Modeling of Cohesive Zone and Crack Growth in Ni-Al Thin-Film Using MD-XFEM Based Approach

Intermetallic alloys of Ni-Al have important applications in high temperature anti-corrosive coatings, engine and turbine related materials, and shape memory devices. Predicting failure behavior of these materials is difficult using purely continuum model, since several of the material constants are complicated functions of micro and nano-scale details. This includes solid-solid phase transformation. In the present paper, a framework for analyzing fracture in two-dimensional planar domain is developed using a molecular dynamic (MD) simulation and extended finite element method (XFEM). The framework is then applied to simulate fracture in Ni-Al thin-film. Effect of Ni Al crystallites of various sizes on the mechanical properties is analyzed using direct MD simulations. Initiation and growth of crack under slow (quasi-static) tensile loading in mode-I condition is considered. Mechanical properties at room temperature are estimated via MD simulations, which are further used in the XFEM at the continuum scale. A cohesive zone model for the macroscopic XFEM model is implemented, which directly bridges the molecular length-scale via MD framework. Numerical convergence studies are reported for mode-I crack in initially single crystal B2 Ni-Al thin film.