Papers by Author: Karim Inal

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Authors: M. Reda Berrahmoune, Sophie Berveiller, Karim Inal, Etienne Patoor, Christian R. Simon, Jean-Christophe Glez
Abstract: The main objective of this work is to contribute to the study of the 301LN unstable austenitic stainless steel by determining the distribution of residual stresses after deep drawing, taking into account the phase transformation. In the first part, kinetics of martensitic transformation are determined for uniaxial loading. Tensile tests are performed at different pre-strains at room temperature for two different strain rates. The austenite/martensite content is measured by X-ray diffraction and is coupled with the determination of residual stresses distribution. In addition, to establish a relation between the complex loading path effect and the residual stresses state, deep drawing are done for different drawing ratios for two different temperatures. Macroscopic tangential residual stresses are determined by the separation technique. It appears that the residual stresses increase with increasing drawing ratios and the maximum value is located at middle height of the cup.
Authors: Hakim Bougrab, Karim Inal, Marcel Berveiller
Authors: L. Arnault, S. Branchu, Manuel François, Ronald Guillén, Karim Inal, Jean Lu Lebrun, C. Vial
Authors: Sophie Berveiller, Pascal Dubos, Karim Inal, André Eberhardt, Etienne Patoor
Abstract: We have developed a new convenient tool for local stress and strain analysis in the scanning electron microscope. It is based on the Kossel diffraction, physical phenomenon that is known for a long time because of its high accuracy for lattice constant determination in micron regions. The pattern is recorded on a CCD camera allowing a fast and reliable analysis. This technique has been applied to several materials. In-situ tensile tests were performed on a shape memory alloy. During loading, we observe clearly a shift of Kossel lines on the diagram, whose magnitude depends on the (hkl) crystallographic planes. The stress can be deduced from the diffracting plane strain measurement using a single crystal stress analysis.
Authors: Raphaël Pesci, Karim Inal, Sophie Berveiller, Etienne Patoor, Jean Sébastien Lecomte, André Eberhardt
Abstract: A Kossel microdiffraction experimental set up is under development inside a Scanning Electron Microscope (SEM) in order to determine the crystallographic orientation as well as the inter- and intragranular strains and stresses on the micron scale, using a one cubic micrometer spot. The experimental Kossel line patterns are obtained by way of a CCD camera and are then fully indexed using a home-made simulation program. The so-determined orientation is compared with Electron Back-Scattered Diffraction (EBSD) results, and in-situ tests are performed inside the SEM using a tensile/compressive machine. The aim is to verify a 50MPa stress sensitivity for this technique and to take advantage from this microscope environment to associate microstructure observations (slip lines, particle decohesion, crack initiation) with determined stress analyses.
Authors: Raphaël Pesci, Karim Inal, Marcel Berveiller, Jean Lu Lebrun
Authors: K.W. Neale, Karim Inal, Pei Dong Wu
Authors: Jean Philippe Mathieu, Denis Bouscaud, Karim Inal, Sophie Berveiller, Olivier Diard
Abstract: This paper reports experimental characterisation of stress heterogeneities in a French RPV bainitic steel (16MND5) determined by X-Ray diffraction during in-situ tensile testing at low temperature (until –150°C). Results are compared successfully to simulation results, obtained by post-processing of Finite Elements computations of realistic 3D aggregates.
Authors: M.N. Shiekhelsouk, Véronique Favier, Karim Inal, Sebastien Allain, Olivier Bouaziz, M. Cherkaoui
Abstract: A new variety of duplex steels with superior mechanical properties has been studied. They exhibit a very interesting combination of strength (tensile strength of 680 MPa) and ductility values (more than 45% total elongation) due to the competition between different plasticity mechanisms. These steels contain two phases: austenite and ferrite and are characterized by low stacking fault energy at room temperature. In this work, four duplex steels with different chemical composition and phase volume fraction are studied. Residual and internal stresses in each phase were determined using the classical X-ray diffraction sin²ψ method. In the as-received state, both longitudinal and transverse residual stresses are in compression (until -350 MPa) for the ferrite and in tension (until +410 MPa) for the austenite. However, residual stresses in the austenitic phase decrease when its volume fraction increases. Moreover, internal stress distribution in one alloy was determined by X-ray diffraction during an in situ tensile test. The austenitic phase stress along the loading direction is higher than the macroscopic applied one, which is higher than the ferritic stress state, verifying a mixture rule and consistent with the initial residual stresses. For an applied macroscopic strain of about 1%, the austenite phase is subjected to a stress of about 600 MPa whereas the stress in the ferritic phase is about 300 MPa. It was also observed that as macroscopic strain increases, stress difference between the austenite and the ferrite decreases.
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