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Rethore J.,INSA Lyon | Estevez R.,CNRS Materials Science and Engineering
Journal of the Mechanics and Physics of Solids | Year: 2013

We present a new methodology for the identification of a zone cohesive model that describes material failure. The material under consideration fails by crazing. The study is conducted at the micron scale in order to capture and analyze the fracture mechanism. The crack tip displacement fields are measured optically by Digital Image Correlation. The local stress intensity factors (mode I and II) and the location of the equivalent elastic crack tip are calculated during the loading. The variation of the location of the equivalent crack tip is used to track the initiation and growth of the process zone, up to the onset of crack propagation. These experimental measurements are used to define the appropriate parameters in a cohesive zone model. The methodology addresses the onset of crazing, the traction-separation profile and the maximum opening corresponding to the local nucleation of a crack. The cohesive parameters that are derived from the experimental data are consistent with results available in the literature. In addition, the model enables the characterization of the normal and tangential mode of the cohesive model. © 2013 Elsevier Ltd. Source


Lepinoux J.,CNRS Materials Science and Engineering
Philosophical Magazine | Year: 2010

Kinetic Monte Carlo simulations of precipitation in AlZr alloys are compared with predictions of cluster dynamics based on an enhanced thermodynamic model. A methodology and various tools are proposed to learn as much as possible from such comparisons. Important deviations between the two methods are investigated and interpreted through the role of different mechanisms. © 2010 Taylor & Francis. Source


Barlat F.,Pohang University of Science and Technology | Barlat F.,University of Aveiro | Gracio J.J.,University of Aveiro | Lee M.-G.,Pohang University of Science and Technology | And 2 more authors.
International Journal of Plasticity | Year: 2011

In this work, an approach is proposed for the description of the plastic behavior of materials subjected to multiple or continuous strain path changes. In particular, although it is not formulated with a kinematic hardening rule, it provides a reasonable description of the Bauschinger effect when loading is reversed. This description of anisotropic hardening is based on homogeneous yield functions/plastic potentials combining a stable, isotropic hardening-type, component and a fluctuating component. The latter captures, in average, the effect of dislocation interactions during strain path changes. For monotonic loading, this approach is identical to isotropic hardening, with an expanding isotropic or anisotropic yield surface around the active stress state. The capability of this constitutive description is illustrated with applications on a number of materials, namely, low carbon, dual phase and ferritic stainless steel samples.© 2011 Elsevier Ltd. All rights reserved. Source


Colinet C.,CNRS Materials Science and Engineering | Tedenac J.-C.,Charles Gerhardt Institute
Intermetallics | Year: 2010

The total energies of intermetallic compounds in the Si-Ti system are calculated employing electronic density functional theory (DFT). The calculations are performed for the experimentally observed compounds and selected structures at their ideal stoichiometry. The calculated formation enthalpies are in good agreement with the available experimental data. For the stable intermetallic compounds, the calculated zero-temperature lattice parameters agree well with those obtained experimentally at ambient temperature. The point defect formation energies in D88-Si3Ti5 (hP16, P63/mcm, prototype Mn5Si3) are obtained from first principles calculations. Four sublattices are introduced to account for the D88 structure and for the possibility of inserting atoms (2b Wyckoff positions of P63/mcm space group). The total energies of supercells containing one defect are calculated. A statistical model based on a mean-field approximation is used to obtain the defect concentrations, the chemical potentials and the Gibbs energy of formation as functions of temperature and deviation from stoichiometry. Analytical expressions of the defect concentrations, chemical potentials and Gibbs energy as functions of composition for various temperatures are provided. The off-stoichiometric domain of D88-Si3Ti5 is discussed. © 2010 Elsevier Ltd. All rights reserved. Source


Colinet C.,CNRS Materials Science and Engineering | Tedenac J.-C.,Charles Gerhardt Institute
Intermetallics | Year: 2010

The point defect formation energies in D88-Sn3Ti5 are obtained from first principles calculations. The D88 structure is hexagonal, hP16, P63/mcm, prototype Mn5Si3. Four sublattices are introduced to account for the D88 structure and for the possibility of inserting atoms in the 2b sites of the structure P63/mcm. The 2b sites are not occupied in the stoichiometric compound at T = 0 K. But the possibility exists that a few atoms occupy these sites at high temperature or for off-stoichiometric alloys. A statistical model based on a mean-field approximation is developed in the canonical ensemble. The defect concentrations are calculated as function of temperature and deviation from stoichiometry. For stoichiometric D88-Sn3Ti5 alloys, the dominant thermal defects are composed of Sn atoms in interstitial positions 2b of the D88 structure and Ti atoms in antisite position on the sites preferentially occupied by Sn atoms. In the Sn-rich D88-Sn3Ti5, the constitutional defects are Sn atoms in interstitial positions. In the Ti-rich D88-Sn3Ti5, the constitutional defects are Ti atoms in antisite position. The chemical potentials as well as the Gibbs energy are obtained as function of composition for various temperatures. The extension of the one-phase domain of D88-Sn3Ti5 in the Sn-Ti phase diagram is calculated. © 2009 Elsevier Ltd. All rights reserved. Source

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