Day: January 12, 2012

Two- and Three-Dimensional Micromechanical Constitutive Modeling of Heterogeneous Infrastructure Materials with X-Ray Computed Tomography Images

Civil Engineering CE 5990 Graduate Seminar

Thursday, Jan. 12
Time: 4-5 p.m.
Location: Dow 642

Public is welcome

Presenter: Dr. Qingli Dai, Assistant professor, Department of Civil and Environmental Engineering.

Abstract: This study developed two-dimensional (2D) and three-dimensional (3D) micromechanical finite element (FE) models to study the viscoelastic properties of heterogeneous infrastructure materials. For example, asphalt mixtures are consisted of very irregular aggregates, asphalt matrix and a small amount of air voids. The internal microstructure of asphalt mixtures was captured with X-ray Computed Tomography (CT) imaging techniques. The 2D and 3D digital samples were created with the reconfiguration of the scanned slice images. The FE mesh of digital samples was generated with the locations of image pixels within each aggregate and asphalt matrix. Along the boundary of these two phases, the aggregate and matrix FEs share the nodes to connect the deformation. The micromechanical FE modeling was conducted by incorporating the captured microstructure and ingredient properties (viscoelastic asphalt matrix and elastic aggregates). The generalized Maxwell model was applied for viscoelastic asphalt matrix with calibrated parameters from the nonlinear regression analysis of the lab test data. The 3D simulation with digital samples generated better prediction than the 2D models. These favorable comparison results indicate that the developed micromechanical FE models have the ability to accurately predict the global viscoelastic properties of the heterogeneous infrastructure materials.


An EXtended Finite Element Model (XFEM) for Predicting Crack Propagation within Infrastructure Materials

Thursday, Jan. 12
Time: 4-5 p.m.
Location: Dow 642

Public is welcome

Presenter: Kenny Ng, Ph.D. candidate, Department of Civil and Environmental Engineering, (Adviser: Dr. Qingli Dai).

Abstract: The object of this study is to employ XFEM and image analysis techniques to numerically investigate crack propagation within infrastructure materials. The XFEM has been recently developed to eliminate remeshing by allowing crack propagation within continuous elements. The discontinuous crack and inclusion enrichment functions with level set method (LSM) were addressed in the XFEM. The crack growth angle and stress intensity factors (SIFs) were also formulated to predict the crack growth direction. The XFEM was developed with MATLAB program for predicting micro-crack behavior with Compact Tension (CT), single-edge notched beam (SEB) and indirect tension (IDT) tests. The developed XFEM was firstly validated with CT and SEB tests on a homogeneous sample. In order to capture the real material microstructure, the digital samples were generated with imaging processing and ellipse fitting techniques. The predicted crack propagation with XFEM simulation on digital samples was compared with fracture pattern of lab-tested SEB and IDT specimens. The comparison results on open-mode middle-notched and mixed-mode offset-notched SEB and IDT tests indicate the developed XFEM has the ability to accurately predict fracture behavior within heterogeneous infrastructure materials. In addition, the internal frost-induced damage within an idealized pore system was also analyzed and simulated using XFEM.