Simulation Of Forming Process And Mechanical Properties Of TC4 Pyramid Lattice Structure

Titanium alloy,known as "space metal",has excellent mechanical properties,which is favored by the aviation industry.As a new generation of ultra light material,sandwich panel structures can not only possess low relative density,but also can be integrated with liquid flow?energy absorption?noise reduction and some other functions through internal space structure design,so it is perfectly accord with the demands of spacecraft.Fabricating microtruss cores from perforated metal sheets by stretch-forming process could introduce plastic strain into the metal struts during tensile elongation,making the microtruss stronger due to intrinsic dislocation strengthening.However,this process requires high plasticity for the base metal,so it is only applied to materials with good plasticity,such as aluminum alloy and stainless steel.The plastic forming properties of Ti6Al4V alloy at normal temperature is very poor.This paper studied the material flow law of Ti6Al4V alloy at high temperature,and optimized the process of stretch-forming based on finite element simulation.The effect of temperature and strain rate on material flow behavior of Ti6Al4V alloy was studied by high temperature tensile test,and true stress-strain curves show that the plastic flow ability increases with higher temperature and lower strain rate.The effect of deformation parameters on microstructure evolution is analyzed by optical microscope.It is proved that the temperature increase and rate decrease could promote the precipitation of beta phase which can enhance the plastic deformation ability of Ti6Al4V alloy.Fracture morphology of specimen was observed by scanning electron microscope,showed that the number and depth of the dimples were enhanced with the increase of temperature and the decrease of the strain rate.constitutive equations were derived based on strain compensated Arrhenius model and modified Johnson-Cook model,furthermore,average absolute relative error(AARE)are 6.74%and 3.02%respectively,which means the prediction accuracy of two indicating that the two established models can accurately characterize the high temperature flow law of Ti6Al4V alloy.The properties of the TC4 titanium alloy were assigned to the finite element model.The initial selection and optimization of forming punch are carried out through finite element simulation.The results showed that the cylindrical punch and the square punch can achieve higher forming height and reduce the strain concentration of truss.Based on punch optimization,the surface response method was used to optimize the parameters of the pre-fabricated blank,and build the foundation for subsequent mold design.The theoretical calculation of the mechanical properties of pyramid lattice structure shows that the parameters such as the thickness of the panel,the thickness of the core,the width of the truss and the size of the cell have an huge influence on the mechanical properties of the lattice structure.Moreover,The core is the main bearing part of the pyramid structure,we can improve the mechanical properties by increasing the thickness of the core or the width of the truss.In addition,the inclination angle of truss will affect its bearing efficiency.