Abstract: In order to overcome the disadvantages of the inexactness of the numerical simulation of shape memory alloy (SMA) pipe connection system and the abridgement of the research of influence factors on the fastening force of the SMA pipe connection during the total assemble process, based on the thermodynamic Gibbs free energy, the incremental relationship between the stress tensor and the martensitic volume fraction is derived and written in an ABAQUS user-defined material subroutine with considering the change of elastic modulus and the temperature effect of the martensite transition. The assemble process of the SMA pipe connection system is simulated and the phase transition and mechanical behavior of the whole pipe connection system subjected to thermo-mechanical coupling are described effectively. The numerical results indicate that the maximum stress of the connected pipe occurs at the inner wall near the pipe connection port. The contact pressure between the outer wall of the connected pipe and the inner wall of the SMA pipe connection has a large gradient near the port of the SMA pipe connection, which increases rapidly from zero to the maximum and then gradually falls back to a higher stable value along the axial direction. The stress and martensitic volume fraction all have a gradient distribution in the pipe connection wall from inward to outward. In addition, the contact pressure level shows a positive correlation with the thickness, which is negatively correlated with the inner diameter, and is not related to the internal loading pressure. The phase transition and mechanical behavior of the SMA pipe connection system are simulated more accurately, and the influence factors on the fastening force are analyzed in detail, which provides a theoretical basis and guidance for the design of the SMA pipe connection.[1]

Key words: constitutive equation, finite element analysis, pipe connection, shape memory alloy