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Bouguenais, France

Ghnatios C.,IRT Jules Verne | Chinesta F.,Ecole Centrale Nantes
Computational Plasticity XII: Fundamentals and Applications - Proceedings of the 12th International Conference on Computational Plasticity - Fundamentals and Applications, COMPLAS 2013 | Year: 2013

Nowadays, composite materials are replacing metallic ones thanks to their excellent mechanical performances and reduced weight. However, many difficulties are encountered during composite forming processes. Infact, autoclave curing process is too expensive and limits the part size to the autoclave dimensions. Out-Of-Autoclave processes reduce substantially the cost of forming processes. However, the absence of autoclave pressure in out-of-autoclave manufacturing processes leads nowadays to high porosity and poor consolidation at the interface between the tows[1]. Moreover, the effect of the process parameters on the consolidation is still unknown and thus controlling the final parts quality is not obvious. Despite the high potential offered by the Out-of-Autoclave processes, only few researches has been made in the last few years, in order to quantify the consolidation of the tows while using such processes[2]. Infact, only few models addressing void dynamics in thermoplastic composites has been carried out[3,4]. In this work, we are using a novel coupled approach involving modeling and simulation in order to quantify the consolidation in Out-of-Autoclave processes. Advanced model reduction techniques (POD,PGD...) are employed in order to predict thermal fields during manufacturing processes and coupled to the subsequent squeeze flow.

Younes W.,IRT Jules Verne | Giraud E.,LAMPA | Dal Santo P.,LAMPA
Key Engineering Materials | Year: 2015

Anisotropic behavior at high temperature of an Aluminum-Lithium alloy was studied. Mechanical tests at a temperature of 350°C and a strain rate of 10-2 s-1 were carried out on samples taken at different angles with respect to the rolling direction of the sheet. Two plasticity criteria (HILL48 and HU2005) were identified and implemented in ABAQUS to predict the anisotropic behavior of the alloy for other angles. Results show that: (i) the alloy exhibits an anisotropic behavior at high temperature and some recrystallization occurs during plastic deformation; (ii) the coefficients of anisotropy depend on strain level and (iii) HU2005 criterion allows describing the behavior of the alloy at high temperature. © (2015) Trans Tech Publications, Switzerland.

Tardif X.,IRT Jules Verne | Pignon B.,CNRS Nantes Thermocinetique Lab | Boyard N.,CNRS Nantes Thermocinetique Lab | Schmelzer J.W.P.,University of Rostock | And 3 more authors.
Polymer Testing | Year: 2014

The recently developed fast scanning differential calorimetry is used for the first time to determine the crystallization kinetics of Poly(EtherEtherKetone) (PEEK). In our experiments, crystallization is studied in isothermal conditions over a large temperature range from 170 °C to 310°C. Two different measurement protocols were employed. Between 200°C and 300°C the heat flow was directly measured during isothermal crystallization. Outside this temperature range we measured the heat of fusion on heating after interrupted isothermal crystallization. We show that data can be analyzed with the Avrami approach incorporating a term describing secondary crystallization. The crystallization half-times are measured. The Avrami kinetic coefficient KAv associated with primary crystallization is evaluated from isothermal crystallization between 170°C and 310 °C where data were not previously available. The kinetics of crystallization of PEEK has only one maximum located around 230 °C and its Avrami exponent is close to 3, suggesting instantaneous nucleation with subsequent spherical growth. The whole isothermal crystallization process is modeled in terms of Hillier's model since it takes secondary crystallization kinetics into account. Finally, it is shown that the double melting peak behavior observed after isothermal crystallization (below 260 °C) is a consequence of the reorganization process during heating. © 2014 Elsevier Ltd. All rights reserved.

Zghal J.,IRT Jules Verne | Gmati H.,Arts et Metiers ParisTech | Mareau C.,Arts et Metiers ParisTech | Morel F.,Arts et Metiers ParisTech
International Journal of Damage Mechanics | Year: 2016

In this paper, a polycrystalline model is proposed to describe the fatigue behaviour of metallic materials in the high cycle fatigue regime. The model is based on a multiscale approach, which allows the connection of local deformation and damage mechanisms to macroscopic behaviour. To consider the anisotropy of plastic properties, the constitutive model is developed at the grain scale within a crystal plasticity framework. A phenomenological approach, which requires the introduction of a damage variable for each slip system, is used to account for the anisotropic nature of damage. The constitutive model is then integrated within a self-consistent formulation to consider the polycrystalline nature of metallic materials. Finally, the proposed model is used to describe the high cycle fatigue behaviour of a medium carbon steel (0.35% C). With a proper adjustment of material parameters, the model is capable of correctly reproducing fatigue test results, even for complex loading conditions (multiaxial, non-proportional). According to the model, damage is found to be highly localized in some specific grains. Also, while fatigue damage results in a progressive decrease in elastic stiffness at the crystal scale, the elastic properties are not significantly affected at the macroscopic scale. The model is used to study the correlation between energy dissipation and fatigue damage. According to the numerical results, no evident correlation between fatigue damage and energy dissipation is observed. © SAGE Publications.

Chausse F.,IRT Jules Verne | Paillard P.,Jean Rouxel Institute | Bertrand E.,Jean Rouxel Institute | Ruckert G.,DCNS S.A.
Journal of Laser Applications | Year: 2016

This work investigates the weldability of S460ML steel using a hybrid laser-metal active gas (MAG) process and the effect of dropping on material properties. Dropping is the creation of regularly scattered drops on the back side of thick plates during full penetration hybrid laser-MAG welding. As these drops can reach several millimeters in diameter, it is an unacceptable defect since it lowers esthetic properties. Besides the geometrical aspect, mechanical properties are also affected by dropping. In order to check the consequences of dropping on weld quality: metallographic, mechanical, and dilution analyses have been performed. Results confirm the good weldability of S460ML using hybrid welding with proper welding parameters. If dropping occurs, it enhances heterogeneity in chemistry and microstructure, and welding defects such as porosity and undercuts. However, these properties and defects remain tolerable. Drops can be removed by grinding, making the weld acceptable. © 2016 Laser Institute of America.

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