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No description available.

This thesis examines the effects of reinforcement ductility on the strength and ductility of reinforced concrete slabs. An extensive experimental program examining the ultimate strength, ductility and failure mode of one-way and two-way reinforced concrete slabs is described and the results are presented and analysed. A numerical finite element model is developed and calibrated using the experimental data. The model is described and shown to accurately simulate the collapse load behaviour of reinforced concrete slabs containing reinforcement of any ductility class, including Class L welded wire fabric. Parametric studies using the numerical model to assess the effects of reinforcement ductility on structural behaviour are also presented and recommendations are made on the minimum reinforcement ductility levels appropriate for use in suspended slabs. The experimental and numerical tests investigated slabs with different types of boundary conditions (simply supported and continuous one-way slabs, corner-supported single panel two slabs and edge-supported two-way slabs), support settlement, steel reinforcement ratio, steel uniform elongation (su), steel ultimate to yield stress ratio (fsu/fsy) and rectangularity aspect ratio in the two-way slabs. In total, thirty one slabs were tested. The one-way slabs included four simply supported slabs, seven continuous slabs, and five continuous slabs with support settlement. The two-way slabs included eleven square and rectangular corner-supported slabs and four rectangular edge-supported slabs. The one-way simply-supported slabs were 850mm in width, 100mm in depth and 2,500mm in length. The continuous one-way slabs were 850mm in width, 100mm in depth and 4,350mm in length. The continuous one-way slabs and subjected to support settlement were 850mm in width, 120mm in depth and 6,300mm in length. The square two-way slabs had an edge length of 2,400mm and a depth of 100mm and the rectangular two-way slabs had width of 2,400mm, a length of 3,600mm and a depth of 100mm.

This thesis examines the effects of reinforcement ductility on the strength and ductility of reinforced concrete slabs. An extensive experimental program examining the ultimate strength, ductility and failure mode of one-way and two-way reinforced concrete slabs is described and the results are presented and analysed. A numerical finite element model is developed and calibrated using the experimental data. The model is described and shown to accurately simulate the collapse load behaviour of reinforced concrete slabs containing reinforcement of any ductility class, including Class L welded wire fabric. Parametric studies using the numerical model to assess the effects of reinforcement ductility on structural behaviour are also presented and recommendations are made on the minimum reinforcement ductility levels appropriate for use in suspended slabs. The experimental and numerical tests investigated slabs with different types of boundary conditions (simply supported and continuous one-way slabs, corner-supported single panel two slabs and edge-supported two-way slabs), support settlement, steel reinforcement ratio, steel uniform elongation (su), steel ultimate to yield stress ratio (fsu/fsy) and rectangularity aspect ratio in the two-way slabs. In total, thirty one slabs were tested. The one-way slabs included four simply supported slabs, seven continuous slabs, and five continuous slabs with support settlement. The two-way slabs included eleven square and rectangular corner-supported slabs and four rectangular edge-supported slabs. The one-way simply-supported slabs were 850mm in width, 100mm in depth and 2,500mm in length. The continuous one-way slabs were 850mm in width, 100mm in depth and 4,350mm in length. The continuous one-way slabs and subjected to support settlement were 850mm in width, 120mm in depth and 6,300mm in length. The square two-way slabs had an edge length of 2,400mm and a depth of 100mm and the rectangular two-way slabs had width of 2,400mm, a length of 3,600mm and a depth of 100mm.

Includes reprints of author's related articles. / Bibliography: pages 187-201. / The competition between microfracture and plastic flow has been studied in relation to the thermomechanical processing parameters and minor element chemistry of wrought super-ferritic alloys based on a composition of Fe-40wt% Cr. These alloys have been developed for corrosion-resistant applications, specifically by micro-alloying with platinum group metals to induce cathodic modification, but their use has been hampered by inadequate toughness at ambient temperatures. Brittle cleavage of the alloys is a consequence of the high resistance to plastic flow required to accommodate local stresses, such as those found ahead of a loaded crack. Once initiated, a crack propagates in a brittle manner with minimal ductility. The impact toughness therefore relies on the ability of the alloys to withstand crack initiation. The frequency of the crack initiation events is related to the distribution of secondary phases within the matrix and at the grain boundaries. A direct means of improving the toughness and the ductility is accordingly via annealing cycles and minor alloying additions to control the precipitation of second phases. The ductility is enhanced by raising the mobile dislocation density, and this may be achieved by pre-straining recrystallised material, or increasing the number of dislocation sources in the otherwise source-poor material. The generation of mobile dislocations by prismatic punching at second phase particles in response to local or tessellated stresses was found to increase the ductility and the impact toughness of the alloy. The addition of nickel also increases the brittle fracture resistance by promoting stress accommodation at the crack tip, a result which can, in principle, be explained on the basis of enhanced dislocation dynamics. The tendency of the alloys to form a stable recovered substructure was identified as a critical parameter for both the mechanical and corrosion properties. The low-angle dislocation sub-arrays contribute to overall strain-hardening, but destabilise the passivity of the alloys in acid media. In practice, rationalisation of the microstructural parameters has enabled the practicable fabrication of tough, corrosion-resistant alloys, suitable for commercial development.

