| Based on additive manufacturing techniques capable of producing highly complex structures,it has become the focus of current research to develop high-performance structures with limited material consumption.Heterogeneous multi-hierarchical structures with excellent structure and multi-disciplinary performance are important structural forms of high performance structures.It is urgent to research and establish the heterogeneous multilevel structure design method for additive manufacturing,so as to realize the high-quality heterogeneous multilevel structure design which can adapt to the manufacturing process limitations,can be manufactured and can be easily manufactured.To realize such a design,it is necessary to determine the macroscopic configuration,microscopic configuration and reasonable changes of microscopic configuration in space.The design scheme that fully realizes the collaborative design of micro and macro configurations(the topology of micro configurations has dimensional parameters that can be changed in space)is very difficult to manufacture because its structure is often too complex.Therefore,according to specific needs,the development of accurate and convenient description of microstructures and the development of simplified implementation methods has become the main research direction.This paper studies the design method of heterogeneous multilevel structure based on specific microstructure,realizes the design of structural configuration by designing the spatial layout of materials containing specific microstructure,and realizes the design of heterogeneous structure by reasonably adjusting the description parameters changing with space under the given microstructure topology.Two microstructural selection methods are proposed: one based on the existing microstructural selection method and the other based on the optimal configuration of microstructures.Based on these two methods,a heterogeneous multilevel structure design method is proposed.Specific research contents and results are as follows:(1)Design method of heterogeneous structure configuration based on existing microstructures.Based on the existing microstructures,appropriate microstructures are selected,and additional parameters are introduced to define the specific modes and non-uniform distribution of microstructures based on the topological form of the microstructures;the relationship between equivalent properties and microstructural parameters of the substructured materials is constructed by a new homogenization method based on commercial finite element software;and the parameters and microstructures are described by material layout.A topology optimization model for heterogeneous multi-layer structure configuration design based on existing microstructures was established with the description parameters as design variables and the objective of minimizing flexibility.The sensitivity of global structural compliance for pseudo-density and micro-structure parameter variables is derived,and an optimization model solution method based on MMA method is constructed.The numerical examples show that the design method based on the existing parameterized microstructures can not only obtain ideal topological optimization results,but also have good manufacturability,which proves the validity of the design method proposed in this paper.(2)Topological optimization design method for material microstructure based on macroscopic performance requirement.The ideal design should consider the shape of macrostructure,geometric parameters,shape of carrier,microstructure configuration and composition of material at the same time,so as to maximize the potential performance of material.In the case of given material consumption,the optimization objective model of global minimum compliance was constructed,and two initial microstructure design methods that could meet the requirements of different working conditions were selected and applied.Firstly,the macroscopic design domain is fixed,and a microstructure with the optimal flexibility of homogeneous two-layer structure is designed as the initial microstructure under this condition.The other method divides the macroscopic and microcosmic design domains at the same time,and obtains the optimal microstructure through the macroscopic and microcosmic collaborative optimization design method.At the same time,the nonlinear filter strategy is used to get clear microstructure boundary.By comparing the two methods and selecting the better results,an effective way of initial microstructure configuration is provided for the subsequent heterogeneous and two-level design.(3)Heterogeneous multilevel design method combining microstructure and macrostructure.Structure and material,macro and micro overall topology optimization technology and theory is an important direction of spatial structure development,has become the future development trend of optimization design field.In this paper,a concurrent design method combining microstructure design with macrostructure design is proposed.On the basis of selecting the optimal microstructure configuration,the initial design of the microstructure is obtained by extracting the key structural information,and the microstructure is taken as the configuration of the specific microstructure.A description model of the microstructure is established and the relationship between the material equivalent properties and these parameters is given.The overall distribution under the configuration is described in detail by combining the material microstructure design with the macro structure topology optimization,so as to establish the global heterogeneous structure design.The Heaviside filtering strategy is also employed to obtain the macroscopic and microcosmic layout design with overall clarity.Numerical examples show that,compared with traditional topology optimization and macro and micro design under single parameter,heterogeneous multi-level design method can obtain structures with lower flexibility and lower difficulty for subsequent manufacturing. |
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