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Title: Micromechanical constitutive models for cementitious composite materials
Author: Mihai, Iulia
ISNI:       0000 0004 2733 1475
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2012
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A micromechanical constitutive model for concrete is proposed in which microcrack initiation, in the interfacial transition zone between aggregate particles and cement matrix, is governed by an exterior-point Eshelby solution. The model assumes a two-phase elastic composite, derived from an Eshelby solution and the Mori-Tanaka homogenization method, to which circular microcracks are added. A multi-component rough crack contact model is employed to simulate normal and shear behaviour of rough microcrack surfaces. It is shown, based on numerical predictions of uniaxial, biaxial and triaxial behaviour that the model captures key characteristics of concrete behaviour. An important aspect of the approach taken in this work is the adherence to a mechanistic modelling philosophy. In this regard the model is distinctly more rigorously mechanistic than its more phenomenological predecessors. Following this philosophy, a new more comprehensive crack-plane model is described which could be applied to crack-planes in the above model. In this model the crack surface is idealised as a series of conical teeth and corresponding recesses of variable height and slope. Based on this geometrical characterization, an effective contact function is derived to relate the contact stresses on the sides of the teeth to the net crack-plane stresses. Plastic embedment and frictional sliding are simulated using a local plasticity model in which the plastic surfaces are expressed in terms of the contact surface function. Numerical simulations of several direct shear tests indicate a good performance of the model. The incorporation of this crack-plane model in the overall constitutive model is the next step in the development of the latter. Computational aspects such as contact related numerical instability and accuracy of spherical integration rules employed in the constitutive model are also discussed. A smoothed contact state function is proposed to remove spurious contact chatter behaviour at a constitutive level. Finally, an initial assessment of the performance of the micromechanical model when implemented in a finite element program is presented. This evaluation clearly demonstrates the capability of the proposed model to simulate the behaviour of plain and reinforced concrete structural elements as well as demonstrating the potential of the micromechanical approach to achieve a robust and comprehensive model for concrete.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)