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Sainte-Foy-lès-Lyon, France

Valiorgue F.,LTDS | Brosse A.,ESI France | Naisson P.,LTDS | Rech J.,LTDS | And 2 more authors.
Applied Thermal Engineering | Year: 2013

This paper will present the infrared thermography principles applied to the thermal fields recording during orthogonal cutting of 316L stainless steel. This paper is divided in three parts. First, emissivity curve of 316L is extracted by warming up a sample and dividing recorded grey levels by black body ones. This first step requires the design of special equipment that allows controlling temperatures and atmosphere while recording. Next, the IR camera equipped with a microscope is integrated in a CNC lath to record grey levels while orthogonal cuttings of 316L samples. To finish, the recorded grey levels fields are then numerically post treated using homemade emissivity curve to plot the thermal gradient created during machining. All these works are important to increase the cutting analytical and numerical models accuracy especially in the thermal field prediction. © 2013 Elsevier Ltd. All rights reserved.

Cuilliere J.-C.,University of Quebec at Trois - Rivieres | Francois V.,University of Quebec at Trois - Rivieres | Lacroix R.,ESI France
CAD Computer Aided Design | Year: 2016

Through our research on the integration of finite element analysis in the design and manufacturing process with CAD, we have proposed the concept of mesh pre-optimization. This concept consists in converting shape and analysis information in a size map (a mesh sizing function) with respect to various adaptation criteria (refining the mesh around geometric form features, minimizing the geometric discretization error, boundary conditions, etc.). This size map then represents a constraint that has to be respected by automatic mesh generation procedures. This paper introduces a new approach to automatic mesh adaptation around circular holes. This tool aims at optimizing, before any FEA, the mesh of a CAD model around circular holes. This approach, referred to as "a priori" mesh adaptation, should not be regarded as an alternative to adaptive a posteriori mesh refinement but as an efficient way to obtain reasonably accurate FEA results before a posteriori adaptation, which is particularly interesting when evaluating design scenarios. The approach is based on performing many offline FEA analyses on a reference case and deriving, from results and error distributions obtained, a relationship between mesh size and FEA error. This relationship can then be extended to target user specified FEA accuracy objectives in a priori mesh adaptation for any distribution of circular holes. The approach being purely heuristic, fulfilling FEA accuracy objectives, in all cases, cannot be theoretically guaranteed. However, results obtained using varying hole diameters and distributions in 2D show that this heuristic approach is reliable and useful. Preliminary results also show that extension of the method can be foreseen towards a priori mesh adaptation in 3D and mesh adaptation around other types of 2D features. © 2016 Elsevier Ltd. All rights reserved.

Cottier E.,CNRS Tribology and Dynamic Systems Laboratory | Cottier E.,Haulotte Group | Anglade P.,Haulotte Group | Brosse A.,ESI France | Feulvarch E.,CNRS Tribology and Dynamic Systems Laboratory
Mechanics and Industry | Year: 2016

The prediction of welding residual stresses requires accurate account to be taken of the couplings between heat transfer, metallurgy and stresses-strains in the heat affected zone. To begin with, simulations of residual stresses for welding processes were performed at the beginning of the 1970s. Since then, calculations have been compared and validated with experimental measurements, the major problem remaining is the calculation time. Despite the technological evolution of computers, a 3D calculation can last several days. To avoid this difficulty, a 3D simplified approach is proposed in this article. It consists of decreasing the computation time for the current zone of the welds. To show the relevance of such an approach, the methodology developed is presented through the application of a single-pass steel girth weld. For this application, the computing time can be reduced by more than 67% compared to a standard "step by step" simulation. © 2016 AFM, EDP Sciences.

Lohner R.,George Mason University | Britto D.,SL Rasch GmbH | Michailski A.,SL Rasch GmbH | Haug E.,ESI France
Engineering Computations (Swansea, Wales) | Year: 2014

Purpose - During a routine benchmarking and scalability study of CFD codes for typical largescale wind engineering runs, it was observed that the resulting loads for buildings varied considerably with the number of parallel processors employed. The differences remained very small at the beginning of a typical run, and then grew progressively to a state of total dissimilitude. A "butterfly-effect" for such flows was suspected and later confirmed. The paper aims to discuss these issues. Design/methodology/approach - A series of numerical experiments was conducted for massively separated flows. The same geometry - a cube in front of an umbrella - was used to obtain the flowfields using different grids, different numbers of domains/processors, slightly different inflow conditions and different codes. Findings - In all of these cases the differences remained very small at the beginning of a typical run, they then grew progressively to a state of total dissimilitude. While the mean and maximum loads remained similar, the actual (deterministic) instantiations were completely different. The authors therefore suspect that for flows of this kind a "butterfly effect" is present, whereby even very small (roundoff) errors can have a pronounced effect on the actual deterministic instantiation of a flowfield. Research limitations/implications - This implies that for flows of this kind the CFD runs have to be carried out to much larger times than formerly expected (and done) in order to obtain statistically relevant ensembles. Practical implications - For practical calculations this implies running to much larger times in order to reach statistically relevant ensembles, with the associated much higher CPU time requirements. Originality/value - This is the first time such a finding has been reported in the numerical wind engineering context. © Emerald Group Publishing Limited.

Gilles P.,AREVA | Zhang G.,AREVA | Madou K.,ESI France
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2014

In fracture mechanics, several J-estimation schemes are based on the reference stress approach. This approach has been developed initially in the frame of the R5 rule for creep and R6 rule for elasto-plastic fracture assessments. Later other methods, based on the reference stress concept, where derived like the Js method introduced in the French RSE-M code en 1997 and the Enhanced Reference Stress (ERS) method in Korea around 2001. However these developments are based on the J2 deformation plasticity theory and well established for a pure power hardening law. Even in this latter case, the reference stress depends on the hardening exponent. Js and ERS attempt to minimize this dependence and propose some corrections for recorded behavior laws which cannot be fitted by a power law. However their validation has been established mainly on cases where the material behavior is governed by a Ramberg-Osgood (R0) law. The question may be raised, as for the bilinear hardening law case, of the existence of a reference stress for non RO laws. Copyright © 2014 by ASME.

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