Interface dilution and morphology of CdTe/MnTe superlattices studied by small angle X-ray scattering

International audienceWe have performed small angle X-ray reflectivity measurements on CdTe/MnTe superlattices. The Fresnel optical method and the distorted wave Born approximation were used to extract results from the data. The reflectivity shows that the interface roughness (about 7 Å) is quite large for (43 ML CdTe/8 ML MnTe) and (34 ML CdTe/16 ML MnTe) samples. The effective MnTe concentration is determined from the refractive index. A model of correlated interface profiles is successfully used to simulate the diffuse scattering, and to determine the lateral correlation length of the roughness (Λ| = 1500 ± 750 Å); moreover, we demonstrate that the layers are almost completely correlated over the sample thickness in the growth direction

Verfahren zur zerstoerungsfreien Fehlerdiagnose an Verbundbauteilen mit einem Kern aus einem Metall- oder Keramikschaum

DE1004011566 B UPAB: 20050805 NOVELTY - The method involves coupling ultrasonic waves into the component with an actuator mounted on the outer surface of one of the elements and detecting ultrasonic measurement signals with an acoustic detector on the opposite side of the core, determining the time until a threshold is exceeded by the measurement signals and/or determining the absolute magnitude of the measurement signal in a period between starting to couple in ultrasonic waves and a defined time and using the time and/or maximum value for fault diagnosis. USE - For non-destructive fault diagnosis of composite parts with core of metal or ceramic held on opposing sides by elements of homogeneous material with constant speed of sound. ADVANTAGE - Enables more reliable detection of faults

Ductile damage study for load path changes under low stress triaxiality via 3D synchrotron imaging and FE simulations

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Multiscale observation of ductile damage on an Aluminium alloy 2198 under shear

International audienceIn search of the lighter materials and optimized thin-walled components especially for transportation purposes, knowledge about the characteristic ductile damage mechanisms related to their failure, reliability, lifetime etc. in aluminium sheets is crucially needed in manyfold engineering application. Recent reserach has addressed a complex and empirical relationship between strain to fracture and low stress triaxiality below 1 [1] but physical damage mechanisms still remain unclear. Initial void shapes and their shape changes during deformation may be at the origin of the unexpected material failure. In addition, the stages of void nucleation, void shape change and void coalescence are still poorly understood as they are hardly observed experimentally maintaining relevant stress conditions [2].To overcome the inherent shortcomings of other 3D technique on flat sample, advanced techniques in situ synchrotron microlaminography and ex situ nanolaminography provide information from a few hundred micrometers resolution down to the nanometer scale, allowing the ductile damage nucleation and growth kinetics in metal sheets to be studied. A ‘smiley’ shear sample geometry [3] of 1 mm thick sheet made from a latest generation of recrystallized Al-Cu-Li alloy 2198 in T8 condition [4] is chosen to study its shear damage mechanisms down to 50 nm (voxel size) resolution for a test stopped before fracture.The damage features, including oriented cluster of micro-void cracks and damage linked to intermetallic particles, are found at highly-deformed shear band region. The detrimental flat cracks are proved to be intergranular via EBSD analysis. Cracks are also found to nucleate with intermetallic particles and grow during shearing, due to the constraint of the stiff particles. Shear bands on micrometer scale and dispersoids on nanometer scale are observed via SEM, and the latter are probably linked to the onset of micro-void nucleation by fractography of the fractured in situ sample.Reference[1] Y. Bao, et al., On fracture locus in the equivalent strain and stress triaxiality space, Int. J. Mech. Sci., 46 (2004), 81-98[2] T. Petit et al., Effect of hardening on toughness captured by stress-based damage nucleation in 6061 aluminium alloy, Acta. Mater., 180 (2019), 349-365[3] C. C. Roth, D. Mohr, Determining the strain to fracture for simple shear for a wide range of sheet metals, Int. J. Mech. Sci., 149 (2018) 224 – 240.[4] J. Chen, Ductile tearing of AA2198 aluminium-lithium sheets for aeronautic application, PhD thesis (2011