PhD student SeonHong Na won Dongju Lee '03 Memorial Award and the Teaching Assistant Excellence Award
It is my honor to report that our team member PhD student SeonHong Na is selected as the recipient of two awards in the CEEM department annual dinner. The Dongju Lee memorial award is given in recognition of SeonHong's superior achievement and in honor of the integrity, curiosity and creativity. The Dongju Lee Memorial Award and Memorial Lecture were established with a generous contribution from the Lee Family.
Presentation 1: 6/5 9:30am to 9:50am Room: Salon B MS 61 Computational Geomehanics
A critical assessment on phase field and eigen-erosion modeling of fractures in anisotropic fluid-infiltrating porous medias.
WaiChing Sun, SeonHong Na, Kun Wang, Jinhyun Choo, Eric Bryant
The onset and propagation of the cracks and compaction bands, and the interactions between them in the host matrix, are important for numerous engineering applications, such as hydraulic fracture and CO2 storage. A simple way to capture the formation, propagation and coalescence of crack is to incorporate the generalized Griffith theory into a variational framework. Depending on how the regularized Griffith energy functional is formulated, the resultant model may either use a phase field or a binary indicator to represent cracks. This work compares the two theories and their corresponding numerical implementations. In particular, we show that that that the eigen-fracture and operator-split phase field model can be implemented in an almost identical code design. We then extend the formulation to incorporate the hydro-mechanical coupling effect and show the importance of the hydraulic dissipation to the resultant crack pattern of the porous media through numerical examples. Further improvement of the model, such as the incorporation of the anisotropic fracture energy and the generalization for capturing compaction band as Mode I anti-crack are also highlighted.
Presentation 2: 6/6 3:55pm-4:15pm
Data-driven discrete-continuum method for partially saturated porous media
Kun Wang, WaiChing Sun
We presents a hybrid data-driven approach to model multi-physical process in fluid-infiltrating porous media across length scales. Unlike single-physical problems where data-driven model is often used as a replacement of solid constitutive law, a hydro-mechanical problem often leads to more complex hierarchical relations among physical quantities which complicates the design of the data-driven solver. In the case when artificial neural network is used, additional issues may arise when constraints and rules, such as material frame indifference, cannot be explicitly enforced without artificially expanding the training dataset. In this work, we introduce a component-based strategy in which a multiphysical computational model are viewed as a directed graph, a network consisting of inter-connected vertrices representing physical quantities. This strategy enables modelers to couple data-driven model with conventional mathematical expression methods by considering different hierarchical relations among data. Depending on the availability of data, hybridization of data-driven and mathematical models may take different form. To enforce material frame indifference efficiently, we employ spectral decomposition to handle the invariant and spin terms via Lie algebra.
Computational thermo-hydro-mechanics of crystalline rock salt for nuclear waste disposal
SeonHong Na, WaiChing Sun
Rock salt is one of the major materials used for nuclear waste disposal. The desired characteristics of rock salt, i.e. the high thermal conductivity, low permeability and self-healing is highly related to the crystalline microstructure. Conventionally, this microstructural effect is often incorporated phenomenologically in macroscopic models. Nevertheless, Rock salt is a crystalline material of which the thermo-mechanical behavior is dictated by the nature of crystal lattice and mcriomechanics the slip system. This paper present a model proposed to examine these fundamental mechanisms at the grain scale level. We employ the single-crystal plasticity framework on salt and idealized it as an FCC crystal lattice with a pair of Na+ and Cl- ions as basis. Utilizing an viso-elasto-plastic framework, we capture the existence of elastic region in the stress space and the sequence of slip system activation of salt under different temperature ranges. To capture the intragranular fracture, we introduce an anisotropic phase-field based model to capture the anisotropy of critical energy release rate of a single crystal. Numerical examples demonstrated that the proposed model is able to capture the brittle-ductile transition under various of loading rate, temperature and confining pressure.
A combined phase field and crystal plasticity approach for capturing thermo-mechanical behavior of polycrystalline rock salt
SeonHong Na, WaiChing Sun
Department of Civil Engineering and Engineering Mechanics, Fu Foundation School of Engineering and Applied Science, Columbia University, New York
Rock salt or halite is one of the major materials used for nuclear waste disposal. The desired characteristics of rock salt, i.e. the high thermal conductivity, low permeability and self-healing are highly related to the crystalline microstructure. Conventionally, this microstructural effect is often incorporated phenomenologically in macroscopic models. Nevertheless, effort to directly simulate the interplays among micro-mechanical mechanisms, such as micro-cracking, inelastic dilatancy, grain boundary sliding and dislocation creeping, which may bring more reliable and robust forward predictions for the long-term thermo-mechanical behavior of salt, are lacking. The goal of this research is to fulfill this knowledge gap. In particular, we first formulate a computational framework that may predict multi-slip system crystal plasticity of single crystal in rate-independent and rate-dependent regimes. Using this as a starting point, we introduce an anisotropic phase-field based model in which displacement and temperature jumps are regularized to model the grain boundary where the temperature-dependent plastic flow is parallel to the ground boundaries. The texture of the polycrystalline salt is assumed to be random by assigning different sets of orientations to each grain. The grain boundary is approximated using the crystal plasticity constitutive model with single slip system to include the inelastic behavior, while the fracture response is captured via the evolving phase field. Numerical examples demonstrate that the proposed model is able to capture the brittle-ductile transition under various of loading rate, temperature and confining pressure with a minimal set of material parameters.
