Dr. Sun has been accepted to become one of the 44 active member of   ASCE EMI Computational Mechanics Technical Committee by majority vote. 

The current roster can be found at:
https://sites.google.com/site/ascecompmech/roster

Full paper can be downloaded here.


Abstract

The loading of a granular material induces anisotropies of the particle arrangement (fabric) and of the material’s strength, incremental stiffness, and permeability. Thirteen measures of fabric anisotropy are developed, which are arranged in four categories: as preferred orientations of the particle bodies, the particle surfaces, the contact normals, and the void space. Anisotropy of the voids is described through image analysis and with Minkowski tensors. The thirteen measures of anisotropy change during loading, as determined with three-dimensional discrete element simulations of biaxial plane strain compression with constant mean stress. Assemblies with four different particle shapes were simulated. The measures of contact orientation are the most responsive to loading, and they change greatly at small strains, whereas the other measures lag the loading process and continue to change beyond the state of peak stress and even after the deviatoric stress has nearly reached a steady state. The paper implements a methodology for characterizing the incremental stiffness of a granular assembly during biaxial loading, with orthotropic loading increments that preserve the principal axes of the fabric and stiffness tensors. The linear part of the hypoplastic tangential stiffness is monitored with oedometric loading increments. This stiffness increases in the direction of the initial compressive loading but decreases in the direction of extension. Anisotropy of this stiffness is closely correlated with a particular measure of the contact fabric. Permeabilities are measured in three directions with lattice Boltzmann methods at various stages of loading and for assemblies with four particle shapes. Effective permeability is negatively correlated with the directional mean free path and is positively correlated with pore width, indicating that the anisotropy of effective permeability induced by loading is produced by changes in the directional hydraulic radius.

The Columbia Poromechanics lab is among the winner of the 2015 competition under the defense university research instrumentation program. The awards are the result of a merit competition jointly conducted by three DoD research offices: the Army Research Office, Office of Naval Research, and Air Force Office of Scientific Research. Those offices will make the awards, which are subject to the successful completion of negotiations with the academic institutions. The Defense University Research Instrumentation Program is highly competitive. The three DoD research offices solicited proposals from university investigators conducting science and engineering research of importance to national defense. This includes research that underpins advances in materials, structures, and manufacturing science; quantum and nanosciences; computing and networks; electronics, electromagnetics, electro optics; acoustics; neuroscience; fluid dynamics; robotics and autonomous systems; and ocean, environmental, and life sciences and engineering.

The official announcement from DoD can be found at

http://www.defense.gov/Releases/Release.aspx?ReleaseID=17320