Parametric Design Of Gradient Porous Structures And Analysis Of Mechanical Properties

In clinical medicine,mismatches in the elastic modulus of metal implants and human bones can lead to "stress shielding" effects,and the design of porous structures is often introduced to solve the problem of "bone implant" interface looseness caused by them.In view of the complex and randomly distributed pore structure inside the bone,which is a non-homogeneous composite material,and meanwhile,the regular shape and uniform porous structure cannot meet the practical application requirements,therefore,this thesis proposes a controlled gradient porous structure design method,constructs the entity through additive manufacturing technology,and carries out the relevant mechanical property testing and analysis,the main research and conclusions of this thesis are as follows:First of all,random points are uniformly distributed in the specified space,the space is divided based on the Voronoi-Tessellation principle,and the Voronoi cell obtained is used as the geometric basis for pore opening design to construct irregularly connected porous structures.By introducing the Bezier parameter curve to regulate the scaling factor,the differentiated design of the cell opening is carried out,and finally the model generation with controlled pore gradient and certain biomimetic characteristics is realized.Secondly,the geometrical characteristics of the porous structure were extracted and the characterization method was proposed,and the correlation between the design parameters(Scaling factor,Number of random points)and the geometrical characteristics(Porosity,Pore diameter,Pore prism diameter,Specific surface area,Porosity gradient)was investigated.The functional correspondence between porosity and scaling factor was determined through research,and at the same time,the results showed good controllability of the geometric characteristic parameters.There is a strictly linear correspondence between pore diameter,pore prism diameter and the scaling factor,and a power function relationship between the number of random points,the specific surface area has a power function relationship with both design parameters.In addition,the method of calculating porosity by model slicing can effectively characterize the porosity gradient.The aforementioned findings provide a data base for the parametric design of porous models.Subsequently,quasi-static compression simulations of uniform/gradient porous models with different morphologies and investigation of the deformation and damage mechanism were carried out by Abaqus.The results show that the deformation of the prisms is influenced by the angle between their alignment direction and the load direction,which is mainly dominated by stretching and bending in the compression process,and the irregular design can effectively reduce the apparent elastic modulus of the model.At the same time,the mechanical properties of the structure gradually weaken as the porosity continues to grow.Compared with the uniform structure,the damage of gradient porosity evolves from the high porosity region and passes to the low porosity region by layer collapse.Finally,porous models with porosity series and gradient series were prepared by laser-selective melting technique,and the quasi-static compression test results showed that when the porosity increased from 59.02% to 78.57%,the corresponding elastic modulus decreased from 8.68 GPa to 1.18 GPa,and the compressive strength decreased from 190.89 MPa to 64.54 MPa,which both had a power function relationship with the porosity and can be fitted by Gibson-Ashby model.In addition,the porous structure designed herein was found to be well adapted to the skeletal structure of various parts of the human body in terms of mechanical properties,which to a certain extent can meet the requirements of medical bone implants.