PhD Candidate Yang Liu has just won the 2015 Student Poster Competition among all students presented  at over 100 mini-symposia in the US National Congress of Computational Mechanics at San Diego. Congratulations Yang! [Press release from department]

From their inception in 1991, the biennial congresses of the U.S. Association for Computational Mechanics have become major scientific events, drawing computational engineers and scientists worldwide from government, academia, and industry.  The congress provides a forum for researchers and practitioners all over the world to discuss the latest advancements and future directions in fields pertaining to computational engineering and sciences. The congress will feature plenary speakers, over 100 mini-symposia with keynote lectures and contributed talks, a student poster competition, and exhibits from various sponsors.

Title: A Discrete Continuum-Coupling Approach for Predicting Anisotropic Damages in Water-Saturated Brittle Rocks

Minisymposium: Multiscale Modeling of Granular Materials
Authors: WaiChing Sun* , Kun Wang

Time/Location: July 30, 2015 @ 11:40 a.m.-noon in Cove
Abstract: We develop a dual-scale model to predict the brittle behavior of water-saturated rocks under various drainage condition across length scale. In this formulation, we exploit the effect stress principle to partition stress stemming from grain contact and grain-to-grain bonding and those from fluid-solid interfaces at grain-scale. While the evolution of microstructures of solid skeleton is simulated explicitly at grain scale via discrete mechanics approach, the interaction of pore fluid and solid grain is captured at continuum scale via a mixed finite element u-p formulation. As a result, there is no need to incorporate phenomenological law to govern damage or phase field evolutions at the macroscopic continuum level. Various strategies to overcome mesh bias will be compared. Numerical examples will be used to demonstrate the accuracy and robustness of the multiscale multiphysics model.

A new research conducted by group member Kun Wang has results in a journal article accepted by Journal of Engineering Mechanics. This research focuses on the hydro-mechanical responses of wetted granular matters at the pendular regime. By analyzing the tensorial Bishop's coefficient using Young-Laplace equation and DEM, we study the relation between the macroscopic apparent cohesion and the formation and rupture of liquid bridges. We also examine the path dependence and anisotropy of the Bishop's coefficient from the force chain evolution simulated in DEM. Further information can be found in the preprint [PDF]. 

Abstract
The objective of this research is to use grain-scale numerical simulations to analyze the evolution of stress anisotropy exhibited in wetted granular matters. Multiphysical particulate simulations of unsaturated granular materials were conducted to analyze how the interactions of contact force chains and liquid bridges influence the macroscopic responses under various suction pressure and loading history. To study how formation and rupture of liquid bridges affect the mechanical responses of wetted granular materials, a series of suction-controlled triaxial tests were simulated with two grain assemblies, one composed of large particles of similar sizes, another one composed of a mixture of large particles with significant amount of fines. Our results indicate that capillary stress are anisotropic in both sets of specimens, and that the stress anisotropy is more significant in granular assemblies filled with fine particles. A generalized tensorial Bishop's coefficient is introduced to analyze the connections between microstructrual attributes and macroscopic responses. Numerical simulations presented in this paper indicate that the principal values and directions of this Bishop's coefficient tensor are path dependent. 
 

Press release from Fu Foundation School of Engineering, Columbia University:

http://engineering.columbia.edu/professor-steve-sun-receives-army%E2%80%99s-young-investigator-award#

A multi-university collaborative NSF proposal "Collaborative Research: Alteration of mantle peridotite: Geochemical fluxes and dynamics of far from equilibrium transport" (EAR#1516300), in which Sun served as co-PI (Columbia PI: Peter Kelemen, Co-PI: WaiChing Sun, Heather Savager, Martin Stute, Marc Spiegelman), has received funding for 36 months. The poromechanics research group will be a part of the Columbia team focusing on modeling reaction-driven deformation and fractures.

Dr. Sun has been elected to join the Granular Materials Committee of the ASCE Engineering Mechanics Institute. EMI's technical committees develop conference sessions and symposia for Institute and Society conferences and for other initiatives to foster technical activities within the area of engineering mechanics. The purpose of the EIM Granular Materials COmmittee is to promote and support the advancement of knowledge and understanding in the mechanics of granular or particulate materials, utilising analytical, numerical and experimental techniques.