By virtue of high strength and stiffness to weight ratio, outstanding designability and functionality, the continuous fiber-reinforced composites have attracted extensive attention in academic circles and have been widely used in various industrial departments, especially in aircraft structural parts, such as aircraft composite beam elements. However, with the increasing demands of lightweight and other special performance requirements of structures in aerospace industry, the traditional design methods based on ply optimization (such as fiber angle, thickness and stacking sequence optimization) cannot fully meet the above requirements sufficiently. Topology optimization is an advanced structural design method widely recognized by academia and engineering, which can maintain mechanical performance while reducing the weight of the structure. Topology optimization using isotropic materials is a well-researched area and has been widely used in industry. However, topology optimization of fiber-reinforced composite structures is still in the exploratory stage and has become a hot spot in recent years. In addition, the issues of technology for the production of optimized composite structures remain open, especially when the processes of design, optimization and production go side by side and certain technological limitations are imposed.
Therefore, the purpose of this dissertation is to mass minimization of the aircraft composite beam structures, based on the composite laminate theory and the method of topological optimization with consideration of the technological restrictions.
The object of research is the aircraft composite beam structures, such as spars, ribs, etc.
The subject of research is the design of composite beam structures using the topology optimization method with consideration of technological restrictions.
The theoretical part of the work is based on the mechanics of composite materials, the theory of finite element, the theory of topology optimization, and the theory of vibration. The developed finite elements and optimization frameworks in Chapters 2 and 5 are implemented using self-programmed MATLAB code. The optimization algorithm used in this work includes MMA, GCMMA, and IDSA algorithms. In Chapters 3 and 4, the topology optimization process is performed by the commercial software Altair-Inspire, the finite element simulation is implemented by the commercial software ANSYS. The feasibility and effectiveness of the proposed optimization framework are verified by numerical examples and finite element simulation.
The scientific novelty of the obtained results
1. For the first time, a hybrid multilevel optimization scheme was proposed for the simultaneous optimization design of the fiber orientation and the structural topology. The hybrid multilevel method can avoid the poor convergence and local optima behaviors in the optimization of laminated plates. This proposed method considers both the material and topological configuration design, and lays a theoretical foundation for the optimal design of constant stiffness laminated beam structures.
2. For the first time, a novel design method that combines topology optimization approach and RFW technology were developed for composite beam structures. And the conceptual design of the RWF system for manufacturing the optimized structures was also presented. This proposed method provides a new idea for the integration of design and manufacture of composite beam structures.
3. For the first time, topology optimization of laminated composite structures under harmonic excitations was studied. A novel method for calculating the harmonic response of composite laminates was proposed, which provides an effective solution for the topology optimization of composite structures under harmonic force excitations.
The work of this dissertation improves the practicability of the topology optimization method, expands the application range, provides important theoretical significance and lays a necessary research foundation for the application of lightweight design of fiber-reinforced composite structures in engineering structures.
