ParisTech

About: ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Finite element method & Residual stress. The organization has 1888 authors who have published 1965 publications receiving 55532 citations. The organization is also known as: Paris Institute of Technology & ParisTech Développement.

Calcium phosphate grafts produced by rapid prototyping based on laser cladding

Abstract: Rapid prototyping based on laser cladding by powder injection has been used to produce calcium phosphate three-dimensional grafts without using molds. Precursor material comprising of hydroxyapatite (HA) powder was irradiated by means of an infrared Nd:YAG laser. The processing parameters and the thermal history of the processed material have been assessed and the process has been optimized to obtain solid parts. Processing by laser cladding lead to complete dehydroxylation of the precursor HA, the obtained microstructure is composed by an alpha-tricalcium phosphate (α-TCP) matrix with nucleated tetracalcium phosphate (TTCP) grains, in coexistence with oxyapatite and amorphous calcium phosphate. The produced bioceramic grafts were observed to be bioactive, leading to calcium-deficient hydroxyapatite precipitation and promoting pre-osteoblastic cell attachment and proliferation during “ in vitro ” cell culture test.

Cathodoluminescence in a Scanning Transmission Electron Microscope: A Nanometer-Scale Counterpart of Photoluminescence for the Study of II–VI Quantum Dots

Abstract: We report on nanometer-scale cathodoluminescence (nanoCL) experiments in a scanning transmission electron microscope on individual core–shell CdSe/CdS quantum dots (QDs). By performing combined pho...

Oxidation-assisted creep damage in a wrought nickel-based superalloy: Experiments and modelling

Abstract: Creep damage investigation was carried out in wrought nickel-based superalloy Udimet 720LI in air at 850 °C using multiple cross-sections specimens in order to be able to make interrupted tests. In all tests conducted on this material, creep curves showed only tertiary stage and the surface connected intergranular cracking was found to be dominant in creep fracture. It was shown that γ′ precipitate coarsening occurs in the bulk of the specimens and obeys the LSW kinetics. Metallographic analysis led to the conclusion that creep does not alter oxidation, except at grain boundaries, where oxide spikes can be developed under creep. Therefore grain boundary oxidation was found to be creep strain-assisted. A constitutive model accounting for precipitate coarsening was proposed. The oxidation-assisted intergranular damage and the oxidation embrittlement of the microstructure elements phenomena were successfully described using the continuum damage mechanics and the local ductility exhaustion laws, respectively. Creep rupture and elongation curves were taken into account by the model with suitable accuracy, as well. The model was found able to figure the specimen's geometry variations effects on lifetime and creep elongation curves.

Statistical axisymmetry of the turbulent sphere wake

Abstract: The turbulent sphere wake is studied experimentally at $${Re}=1.9\,10^4$$ using an axisymmetric support that holds the body from upstream. This setup allows the axisymmetry of the mean wake and preserves the global mode activity at $${St}=0.19$$ . The analysis of the PIV snapshots in a cross-flow plane indicates that this axisymmetry is due to an equal exploration of all the azimuths by the instantaneous wake. Using conditional averaging techniques, we extract the flow topology associated with one azimuthal direction; the obtained wake shows strong similarities with the unsteady planar symmetric flow reported in the laminar regime. In addition, the use of perturbations of the axisymmetry leads to modifications of the azimuthal statistics: The periodicity of the perturbation is recovered in the wake since one or several preferred orientations are identified. Hence, such statistics pave the way to multi-stable behaviors in three-dimensional wakes.