A numerical study of the indentation mechanics of shape memory alloys in different temperature regimes

Instrumented indentation is a versatile technique to quantify not only the mechanical properties but also the phase transformation and recovery characteristics of shape memory alloys (SMAs). The objective of this work is to investigate the effect of temperature on the mechanics of spherical indentation of SMAs as manifested through stress induced martensite transformation (SIMT) and plastic yielding. To this end, finite element simulations of spherical indentation response of Ni-Ti based SMAs are carried out using a constitutive model that incorporates the combined effects of superelasticity and plasticity. A range of temperatures from well below to above the austenite finish temperature A(f) is considered. It is found that while SIMT is the governing deformation mode during indentation at temperatures below A(f), plastic yielding becomes significant at temperatures close to and above A(f). The load and mean contact pressure increase with temperature above A(f) at a given indentation depth. Also, the remnant depth ratio for a given load is lowest close to A(f). SIMT and plastic deformation influence the stress distribution differently depending on the temperature.