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Numerical modelling of micro and macro cracking in plain and fibre-reinforced cementitious composites

Bains, Amrit 2021. Numerical modelling of micro and macro cracking in plain and fibre-reinforced cementitious composites. PhD Thesis, Cardiff University.
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A micromechanical constitutive model for plain concrete and other quasi-brittle materials was formulated using a micromechanical damage approach. The model improved upon predecessors via the inclusion of a mechanism which simulated the transition from diffuse directional microcracking to localised macrocracking at the constitutive level. The mechanism was formulated using observations from nondestructive testing and numerical experiments carried out via lattice simulations. Lattice model simulations were used to gain insight into the crack localisation process. Modelling the transition to localised cracking was found to give more realistic results, especially under tensile loading paths where the post-peak response was too ductile with only diffuse microcrack growth. Also, by simulating the development of macrocracks, the model was able to capture tensile-splitting. The constitutive model was extended to simulate the behaviour of fibre-reinforced cementitious composites by incorporating micromechanical solutions for the crackbridging mechanism of short fibres. Comparison of the behaviour predicted by the model with experimental results showed that the model gave realistic results. Next, a plastic-damage approach was used to formulate a micromechanical constitutive model for quasi-brittle materials where crack-planes were represented by local plastic yield surfaces and separate hardening parameters were used to capture isotropic and directional effects. The new model built on the previous micromechanical damage constitutive model for plain concrete by allowing for permanent deformations. Comparing numerical simulations to experimental data showed that the model matched the expected characteristic behaviour well. Suggestions were made on how the predictions could be improved further in the future. The micromechanical plastic-damage model was implemented in the LUSAS finite element software package and regularised using the crack band method. Initial assessments of the performance of the implemented model were made by simulating a direct fracture test and a four-point bending test. Localised cracking behaviour was successfully predicted

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Date of First Compliant Deposit: 8 February 2022
Last Modified: 08 Feb 2022 15:39

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