In-situ experimental and numerical studies of the damage evolution and fracture in a Fe-TiB2 composite

A joint experimental and modelling study of plastic strain and ensuing damage in a novel metal matrix composite (Fe-TiB2) is presented. Damage is observed and quantified using SEM images processing and Acoustic Emission (AE) analysis. The use of AE confirms that the surface damage observed is strongly correlated to damage in the bulk of the material. The primary mode of damage is particle fracture. Very little particle decohesion is observed, indicating an exceptionally good cohesion of the steel/particle interface. Damage is initiated soon after the composite yield point is reached and increases significantly with strain. Macroscopic failure of the tensile specimen occurs when about 25% of the particles are fractured. This corresponds to about 21% engineering strain. Using in-situ SEM tensile tests with quantitative digital image correlation (DIC), full-field strain measurements are obtained and particle fracture quantified. The results of fields measurements are compared to results of a FFT based homogenization method with boundary conditions retrieved from the experiment. A good agreement is found between the DIC-measured and FFT-predicted results. Estimated values of the particle fracture stress are obtained

Experimental investigation of the free swelling of crushed argillite

International audienceCallovo-Oxfordian argillite is studied in France as a possible host rock for repository of high-level radioactive wastes. A new experimental procedure is proposed to quantify the free swelling of its main constitutive clay phase, which is a key parameter to model the hydromechanical behaviour of this rock. The material was pulverised finely enough to remove any local stress that may prevent the free swelling induced by a change in water content. Powders were observed using an environmental scanning electron microscope and images recorded at various degrees of relative humidity were analysed by digital image correlation techniques to measure swelling strains. The investigation showed that the free swelling is moderate in comparison to other expansive clays (e.g. bentonite MX80). The magnitude of deformation becomes significant at high relative humidity. This swelling is not reversible and residual contraction is found after a wetting/drying cycle. These results confirm and provide a possible interpretation of some macroscopic phenomena

Characterization and analysis of deformation heterogeneities in commercial purity titanium

International audienceThe effects of solute oxygen, loading direction and strain level on the microscale plastic strain distribution in representative areas of commercially-pure titanium have been characterized by correlation of high resolution SEM images captured during in situ tensile tests. A spatial organization of highly-deformed bands was observed from the early stages of plastic flow and remained nearly unchanged as the materials were strained. The high strains close to grain boundaries were related to intense local slip activity, grain boundary sliding or kink bands formation. The plastic strain field was more homogeneous in the oxygen-rich material, which was attributed primarily to a smaller contribution of grain boundary sliding, due to the presence of hard β phase particles along the grain boundaries

Etude expérimentale et modélisation du comportement mécanique des alliages TiAl à l'échelle du grain

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Simulations and microstructural effects on macroscopic mechanical behavior and local strain and stress field heterogeneities. Application to zirconium alloys

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Micromechanical experimental investigation of mudstones

International audienceThis paper reports on a micromechanical investigation of mudstones using a novel experimental method, based on a combination of environmental scanning electron microscopy (ESEM) and digital image correlation techniques. A specifically designed rig was developed, allowing in situ tests under combined hydric and mechanical loadings in the ESEM chamber. Observations were performed on the scale of the composite microstructure of the involved rocks (i.e. numerous grains of carbonate and quartz embedded in a clay matrix). Preliminary results from a uniaxial compression test on a sample with 5?4% water content are presented. Heterogeneous strain fields that correlate well with the microstructure of mudstones are illustrated, enabling different deformation modes (particularly shear bands and tensile microcracks) and their interactions to be identified

On the Identification of multiscale crystal plasticity models of Titanium Aluminides

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A simple experimental procedure to quantify image noise in the context of strain measurements at the microscale using DIC and SEM images

International audienceImage noise is an important factor that influences the accuracy of strain field measurements by means of digital image correlation and scanning electron microscope (SEM) imaging. We propose a new model to quantify the SEM image noise, which extends the classical photon noise model by taking into account the brightness setup in SEM imaging. Furthermore, we apply this model to investigate the impact of different SEM setting parameters on image noise, such as detector, dwell time, spot size, and pressure in the SEM chamber in the context of low vacuum imaging