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Modeling Fracture Problems with X-FEM

Broumand, Pooyan | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39959 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khoei, Amir Reza
  7. Abstract:
  8. Every year, fracture imposes high economic costs and casualties to all societies. Since the beginning of the twentieth century, scientific approach to this issue has lead to invention of a new branch in mechanics, called fracture mechanics. In general, fracture problems fall into two categories. Brittle fracture, like what happens in glass, in which, few plastic deformations and energy absorption occurs and ductile fracture, which is preceded by large plastic deformations and energy absorption. This kind of fracture is usual in ductile metals like low carbon steel. Finite Element which is considered as the most important numerical method in the mechanics of materials, is also, widely used in fracture mechanics. One of the newly developed methods based on FEM is Extended Finite Element (X-FEM). This method has been successfully used in the simulation of linear elastic fracture mechanics (LEFM) and has been implemented in commercial softwares like ABAQUS. In this thesis, both kinds of fracture are considered in isotropic metals in 2-D problems. Brittle fracture is modeled based on LEFM using X-FEM and Ductile fracture is modeled using damage-plasticity coupled with X-FEM. In fact ductile fracture is due to void initiation and coalescence of micro-cracks at the crack tips and damge-plasticity can best model these processes. For this purpose Lemaitre’s decoupled damage-plasticity model is used. X-FEM is also used to account for displacement discontinuities due to crack. Changes have been made to include damage-plasticity effects in X-FEM. Since large deformations are expected in ductile fracture, Updated Lagrangian description is used in the modeling. Robustness and accuracy of the above methods are verified in some numerical examples.
  9. Keywords:
  10. Fracture Mechanics ; Extended Finite Element Method ; Ductile Fracture Criteria ; Brittle Fracture

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