Multi-Scale Structural Simulations Laboratory

A virtual interrogation tool for microstructures

Currently available tools for virtually loading and testing microstructures (eg. OOF) evaluate mechanical properties by imposing small deformations. However, many engineering properties of interest (eg. yield strength, ultimate tensile strength) of polycrystalline metals can only be interrogated by imposing large strains. We have developed an algorithm for large strain homogenization of microstructures using which plastic properties of microstructures can be calculated by virtually instantiating and loading microstructures. The technique computes stress response based on a multiscale energy equivalence principle, which equates variation of the internal work performed by the homogenized stresses on arbitrary virtual displacements of the microstructure to the work performed by the external loads on the microstructure. In these simulations, crystal thermo–elasto–visco–plasticity (continuous slip and crystal reorientation) dictates the compatible local deformation behavior within grains. Homogenization approach proposed also allows additional convenience of using the same algorithm in large strain continuum scale simulations with minimal modifications to account for microstructural degrees of freedom.

1. V. Sundararaghavan and N. Zabaras, "Design of microstructure-sensitive properties in elasto-viscoplastic polycrystals using multi-scale homogenization techniques", presented at the `Multiscale computational design of products and materials' symposium (W. Chen et al., organizers) in the Seventh World Congress on Computational Mechanics, Century Plaza Hotel & Spa Los Angeles, California, USA, July 16-22, 2006[PPT]
2. V. Sundararaghavan and N. Zabaras, "Design of microstructure-sensitive properties in elasto-viscoplastic polycrystals using multi-scale homogenization" International Journal of Plasticity, In press, 2006. (Figured in TOP25 articles in ScienceDirect)[PDF]

Multiscale modeling of thermal oxidation

We are developing a multi-scale (macro-micro) methodology to study degradation of ceramic matrix fiber reinforced composites in high temperature oxidizing environments.

The method integrates multiple physics associated with microstructure degradation. This includes thermal transport, chemical reaction kinetics, thermo-mechanical deformation, matrix damage accumulation, diffusion of oxygen/oxides and carbon fiber surface recession at the microstructural level. The model will have the ability to quantitatively capture oxidative mass loss and mechanical behavior at high temperatures as reported in published experiments and allows design of new degradation resistant composite microstructures for high temperature use. (Graduate student: Sangmin Lee)