Finite Element Modeling of Indentation Behavior of Dual Phase Steels: Role of Plastic Zone Size in Property Mapping

Instrumented indentation is gaining ground as a tool for generating mechanical phase maps in composite structures such as dual phase (DP) steels. The plastic zone evolution dictates the indentation parameters in such measurements and needs to be estimated accurately. This study uses finite element modeling to simulate nanoindentation responses on a ferrite–martensite DP steel to directly quantify the plastic zone in the heterogeneous microstructure. The polycrystalline tensile deformation response of individual phases of the composite structure are fed as input to a micro-mechanical finite element model to determine the indentation response. The effect of extrinsic parameters, such as tip radius and geometry, and intrinsic microstructural parameters, like the martensite volume fraction and hardness on the plastic zone evolution and the hardness derived thereof, is established. The model correctly predicts the trend in hardness of individual phases as well as the two-phase composite structure. More importantly, it allows for direct visualization of the plastic zone and the stress triaxiality underneath the complex stress state, enabling prediction of failure modes in these microstructures. This offers a complementary tool to the expensive process of locating and cross-sectioning the indents through site-specific micromachining tools to assess the damage zone under them.