ACME 2011 Proceedings of the 19 UK National Conference of the ...

Proceedings of the 19 th UK Conference of the
Association for Computational Mechanics in Engineering
5 – 6 April 2011, Heriot-Watt University, Edinburgh
Challenges in the Modelling of Particulates and Multi-Fracturing Materials
with Coupled Field Effects
D. R. J. Owen, Y. T. Feng, K. Han and C. R. Leonardi
Civil & Computational Engineering Centre, Swansea University, Singleton Park, Swansea, SA2 8PP, UK
D.R.J.Owen@swansea.ac.uk
Key Words: Multi-fracturing solids, multi-field coupling, discrete element modeling, adaptive mesh
refinement, lattice Boltzmann solution strategies
ABSTRACT
Significant progress has been made over the last decade in the effective modeling of the failure and
transition from continuum to discontinuum of quasi-brittle materials in many defence, mining and geomechanical
applications. However, in several problems, the presence of an additional phase, either
gaseous, liquid or both, often controls the behaviour of multi-fracturing material systems. Examples of
such interaction include fracture induced in rock masses by the presence of fluid flow and the generation
of gas pressure fields due to explosive detonation which drives the fracturing process in rock blasting.
Although a generic modelling strategy can be developed for a broad range of such problems, nevertheless,
some applications require an individual approach to solution. The main objectives of the presentation is
to (i) consider the essential issues related to an effective computational implementation of a continuumdiscontinuum
formulation of quasi-brittle materials under various loading conditions, particularly
involving fluid interaction and (ii) model the subsequent flow of fragments within such a secondary
medium.
Introduction
Key issues that need to be addressed for the successful modeling of continuous/discontinuous
transformation of quasi-brittle materials include (i) the development of constitutive models which govern
the material failure; (ii) the ability of numerical approaches to introduce discontinuities such as shear
bands and cracks generated during the material failure and fracture process and (iii) the effective
simulation of contact between the region boundaries and crack surfaces both during and after the failure
process. The numerical treatment of multi-fracturing solids necessitates a blend of continuous and discrete
computational processes to provide adequate solution. Modeling aspects related to continuum mechanics
include the development of constitutive models for a range of materials under a variety of loading
conditions, element technology for near-isochoric deformation conditions, adaptive mesh refinement and
damage modelling for prediction of the onset of fracture (de Souza Neto et al. 1998, Klerck et.al 2003,
Owen et al. 2004). With the development of fractures, the domain becomes discontinuous in nature and
computational issues include strategies for discrete crack insertion that preserve the system energy,
adaptive remeshing to accommodate the fracture distribution, global search algorithms to monitor contact
between the resulting particle system, development of appropriate contact interaction models and time
integration of the system equations. Implementation of the entire solution strategy within a parallel
processing environment is a further issue.
Failure Strategies Several fracture criteria available in the literature have been previously employed to
predict material failure that may result from the gradual internal deterioration associated with high
straining. These predictions remain, to a great extent, relegated to post-simulation analyses. The adoption
of a methodology, whereby the coupling between material behaviour and deterioration is considered at
the constitutive level during the process simulation offers a more scientifically based alternative to
empirical methods with a potential improvement in predictive capability (de Souza et al. 1998). Fracture
in quasi-brittle materials is generally an anisotropic phenomenon, with the coalescence and growth of
micro-cracks occurring in the directions that attempt to maximise the subsequent energy release rate and
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