Attended the ICE Award Ceremony at the Institution of Civil Engineers headquarter. I am so honored to receive the Zienkiewicz Medal. Also great to meet Prof. David Potts from Imperial College London again. What a day! #CUSEAS #Zienkiewicz #geomechanics #ICE #geotechnics
A multiscale damage-plasticity model for compaction band and fractures in anisotropic fluid-infiltrating porous media
Many engineering applications, such as geological disposal of nuclear waste, require reliable predictions on the hydro-mechanical responses of porous media exposed to extreme environments. This presentation will discuss the relevant modeling techniques designed specific for porous media subjected to such harsh environments. In particular, we will provide an overview of (1) the variational eigen-deformation techniques used to model brittle fracture and compaction bands, (2) the usage of adaptive nonlocal multiscale techniques to link grain-scale simulations to macroscopic predictions and hence bypass the usage of any macroscopic phenomenological law, and the coupling of crystal plasticity and multi-phase-field model designed to replicate the thermal- and rate-dependent damage-plasticity of crystalline rock. Special emphasis is placed on how formation and propagation of flow barrier formed by array of compaction bands and the flow conduit formed by fractures interact and affected the macroscopic hydro-mechanical behavior of brittle porous media.
(hosted by Prof. Robert Zimmerman)
Coupled phase-field and plasticity modeling of geological materials: from brittle fracture to ductile flow
Jinhyun Choo, WaiChing Sun
Oct 4th, 2017
The failure behavior of geological materials depends heavily on confining pressure and strain rate. Under a relatively low confining pressure, these materials tend to fail by brittle, localized fracture, but as the confining pressure increases, they show a growing propensity for ductile, diffuse failure accompanying plastic flow. Furthermore, the rate of deformation often exerts control on the brittleness. Here we develop a theoretical and computational modeling framework that encapsulates this variety of failure modes and their brittle-ductile transition. e framework couples a pressure-sensitive plasticity model with a phase-field approach to fracture which can simulate complex fracture propagation without tracking its geometry. We derive a phase-field formulation for fracture in elastic-plastic materials as a balance law of microforce, in a new way that honors the dissipative nature of the fracturing processes. For physically meaningful and numerically robust incorporation of plasticity into the phase-field model, we introduce several new ideas including the use of phase-field effective stress for plasticity, and the dilative/compactive split and rate-dependent storage of plastic work. We construct a particular class of the framework by employing a Drucker–Prager plasticity model with a compression cap, and demonstrate that the proposed framework can capture brittle fracture, ductile flow, and their transition due to confining pressure and strain rate. [PDF]
Our team member and PhD student SeonHong Na passed his PhD candidacy exam. His PhD proposal entitled "Multiscale thermo-hydro-mechanical-chemical (THMC) coupling effects for fluid-infiltrating dual-porosity crystalline rock: theory, implementation, and validation" is examined by the committee consisted of Professor Jacob Fish, Professor Hoe Ling, Professor Jeffery Kysar. We thank all the committee members for their insightful questions, comments and time. Congratulations for this well-deserved achievement, SeonHong! Good luck for your final PhD defense!
Our postdoc research scientist Dr. Jinhyun Choo will join the University of Hong Kong as an assistant professor in Spring 2018
It is my great pleasure to announce that our postdoc research scientist, Dr. Jinhyun Choo has accepted a tenure-track position as assistant professor at the University of Hong Kong. Jinhyun joined our research group as a postdoctoral research scientist in Fall 2016 after finishing his PhD under the tutelage of Professor Ronaldo Borja at Stanford University. During his productive tenure at Columbia, we have submitted three journal articles with Jinhyun, of which one is accepted. He is the first author of the other two works on modeling brittle-ductile transition and on chemoporomechanics of brittle porous materials. Prior to Stanford and Columbia, he obtained his B.S. and M.S. degrees from Seoul National University, and worked at an engineering firm and a government funded research institute in Korea. He is the recipient of several prestigious awards including a Fulbright Scholarship and a Charles H. Leavell Fellowship for research on sustainable built environment. For more information, please visit his website: http://jinhyunchoo.com/
His work with us are listed below.
Author List: S. Na, W.C. Sun, H. Yoon, M. Ingraham
Abstract: For assessing energy-related activities in the subsurface, it is important to investigate the impact of the spatial variability and anisotropy on the geomechanical behavior of shale. The Brazilian test, an indirect tensile-splitting method is performed in this work, and the evolution of strain field is obtained using digital image correlation. Experimental results show the significant impact of local heterogeneity and lamination on the crack pattern characteristics. For numerical simulations, a phase field method is used to simulate the brittle fracture behavior under various Brazilian test conditions. In this study, shale is assumed to consist of two constituents including the stiff and soft layers to which the same toughness but different elastic moduli are assigned. Microstructural heterogeneity is simplified to represent mesoscale (e.g., millimeter scale) features such as layer orientation, thickness, volume fraction, and defects. The effect of these structural attributes on the onset, propagation, and coalescence of cracks is explored. The simulation results show that spatial heterogeneity and material anisotropy highly affect crack patterns and effective fracture toughness, and the elastic contrast of two constituents significantly alters the effective toughness. However, the complex crack patterns observed in the experiments cannot completely be accounted for by either an isotropic or transversely isotropic effective medium approach. This implies that cracks developed in the layered system may coalesce in complicated ways depending on the local heterogeneity, and the interaction mechanisms between the cracks using two-constituent systems may explain the wide range of effective toughness of shale reported in the literature. [URL]
MR004: Data-driven and theoretical approaches for modeling, prediction, analysis of thermo-hydro-mechanical behaviors of frozen soil and rocks
Submit an Abstract to this Session Session ID#: 27208
Frozen soil and rocks are integrated parts of the Earth’s climate system. The timing, duration, thickness and distribution of frozen geomaterialsare dominated by heat exchanges between the environment and the land surface and the multiphysical coupling effects. During freezing and thawing cycles, microscopic mechanisms such as cryo-suction, thermal and hydraulic convection-diffusion, micro-cracks, enhanced particle interlocking and ice strengthening may have a profound effect on the land surfaces at the field scale. Yet, incorporating these complex micro-mechanical coupling effects for applications to earth system modeling remains difficult. This AGU session seeks contributions that innovate new techniques in (1) experimental and field works across length scales (e.g. micro-CT imaging, Lidar scan); (2) numerical modeling of frozen geomaterials, and (3) emerging technologies in data generation, collection and interpretation, such as climate-controlled experimental tests, data-driven machine learning and other approaches that improve the forward prediction and understanding of frozen geomaterials.
Primary Convener: WaiChing Sun, Columbia University, Civil Engineering and Engineering Mechanics, New York, NY, United States
Conveners: Seth Saltiel, Lawrence Berkeley National Laboratory, Berkeley, CA, United States and Jonathan Blair Ajo Franklin, Lawrence Berkeley National Laboratory, Geophysics, Berkeley, CA, United States
0702 Permafrost [CRYOSPHERE]
0704 Seasonally frozen ground [CRYOSPHERE]
0798 Modeling [CRYOSPHERE]
3902 Creep and deformation [MINERAL PHYSICS]
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.
News about Computational Poromechanics lab at Columbia University.