A numerical study of the indentation mechanics of shape memory alloys in different temperature regimes. (December 2019) - Anuja, J.
Highlights: Numerical study conducted to investigate indentation mechanics of Ni–Ti based SMAs over a wide temperature range. Constitutive model employed represents phase transformation and plastic yielding in both austenite and martensite phases. Size of transformed martensite region diminishes while the plastic zone enhances with increase in temperature above Af at a fixed depth. Indentation load and mean contact pressure at a given depth increase with temperature. Remnant depth ratio is found to be minimum near the Af, which is attributed to maximum influence of superelasticity. Abstract: 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 Af is considered. It is found that while SIMT is the governing deformation mode during indentation at temperatures below Af, plastic yielding becomes significant at temperatures close to and above Af . The load and mean contact pressure increase with temperature above Af at a given indentation depth. Also, the remnant depth ratio for a given load is lowest close to Af . SIMT and plastic deformation influence the stress distribution differently depending on the temperature.