Experimental and numerical investigation of thermomechanical cycling of notched NiTi shape memory ribbon using SMA model accounting for plastic deformation

0549526 - ÚJF 2022 RIV BR eng J - Journal Article
Shayanfard, P. - Heller, Luděk - Šandera, P. - Šittner, Petr
Experimental and numerical investigation of thermomechanical cycling of notched NiTi shape memory ribbon using SMA model accounting for plastic deformation.
Journal of Materials Research and Technology-JMR&T. Roč. 15, NOV (2021), s. 1759-1776. ISSN 2238-7854. E-ISSN 2214-0697
R&D Projects: GA MŠMT EF16_013/0001794
Institutional support: RVO:61389005
Keywords : conventional plasticity * DIC * double notched ribbon * finite element analysis * martensitic transformation * plastic deformation * shape memory alloy actuator * SMA model * stress riser * thermal actuator
OECD category: Condensed matter physics (including formerly solid state physics, supercond.)
Impact factor: 6.267, year: 2021
Method of publishing: Open access
https://doi.org/10.1016/j.jmrt.2021.08.132

Shape memory alloys (SMAs) are being increasingly applied as thermally driven actuators. The commercially available SMA elements, however, frequently contain stress risers, either due to internal or surface defects or due to the required component shape. Stress risers represent a potential danger for the preliminary fatigue failure of such actuators but its actual mechanism is not very clear. This paper presents a combined experimental (2D DIC analysis of surface strains) and numerical analysis (SMA model with plastic deformation) of the stress, strain and phase fraction fields evolving in a thin NiTi shape memory ribbon with an artificial notch subjected to cyclic cooling-heating through transformation range under constant external force. It appeared that, even if only very low tensile stress is externally applied upon thermal cycling, local tensile stress at the notch tip sharply increases during the first cooling due to the forward martensitic transformation (MT) proceeding heterogeneously in space. This heterogeneity gives rise to plastic deformation at the notch-tip, which gradually accumulates upon thermal cycling and shields the notch tip from tensile overloading. Hence, fatigue performance of thermal NiTi actuator with stress riser depends very much on the plastic deformability of the alloy.
Permanent Link: http://hdl.handle.net/11104/0325520