structures, Load path, U* index, Finite element analysis, Vehicle impact