Topology Optimization Design Of Shell-Infill Structures With Porosity And Seepage Constraints

Shell-infill structures are the bionic structure with the high stiffness-to-mass ratio and the well buckling resistance,and has been widely applied.Medical implant is the shell-infill structure,the surface is a thin-walled shell,and the inside is the porous structure with the stiffness and seepage performance.This dissertation studies topology optimization design method of shell-infill structures with porosity and seepage constraints for structural properties and mechanical properties of medical implant.Firstly,the microstructure topology optimization design model with the stiffness and seepage performance is proposed.This dissertation adopt the structural homogenization method to improve the stiffness performance of the microstructure with the objective optimization of maximizing the bulk modulus;and adopt the fluidic homogenization method to improve the seepage performance of the microstructure with the objective optimization of maximizing the equivalent seepage coefficient.This dissertation normalize the two optimization goals and impose the minimum seepage penalty to obtain the optimal topological configuration of the microstructure with the stiffness and seepage performance.According to actual demand,the topological configuration of the microstructure can be obtained by given the values of the stiffness and seepage weight parameters.Secondly,the structural multiscale topology optimization design model with porosity constraints is proposed.Most porous structures often have the features of different porosity.Microstructures with different porosities are regarded as different kinds,and their configuration in the macrostructure can further improve the structural performance.The overall optimization process is two stages.In the optimization of material distribution,this dissertation adopt the ordered SIMP model to optimize the material density distribution at macroscale.In the concurrent topology optimization,the ordered SIMP(Solid Isotropic Microstructures with Penalization)model and the energy-based homogenization method are adopted to achieve the macro-micro structure collaborative topology and the distribution of the microstructures with different porosity in the macrostructure.This dissertation compare and analyze the influence of the kinds of microstructures on the structure performance.The optimal multiscale design with multiple kinds of microstructures distribution is obtained to improve the structure performance as much as possible under the low computational cost.Then,the structural multiscale topology optimization design model with porosity and seepage constraints is proposed.By adding a normalized seepage penalty term to the objective function instead of the equality constraint,the seepage at macroscale results can satisfy the seepage constraint.The material density field at microscale and sensitivity field are adopted a volume preserving nonlinear projection function.The sensitivity value at the material boundary is increased,which effectively achieves the size requirement of microstructure flow channel.Thereby the seepage at macroscale is converged to the constraint value.The optimization process is still the material distribution optimization and concurrent topology optimization.The optimal topology configuration of the porous structure with multiple kinds of microstructures is obtained,and satisfies the certain seepage performance.According to actual demand,the topological configuration of the porous structure can be obtained by given the value of the seepage constraint.Finally,the topology optimization design model of shell-infill structures with porosity and seepage constraints is proposed.In this dissertation,The shell-infill structure is a special sandwich structure.The surface thin-walled shell can remain the structure shape and improve the buckling resistance.The inside is filled with microstructures of different porosity.And it has the certain seepage performance.The optimization design process is three stages.The first stage is the optimization of the shell material distribution,and this dissertation adopt the shellinfill topology optimization method.After the two stages of material density filtering and mapping,the optimal distribution of the shell material is obtained.The second stage is the optimization of the infill material distribution,and multiple kinds of microstructures are predistributed in the infill material.The third stage is the concurrent topology optimization of the infill material.The microstructures with different porosity are filled in the infill material.The seepage at macroscale can effectively satisfy the the requirements.According to the actual demand,the topological configuration of the shell-infill structure can be obtained by given the values of the material parameters,the shell thickness and the specified seepage.