Study On Interference Connection Based On Shape Recovery Of Ni-Ti Shape Memory Alloy

Interference connection can effectively improve the fatigue life of aircraft mechanical joints.There are some defects in interference connection,such as low interference,non-uniform interference and damage to structural parts during installation.Due to the defects of interference connection at present,the design idea of interference connection based on shape memory alloy shape recovery characteristics is proposed.NiTiNb memory alloy is taken as the research object,with the help of elastic-plastic theory analysis,constitutive model of shape memory alloy,finite element simulation and experimental verification,etc.The interference connection of shape memory alloy(SMA)was studied systematically.Based on the theory of elastic-plastic mechanics,the stress and strain equations of the hole wall under the condition of elastic and elastic-plastic deformation between the connecting hole and the axis are obtained through the analysis of the thick-walled cylinder under compression.The relationship between the deformation of the plastic zone and the interference is deduced when the elastic-plastic deformation occurs.Based on the constitutive model of shape memory alloy,the stress and strain equations of interference connection of NiTiNb memory alloy at different stages were established.The analysis of the stress distribution at the hole edge of the plate with holes shows that with the increase of the interference,the deformation of the hole wall of the plate with holes gradually changes from elastic interference to elastic-plastic interference,and the radial stress is always compressive stress,while the tangential stress gradually changes from tensile stress to compressive stress with the increase of the interference.The finite element analysis shows that when the interference is less than 1%,the elastic deformation of the connecting hole occurs.When the interference is 1.5%,the plastic deformation of the hole wall occurs.When the interference is 2.5%,the maximum stress of the connecting plate is close to the tensile limit of the material.Continuous increase of the interference will have a negative impact on the strength of the connecting structure.When the interference is low,the deformation of the hole wall is in the state of elastic deformation,and the tangential stress is tensile stress,which is unfavorable to fatigue life.With the increase of the interference,the deformation of the hole wall enters the stage of elastic-plastic deformation,and the tangential stress becomes compressive stress,whose value increases with the increase of the interference,which helps to improve the fatigue life of the structure.Through uniaxial tension test,the radial recoverable strain of NiTiNb memory alloy after 16%axial tension at-60 C is about 2.39%.Based on this,the connection tests with different interferences are designed.The interference force is calculated by measuring the pull-off force.The results are compared with the results of finite element calculation.It is found that the interference force of the joint increases with the increase of the interference,and the interference force and the interference force of the joint increase with the increase of the interferences.The trend of unrecoverable strain is basically the same,which verifies the rationality of finite element simulation.