Numerical simulation of the behavior of steel T-stubs connected by Fe-based shape memory alloy bolts

The article focuses on the numerical simulation of the thermomechanical behavior of steel T-stubs connected by iron-based shape memory alloys bolts. The three-dimensional macroscopic model used in this work was previously developed by the authors considering different thermomechanical properties between austenite and martensite, and coupling between phase transformation and plasticity. The model is implemented in a UMAT code using an implicit time-discrete integration scheme that follows a "multisurface plasticity"-like approach. The numerical results show that the shape memory effect can be used to preload the bolt if the initial length of its shank is less than the total thickness of the flanges. For an initial shank length of 21.38 mm and a total flange thickness of 21.4 mm, the shape memory effect produced average contact forces of 101 N between the bolt head and the flange, and 37 N between the two flanges. The resulting average contact pressures were 210 and 25 MPa, respectively. The average bolt force after preload was approximately 22.6 kN. Subsequent application of 2 mm normal displacements at the top and bottom faces of the upper and lower webs induced local plastic deformation around the flange holes and phase transformation in the bolt. The reversibility of martensitic transformation and the confinement of the plastic deformation in a limited zone around the holes allowed nearly complete shape recovery by heating. The obtained results highlight the advantage of using low-cost iron-based shape memory alloys as alternatives to steel bolts for connecting T-stubs.