SAM

Direct measurement of local constitutive relations, at the micrometre scale, in bulk metallic alloys

PLANCHER, E — Sun, 01 Jan 2017 00:00:00 GMT

Direct measurement of local constitutive relations, at the micrometre scale, in bulk metallic alloys PLANCHER, E; MAURICE, C; LOISNARD, D; RUPIN, N; MARIJON, Jean-Baptiste; MICHA, Jean-Sébastien; ROBACH, Odile; CASTELNAU, Olivier; BOSSO, E; STODOLNA, J; PETIT, J; FAVIER, Véronique Multiscale models involving crystal plasticity are essential to predict the elastoplastic behavior of structural materials with respect to their microstructure. However, those models are often limited by a poor knowledge of the local constitutive behavior. This article reports a method to measure the mechanical behavior directly, at the micrometre scale, in bulk crystalline materials. Local strain and stress states were evaluated at the surface of a bent stainless steel crystal by combining total strain measurements – performed with the digital image correlation technique on optical images – with elastic strain measurements obtained by Laue microdiffraction. A local constitutive relation was measured, in an efficient nondestructive way, without the need for full-field simulations. The method was validated by a comparison between the measured local behavior and the macroscopic behavior of the single crystal.

Combining Laue microdiffraction and digital image correlation for improved measurements of the elastic strain field with micrometer spatial resolution

PETIT, Johann — Sun, 01 Jan 2012 00:00:00 GMT

Combining Laue microdiffraction and digital image correlation for improved measurements of the elastic strain field with micrometer spatial resolution PETIT, Johann; BORNERT, Michel; HOFMANN, Felix A.; ROBACH, Odile; MICHA, Jean Sébastien; ULRICH, Olivier; LE BOURLOT, Christophe; FAURIE, Damien; KORSUNSKY, Alexander; CASTELNAU, Olivier The X-ray Laue microdiffraction technique, available at beamline BM32 on the synchrotron ESRF, is ideally suited for probing the field of elastic strain (and associated stress) in deformed polycrystalline materials with a micrometric spatial resolution. We show that using Digital Image Correlation for measuring Laue pattern distortions between two mechanical states improves significantly the estimate of elastic strain increment. The potentiality of this new Laue-DIC method is illustrated on an elastically bent Si single crystal, for which the measured elastic strain deviates not more than 10-5 from the theoretical strain distribution provided by standard solutions

Validity of Crystal Plasticity Models Near Grain Boundaries: Contribution of Elastic Strain Measurements at Micron Scale

PLANCHER, E. — Tue, 01 Jan 2019 00:00:00 GMT

Validity of Crystal Plasticity Models Near Grain Boundaries: Contribution of Elastic Strain Measurements at Micron Scale PLANCHER, E.; TAJDARY, Pouya; AUGER, Thierry; CASTELNAU, Olivier; LOISNARD, Dominique; MARIJON, Jean-Baptiste; MAURICE, Claire; MICHEL, Vincent; ROBACH, Odile; STODOLNA, Julien Synchrotron Laue microdiffraction and digital image correlation measurements were coupled to track the elastic strain field (or stress field) and the total strain field near a general grain boundary in a bent bicrystal. A 316L stainless steel bicrystal was deformed in situ into the elasto-plastic regime using a four-point bending setup. The test was then simulated using finite elements with a crystal plasticity model comprising internal variables (dislocation densities on discrete slip systems). The predictions of the model are compared with both the total strain field and the elastic strain field obtained experimentally. While activated slip systems and total strains are reasonably well predicted, elastic strains appear overestimated next to the grain boundary. This suggests that conventional crystal plasticity models need improvement to correctly model stresses at grain boundaries.

Laue microdiffraction at the ESRF

ROBACH, Odile — Wed, 01 Jan 2014 00:00:00 GMT

Laue microdiffraction at the ESRF ROBACH, Odile; KIRCHLECHNER, Christoph; MICHA, Jean Sébastien; ULRICH, M. Olivier; BIQUARD, Xavier; GEAYMOND, M. Olivier; CASTELNAU, Olivier; BORNERT, Michel; PETIT, Johann; SICARDY, Olivier; VILLANOVA, Julie; RIEUTORD, François; BERVEILLER, Sophie This book highlights emerging diffraction studies of strain and dislocation gradients with mesoscale resolution, which is currently a focus of research at laboratories around the world. While ensemble-average diffraction techniques are mature, grain and subgrain level measurements needed to understand real materials are just emerging. In order to understand the diffraction signature of different defects, it is necessary to understand the distortions created by the defects and the corresponding changes in the reciprocal space of the non-ideal crystals. Starting with a review of defect classifications based on their displacement fields, this book then provides connections between different dislocation arrangements, including geometrically necessary and statistically stored dislocations, and other common defects and the corresponding changes in the reciprocal space and diffraction patterns. Subsequent chapters provide an overview of microdiffraction techniques developed during the last decade to extract information about strain and dislocation gradients. X-ray microdiffraction is a particularly exciting application compared with alternative probes of local crystalline structure, orientation and defect density, because it is inherently non-destructive and penetrating.

