Simulation Calculation And Design Of Connector Structure Of Porous Si₃N₄ Radome Connector

Missile radome usually requires materials with good dielectric properties and thermal shock resistance,low thermal expansion coefficient,in addition to the need to have resistance to thermal erosion,wave penetration,heat release and other characteristics.Porous Si₃N₄ ceramics can exactly meet the above requirements,but if a porous Si₃N₄ ceramic is used to make the missile radome,a metal connecting ring is needed to connect the radome with the projectile.The metal connecting ring material chosen for this project is Invar alloy because Invar alloy has a smaller coefficient of expansion and higher shaping and toughness.However,due to the brittleness and fragility of porous Si₃N₄,it is critical to reduce the residual stress of the joint.This topic will focus on exploring the effect of macroscopic factors such as Invar ring thickness,equal parts number,solder layer thickness,overlap length,and ring wall inclination on the residual stress.First,two types of solders,Ag-Cu-Ti and Ag-Cu/Cu/Ag-Cu-Ti,were used to conduct the connection experiments of microstructure and performance parts,respectively.The solder used in the simulation was selected to be Ag-Cu/Cu/Ag-Cu-Ti by comparing the microstructure and shear properties.Based on the microstructure distribution of the solder joints,the design model was divided into five parts.From the inside to the outside,the Invar alloy ring,the Ag-Cu ring,the pure Cu ring,the Ag-Cu ring,and the porous Si₃N₄ ring were in this order.After the cooling of the model,the residual stress is analyzed.From the simulation results,it can be found that the thickness reduction of the Invar ring can effectively reduce the residual stress;after the Invar alloy ring is divided into 2 equal parts,the residual stress drop is very obvious,continue to increase the equal parts.The residual stress did not decrease more significantly;as the thickness of the solder layer decreased,the residual stress first decreased slowly,but when the solder layer continued to decrease to 0.1mm,the residual stress increased again;The lap length of the material ring has obvious influence on the residual stress,the stress increases first and then decrea ses with decreasing lap length,and the residual stress is the smallest when the lap length is 5 mm;in order to verify the change of ring wall inclination For the influence of residual stress,this project separately designs two Invar ring tilt models.The first scheme is that the inner wall of the Invar ring is vertical,and the second scheme is that the inner and outer walls of the Invar ring are inclined and parallel to each other.Through comparison and verification of the two schemes,it was found that the ring wall inclination has little effect on the size and distribution of the residual stress.The simulation of the loading process mainly analyzes the bearing capacity of the connectors and the distribution of stress after the load.The simulation results show that the stress on porous Si₃N₄ rings decreases as the Invar ring is thinned under the same applied load.However,when the Invar ring is thinned to 1 mm,the bearing capacity is greatly reduced;the Invar ring has the smallest stress and the largest effective connection area on the porous Si₃N₄ ring when it is divided into 2 equal parts and 4 equal parts.Continuing to increase the number of equal parts,the stress will increase,and the effective connection area will decrease;for the simulation of changing the thickness of the solder layer,we find that the thinner the solder layer is,the smaller the stress is after loading,and the larger the effective connection area;during the loading process The smaller the lap length is,the worse the bearing capacity is.With the increase of external load,the stress on the porous Si₃N₄ ceramic ring also increases faster;with the increase of the ring wall inclination,the stress appears to decrease first and then increase,and the stress concentration area shifts from the edge to the middle position.Then back to the edge.From the above simulation calculations,it was determined that the Invar ring thickness is 2 mm,the Invar ring is divided into 4 equal parts,the thickness of the solder layer is 0.4 mm,the overlap length is 10 mm,and the ring wall inclination is 80° as the optimal connection parameter.Finally,the actual components were connected using the best parameters obtained from the simulation.The shear performance was tested.The load capacity of the Invar ring completely cut connectors reached 2238 N.