3-D Computational Elasto-plastic Damage, Fracture Mechanics & XFEM Modeling

This is a computational mechanics problem, and profound knowledge on nonlinear mechanics is desirable. In a stage by stage manner, crack tip remeshing and node release method and extended finite element method will both be employed to model the concrete cracking in continuum scale. Then fluid transport (chemical ingress into concrete) will be characterized by multiphysics models and simulated by direct coupling of chemical-physical field partial differential equations. Sequentially, the growth of crack will in return change the transport field of fluid. Information passing through from one another stage is called homogenization process. This is an interesting solid-liquid coupling phenomena. I am working on this topic using fracture mechanics, continuum mechanics, multiphysics simulation to model the effect of transport on crack growth.

Necking of a Nonlinear Bar using Elastoplastic and Mohr-Coulumb materials model

A circular bar of elastoplastic material with nonlinear isotropic hardening is subjected to a uniaxial tensile test. When subjected to large deformations, the specimen experiences significant plastic deformations and necking in its central cross section. This example demonstrates the large strain plasticity option available in the Nonlinear Structural Materials Module. The hardening stress expression assumes zero stress for no plastic strain. The yield stress is defined as the sum of the initial yield stress and the stress hardening function. Press the following images to watch the simulation animations.

1a).The animation shows the surface contour of effective plastic strain, with nonlinear isotropic hardening function.

1b). The animation shows the surface contour of von Mises stress, with nonlinear isotropic hardening function.

2a). The animation shows the surface contour of von Mises stress evaluated at Gauss-point, using Mohr-Coulomb yield criterion.

2b). The animation shows the surface contour of effective plastic strain evaluated at Gauss-point, using Mohr-Coulomb yield criterion.

Crack Propagation Simulation

3-D Crack tip remeshing and node release method

XFEM (eXtended Finite Element Method) method alleviates the shortcomings associated with traditional approaches that require meshing cracked surfaces and updating the mesh for a growing crack.

The conventional Finite Element Methods using fixed meshes can only deal with this type of problem, either if the crack path travels through mesh nodes, or if we remove mesh elements. This is an extremely important limitation in industrial applications.

The XFEM method on longer requires the mesh to be constantly stuck to discontinuous finite elements. It uses, as in other known methods, the partition of unity and introduces level sets to model the crack surface and the crack front, while maintaining the same mesh.

When using XFEM, the following key points need to be addressed:

• Proper modeling techniques for capturing crack-tip singularities in fracture mechanics problems

• Using mesh modeling tools to create 3-D meshes (brick elements or tetrahedral elements) appropriate for fracture studies

• Calculation of stress intensity factors and contour integrals around a crack tip using conventional techniques and using XFEM

• Simulating crack growth using the eXtended Finite Element Method (XFEM)

3-D Crack Propagation using XFEM