Cyclic Characteristics of the Shape Memory Effect in Ti-Ni Alloy Wires and Helical Springs

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The cyclic characteristics of the shape memory effect (SME) in Ti-Ni alloy wires and helical springs are investigated in thermomechanical cycles. In the experiment on a helical spring, an offset crank shape memory alloy heat engine is used. The results obtained are summarized as follows. ( 1 ) The nonrecoverable elongation and the recovery rate vary significantly in the early cycles, but show slight variations in later cycles. ( 2 ) The two-way strain with reversible shape memory effect increases with the number of cycles. ( 3 ) The yield stress of stress-induced martensitic transformation decreases significantly in the early cycles, but decreases gradually in later cycles. The yield stress decreases for high shape memory processing temperature. ( 4 ) The stable cyclic properties of SME may be obtained by training before practical use. ( 5 ) When the maximum shear strain on the surface of the helical spring becomes larger than 2%, the rate of increase in nonrecoverable strain becomes greater while that for axial force decreases. ( 6 ) The number of cycles to failure decreases linearly with the range of torsional strain on the surface of the helical spring.
一般社団法人日本機械学会の論文
1990-04-15