Mechanical and recovery behavior of a new iron-based shape memory alloy plate

In this study, a new iron-based shape memory alloy (Fe-SMA) plate with a thickness of 3 mm was developed in China, and its mechanical and recovery behavior was experimentally investigated. The influences of various activation temperatures (100 ℃ ∼ 480 ℃), prestrain levels (2%, 4%, 6%, 8%, 10%), and initial stresses (50 MPa, 75 MPa, 100 MPa) on the recovery stress were investigated. Stress-temperature curves after secondary activation and recovery stress relaxation were also measured. The experimental results indicated that the Fe-SMA plate exhibited excellent mechanical properties, including an elastic modulus of 162 GPa, yield strength of 512 MPa, ultimate strength of 952 MPa, and ultimate strain of 40.5%. The recovery stresses of the Fe-SMA plates ranged from 191 MPa to 417 MPa. The recovery stress increased with the increase of activation temperature, but the increment decreased gradually. At activation temperatures of 100 ℃ ∼ 200 ℃ and 250 ℃ ∼ 480 ℃, the recovery stresses of Fe-SMA plates with prestrain levels of 6% and 8% were larger than that of Fe-SMA plates under other prestrain levels. The tested recovery stress relaxation was 10.8% ∼ 13.5% after 1500 h. The recovery stress relaxation within the first 24 h and 240 h accounted for 48.7% ∼ 56.5% and 78.7% ∼ 79.3% of the total stress relaxation in 1500 h, respectively. Based on the test results for the mechanical properties, a modified stress-strain model was proposed for the Fe-SMA plate without prestrain.