Four-point bending tests to reveal tension-compression flow stress asymmetry in NiTi shape memory alloy thin plate

摘要

A Nickel Titanium (NiTi) shape memory alloy band plate (strip) of less than 0.8 mm thickness was strained by four-point bending at various temperatures. When the bending stress was beyond the elastic range, the inelastic strain on the top surface deviated from that on the bottom surface, which resulted in two different bending curves. The bending strain in tension under a given load was always larger than that in compression in both cubic and martensite phases. The crystallographic theory of martensite was applied to calculate the strains of a variant (Bain correspondence variant), a variant pair (correspondent variant pair), and the reorientation of martensite variants (detwinning). It is concluded that the asymmetry observed in the band plate may due to [111] texture in the rolling direction, as has been pointed out in former studies of bulk alloys.