Mechanical Characterization of Shape Memory Alloy with Nanoindentation Measurements and Finite Element Analysis

摘要

The quantitative study on the mechanical properties of shape memory alloys at nano-scale is motivated by increasing demand for micro-electro-mechanical systems.Based on the nano-indentation tests of super-elastic NiTi polycrystalline shape memory alloy, the stress-induced martensite transformation and nanoindentation hardness of the alloy were numerically studied by using finite element (FE) code MSC.MARC and employing a thermo-mechanical constitutive model.The load-displacement curves obtained from FE simulation were compared with those from nano-indentation tests,and it is seen that the simulations are in a good agreement with the experimental ones. It is also confirmed that the stress-induced transformation plays a key role in high work output of the material. Finally, comparison of nano-indentation hardness obtained by FE and the Oliver and Pharr methods shows that the hardness obtained by FE method is more accurate since the real contact area of indentation can be directly measured from FE simulation.