Keywords: salt, halite, crystal plasticity, slip system, thermo-mechanical analysis, constitutive model
PhD graduate Yang Liu joined Northeastern University as assistant professor of Mechanical and Industrial Engineering
It is my great pleasure to announce that our former PhD student of the research group, Dr. Yang Liu has accepted a tenure-track position as assistant professor of mechanical and Industrial Engineering at Northeastern University. Yang currently works as a postdoctoral scholar at the Institute For Soldier Nanotechnologies of MIT. She is the first PhD graduate of our research group. In 2015, she won the best paper competition among students from more than 100 minisymposia at USNCCM San Diego. She has published the following two journal articles during her tenure in our group.
Congratulations Yang for this wonderful accomplishment!
A hierarchical sequential ALE poromechanics model for tire-soil-water interaction on fluid-infiltrated roads
Authors: Ines Wollny, WaiChing Sun, Michael Kaliske
This paper introduces a hierarchical sequential arbitrary Lagrangian-Eulerian (ALE) model for predicting the tire-soil-water interaction at finite deformation. Using the ALE framework, the interaction between a rolling pneumatic tire and the fluid infiltrated soil underneath will be captured numerically. The road is assumed to be a fully saturated two-phase porous medium. The constitutive response of the tire and the solid skeleton of the porous medium are idealized as hyperelastic. Meanwhile, the interaction between tire, soil and water will be simulated via a hierarchical operator-split algorithm. A salient feature of the proposed framework is the steady state rolling framework. While the finite element mesh of the soil is fixed to a reference frame and moves with the tire, the solid and fluid constituents of the soil are flowing through the mesh in the ALE model according to the rolling speed of the tire. This treatment leads to an elegant and computationally efficient formulation to investigate the tire-soil-water interaction both close to the contact and in the far field. The presented ALE model for tire-soil-water interaction provides the essential basis for future applications e.g. to a path-dependent frictional-cohesive response of the consolidating soil and unsaturated soil, respectively. [URL]
Our paper "A stabilized finite element formulation for monolithic thermo-hydro-mechanical simulations at finite strain" published in IJNME at 2015 is the top 5 most cited papers from 2015 to 2016. The paper can be downloaded via the Wiley Online Library [URL].
International Symposium on Multiscale Computational Analysis of Complex Materials, 29-31.August 2017, Denmark
Dates and Location: August 29-31, Copenhagen/Lyngby, Denmark
Overview and Objectives:
Complex materials play an essential role in many applications, ranging from turbine blades, car chassis, computer and cell phone cases, battery systems, stretchable and wearable electronics, to biomedical applications. Those materials often operate and must maintain their high performance in harsh environments. The advancement of computationalmethods at multiple scales opens new possibilities for the design of such complex materials and the optimization of their intrinsic properties under extreme events. The bridging of different length and time scales though still represents an area of active research with many unresolved challenges. For example, material degradation is considered as a typical multiscale process, controlled by nanoscale defects, highly affecting the macroscopic material response.
The confirmed presenters include Jose E. Andrade (Caltech), Ronaldo I. Borja (Stanford), JS Chen (UC San Diego), William Curtin (EPFL), Jacob Fish (Columbia), Somnath Ghosh (Johns Hopkins), Ellen Kuhl (Stanford), Lars P. Mikkelsen (TU Denmark ), Christian Frithiof Niordson (TU Denmark), Stefanie Reese (RWTH Aachen), Siegfried Schmauder (Stuttgart), Jörg Schröder (Universität Duisburg-Essen), Mads Peter Sørensen (TU Denmark) and others.
Symposium Topics include but are not limited to • Multiscale modeling of materials • Multiphysics modeling of materials • Computational materials science • Micromechanics of materials • Scale bridging and homogenization • Materials under extreme environments • Hierarchical materials • Nanomaterials • Biological and natural materials • Geomaterials
News about Computational Poromechanics lab at Columbia University.