Stress recovery and cyclic behaviour of an Fe–Mn–Si shape memory alloy after multiple thermal activation

Abstract

The stress recovery and cyclic deformation behaviour of Fe-17Mn-5Si-10Cr-4Ni-1(V,C) shape memory alloy (Fe-SMA) strips, which are often used for pre-stressed strengthening of structural members, were studied. The evolution of recovery stress under different constraint conditions was studied. The results showed that the magnitude of the tensile stress in the Fe-SMA member during strengthening can have a signification effect on the final recovery stress. The higher the tensile stress in the Fe-SMA (e.g., caused by deadload or thermal expansion of parent structure during heating phase), the lower the final recovery stress. Furthermore, this study investigated the cyclic behaviour of the pre-stressed alloy followed by a second thermal activation. Although the magnitude of the recovery stress decreased during the cyclic loading, the second thermal activation could retrieve a significant part of the relaxed recovery stress. This observation suggests that the relaxation of recovery stress is due to a reversible phase transformation-induced deformation (i.e., forward austenite-to-martensite transformation) rather than an irreversible dislocation-induced plasticity. Retrieval of the relaxed recovery stress by the reactivation process has important practical implications as the prestressing loss in pre-stressed civil structures can be simply recovered by reheating of the Fe-SMA elements.

Microstructure and Thermomechanical Characterization of Fe-28Mn-6Si-5Cr Shape Memory Alloy

“…The stress-strain evolution under these conditions is shown in Figure 15. The general trend follows the pattern observed by other researchers in shape memory steels [3,17,[44][45][46]. The non-linear deformation response during loading is noteworthy.…”

Strengthening of Reinforced Concrete Beams with Externally Mounted Sequentially Activated Iron-Based Shape Memory Alloys

“…Since the stress in the SMA strip increases from sequence to sequence, the affordable temperatures to induce the phase change A s and to finish the phase change A f are increasing as can be seen from the dashed lines in Figure 2b. This effect is also described in [23]. For inhomogeneously heated SMA strips a higher activation temperature below A f may increase the total transformation from martensite to austenite as long as the temperature stress state of the material does not exceed the limit of irreversible plasticity which is indicated by the dotted line in Figure 2b.…”

Evaluation of Fe-Based Shape Memory Alloy (Fe-SMA) as Strengthening Material for Reinforced Concrete Structures

“…As a preliminary test for this paper, a direct tensile test was conducted to investigate the mechanical properties and material behavior on the Fe-SMA. As a result of the tests in Figure 1, the modulus of elasticity, limit of proportionality (σ 0.01 ), 0.2% proof stress (σ 0.2 ), and the stress at fracture of the Fe-SMA referred to as ultimate tensile strength (σ UTS ) were taken as 133 GPa, 200 MPa, 463 MPa, and 863 MPa, respectively, which are lower than the 173 GPa, 230 MPa, 546 MPa, and 1015 MPa reported in [31].…”