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Title: Nonlocal modelling of fracture in heterogeneous quasi-brittle materials
Author: Xenos, Dimitrios
ISNI:       0000 0004 5348 1426
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2015
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; TA Engineering (General). Civil engineering (General) ; TJ Mechanical engineering and machinery