Pyrosol deposition of anatase TiO2 thin films starting from Ti(OiPr)4/acetylacetone solutions

TiO2 thin films were deposited on Si(100) and steel substrates by Pyrosol technique. The layer morphology depends on the concentration of titanium tetra-isopropoxide (TTIP) used as molecular precursor in solutions with acetylacetone (Acac). The concentration and, as a result, the viscosity of these TTIP/Acac starting solutions plays an important role on the efficiency of their nebulization and, consequently, on the microstructure and the growth kinetics of the TiO2 thin films. The correlations between the composition of the TTIP/Acac solutions and the structure, the morphology, optical properties and the deposition rate of the films are presented and discussed. Growth rates as high as 1.8 μm/min are obtained using pure TTIP without Acac solvent. The photocatalytic activity of these Pyrosol TiO2 thin films grown using TTIP with and without Acac solvent has been investigated and a negative effect of the solvent was found

Modeling the kinematics of multi-axial composite laminates as a stacking of 2D TIF plies

Thermoplastic composites are widely considered in structural parts. In this paper attention is paid to sheet forming of continuous fiber laminates. In the case of unidirectional prepregs, the ply constitutive equation is modeled as a transversally isotropic fluid, that must satisfy both the fiber inextensibility as well as the fluid incompressibility. When the stacking sequence involves plies with different orientations the kinematics of each ply during the laminate deformation varies significantly through the composite thickness. In our former works we considered two different approaches when simulating the squeeze flow induced by the laminate compression, the first based on a penalty formulation and the second one based on the use of Lagrange multipliers. In the present work we propose an alternative approach that consists in modeling each ply involved in the laminate as a transversally isotropic fluid – TIF - that becomes 2D as soon as incompressibility constraint and plane stress assumption are taken into account. Thus, composites laminates can be analyzed as a stacking of 2D TIF models that could eventually interact by using adequate friction laws at the inter-ply interfaces.Peer ReviewedPostprint (published version

The Schrödinger Equation

The finest scale in the matter description consists of the one of quantum mechanics. In this chapter we revisit some valuable concepts of quantum mechanics, and more particularly the Schrödinger equation governing the time evolution of the so-called wavefunction, from which expectations can be easily derived. Another important output is the interatomic potentials responsible of the chemical bonds determining the structure and properties of materials. Even if the quantum framework is able to define the big picture, an important difficulty remains: the Schrödinger equation is defined in a highly multidimensional space and its solution is in most cases unattainable

Kinetic Theory Models

Discrete techniques (MD or BD), despite their conceptual simplicity, are very often too expensive from the computational point of view. Kinetic theory approaches seem, in many cases, a suitable compromise between the accuracy of finer descriptions and the computational efficiency of macroscopic descriptions. In this chapter, we revisit some kinetic theory models. Even if there is a common rationale for deriving the different models, in order to emphasize their physical contents, we will follow a diversity of alternative routes to derive them

Ab-Initio Calculations

Due to the difficulties found in the direct solution of the Schrödinger equation, different simplified approaches were proposed and are nowadays widely used. Among them, those most usually employed are the Hartree–Fock and the Density Functional Theory, which we revisit in the present chapter. The former makes use of nonstandard numerical approximations in order to calculate the wavefunction while circumventing the curse of dimensionality, whereas the latter involves the electronic density that is now defined in three dimensions but requires deeper analyses to retain the most relevant features present in the wavefunction description in a coarse 3D model

A journey around the different scales involved in the description of matter and complex systems

This book covers the main scales of description of matter, starting at its finest level, the quantum scale, moving through ab-initio, molecular dynamics, coarse grained approaches, to finish at the scale of kinetic theory models that allows a nice compromise between the rich but expensive microscopic descriptions and the computationally cheap but sometimes too coarse macroscopic descriptions. The book addresses undergraduate and graduate students, as well as beginners in multi-scale modeling of materials. (4th cover, excerpt from publisher's website

