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A better understanding of the effective mechanical behavior of polycrystalline materials requires an accurate knowledge of the behavior at a scale smaller than the grain size. The X-ray Laue microdiffraction technique available at beamline BM32 at the European Synchrotron Radiation Facility is ideally suited for probing elastic strains (and associated stresses) in deformed polycrystalline materials with a spatial resolution smaller than a micrometer. However, the standard technique used to evaluate local stresses from the distortion of Laue patterns lacks accuracy for many micromechanical applications, mostly due to (i) the fitting of Laue spots by analytical functions, and (ii) the necessary comparison of the measured pattern with the theoretical one from an unstrained reference specimen. In the present paper, a new method for the analysis of Laue images is presented. A Digital Image Correlation (DIC) technique, which is essentially insensitive to the shape of Laue spots, is applied to measure the relative distortion of Laue patterns acquired at two different positions on the specimen. The new method is tested on an in situ deformed Si single-crystal, for which the prescribed stress distribution has been calculated by finite-element analysis. It is shown that the new Laue-DIC method allows determination of local stresses with a strain resolution of the order of 10−5. [ABSTRACT FROM AUTHOR]

A prototype X-ray pixel area detector (XPAD3.1) has been used for X-ray diffraction experiments with synchrotron radiation. The characteristics of this detector are very attractive in terms of fast readout time, high dynamic range and high signal-to-noise ratio. The prototype XPAD3.1 enabled various diffraction experiments to be performed at different energies, sample-to-detector distances and detector angles with respect to the direct beam, yet it was necessary to perform corrections on the diffraction images according to the type of experiment. This paper is focused on calibration and correction procedures to obtain high-quality scientific results specifically developed in the context of three different experiments, namely mechanical characterization of nanostructured multilayers, elastic-plastic deformation of duplex steel and growth of carbon nanotubes. [ABSTRACT FROM AUTHOR]

Synchrotron x-ray radiation was used for in situ strain measurements during uniaxial tests on polymer substrates coated by a metallic gold film 400 nm thick deposited without interlayer or surface treatment. X-ray diffraction allowed capturing both components elastic strains and determining how these were partitioned between the metallic film and the polymeric substrate. For strains below 0.8%, deformation is continuous through the metal-polymer interface while above, the onset of plasticity in the metallic film induces a shift between film and substrate elastic strains. [ABSTRACT FROM AUTHOR]

The dislocation densities were measured on the same samples using transmission electron microscopy (TEM), scanning electron microscopy (electron channeling contrast imaging (ECCI) and high-angular-resolution-electron backscattered diffraction (HR-EBSD)), and X-ray diffraction (XRD). Notably, these different methods do not observe the same types of dislocations, i.e., statistically stored dislocations (SSDs) and/or geometrically necessary dislocations (GNDs). ECCI and TEM imaging are direct-measurement techniques, whereas HR-EBSD and XRD are indirect methods. Therefore, a quantitative comparison of the measurements obtained using these four techniques on undeformed and deformed duplex steels is proposed. For low deformation, where the dislocation density is quite small (1 − 5 × 1013 m−2), imaging methods are rather performant, whereas XRD measurements suffer from high uncertainty levels. HR-EBSD measurements show results that are in good agreement with the other methods for these deformation levels. For higher deformation levels (with dislocation densities above 1 − 3 × 1014 m−2), imaging methods are no longer relevant because of the increasing uncertainty arising from local contrast variation and overlapping of dislocations. The different results obtained highlight the necessity of taking a step back on each method used. Correctly defining what is to be measured (SSDs or GNDs), in which condition (solid material or thin plate) as well as the parameters (pixel size, area, etc.) and their bias is essential, especially if the objective is to use the measurement in a micromechanical model. • Different measurement techniques lead to different dislocation density measurement. • XRD measurement are more adequate for high density values (>1014m−2). • Imaging techniques are more adequate for densities less than(<1014–15 m−2. • EBSD/HR-EBSD are the most versatile techniques and accurate for the larger range. • Combining EBSD/HR-EBSD and ECCI seems ideal to describe a dislocation population. [ABSTRACT FROM AUTHOR]