Development of multi-scale computation framework to investigate the failure behavior of the materials

With the development of material science, especially as MEMS/NEMS are playing a more and more important role in modern engineering, some mechanical behaviors of materials, e.g., fracture, shear instability, need to be investigated from multidisciplinary perspective. The molecular dynamics (MD) Simulations are performed on single-crystal copper block under simple shear to investigate the size and strain rate effects on the mechanical responses of face-centered cubic (fee) metals. It is shown that the yield stress decreases with the specimen size and increases with the strain rate. Based on the theory of dislocation nucleation, a modified power law is proposed to predict the scaling behavior of fee metals. In the MD simulations with different strain rates, a critical strain rate exists for each single-crystal copper block of given size, below which the yield stress is nearly insensitive to the strain rate. A hyper-surface is therefore formulated to describe the combined size and strain rate effects on the plastic yield stress of fee metals. Molecular dynamics (MD) simulation is restricted by its length scales and time scales, and the loading rate is often very high. Continuum mechanics (FE) can not capture the physical process occurring at meso-scale, which (where) doesn't exist a proper constitutive form currently. In this investigation, FEM simulation is combined with discrete dislocation dynamics (DD). The DID code yields the plastic strain based on the slip of dislocations, and the material parameters are provided by MD simulation. On the other hand, the FE code computes the displacement field and stress field during deformation. The DD code serves as a substitute for the constitutive form used in the general FE computation. This 3D model is implemented in a user-defined subroutine in ABAQUS/Explicit and /Standard codes. Through this work, a multi-scale framework is established. Some examples, like indentation and dynamic deformation, are given to demonstrate the multi-scale computation effectively.