Constitutive modelling of multi-phase transformation of silicon under nano-scale deformation

This study aims to establish a mechanical constitutive model for the multiphase transformation of mono-crystal silicon in a complex stress state, based on the mathematical theory of plasticity. An initial yield surface and subsequent phase-transformation surfaces are proposed for both loading and unloading. To verify the constitutive model, an FEA simulation is performed for nano-indentation with a spherical indenter. A close agreement is obtained with the corresponding experiment, including the pop-ins and pop-outs in the force-penetration curve.