Nanometric Scale Investigation of Phase Transformations in Advanced Steels for Automotive Application

The current trend toward producing lighter vehicles in the automotive industry is driven by the need to conform to the new exhaust emission control regulations. This objective presents a challenge to steel manufacturers. The difficulty lies in designing new alloys with an optimum strength/formability/cost balance for the various components. Here, the key to success lies in controlling the steel microstructure and especially the phase transformations at the smallest possible scale. Among the different alloying elements, light elements such as carbon and boron are of prime importance due to their major effects on the kinetics of phase transformations. Characterization tools combining high spatial and analytical resolution such as secondary ion mass spectrometry (SIMS) and field emission gun-transmission electron microscopy (TEM) were used. In this article, the examples presented are as follows. (1) Boron segregation and precipitation effects to control hardenability in martensitic steels. (2) Local carbon distribution in advanced high-strength steels, with a specific emphasis on martensite tempering. Links have been established between the boron and carbon distribution and the formability.     

Numeration and discrete dynamical systems

This survey aims at giving both a dynamical and computer arithmetic-oriented presentation of several classical numeration systems, by focusing on the discrete dynamical systems that underly them: this provides simple algorithmic generation processes, information on the statistics of digits, on the mean behavior, and also on periodic expansions (whose study is motivated, among other things, by finite machine simulations). We consider numeration systems in a broad sense, that is, representation systems of numbers that also include continued fraction expansions. These numeration systems might be positional or not, provide unique expansions or be redundant. Special attention will be payed to β-numeration (one expands a positive real number with respect to the base β > 1), to continued fractions, and to their Lyapounov exponents. In particular, we will compare both representation systems with respect to the number of significant digits required to go from one type of expansion to the other one, through the discussion of extensions of Lochs’ theorem.     

Multiparametric analysis within the proper generalized decomposition framework

Optimization campaigns, which are being launched more and more often, require the execution of many parametric studies which can make the approach very costly in terms of computation time. Here, in order to reduce these computation times, we undertake to develop a multiparametric strategy using the LATIN method along with Proper Generalized Decomposition. This approach is compared to other common strategies, especially those based on POD.     

Guaranteed error bounds on pointwise quantities of interest for transient viscodynamics problems

A new method is developed to obtain guaranteed error bounds on pointwise quantities of interest for linear transient viscodynamics problems. The calculation of strict error bounds is based on the concept of “constitutive relation error” (CRE) and the solution of an adjoint problem. The central and original point of this work is the treatment of the singularity in space and time introduced by the loading of the adjoint problem. Hence, the adjoint solution is decomposed into two parts: (i) an analytical part determined from Green’s functions; (ii) a residual part approximated with classical numerical tools (finite element method, Newmark integration scheme). The capabilities and the limits of the proposed approach are analyzed on a 2D example.     

Synthesis and characterization of NiPcTSTNa(L) thin films

NiPcTSTNa(L) [L = ethylenediamine (EDA); 1,4-diaminobutane (BDA); and 2,6-diamineanthraquinone (AqDA)] thin films were deposited by thermal evaporation. Their surface morphology was studied by AFM and SEM, and their chemical composition determined by EDS. Optical absorption studies of NiPcTSTNa(L) films were performed in the 200?C1150?nm wavelength range. The optical bandgap of thin films was determined from the (??h ??)^1/2 vs h?? plots for indirect allowed transitions. The temperature dependence of electrical conductivity shows a semiconducting behaviour. The amorphous semiconductor films show thermal activation energies of electrical conduction between 3·3 and 3·7?eV.     

Coatings against corrosion and microbial adhesion

A systematic study on anti‐corrosion and anti‐fouling effect of hydrophobic Langmuir–Blodgett and self‐assembled molecular layers deposited on metal surfaces, as well as anti‐microbial adhesion properties of coatings with biocide is presented. Both types of efficiencies produced by LB films are enhanced by Fe³⁺ ions built in the molecular film. The quaternary ammonium type biocide embedded into the cross‐linked gelatin decreased significantly the microbial adhesion, the biofilm formation.     

Optimization method for stamping tools under reliability constraints using genetic algorithms and finite element simulations

Controlling variability and process optimization are major issues of manufacturing processes which should be tackled together since optimal processes must be robust. There is a lack of numerical tool combining optimization and robustness. In this paper, a complete approach starting from modelling and leading to the selection of robust optimal process parameters is proposed. A model of stamping part is developed through Finite Element simulation codes and validated by experimental methods. The search for optimal tool configurations is performed by optimizing a desirability function and by means of a genetic algorithm based optimization code. Several tool configurations are selected from the resulting solutions and are observed through robustness analysis. Noise parameters relating to friction and material mechanical properties are taken into consideration during this analysis. A quadratic response surface developed with design of experiments (DOE) links noise parameters to geometrical variations of parts. For every optimal configuration, the rate of non-conform parts which do not satisfy the design requirements is assessed and the more robust tool configuration is selected. Finally, a sensitivity analysis is performed on this ultimate configuration to observe the respective influence of noise parameters on the process scattering. The method has been applied on a U-shape part.     

Geometrical analysis of thread milling—part 2: calculation of uncut chip thickness

Thread milling offers interesting possibilities for machining internal or external threads. This machining technique uses a mill with a triangular profile for metric threads and a helical interpolation strategy. Thus, the uncut chip thickness cannot be easily evaluated from a simplified approach. The present study deals with a model for calculating uncut chip thickness during internal thread milling. This step is needed to understand and model the cutting forces. The model developed uses the geometrical definitions of the mill and takes into account the milling mode and the cutting conditions. The link with the interferences between the tool and the thread is also established and corroborates a previous study. A full analytical formulation of the problem is proposed, and results from different milling settings are presented.     

Comparative analysis of passive algorithms in adaptive control

Representative passive adaptive algorithms have been developed with a wide variety of applications. However, to the best of our knowledge, the attempt to unify or to compare them has not been clearly established in literature. In this article, we provide a passive adaptive framework which encompasses all those algorithms including the recently developed proportional‐integral (PI) adaptive scheme. A comparative analysis among performances of the passive algorithms is carried out by means of simulations considering the problem of passivity‐based adaptive tracking control of a simple pendulum. In addition, passivity property for PI algorithm is rigorously shown in case of linear parametrization. Copyright © 2013 John Wiley & Sons, Ltd.