Nonlocal modelling of fracture in heterogeneous quasi-brittle materials

Xenos, Dimitrios (2015) Nonlocal modelling of fracture in heterogeneous quasi-brittle materials. PhD thesis, University of Glasgow.

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Abstract

Integral-type nonlocal models provide a mesh-independent description of fracture in quasi-brittle materials. According to these constitutive models, the stress at a point is evaluated by a weighted average of the variable describing the state of the material in the vicinity of this point. The weights of the material points depend on a model parameter, called interaction radius, that controls the size of the final failure zones. The objective of the present thesis is to develop nonlocal models, that can provide a realistic description of failure in quasi-brittle materials. In particular, it is aimed to identify a realistic approach to take into account boundaries. Furthermore, a strategy to calibrate the nonlocal radius is developed. It is also required to demonstrate that the nonlocal models can describe fracture in reinforced concrete structures mesh-independently.

The performance of different nonlocal models in analysing boundaries is investigated. Nonlocal damage models with different averaging schemes as well as nonlocal and overnonlocal damage-plasticity models are applied to analyse failure in beams subjected to three-point bending. The original formulation of nonlocal averaging and the overnonlocal damage-plasticity model lead to excessive energy dissipation close to boundaries compared to meso-scale analysis results. The spurious energy dissipation is reduced in the analyses with the modified averaging schemes.

A new calibration strategy to determine the interaction radius is proposed based on the final experimental fracture patterns. The main assumption is that the majority of energy is dissipated in a localised rough crack and is validated based on meso-scale analyses results. The potential of the calibration strategy was shown by applying it to calibrate a nonlocal damage model based on the experimental fracture surface and load-displacement curve of a beam subjected to three-point bending.

Furthermore, a nonlocal extension of the damage-plasticity model CDPM2 is applied in the analyses of a reinforced concrete beam and a column. These experiments were selected because both localised and distributed cracking are experimentally observed and the material points are subjected to various stress states. It was illustrated that nonlocal models describe failure in reinforced concrete mesh-independently.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: nonlocal model, damage mechanics, fracture, calibration, quasi-brittle materials, lattice, constitutive model, plasticity, mesh dependence
Subjects: Q Science > QC Physics
T Technology > TA Engineering (General). Civil engineering (General)
T Technology > TJ Mechanical engineering and machinery
Colleges/Schools: College of Science and Engineering > School of Engineering > Infrastructure and Environment
Supervisor's Name: Grassl, Dr. Peter
Date of Award: 2015
Depositing User: Mr Dimitrios/D Xenos
Unique ID: glathesis:2015-6515
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 29 Jun 2015 08:23
Last Modified: 29 Jun 2015 08:25
URI: http://theses.gla.ac.uk/id/eprint/6515
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