The effect of employed loading mode on the mechanical cyclic stabilization of NiTi shape memory alloys

• Published in: Intermetallics Vol. 89; pp. 1 - 9
• Main Authors: Dilibal, S., Hamilton, R.F., Lanba, A.
• Format: Journal Article
• Language: English
• Published: Barking Elsevier Ltd 01.10.2017; Elsevier BV
• Subjects: Austenitic transformations; Digital imaging; Evolution; Intermetallic compounds; Mechanical cycling; Mechanical hysteresis; Nickel base alloys; Nickel compounds; Nickel titanides; Nickel-titanium; Pseudoelastic response; Shape memory alloys; Stabilization; Strain localization; Stress-strain curves; Tensile tests; Thermal cycling; Titanium base alloys; Titanium compounds; Uniaxial tensile test; Uniaxial tensile test; Mechanical cycling; Pseudoelastic response; Nickel-titanium
• ISSN: 0966-9795; 1879-0216
• DOI: 10.1016/j.intermet.2017.05.014

One of the effective parameters on the characteristic response of the nickel-titanium (NiTi) shape memory alloy (SMA) is the employed loading mode during the uniaxial cycling. In this study, the uniaxial tensile tests are conducted under an extended number of mechanical cycles in order to investigate the effect of force control on the pseudoelastic response of the NiTi SMA. The results which are obtained under the force control are compared with the mixed (force/displacement) control counterpart. An evolutionary stress-strain pattern is observed during the 100 cycles of mechanical loading. Additionally, it is noticed that the residual strain and mechanical hysteresis area also show an evolutionary pattern. The observed evolutionary patterns are delineated in three regimes: (i) early evolution; (ii) approach to a nearly stable stage (transient); and (iii) stabilization stage. Furthermore, the in-situ digital image correlation (DIC) is applied to receive the meso-/micro-scale full-field strain measurements. Severe strain localization is observed under force-controlled tensile test during meso-,/micro-scale DIC analysis. •The selected loading mode is one of the effective test parameters in mechanical cyclic stabilization.•It plays a notable role in dictating the evolutionary pattern of the stress-strain curves and the amount of cumulative residual strain.•It affects the required number of cycles to stabilization and the shape of stabilized stress-strain hysteresis area.•The mechanical cyclic stabilization occurred at a fewer number of cycles under force control.•At meso and micro-scales, the DIC analysis unveiled that severe strain localization is formed under force control.•The local field average strains follow a similar evolutionary pattern with the macroscopic counterparts.