For the purpose of applying a shape memory alloy ring to combining two separated pipes, the way to exchange the reverse transformation properties of uni-axial stress for those of multi-axial stress was proposed by modeling σ-ε behaviors not only in the process of loading and unloading but also in the process of heating for using to make a FEM analysis. Using the new idea way, the behaviors of deformation recovery and pressure against inserted pipe in the process of ring diameter enlarging and heating for combining two separated pipes were clarified considering the effects of ring diameter enlarging rate and ring thickness. From the viewpoint of saving SMA material cost as well as improving efficiency of ring diameter enlarging works, it was clarified that optimum thickness of ring is about 3mm to 5mm.
