MECHANICS OF QUASI-BRITTLE MATERIALS
HAO YIN
PhD Candidate of Civil Engineering
Northwestern University
Google Scholar ORCID: 0000-0003-4921-9786
Overview
I am a fourth-year Ph.D. candidate of Civil Engineering within the Mechanics, Materials, and Structures (MMS) Group at Northwestern University. I received a Bachelors of Engineering in Civil Engineering from China Agricultural University (CAU), China, and a Masters of Science in Civil Engineering from the University of Illinois at Urbana-Champaign (UIUC). Before joining Northwestern Univerisity, I worked on a dynamic finite element analysis project of rail infrastructure at the University of Illinois at Urbana-Champaign, Rail Transportation and Engineering Center (RailTEC). My current research interests include computational mechanics, computational geometry, and multiphysics modeling. Finite Element Method (FEM), Isogeometric Analysis (IGA), plate, shell and beam theories, and quasi-brittle material behaviors, specifically.
Current Research
Computational modeling of wood, cross-laminated timber (CLT), and other quasi-brittle materials
A 3D discrete lattice model to simulate the mechanical behaviors of wood materials (such as wood panel, ply-wood, CLT, etc.) at the mesoscale level is currently under development. The basic elements of such a lattice model are 3D curved beams characterized by (a) a general geometrical curvature and torsion of the axis as well as (b) an irregular cruciform cross-section. The various branches for the cross-section represent the walls of the wood cellular structure and the beam axis is the line at which various cell walls meet. The Isogeometric Analysis (IGA) techniques are employed in order to describe the beam geometries accurately. The connections between neighboring beams are characterized by the cohesive fracture laws for quasi-brittle materials in both normal and shear directions. The beam element and connection element formulations have been implemented in Abaqus user subroutines "UEL" and "VUEL" for both implicit and explicit analyses. The aim of this model is to simulate the orthotropic nature, as well as the fracture behaviors of the wood materials. The relationship between the mesostructure and the macroscopic properties of the material can be also investigated with the help of this model.
Wood lattice model - from macroscale to mesoscale
The 3D curved beam formulation with irregular cross-sections
Isogeometric analysis (IGA) technique of curved beams
IGA beam element verifications
Lattice explicit dynamic analysis in Abaqus
Single beam verification in Abaqus
Macroscopic orthotropy of a cubic wood specimen
Theoretical verifications of the lattice model - regular meshes
Voronoi tessellation-based mesh generator for the mesoscale structure of wood
The lattice mesh generator for the microstructure of timber has been developed. The plane section mesh is featured by its Voronoi tessellation-based plane partition algorithm, each polygon in the plane mesh can be seen as a cell and the boundaries can be seen as the cell walls of the wood. The radius of the timber section, the annual ring width, the earlywood and latewood distribution, and the representative cell size are taken into consideration in lattice mesh generation, while the longitudinal extrusion algorithm is characterized by the microfibril angle, the longitudinal fiber length, and the segment length distribution. The clipping box technique is implemented to cut the 3D wood lattice mesh into any desired shape of the specimen. The small element removal technique is also developed in order to speed up the explicit analyses of the lattice model, by taking out elements with critical time steps smaller than the threshold.
2D Voronoi tessellation based wood mesh
Annual rings structure, random circle placement, and 2D wood mesh
Work flow of wood mesh generation
3D Extrusion in Rhino
Edge clipping
Small element removal
A 3D examplar mesh for tension test simulations with pre-cracks
Two-way coupling framework for Multiphysics-LDPM
Previously proposed for Multiphysics-LDPM (M-LDPM), the Flow Lattice Model (FLM) has proved its capability of capturing the mass transport and heat transfer with a discrete-type dual mesh of LDPM. Now coupled with LDPM, the multiphysics problems such as the thermal-hydro-mechanical problem can be solved in a two-way coupled FLM-LDPM analysis framework with the help of the Interprocess Communication (IPC). The periodic data communication between two Abaqus solvers (Abaqus/standard for the thermal/diffusion part and Abaqus/Explicit for the mechanical part) and spatial & temporal mappings between the two solvers allow the coupling process to run smoothly and robustly.
Schematic diagram of the data communication
Two-way coupling verification: pore pressure diffusion
Two-way coupling verification: poroelastic response, radial displacement distribution in a thickwalled cylinder due to pore pressure diffusion
Arc-length method for nonlinear problems