Phase-field modelling of fracture in brittle materials by introducing strain energy threshold

Rijal, Sapan

Phase-field modelling of fracture in brittle materials by introducing strain energy threshold

Rijal, Sapan

Permalink

Publication Type:: Thesis
Issue Date:: 2023

Open Access

Copyright Clearance Process

Recently Added
In Progress
Open Access

This item is open access.

Adobe PDF

Download thesisAdobe PDF (4.92 MB)

View statistics

Full metadata record

Field	Value	Language
dc.contributor.author	Rijal, Sapan
dc.date.accessioned	2023-07-11T04:15:18Z
dc.date.available	2023-07-11T04:15:18Z
dc.date.issued	2023
dc.identifier.uri	http://hdl.handle.net/10453/171442
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_US.UTF-8
dc.description.abstract	Prediction of brittle fracture phenomena is a crucial task for many construction materials (concrete, brick, tiles, etc.) which has been a great interest in construction industries and research communities. The displacement field in sharp crack approach (Dirac delta function) suffering the occurrence of discontinuities, which are very difficult to deal with, can be resolved by adopting diffusive fracture approach. The diffusive fracture approach implements a continuous field with high gradients and models the fracture as a diffusive object, setting the magnitude of a variable within a limit. Phase-field method of diffusive fracture is adopted in this study that comprises a scalar variable with magnitude between 0 & 1, 0 referring to undamaged or intact material state and 1 referring to fully fractured or broken state. For controlling the width of transition region between 0 & 1, a length scale parameter is required. By using commercial finite element code Abaqus/Standard a rate-independent principle based on phase field method for one- and two-dimensional geometry have been proposed in this study. Phase field models have been used by many researchers to describe the brittle fracture where the damage evolution takes place as soon as the material deformation starts which does not agree with the realistic problems. A threshold criterion would be introduced so that the damage evolution can be controlled. Utilizing the staggered algorithm with decoupled displacement field and phase field, an elastic strain energy threshold has been proposed in this study. To trigger the energy threshold, there exist a point at which the strain energy should be locked as a threshold. This demands a criterion to be incorporated in the model that can determine the threshold point. The unified yield criterion (Yu et al. 2011) is implemented as a unified failure criterion in principle stress space is utilised for triggering the point of threshold, which is also defined as a point of damage initiation. In other words, as soon as the unified failure criteria is satisfied the damage evolution takes place and the strain energy at that point is locked as an elastic strain energy threshold. Finally, a source code for finite element implementation has been developed for two-dimensional model, based on Abaqus/standard UEL and UMAT in FORTRAN environment, and validated with various benchmark tests. Mesh convergence test and the simulation step size convergence tests are undertaken until the converged responses are recorded.	en_US.UTF-8
dc.format	Thesis (ME)
dc.language.iso	en_US	en_US.UTF-8
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/171442/1/thesis.pdf
dc.rights	info:eu-repo/semantics/openAccess
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	© 2023 Sapan Rijal
dc.rights	au.edu.uts.lib/cph
dc.title	Phase-field modelling of fracture in brittle materials by introducing strain energy threshold	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

Prediction of brittle fracture phenomena is a crucial task for many construction materials (concrete, brick, tiles, etc.) which has been a great interest in construction industries and research communities. The displacement field in sharp crack approach (Dirac delta function) suffering the occurrence of discontinuities, which are very difficult to deal with, can be resolved by adopting diffusive fracture approach. The diffusive fracture approach implements a continuous field with high gradients and models the fracture as a diffusive object, setting the magnitude of a variable within a limit. Phase-field method of diffusive fracture is adopted in this study that comprises a scalar variable with magnitude between 0 & 1, 0 referring to undamaged or intact material state and 1 referring to fully fractured or broken state. For controlling the width of transition region between 0 & 1, a length scale parameter is required. By using commercial finite element code Abaqus/Standard a rate-independent principle based on phase field method for one- and two-dimensional geometry have been proposed in this study. Phase field models have been used by many researchers to describe the brittle fracture where the damage evolution takes place as soon as the material deformation starts which does not agree with the realistic problems. A threshold criterion would be introduced so that the damage evolution can be controlled. Utilizing the staggered algorithm with decoupled displacement field and phase field, an elastic strain energy threshold has been proposed in this study. To trigger the energy threshold, there exist a point at which the strain energy should be locked as a threshold. This demands a criterion to be incorporated in the model that can determine the threshold point. The unified yield criterion (Yu et al. 2011) is implemented as a unified failure criterion in principle stress space is utilised for triggering the point of threshold, which is also defined as a point of damage initiation. In other words, as soon as the unified failure criteria is satisfied the damage evolution takes place and the strain energy at that point is locked as an elastic strain energy threshold. Finally, a source code for finite element implementation has been developed for two-dimensional model, based on Abaqus/standard UEL and UMAT in FORTRAN environment, and validated with various benchmark tests. Mesh convergence test and the simulation step size convergence tests are undertaken until the converged responses are recorded.

Please use this identifier to cite or link to this item:

http://hdl.handle.net/10453/171442