Granular materials are the second most manipulated materials across all industries, only after water. Currently, the global rate of production of concrete (a bonded granular material) stands at about 20 billion tons per year, which contributes to about 10% of worldwide CO2 production on its own. Further granular materials, including unbonded materials such as various soils, and other bonded materials such as asphalt, are ubiquitous in the built environment. The complicated microstructure of these materials, in combination with the sheer rate of their consumption, implies the necessity of developing methodologies for modeling their behavior in a manner that is not only realistic and informed by their microstructure, but is also computationally efficient allowing their application in real life engineering problems.
Methods aiming at deriving the mechanical behavior of granular materials can be categorized into two groups: (1) discrete models which derive the material behavior by realizing every particle and all its contacts and enforcing equilibrium on every particle and (2) continuum models which envision the material as a homogeneous systems and describe its behavior in terms of continuous stress and strain functions. While discrete models can provide results with unmatched levels of detail and generality, they are limited in their application due to their large computational demand. Continuum models, on the other hand, although computationally affordable, lead to neglect of material’s microstructure and micromechanical features. In this project, we seek to bridge the gap between discrete and continuum models by developing a multiscale methodology. We will use our in-house discrete simulation scheme to derive important information about the material behavior through various loading scenarios. This includes probability distribution and the directional distribution of inter-particle forces and displacements (see Fig. 1), as well as the evolution of macroscopic material parameters during loading. We will then use this data to inform our micromechanics-based continuum model wherein the statistical information describing the average behavior of inter-particle contacts in all orientations combine to form the macroscopic behavior of the material.
Figure 1 – Evolution of particle system from low confinement to high confinement. The system has 40,000 particles.
[Gonzalez, Poorsolhjouy, et al., Mechanics Research Communications, 2018]
Some of the main interesting challenges of the proposed research are as follows:
- Incorporation of shear in large deformation,
- Incorporation of periodic boundary conditions in the simulation,
- Study spatial correlation of inter-particle forces and displacements, both with and without periodic boundary conditions.