Lightweight design on tubular structures by integrating optimized high-strength nano-materials


Student thesis: Doctoral Thesis

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  • Ying LI


Awarding Institution
Award date2 Oct 2013


This research reports a new scheme for accomplishing lightweight design in tubular structures. This design scheme is based on the integration of nano-structured materials produced by Surface Mechanical Attrition Treatment (SMAT) processing and the tubular structural selection system. The application of this design scheme is for wind turbine tower weight reduction. Since a component is a material made into a shape to realize a particular function, an effective choice of the material properties and optimized selection of the shape of the structure aid in the implementation of a lightweight structural design. SMAT creates a nano-crystallized layer on the metal surface which can effectively improve the strength of the original metal material, while maintaining the material’s ductility at a certain level. To support the optimization concept in this research, the related processing method on a tubular structure was developed. This method solves the problem of how to conduct SMAT on the inner surface of a tube. In this research, the processing method is proposed and verified by both computational and experimental tests. The RSM method and dynamic simulation are introduced to identity the best design for a reflector. Several reflectors were produced and compared to evaluate their efficiency and effects. The samples after treatment were inspected by various material characterization techniques from the first few micrometers below the treated surface. Another important part of this research was to optimize the sectional shape of tubular structures. A tubular structural selection system was programmed based on shape factor and performance indices to determine the optimal shape for a tubular structure. This system suggests an appropriate material type and related dimension parameters of a tubular cross-section, according to the requirements of designers, to reach a minimum weight of the structure. It can also provide the best sectional parameters by using the required material according to an equivalent strength or stiffness design. In addition, weight reduction can be accomplished by optimizing the wall thickness of the tubular structure. Axial compression tests were conducted on the tubes with-and-without full treatment. Comparison of compression results explicitly proves the advantage of SMAT materials. A wind turbine tower was selected as the industrial application of the design scheme proposed in this research. In the wind energy industry, as the height of the tower increases to accommodate larger turbines, the transportation, assembly, installation, and servicing of the components become increasingly difficult and costly; this is especially the case in China, where road density is not very high for high-density energy areas. One central problem with respect to the future economy is to explore cost-reduction potential. Unlike previous research, this study works on a tapered tube. A tubular structure with varying wall thickness was studied as well. Two main kinds of static loads on the wind turbine tower were bending and buckling loads. Individual, as well as combined, influence of loads was studied. The eccentric compression on the tapered tube was also discussed. The study results show that there are still enough margins for weight reduction in traditional wind turbine tower design. The design scheme can determine the most critical zones that the wind turbine tower can enhance. It can also achieve enhancement of the entire tower. Compared with other current weight-reduction schemes reported in the wind energy industry, using nano-structured materials possesses strong competitive potential. Additionally, the analytical method was supported by FEA simulation. This new design scheme is flexible, cost-effective and relatively easy to realize. It offers the benefits of adopting SMAT materials as new high-strength materials compared with traditional mild steel. It also provides better design solutions, in a succinct and direct way, for the weight reduction of tubular structures for designers.

    Research areas

  • Nanostructured materials, Design and construction, Nanotubes