Experimental investigation and modeling of the loading rate and temperature dependent superelastic response of a high performance shape-memory alloy

This study explores the superelastic behavior of a recently developed Ni_45.3Ti_29.7Hf₂₀Pd₅ alloy that has more favorable mechanical properties (high strength and hysteresis) than many well-known shape-memory alloys. The effects of aging on the shape-memory properties of Ni_45.3Ti_29.7Hf₂₀Pd₅ polycrystalline alloys are revealed first. Next, the dependence of the superelastic response of an aged Ni_45.3Ti_29.7Hf₂₀Pd₅ alloy on the strain amplitude, loading rate, and test temperature are examined via uniaxial compression tests. Then, the superelastic response of a solutionized sample is compared with that of the aged sample. Finally, a soft-computing approach that employs neural networks and fuzzy logic is used to model the highly nonlinear behavior of Ni_45.3Ti_29.7Hf₂₀Pd₅ alloys by considering the loading rate and temperature effects. The tests results show that the solutionized sample has wider stress hysteresis, larger energy dissipation, and the equivalent viscous damping of the aged sample. It is found that the loading rate does not significantly influence the superelastic behavior of NiTiHfPd. In addition, an increase in temperature shifts the hysteresis loops upward, but results in no considerable change in damping characteristics.