Determination of the recovery stress under constraint in Fe29Mn7Si5Cr SMA
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Ferrous shape memory alloys (SMAs) do not possess a complete shape recovery. Several attempts to improve the shape recovery still fail to achieve 100% recovery. For some applications, however, the recovery stress under constraint might be more important. In this work, a procedure was designed to measure these stresses under constraint in a Fe29MnSiCr SMA. The net recovery stress was defined as the maximal difference between the stresses developed in deformed and an undeformed sample. The calculation of σthermal(T) = E(T)α(T)(T-T0) can replace the measurement of the stress developed in the undeformed sample. The effect of partially free recovery before recovery under constraint is also investigated. It was remarkable that after annealing at 200°C, the net stress did not decrease although about 50% of the shape recovery has already taken place. This allows to use this alloy as a pipe joint, where the diameter of the joint can be larger than the one of the pipes, since the free recovery will hardly lower the recovery stresses under constraint.
KeywordsAustenite Thermal Expansion Stress Relaxation European Physical Journal Special Topic Shape Recovery
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