Integrated Optimization Methods For Topology And Actuation Layout Designs Of Smart Morphing Structures

As a new type of smart structures,flexible structures which are actuated with smart materials can sense external electrical,thermal,mechanical stimuli and adaptively change their configurations.Therefore,they have important application prospects in the fields of variablegeometry aircrafts,soft robotics and so on.On the one hand,under coupling multi-physics fields,the active morphing and mechanical load-bearing performances of smart structures are affected by many parameters,such as types and geometrical forms of conventional and smart materials,mechanical load,control strategy and so on.Establishing corresponding numerical simulation models helps designers obtain accurate mechanical responses of smart structures,and understand internal functioning mechanisms.On the other hand,the existing variable density topology optimization methods lack considerations for the physical properties of smart materials.The optimized designs usually have complex geometries and vague material boundaries,thus violate manufacturable constraints.Meanwhile,the optimization methods dealing with actuators’ spatial layout problem only change a small number of design parameters in smart structures,which cannot realize the best match between mechanical performances and structural lightweight.This work uses smart materials with different response characteristics,and focuses on a series of key issues relating to the designs of smart morphing structures.By developing new integrated optimization methods for smart structures,the shape morphing precision and multidisplinary performances can be improved.The main research contents are as follows:(1)For ensuring designated shape morphing performance during the process of geometric model reconstruction,this dissertation studied the basic methods for considering member size control in the initial conceptual design stage of smart structures.Within the framework of threefield topology optimization method,new structural indicator functions are proposed based on sufficient condition for minimum size control of both solid and void material phases.Numerical results show that performances of proposed structural indicator functions are not affected by the size and dimension of finite elements,and they can accurately identify the structural“interior skeletons”.This enables minimum size optimization algorithm to generate topologically optimized solutions independent of finite-element discretization,and prevent the appearance of hinge-like and fine branch structures,then the integrity of optimized smart flexible structures can be guranteed;By introducing certain pore volume in the local neighborhood,the formations of solid features larger than prescribed maximum length scale are further limited,so the maximum and minimum member size can be precisely controlled at the same time.(2)Based on Multi-Point Constraints(MPC),an efficient finite element analysis method for piezoelectric composite smart morphing structures is proposed.For freely placing piezoelectric actuators on the surface of base structure in Classical Lamination Theory(CLT),and avoiding complex material interface recognition process,independent meshes are used between different layers.‘Perfect bonding’ connections between interlayers are achieved using sets of MPC.Through active shape morphing test of piezoelectric composite cantilever plate,the agreement between theoretical calculation results and experimental measurements is verified,and the causes of calculation errors are analyzed.(3)Aiming at piezoelectric composite structures with prescribed shape morphing requirements,this work proposes new integrated optimization method.New shape error function constituted of the relative errors between actual and expected shapes is constructed.Three types of design variables,namely the position of piezoelectric actuator,the applied voltage control parameter and the pseudo-density of host structural element,are optimized simultaneously to design several piezoelectric composite structures.The shape morphing control accuracy and overall mechanical load-bearing performance of composite structures are therefore improved.The actuation strain response of PZT-5A piezoceramic material under strong electric field is measured experimentally and its nonlinear constitutive behavior is further considered into the integrated optimization method.Consequently,when driven by high voltage,the optimal design schemes can be effectively searched for precise large deformation control.(4)To achieve precise control over the large deformation of Shape Memory Alloys(SMA)smart structures,based on macro material model of SMA and the three-field scheme,this work develops a new topology optimization method considering two-way shape pattern control.Since unexpected geometric distortions may occur in the maximizing stiffness topology optimization design,here we propose to use the target geometries as design objective.By rationally distributing the SMA material in macroscope.Withstanding external mechanical load,the key structural surface can reach expected geometrical shape by forming microscopic detwined martensite in certain local region.Meanwhile raising(or lowering)the material temperature,the geometrical configurations of SMA smart structures can change precisely between two prescribed shape patterns via martensite-austenite phase transformation.By applying geometrical size constraints on structural member features,two-way SMA smart morphing designs which satisfy manufacturing constraints can be obtained.