A mixed-mode phase field fracture model in anisotropic rocks with consistent kinematics

Under a pure tensile loading, cracks in brittle, isotropic, and homogeneous materials often propagate such that pure mode I kinematics are maintained at the crack tip. However, experiments performed on geo-materials, such as sedimentary rock, shale, mudstone, concrete and gypsum, often lead to the c...

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Bibliographic Details
Published in:Computer methods in applied mechanics and engineering 2018-12, Vol.342 (C), p.561-584
Main Authors: Bryant, Eric C., Sun, WaiChing
Format: Article
Language:English
Subjects:
Brittle materials
Crack propagation
Crack tips
ENGINEERING
Fracture mechanics
Gypsum
Kinematics
Mathematical models
Mixed-mode fracture
Mudstone
Phase field fracture
Propagation modes
Rocks
Secondary crack
Sedimentary rocks
Shear
Surface energy
Tensile strength
Triaxial compression tests
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Summary:Under a pure tensile loading, cracks in brittle, isotropic, and homogeneous materials often propagate such that pure mode I kinematics are maintained at the crack tip. However, experiments performed on geo-materials, such as sedimentary rock, shale, mudstone, concrete and gypsum, often lead to the conclusion that the mode I and mode II critical fracture energies/surface energy release rates are distinctive. This distinction has great influence on the formation and propagation of wing cracks and secondary cracks from pre-existing flaws under a combination of shear and tensile or shear and compressive loadings. To capture the mixed-mode fracture propagation, a mixed-mode I/II fracture model that employs multiple critical energy release rates based on Shen and Stephansson, IJRMMS, 1993 is reformulated in a regularized phase field fracture framework. We obtain the mixed-mode driving force of the damage phase field by balancing the microforce. Meanwhile, the crack propagation direction and the corresponding kinematics modes are determined via a local fracture dissipation maximization problem. Several numerical examples that demonstrate mode II and mixed-mode crack propagation in brittle materials are presented. Possible extensions of the model capturing degradation related to shear/compressive damage, as commonly observed in sub-surface applications and triaxial compression tests, are also discussed.
ISSN:0045-7825
1879-2138
DOI:10.1016/j.cma.2018.08.008