Tests And Analyses Of NiTi Shape Memory Alloy Bars’ Restrained Recovery And Heating

Because of the excellent characteristics of shape memory alloys, their applications havebroad prospects in civil engineering. If we make shape memory ally bars into bolts, and usethem in the connection of subway shield segments, when the shield segments appear openingin some degree, shape memory alloy bars can provide closing restoring forces by theirrestrained recovery property, and then create more favorable conditions for subsequentpassive repair. For this, the restrained recovery property and heating methods of shapememory alloy bars were studied preliminarily in this article. The main work includes thefollowing three parts:(1) Through tensile and shear restrained recovery tests of shape memory ally bars, weinspected how the restrained recovery stress changed with temperature when the residualdeformations were different. Research shows that, whether in heating stage or cooling stage,the biggest restrained recovery stress increases with the increase of residual deformation ofshape memory ally bars; thermal expansion and contraction of shape memory ally bars andrestraint devices have an apparent influence on restrained recovery stress.(2) Based on Brinson model, we theoretically analyzed the restrained recovery process,pointed out main problems of this model, and did some improvements to this model; thenbased on improved Brinson model, we theoretically analyzed the restrained recovery processagain, found that the calculated curves in heating stage and the first half calculated curves incooling stage were in good agreement with the experimental curves when the residualdeformations were different, especially the calculated biggest restrained recovery stresseswere relatively close to experimental values.(3) This article proposed a new heating method for shape memory alloy bars,corresponding heating tests and computational analyses were did to preliminarily verified itsfeasibility. Research shows that, Time needed for the temperature of shape memory alloy barrose to110℃from room temperature is less than20minutes, heating efficiency is relativelyhigh and the effect is good.