Computational materials science of cement-based materials

This paper describes recent research and theoretical results obtained for cement-based materials using computational materials science techniques. Computer-generated microstructure models are used to simulate the microstructure development during hydration, and exact algorithms are applied to these models to compute experimentally verifiable physical properties. Good agreement is found between experimental and simulation results.

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Resume Cet article décrit les résultats théoriques d'études récentes de matériaux à matrice de ciment au moyen des techniques de modélisation appliquées à la science des matériaux. On a utilisé des modèles de microstructure obtenus par ordinateur pour simuler le développement de la microstructure pendant l'hydratation, et on applique des algorithmes exacts à ces modèles afin de calculer les propriétés physiques vérifiables expérimentalement. On trouve une bonne concordance entre les résultats expérimentaux et ceux obtenus par simulation. Cet article est une adaptation de la conférence présentée à l'occasion de la remise de la Médaille Robert L'Hermite, lors de la 46ème Réunion du Conseil Général de la RILEM à Madrid, le 1 er octobre 1992.

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This paper is a non-verbatim written account of the 1992 Robert L'Hermite Medal lecture presented at the 46th General Council of RILEM, in Madrid, Spain, 1 October 1992.     

Computational materials science: The emergence of predictive capabilities of material behaviour

The availability of high performance computers and development of efficient algorithms has led to the emergence of computational materials science as the third branch of materials research complementing the traditional theoretical and experimental approaches. It has created new virtual realities in materials design that are either experimentally not realizable easily or are prohibitively expensive. The possibilities of doing calculations from first principles have led to predictive capabilities that open up new avenues of discovering novel materials with desired properties, understanding material behaviour on the nano- to the macroscopic scale and helping research in new frontiers that could interface between nano-materials and drug design, as well as in understanding biological systems. Here, we describe some significant recent developments related to alloy and steel design as well as the study of matter on the nano-scale — an area that has gained much prominence in current materials research.     

Computational materials: Multi-scale modeling and simulation of nanostructured materials

The paper provides details on the current approach to multi-scale modeling and simulation of advanced materials for structural applications. Examples are given that illustrate the suggested approaches to predicting the behavior and influencing the design of nanostructured materials such as high-performance polymers, composites, and nanotube-reinforced polymers. Primary simulation and measurement methods applicable to multi-scale modeling are outlined. Key challenges including verification and validation are highlighted and discussed.     

Nanoscale ion beam polishing of optical materials

A method of ion beam polishing is described, the special features of which consist in (i) preferential ion beam assisted deposition of a nanometer-thick layer into depressions of the initial relief by oxygen-ion sputtering of a target with a composition identical to that of the processed object; (ii) sputtering of the resulting surface structure by a normally incident low-energy oxygen ion beam to a depth reaching approximately two layers of the deposited material; and (iii) deposition-sputtering cycles repeated with gradually decreasing thickness of the deposited layer until the necessary final state of the surface is attained. Examples of the surface of quartz, sitall (glass ceramic), and BK-7 optical glass processed using the proposed ion beam polishing method show a more than twofold decrease in the height of the relief protrusions as compared to that on the initial surface. On the ion beam processed quartz surface areas with dimensions 2.5×2.5 μm, the maximum roughness height did not exceed 0.8 nm.     

Computational fretting fatigue maps for different plasticity models

This paper presents qualitative elastoplastic simulations and analyses of fretting fatigue. Three hardening constitutive models are considered, and their effects on stick–slip conditions and lifetime prediction are compared. The computational analysis consists of the estimation of the shakedown limit cycle and the fatigue prediction using Dang Van or Crossland criterion. A particular configuration, the interaction of a flat pad with rounded corners in contact with a flat substrate made, respectively, of Inconel In718 and Titanium Ti64 alloys, is studied. The shakedown state is analysed using the cyclic and ratcheting equivalent strain concepts already discussed in the literature. In the paper, different fretting maps, based on slip, shakedown and fatigue regimes, are numerically produced and analysed. A new variable, the global slip percentage, is proposed for the characterization of the stick–slip regimes. Analyses of a series of slip maps show that the different hardening models do not introduce significant changes in the stick–slip conditions. Using finite element method simulations combined with fatigue limit criteria (Dang Van and Crossland), fretting fatigue maps are qualitatively reproduced. The main contribution of this work is a comparative discussion on the influence of the hardening models complexity on such maps.     

Computational plasticity of mixed hardening pressure-dependency constitutive equations

In the present study, two semi-implicit schemes, based on the exponential maps method, are derived for integrating the pressure-sensitive constitutive equations. In spite of the fact that the consistent tangent operator is necessary to preserve the quadratic rate for the asymptotic convergence of the Newton-Raphson solution in the finite element analyses, there exists no derivation of this operator for the exponential-based integrations of the pressure-sensitive plasticity in the literature. To fulfill this need, the algorithmic tangent operators are extracted for the new semi-implicit as well as the former exponential-based integrations. Moreover, for the accurate integration presented by Rezaiee-Pajand et al. (Eur J Mech A Solids 30:345–361, 2011), the consistent tangent operator is obtained. Eventually, all the investigations are assessed by a broad range of numerical tests.     

Nanoscale materials for tackling brain cancer: recent progress and outlook

This article reports on recent progress in the development of advanced nanoscale photoreactive, magnetic and multifunctional materials applicable to brain cancer diagnostics, imaging, and therapy, with an emphasis on the latest contributions and the novelty of the approach, along with the most promising emergent trends.     

Membrane separations: a materials science approach

An overview of the benefits and limitations of different types of industrial separation membranes is presented. Their properties strongly influence the choice of methods of manufacture. The choice of membrane composition is also influenced by their role in the total filtration plant, especially by methods of cleaning and flow optimisation. The discussion has been limited to liquid filtration systems and concentrates on microfiltration.