Micro-macro investigations on the mechanical behavior and material failure using the framework of extended finite element method (XFEM)

Elruby, Ahmed Youssri (2019) Micro-macro investigations on the mechanical behavior and material failure using the framework of extended finite element method (XFEM). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The current dissertation provides developments on mechanical behavior and material failure modeling utilizing the framework of extended finite element method (XFEM). Different types of materials, i.e., brittle and ductile were numerically investigated at different length scales. Plain epoxy resin representing the brittle behavior was prepared and tested using digital image correlation (DIC) displacement measurement system on an Instron© load-frame under different types of loading. Advanced technology methods such as optical and scan electron microscopy (SEM) were used to characterize the failure mechanisms of the tested specimens. Also, computed tomography (CT) scans were used to identify the void content within the epoxy specimens. In addition, fracture surfaces were also CT scanned to further investigate epoxy’s failure mechanism closely. On the other hand, relevant reported testing results in the literature regarding low and high strength steel materials were used to represent the ductile behavior. Different micromechanical methods such as unit cell (UC) and representative volume element (RVE) were employed in the framework of finite element method (FEM) or XFEM to numerically obtain mechanical behaviors and/or investigate material damage from a microscopic point of view. Several algorithms were developed to automate micromechanical modeling in Abaqus, and they were implemented using Python scripting. Also, different user-defined subroutines regarding the material behavior and damage were developed for macroscopic modeling and implemented using Fortran. A chief contribution of the current dissertation is the extended Ramberg-Osgood (ERO) relationship to account for metal porosity which was enabled by utilizing micromechanical modeling along with regression analyses.

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