On the Accuracy of Elastic Strain Field Measurements by Laue Microdiffraction and High-Resolution EBSD: a Cross-Validation Experiment

PLANCHER, Emeric — Fri, 01 Jan 2016 00:00:00 GMT

On the Accuracy of Elastic Strain Field Measurements by Laue Microdiffraction and High-Resolution EBSD: a Cross-Validation Experiment PLANCHER, Emeric; PETIT, Johann; MAURICE, Claire; SAINTOYANT, Lucie; LOISNARD, Dominique; RUPIN, N.; MARIJON, Jean-Baptiste; ULRICH, Olivier; BORNERT, Michel; MICHA, Jean Sébastien; ROBACH, Odile; CASTELNAU, Olivier; FAVIER, Véronique Determining the accuracy of elastic strain measurements in plastically deformed alloys is an experimental challenge. To develop a novel cross-validation procedure, a controlled elasto-plastic strain gradient was created in a stainless steel single crystal by four point bending deformation. The corresponding elastic strain field was probed, with an intragranular spatial resolution, in-situ by Laue microdiffraction and ex-situ by High Resolution EBSD. Good agreement is found for the two independent measurements and the predictions of a mechanical model, at plastic strains below 0.5 %. The accuracy of the measurements is estimated at 3.2 × 10 − 4 .

LaueNN: neural-network-based hkl recognition of Laue spots and its application to polycrystalline materials

PURUSHOTTAM RAJ PUROHIT, Ravi Raj Purohit — Mon, 01 Aug 2022 00:00:00 GMT

LaueNN: neural-network-based hkl recognition of Laue spots and its application to polycrystalline materials PURUSHOTTAM RAJ PUROHIT, Ravi Raj Purohit; TARDIF, Samuel; CASTELNAU, Olivier; EYMERY, Joel; GUINEBRETIÈRE, René; ROBACH, Odile; ORS, Taylan; MICHA, Jean-Sébastien A feed-forward neural-network-based model is presented to index, in real time, the diffraction spots recorded during synchrotron X-ray Laue microdiffraction experiments. Data dimensionality reduction is applied to extract physical 1D features from the 2D X-ray diffraction Laue images, thereby making it possible to train a neural network on the fly for any crystal system. The capabilities of the LaueNN model are illustrated through three examples: a two-phase nanostructure, a textured high-symmetry specimen deformed in situ and a polycrystalline low-symmetry material. This work provides a novel way to efficiently index Laue spots in simple and complex recorded images in <1 s, thereby opening up avenues for the realization of real-time analysis of synchrotron Laue diffraction data.

Evidence of 3D strain gradients associated with tin whisker growth

HEKTOR, Johan — Mon, 01 Jan 2018 00:00:00 GMT

Evidence of 3D strain gradients associated with tin whisker growth HEKTOR, Johan; MARIJON, Jean-Baptiste; RISTINMAA, Matti; HALL, Stephen A.; HALLBERG, Hakan; SRINIVASAN, Iyengar; MICHA, Jean-Sébastien; ROBACH, Odile; GRENNERAT, Fanny; CASTELNAU, Olivier We have used Differential Aperture X-ray Microscopy (DAXM) to measure grain orientations and deviatoric elastic strains in 3D around a tin whisker. The results show strain gradients through the depth of the tin coating, revealing a higher strain deeper in the Sn layer. These higher strains are explained by the volume change occurring during growth of the intermetallic phase Cu6Sn5 at the interface between the Cu substrate and the Sn coating and at grain boundaries between Sn grains.

LaueNN: neural-network-based hkl recognition of Laue spots and its application to polycrystalline materials

PURUSHOTTAM RAJ PUROHIT, Ravi Raj Purohit — Wed, 01 Jun 2022 00:00:00 GMT

LaueNN: neural-network-based hkl recognition of Laue spots and its application to polycrystalline materials PURUSHOTTAM RAJ PUROHIT, Ravi Raj Purohit; TARDIF, Samuel; CASTELNAU, Olivier; EYMERY, Joel; GUINEBRETIÈRE, René; ROBACH, Odile; ORS, Taylan; MICHA, Jean-Sébastien A feed-forward neural-network-based model is presented to index, in real time, the diffraction spots recorded during synchrotron X-ray Laue microdiffraction experiments. Data dimensionality reduction is applied to extract physical 1D features from the 2D X-ray diffraction Laue images, thereby making it possible to train a neural network on the ﬂy for any crystal system. The capabilities of the LaueNN model are illustrated through three examples: a two-phase nano-structure, a textured high-symmetry specimen deformed in situ and a polycrystalline low-symmetry material. This work provides a novel way to efﬁciently index Laue spots in simple and complex recorded images in <1 s, thereby opening up avenues for the realization of real-time analysis of synchrotron Laue diffraction data.