Computational vademecums for a fast and reliable simulation of RTM processes

Proper Generalized Decomposition methods allow to obtain an efficient solution for multi-parametric problems without the need for simulating numerous problems to obtain a response surface. Instead, PGD obtains a priori a reduced solution in the form of a finite sum of separable functions, easy to store in memory so as to be evaluated under real-time constraints. The present work proposes to use this tool to optimize the main RTM process parameters, the injection flow rate and the injection/mould temperature, in order to ensure the complete filling of the mould and reasonable fabrication costs (fabrication time, mould heating). To do so, the two process parameters should be introduced in the model as new coordinates, and the Proper Generalized Decomposition method used to solve the multiparametric model then obtained. By using this procedure, we could build computational vademecums, having the two parameters of interest as coordinates, allowing the fabricant to define the best compromise between injection time and process cost (mould heating) while ensuring the complete filling of the mould. In this work, after revisiting some applications of PGD in RTM processes, the separability of parametric RTM solutions will be evaluated.Peer ReviewedPostprint (published version

Model and system learners, optimal process constructors and kinetic theory-based goal-oriented design: a new paradigm in materials and processes informatics

Traditionally, Simulation-Based Engineering Sciences (SBES) has relied on the use of static data inputs (model parameters, initial or boundary conditions, ... obtained from adequate experiments) to perform simulations. A new paradigm in the field of Applied Sciences and Engineering has emerged in the last decade. Dynamic Data-Driven Application Systems [9, 10, 11, 12, 22] allow the linkage of simulation tools with measurement devices for real-time control of simulations and applications, entailing the ability to dynamically incorporate additional data into an executing application, and in reverse, the ability of an application to dynamically steer the measurement process. It is in that context that traditional "digital-twins" are giving raise to a new generation of goal-oriented data-driven application systems, also known as "hybrid-twins", embracing models based on physics and models exclusively based on data adequately collected and assimilated for filling the gap between usual model predictions and measurements. Within this framework new methodologies based on model learners, machine learning and kinetic goal-oriented design are defining a new paradigm in materials, processes and systems engineering

kPCA-Based Parametric Solutions Within the PGD Framework

Parametric solutions make possible fast and reliable real-time simulations which, in turn allow real time optimization, simulation-based control and uncertainty propagation. This opens unprecedented possibilities for robust and efficient design and real-time decision making. The construction of such parametric solutions was addressed in our former works in the context of models whose parameters were easily identified and known in advance. In this work we address more complex scenarios in which the parameters do not appear explicitly in the model—complex microstructures, for instance. In these circumstances the parametric model solution requires combining a technique to find the relevant model parameters and a solution procedure able to cope with high-dimensional models, avoiding the well-known curse of dimensionality. In this work, kPCA (kernel Principal Component Analysis) is used for extracting the hidden model parameters, whereas the PGD (Proper Generalized Decomposition) is used for calculating the resulting parametric solution

Interaction of inter- and intralaminar damage in scaled quasi-static indentation tests:Part 1 – Experiments

International audienceThe evaluation of the predictive capabilities of models proposed in the literature for laminated composites calls for experimental testing providing detailed results of both the global and local response in terms of degradation mechanisms, such as delamination, transverse cracking and fibre breaking. Scaled tests, in which one or more characteristic dimensions are modified, allow variation of the different mechanisms. In this paper, a unique series of scaled indentation tests are performed on quasi-isotropic composite plates, and a detailed assessment of the damage evolution is carried out through non-destructive techniques, including ultrasonic C-scan and X-ray Computed Tomography (CT). Four different configurations are tested, presenting changes in both in-plane dimensions and fully three dimensional scaled cases. The latter are performed with sublaminate and ply scaling to show the effect of ply thickness on response. A detailed set of results for both global behaviour and the damage evolution is provided to demonstrate the mechanisms controlling behaviour and to create a reference set of data for model validation. The scaling effects observed are also discussed making use of simplified analytical models