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Quantitative relationships among processing parameters, microstructure, and material properties are of considerable interest in the context of development of robust processing routes that optimize the required material properties. As a result, the scientific literature contains a large number of experimental and theoretical studies on microstructure-properties relationships. Fracture sensitive mechanical properties such as ductility, ultimate tensile strength, fatigue life, and fracture toughness depend on the average microstructural parameters as well as the distributions of microstructural parameters and their extrema.Development of quantitative relationships between such material properties and microstructural distributions and extrema has received considerably less attention, particularly in the wrought metals and alloys. Accordingly, an important objective of this research is to perform a systematic investigation in this direction. The dependence of the fracture-sensitive mechanical properties on the microstructural distributions and extrema often leads to substantial variability in these properties: a set of specimens having the same average chemistry, the same average processing history, and the same average microstructural parameters such as volume fractions of different constituents can exhibit substantially different material properties. The present research (i) is concerned with high strength (~ 1000 MPa) high martensite (>50%) dual phase steel where the martensite is a topologically continuous phase (matrix) containing a dispersion of islands of ferrite, and (ii) focuses on understanding the microstructural origins of the variability in fracture sensitive mechanical properties, in particular variability in the room temperature uniaxial tensile ductility. The research involves quantitative microstructure characterization using stereology and digital image processing and quantitative fractography using scanning electron microscopy (SEM) and fracture profilometry. The analysis of the quantitative fractographic and microstructural data obtained in this research leads to useful guidelines for reducing the variability in the tensile ductility of the dual phase steel under investigation.

L’objectif de ce travail est de développer une modélisation prédictive du comportement et de la rupture ductile des matériaux métalliques à anisotropies initiales et induites par l’endommagement. La thermodynamique des processus irréversibles est utilisée comme cadre pour la formulation proposée. Le modèle de comportement est élastoplastique anisotrope avec écrouissage non linéaire isotrope et cinématique en grandes déformations plastiques, avec une théorie non associée à normalité associée, basée sur des normes de contraintes quadratiques. L’endommagement ductile anisotrope est décrit par un tenseur du second ordre symétrique dont l’évolution est décrites par des relations de type Lemaitre-Desmorat. Le couplage fort comportement-endommagement est réalisé dans le cadre de l’hypothèse de l’équivalence en énergie totale où l’effet de l’endommagement sur le comportement est introduit par un tenseur « effet d’endommagement » d’ordre quatre symétrique de type Murakami. Après une caractérisation expérimentale des mécanismes physiques de l’endommagement dans l’acier AISI 316L, le modèle de comportement avec endommagement a été identifié. Une fois discrétisé et implémenté dans le code de calcul de structures ABAQUS/Explicit®, une étude paramétrique et de nombreuses simulations numériques de l’endommagement anisotrope en mise en forme de quelques structures ont été réalisées et discutées en détail / The objective of this work is to develop a predictive modeling of behavior and ductile fracture of metallic materials with initial anisotropy and induced by the ductile anisotropic damage. Thermodynamics of irreversible processes is used as a framework for the proposed formulation. The model is anisotropic elastoplastic with non-linear isotropic and kinematic hardening under large plastic strains. It is formulated in the framework of the non-associative plasticity theory with associative normality rule and based on quadratic equivalent stress. The anisotropic ductile damage is described by a symmetric second-rank tensor whose evolution is described by Lemaitre /Desmorat type relationships. The strong damage-behavior coupling is done under the assumption of total energy equivalence where the effect of the anisotropic damage is introduced by a fourth-rank symmetric damage-effect tensor of Murakami kind.After an experimental characterization of the main physical mechanisms of anisotropic damage in stainless steel AISI 316L, the behavior model with damage has been identified. Once discretized and implemented in the computer code ABAQUS / Explicit ®, a parametric study and many numerical simulations of anisotropic damage in some metal forming processes have been carried out and discussed in detail