Effect of Thickness on Connection Strength and Pull-Out Behavior of TiNiFe Shape Memory Alloy Pipe Couplings

TiNiFe shape memory alloy pipe couplings exhibit excellent radial recovery capability and therefore show great potential for pipeline fastening applications. In this study, the radial recovery stresses at different locations within a TiNiFe SMA pipe coupling were determined using a finite element inverse method. These stresses were subsequently applied as boundary conditions to establish a numerical model describing the fastening connection and pull-out process between the TiNiFe coupling and a TA18 tube. The effects of coupling wall thickness on the connection state and pull-out failure behavior were systematically investigated. The results indicate that the radial recovery stress increases monotonically with increasing wall thickness, although the growth rate gradually decreases. When the wall thickness ranges from 1.25 to 1.75 mm, the interfacial contact stress increases with thickness, thereby enhancing the fastening effect. However, when the thickness exceeds 1.75 mm, the intensified radial deformation of the inner convexes leads to a significant reduction in contact stress. The pull-out process of the assembly can be divided into three stages, namely the initial, intermediate, and final stages, during which the pull-out force first increases and then decreases with the evolution of the contact state. These findings provide a theoretical basis for the structural optimization and engineering application of TiNiFe SMA pipe couplings.