Cyclic characteristics of the shape memory effect in Ti-Ni alloy helical springs.

Abstract

The cyclic characteristics of the shape memory effect in Ti-Ni alloy helical springs are investigated in thermomechanical cycles. In the experiment, an offset-crank shape memory alloy heat engine is used. The results obtained show that : (1) Nonrecoverable elongation and recovery rate vary significantly in the early cycles, but show slight variations after these cycles. (2) Elongation based on reversible shape memory effect increases gradually with the number of cycles. (3)Axial force corresponding to the maximum deflection decreases slightly in the early cycles, but shows a constant value after these cycles. (4)When the maximum torsional 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. (5) The resting period does not affect shape memory characteristics. (6) The number of cycles to failure decreases linearly with the range of torsional strain on the surface of the helical spring.