Topology Optimization Of Compliant Mechanisms With Multiphysics Fields Coupling And Multiphase Materials

With the development of technology, multi-field coupling play an increasingly significant role in the engineering and integrated product, even it plays a leading role. Therefore, topology optimization design methods under a single physical field cannot meet the practical application when design these engineering products using topology optimization method. There are urgent needs for effective ways to solve the coupling problem. In this paper, topology optimization in multi-field coupling is research object, the topology optimization problems such as structure cooling, material performance and reliability induced by thermal field.(1) Considering the effect of temperature, the topology optimization of rigid structure and compliant structure were carried out. The need for thermal-mechanical-coupling analysis was demonstrated, and a novel method is proposed for topology optimization of multi-field coupling. First, the finite element analysis on thermal field is performed; the thermal strain is included in the constitutive relations. Virtual work principle and finite element method are used to derive equivalent nodal thermal load, and the thermal loads are converted into body forces and applied to the elastic fields, and the coupled control equations of structure are obtained. The thermal- mechanical -coupling topology optimization model is built, and the optimized topology diagrams of thermal- mechanical structure and compliant structure are obtained. Finally, comparison analyses of topology results at different temperatures were carried out.(2) On the basis of the thermal- mechanical coupling model, a multi-objective thermal-electrical-coupling topology optimization method was proposed, and a thermal-and-electrical-driven compliant mechanism was designed. According to Joule theorem, the electric field will produce the equivalent heat, the mechanism will generate thermal stress and deformation under the thermal field, and thus it drives the mechanism to obtain output displacements. Sequential coupling method is applied to perform the analysis of electric-thermal-structural-coupling multi-physics, and the ratio method is used to balance the proportional relation between multiple objectives, and the optimization problem is solved by using MMA approximation algorithm. Thus, it provides a theoretical foundation for the electricity-thermal-structure-material integrated and comprehensive design of MEMS system.(3) A topology optimization method for structure cooling based on convection heat transfer in the boundary conditions was proposed. The optimization model is built using minimum weak degree of heat as optimized object, and the topology results of cooling structure similar to the practical heat exchanger were obtained, thus it illustrates the idea and the model proposed in the paper is correct. And examples have demonstrated that the neglect of heat convection for topology optimization is not entirely correct. In addition, the topology optimization of cooling structure under the non-uniform temperature field is proposed on the basis of uniform temperature field, and the non-uniform temperature field is treat as the superposition of a number of uniform temperature fields and concentrated heat sources by using the superposition principle, and thus the topology optimization problem of cooling structure under non-uniform temperature field is converted into a multi-objective optimal design.(4) Topology results of a variety of material microstructure were obtained according to different objects, and the compliant mechanisms consisting of different materials were designed. The equivalent elastic modulus, off-axis stiffness and overall stiffness matrix of multiphase materials are derived, and the microstructures of main directions of different materials are studied. The multiphase composites of a variety of different properties are obtained according to different functional requirements. The topology optimization of compliant mechanisms based on multiphase composite is studied to achieve multi-functional needs of correspondence between input and output in order to maximize the performance of multiphase materials.(5) Based on probability reliability theory, we study how to reduce the effect of uncertain of temperature environment, geometry and loading. The reliability index is used to quantitatively measure the various random uncertain factors, and the thermal-solid-coupling topology optimization model is built using the reliability index as constraint conditions. By comparing the topology results by using reliability method and deterministic one, it proved that the best combination of economy and performance point can be found by using reliability topology optimization. On the basis of the above study, we presented a method of topology extraction based on density contour boundary contour. And the displacement reverser was machined by wire cutting technology, and its displacement performance and the temperature effect was tested. The test showed the results from test are consistent one from theoretical model, and it illustrated the correctness of the theoretical model.